httpdl/cli: drop --auto-split; classify errors by type, not message text

Two Pike cleanups.

--auto-split was a got-only third connection-count policy (beside -x and -s)
that invented rather than matched aria2. Removing it also retires the now-dead
autoConns/maxAutoConns and the per-host transport cap that existed only to scale
for it; min(split, M*-x) is the sole policy again.

main's exit-code mapping fell back to substring-matching third-party error text
(strings.Contains "connection refused"/"timeout"/...), which rots when a
dependency rewords a message. The typed checks (errors.Is on the syscall errno,
*net.DNSError, net.Error.Timeout, context.DeadlineExceeded) already cover the
real stdlib errors -- verified end to end: refused -> 6, bad host -> 19. The two
cases that genuinely needed the text match are our own errors, now typed
sentinels: httpdl.ErrTimeout (idle timeout) and the bt metadata timeout wrapping
context.DeadlineExceeded.

.gitignore

@@ -7,3 +7,13 @@ ref/
 bin/
 .torrent.db*
 *.part
+
+# media downloaded by running got in the repo tree (never commit content)
+*.mkv
+*.mp4
+*.avi
+*.mov
+*.webm
+*.iso
+*.mp3
+*.flac

README.md

@@ -1,13 +1,8 @@
 # got
 
-A small, Rob-Pike-style command-line download tool in Go: one program that
-downloads HTTP(S) URLs over several connections and BitTorrent
-magnets/torrents, with a focused set of options.
-
-The design leans on Go's runtime instead of a hand-rolled reactor. There is no
-single-threaded event-poll loop: one goroutine per download blocks on real I/O,
-a buffered channel of slots bounds concurrency, and `context` carries shutdown.
-What remains is the data — and, per Pike, the data is the design.
+A command-line download tool in Go. It fetches HTTP(S) files over multiple
+connections and downloads BitTorrent magnets and `.torrent` files — one binary,
+familiar flags.
 
 ## Build
 
@@ -15,148 +10,63 @@ What remains is the data — and, per Pike, the data is the design.
 go build -o got .
 ```
 
-Requires Go 1.25+. The BitTorrent engine is
-[`anacrolix/torrent`](https://github.com/anacrolix/torrent); everything else is
-the standard library plus `golang.org/x/{term,time}`.
+Needs Go 1.25+.
 
-## Use
+## Usage
 
 ```sh
-# segmented HTTP download, 16 connections, into ./downloads
-got -x16 -s16 -d downloads https://example.com/big.iso
+# HTTP download with 16 connections
+got -x16 -s16 https://example.com/big.iso
 
 # resume an interrupted download
-got -c -x16 https://example.com/big.iso
+got -c https://example.com/big.iso
 
-# the same file from several mirrors at once (one file, connections spread
-# across servers, a dead mirror falls over); -Z downloads them separately instead
+# one file from several mirrors (connections spread across servers,
+# a dead mirror falls over); -Z downloads them as separate files instead
 got -x4 https://a.example/big.iso https://b.example/big.iso
 
 # a torrent or magnet; seed for 30 minutes after finishing
 got --seed-time=30 ubuntu.torrent
 got 'magnet:?xt=urn:btih:...'
 
-# list the files in a torrent without downloading
-got -S -T some.torrent
-
-# several downloads at once, two running in parallel
+# many downloads, two at a time
 got -j2 -i urls.txt
 ```
 
-Run `got --help` (or `--help=http`, `--help=bittorrent`, ...) for the full
-option list.
+Run `got --help` (or `--help=all`) for every option.
 
-### Options
-
-A focused subset of options, with familiar short flags and sensible defaults.
+## Common options
 
 | flag | meaning | default |
 |------|---------|---------|
 | `-d, --dir` | output directory | `.` |
-| `-o, --out` | output filename (single download) | from URL |
-| `-i, --input-file` | read downloads line by line (TAB-separated URLs = mirrors; `-` = stdin) | |
+| `-o, --out` | output filename | from URL |
 | `-c, --continue` | resume a partial download | false |
 | `-x, --max-connection-per-server` | connections to one server (1–16) | 1 |
 | `-s, --split` | split a download into N connections | 5 |
-| `-Z, --force-sequential` | download each command-line URL separately, not as mirrors | false |
-| `-k, --min-split-size` | do not split below this size | 20M |
-| `-j, --max-concurrent-downloads` | parallel downloads | 5 |
+| `-j, --max-concurrent-downloads` | downloads at once | 5 |
 | `--max-overall-download-limit` | global speed cap | 0 (off) |
-| `--max-download-limit` | per-download speed cap | 0 (off) |
-| `--retry-wait` | seconds to wait between retries | 0 |
-| `--load-cookies` / `--save-cookies` | read/write a Netscape `cookies.txt` | |
-| `--conditional-get` | skip the download if the local file is up to date | false |
-| `--remote-time` | set the file's mtime from the server | false |
-| `--checksum` | verify the finished file: `TYPE=DIGEST` (sha-256, sha-1, md5, …) | |
-| `--dry-run` | check the file is available but do not download it | false |
-| `--ca-certificate` | verify HTTPS against the CA certificates in FILE (PEM) | |
-| `--stop` | stop the program after N seconds | 0 (off) |
-| `--disable-ipv6` | force IPv4-only connections | false |
-| `-T, --torrent-file` | a `.torrent` file | |
-| `--seed-time` | minutes to seed after finishing | seed by ratio |
+| `--checksum` | verify the finished file: `TYPE=DIGEST` (sha-256, sha-1, …) | |
+| `--seed-time` | minutes to seed after a torrent finishes | by ratio |
 | `--seed-ratio` | stop seeding at this ratio | 1.0 |
-| `--listen-port` | port (range) for incoming peers | 6881-6999 |
-| `--enable-dht` | use the BitTorrent DHT | true |
-| `--select-file` | fetch only these file indexes (`1,3-5`) | all |
 | `-S, --show-files` | list torrent files and exit | |
-| `--bt-stop-timeout` | give up if no download progress for N s | 0 (off) |
-| `--bt-metadata-timeout` | give up if a magnet can't fetch metadata in N s | 60 |
-| `--save-session` | on exit, write unfinished downloads to FILE | |
-| `-q, --quiet` | no progress readout | false |
+| `-q, --quiet` | no progress output | false |
 
-### Resuming across runs
+## Resume
 
-There is no daemon — resume is a plain file. Point
-`--save-session` and `-i` at the same file and add `-c`: unfinished downloads
-are loaded at start and the still-unfinished ones are written back on exit.
+HTTP downloads resume from a small `<file>.got` sidecar — just re-run with `-c`.
+Torrents resume from the data already on disk. To resume across runs, point
+`--save-session` and `-i` at the same file:
 
 ```sh
-got -c --save-session=got.session -i got.session  <new urls/magnets...>
+got -c --save-session=got.session -i got.session  <urls/magnets...>
 ```
 
-On the first run the session file need not exist. HTTP downloads resume from
-their `.got` control file; torrents resume from the data already on disk
-(re-checked by the engine). A magnet with no reachable peers no longer hangs:
-`--bt-metadata-timeout` bounds the metadata fetch and defaults to 60s (set it to
-0 to wait forever).
+## Notes
 
-## Design
-
-```
-main            classify URIs, wire options, run, report exit code
- └─ download    the Download interface + the scheduler (-j semaphore, ctx)
-     ├─ httpdl  []Segment + worker pool + WriteAt + JSON resume sidecar
-     └─ bt      anacrolix/torrent behind the Download interface
- ├─ cli         one flat option table -> hand parser -> layered config
- └─ progress    one ticker goroutine, pull-snapshot, \r line redraw
-```
-
-The contract is one small interface:
-
-```go
-type Download interface {
-        Name() string
-        Run(ctx context.Context) error   // blocks in its own goroutine
-        Stat() Stat                       // a value snapshot, lock-free to read
-}
-```
-
-- **HTTP** splits the file into byte-range `Segment`s handed to a pool of
-  workers. Each worker streams its range straight to one shared file with
-  `os.File.WriteAt` — safe for concurrent non-overlapping writes, so there is no
-  shared seek offset and no mutex. Resume is a small JSON sidecar
-  (`<file>.got`) holding per-segment progress plus validators (length +
-  ETag/Last-Modified) so a stale file is never trusted.
-- **BitTorrent** is `anacrolix/torrent` configured from the CLI options and
-  driven to completion, then seeded for `--seed-time` minutes or up to
-  `--seed-ratio`.
-- **Options** are one flat `[]Opt` table — the single source of truth for
-  parsing, validation, defaults and `--help`. Layers apply in order:
-  built-in defaults, config file, proxy environment, command line.
-- **Progress** is a single goroutine that ticks once a second, pulls a snapshot
-  of the running downloads, derives speeds from the change since the last tick,
-  and redraws one line with `\r` + erase-to-end-of-line.
-
-## Status
-
-Implemented: segmented HTTP(S) with resume — including a foreign/browser-started
-partial file (`-c`) — multi-mirror downloads (several URLs, or TAB-grouped `-i`
-lines, fetch one file with connections spread across servers and fallover; `-Z`
-to download them separately), retries, rate limits, auto-renaming,
-`Content-Disposition` naming, conditional GET, cookies
-(`--load-cookies`/`--save-cookies`), HTTP basic auth, `--remote-time`, whole-file
-checksum verification (`--checksum`), and a `--dry-run` availability check;
-BitTorrent download + seeding (magnet and `.torrent`,
-DHT, trackers, file selection, show-files, metadata-fetch timeout), seeding that
-stops on whichever of `--seed-time`/`--seed-ratio` comes first, and a listen port
-chosen from the whole range so a busy port no longer disables BitTorrent;
-a command-line interface with documented exit codes, config file, live progress,
-and session save/reload for resume across runs.
-
-Deferred (not implemented yet): FTP/SFTP, Metalink, and the
-JSON-RPC server. The architecture leaves room for
-each — a new protocol is just another `Download`. One known limitation: the
-BitTorrent engine (`anacrolix/torrent`) applies download/upload rate limits
-client-wide, so `--max-upload-limit`/`--max-download-limit` act per-run rather
-than per-torrent when several torrents run at once (`--max-overall-*` are exact);
-DHT/PEX likewise cannot yet be disabled per private torrent.
+- BitTorrent uses [`anacrolix/torrent`](https://github.com/anacrolix/torrent);
+  HTTP uses the standard library.
+- Not implemented: FTP/SFTP, Metalink, and the JSON-RPC server.
+- When several torrents run at once, `--max-download-limit` /
+  `--max-upload-limit` apply per run rather than per torrent (`--max-overall-*`
+  are exact).

bt/bt.go

@@ -9,12 +9,16 @@ package bt
 import (
 	"context"
 	"fmt"
+	"io"
+	"log/slog"
+	"os"
 	"path/filepath"
 	"strconv"
 	"strings"
 	"sync/atomic"
 	"time"
 
+	alog "github.com/anacrolix/log"
 	missinggo "github.com/anacrolix/missinggo/v2"
 	"github.com/anacrolix/torrent"
 	"github.com/anacrolix/torrent/metainfo"
@@ -64,15 +68,30 @@ func ParsePorts(spec string) []int {
 		if err != nil {
 			continue
 		}
+		// Clamp to the valid port space before iterating: a parseable but oversized
+		// spec like "1-9999999999" would otherwise spin for ~10^10 iterations and
+		// hang startup, even though only [1,65535] can ever be appended.
+		if a < 1 {
+			a = 1
+		}
+		if b > 65535 {
+			b = 65535
+		}
 		for i := a; i <= b; i++ {
-			if i >= 1 && i <= 65535 {
 			ports = append(ports, i)
 		}
 	}
-	}
 	return ports
 }
 
+// quietSlogger filters anacrolix's structured logging down to Error and above,
+// so the routine webseed/peer/tracker warning chatter (the 403/429 noise) no
+// longer interleaves with — and corrupts — the live progress display. Genuine
+// errors still reach w.
+func quietSlogger(w io.Writer) *slog.Logger {
+	return slog.New(slog.NewTextHandler(w, &slog.HandlerOptions{Level: slog.LevelError}))
+}
+
 // NewClient builds the shared anacrolix client from the run-wide config. When a
 // listen-port spec is given it tries each candidate port in turn, advancing past
 // any that is already in use, and falls back to an OS-chosen port if none bind,
@@ -91,6 +110,11 @@ func ParsePorts(spec string) []int {
 //     prevention must come from a run-wide setting (e.g. --enable-dht=false).
 func NewClient(cfg ClientConfig) (*torrent.Client, error) {
 	c := torrent.NewDefaultClientConfig()
+	// Keep the library's own logging out of the readout. Webseed/peer warnings go
+	// through slog, the rest through the legacy analog logger, so filter both to
+	// Error and above (the analog default is Warning, which is what leaks today).
+	c.Slogger = quietSlogger(os.Stderr)
+	c.Logger = alog.Default.FilterLevel(alog.Error)
 	c.DataDir = cfg.Dir
 	if c.DataDir == "" {
 		c.DataDir = "."
@@ -289,14 +313,17 @@ func (d *Download) Run(ctx context.Context) (err error) {
 		return nil
 	}
 
-	if err := d.choose(t); err != nil {
-		return err
-	}
+	// --check-integrity: re-hash the existing on-disk data BEFORE arming the
+	// request loop, so already-good pieces are not re-requested from peers (aria2
+	// verifies first, then fetches only what is missing).
 	if d.opts.CheckIntegrity {
 		if err := t.VerifyDataContext(ctx); err != nil {
 			return err
 		}
 	}
+	if err := d.choose(t); err != nil {
+		return err
+	}
 
 	if err := d.wait(ctx, t); err != nil {
 		return err
@@ -365,7 +392,9 @@ func (d *Download) awaitInfo(ctx context.Context, t *torrent.Torrent) error {
 	case <-ctx.Done():
 		return ctx.Err()
 	case <-deadline:
-		return fmt.Errorf("timed out fetching metadata after %s", d.opts.MetaTimeout)
+		// Wrap DeadlineExceeded so the exit-code mapping classifies it as a timeout
+		// (2) via errors.Is, rather than matching on the message text.
+		return fmt.Errorf("timed out fetching metadata after %s: %w", d.opts.MetaTimeout, context.DeadlineExceeded)
 	}
 }
 

bt/bt_test.go

@@ -1,10 +1,38 @@
 package bt
 
 import (
+	"bytes"
+	"context"
+	"log/slog"
 	"reflect"
+	"strings"
 	"testing"
 )
 
+// TestQuietSloggerDropsWarnings: the library's warning chatter (the webseed
+// 403/429 noise) is filtered out so it can't corrupt the live display, while a
+// genuine error still gets through.
+func TestQuietSloggerDropsWarnings(t *testing.T) {
+	var buf bytes.Buffer
+	lg := quietSlogger(&buf)
+
+	lg.Warn("webseed request error", "err", "429 Too Many Requests")
+	if buf.Len() != 0 {
+		t.Errorf("warning leaked into output: %q", buf.String())
+	}
+	// anacrolix's webseed code logs via Log(ctx, level, ...); confirm that path is
+	// filtered too, not just the Warn helper.
+	lg.Log(context.Background(), slog.LevelWarn, "another warning")
+	if buf.Len() != 0 {
+		t.Errorf("Log-at-Warn leaked: %q", buf.String())
+	}
+
+	lg.Error("real failure")
+	if !strings.Contains(buf.String(), "real failure") {
+		t.Errorf("error was suppressed, want it kept: %q", buf.String())
+	}
+}
+
 func TestParsePorts(t *testing.T) {
 	tests := []struct {
 		spec string

cli/help.go

@@ -97,7 +97,12 @@ func flagLabel(o *Opt) string {
 	case Int:
 		b.WriteString("=N")
 	case Float:
+		// seed-time is a count of minutes; only seed-ratio is an actual ratio.
+		if o.Long == "seed-time" {
+			b.WriteString("=MIN")
+		} else {
 			b.WriteString("=RATIO")
+		}
 	case Enum:
 		b.WriteString("=" + strings.Join(o.Enum, "|"))
 	default:

cli/option.go

@@ -78,9 +78,9 @@ var options = []Opt{
 	{Long: "human-readable", Kind: Bool, Default: "true", Help: "show sizes as Ki/Mi/Gi", Tag: Basic},
 
 	// --- http ---
-	{Long: "max-connection-per-server", Short: 'x', Kind: Int, Default: "1", Min: 1, Max: 16, Help: "max connections to one server (1-16)", Tag: HTTP},
-	{Long: "split", Short: 's', Kind: Int, Default: "5", Min: 1, Help: "split a download into N connections; actual connections are min(max-connection-per-server, split), and -x defaults to 1", Tag: HTTP},
-	{Long: "min-split-size", Short: 'k', Kind: Size, Default: "20M", Min: 1 << 20, Max: 1 << 30, Help: "do not split a piece smaller than SIZE (1M-1024M)", Tag: HTTP},
+	{Long: "max-connection-per-server", Short: 'x', Kind: Int, Default: "1", Min: 1, Max: 16, Help: "max connections to one server (1-16)", Tag: Basic},
+	{Long: "split", Short: 's', Kind: Int, Default: "5", Min: 1, Help: "split a download into N connections; actual connections are min(max-connection-per-server, split), and -x defaults to 1", Tag: Basic},
+	{Long: "min-split-size", Short: 'k', Kind: Size, Default: "20M", Min: 1 << 20, Max: 1 << 30, Help: "do not split a piece smaller than SIZE (1M-1024M)", Tag: Basic},
 	{Long: "force-sequential", Short: 'Z', Kind: Bool, Default: "false", Help: "download each command-line URI as its own file instead of mirroring them", Tag: HTTP},
 	{Long: "max-tries", Short: 'm', Kind: Int, Default: "5", Min: 0, Help: "max retries per segment (0 = unlimited)", Tag: HTTP},
 	{Long: "timeout", Short: 't', Kind: Int, Default: "60", Min: 1, Help: "connection timeout in seconds", Tag: HTTP},

cli/options.go

@@ -2,6 +2,7 @@ package cli
 
 import (
 	"fmt"
+	"math"
 	"strconv"
 	"strings"
 )
@@ -105,5 +106,10 @@ func parseSize(s string) (int64, error) {
 	if n < 0 {
 		return 0, fmt.Errorf("negative size %q", s)
 	}
+	// Reject a value whose unit multiply would overflow int64 and silently wrap to
+	// a bogus (positive or negative) byte count.
+	if mult > 1 && n > math.MaxInt64/mult {
+		return 0, fmt.Errorf("size %q too large", s)
+	}
 	return n * mult, nil
 }

download/engine.go

@@ -46,6 +46,12 @@ func (e *Engine) Run(ctx context.Context, downloads []Download) []Result {
 		go func(i int, d Download) {
 			defer wg.Done()
 
+			// Track immediately so a download still queued for a concurrency slot
+			// is visible to the progress reporter as Waiting, rather than hidden
+			// until it starts running.
+			e.track(d)
+			defer e.untrack(d)
+
 			// Acquire a concurrency slot, or bail if we're shutting down
 			// before this download ever started.
 			select {
@@ -56,9 +62,6 @@ func (e *Engine) Run(ctx context.Context, downloads []Download) []Result {
 			}
 			defer func() { <-slots }()
 
-			e.track(d)
-			defer e.untrack(d)
-
 			err := d.Run(ctx)
 			results <- Result{Name: d.Name(), Index: i, Err: err, Stat: d.Stat()}
 		}(i, d)
@@ -74,7 +77,8 @@ func (e *Engine) Run(ctx context.Context, downloads []Download) []Result {
 	return out
 }
 
-// Snapshot returns a Stat for every currently running download.
+// Snapshot returns a Stat for every tracked download — those running plus those
+// still queued for a concurrency slot (reported as Waiting).
 func (e *Engine) Snapshot() []Stat {
 	e.mu.Lock()
 	defer e.mu.Unlock()
@@ -91,6 +95,10 @@ func (e *Engine) track(d Download) {
 	e.mu.Unlock()
 }
 
+// untrack removes d from the active set. Every Download implementation is a
+// pointer type, so the == compares identities — never the fields of a value,
+// which could panic on a non-comparable one. (Keying on Stat().ID is not an
+// option: a torrent's ID changes from source to infohash once metadata loads.)
 func (e *Engine) untrack(d Download) {
 	e.mu.Lock()
 	defer e.mu.Unlock()

go.mod

@@ -3,6 +3,7 @@ module github.com/hanbok/got
 go 1.25
 
 require (
+	github.com/anacrolix/log v0.17.1-0.20251118025802-918f1157b7bb
 	github.com/anacrolix/missinggo/v2 v2.10.0
 	github.com/anacrolix/torrent v1.61.0
 	golang.org/x/sys v0.38.0
@@ -19,7 +20,6 @@ require (
 	github.com/anacrolix/envpprof v1.4.0 // indirect
 	github.com/anacrolix/generics v0.1.1-0.20251125230353-15d98d46693b // indirect
 	github.com/anacrolix/go-libutp v1.3.2 // indirect
-	github.com/anacrolix/log v0.17.1-0.20251118025802-918f1157b7bb // indirect
 	github.com/anacrolix/missinggo v1.3.0 // indirect
 	github.com/anacrolix/missinggo/perf v1.0.0 // indirect
 	github.com/anacrolix/mmsg v1.0.1 // indirect

httpdl/control.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"os"
 	"path/filepath"
+	"sort"
 	"sync/atomic"
 )
 
@@ -27,11 +28,13 @@ type segState struct {
 
 func controlPath(out string) string { return out + ".got" }
 
-// snapshot builds a control record from the live segments.
+// snapshot builds a control record from the live segments. The segment slice is
+// fixed once the file is divided and each segment's frontier is owned by one
+// worker, so reading written atomically gives a consistent record with no lock.
 func snapshot(url string, total int64, etag, lastmod string, segs []seg) control {
 	c := control{URL: url, Total: total, ETag: etag, LastModified: lastmod, Segs: make([]segState, len(segs))}
 	for i := range segs {
-		c.Segs[i] = segState{segs[i].start, segs[i].end, atomic.LoadInt64(&segs[i].written)}
+		c.Segs[i] = segState{segs[i].start, segs[i].endOff(), atomic.LoadInt64(&segs[i].written)}
 	}
 	return c
 }
@@ -73,7 +76,35 @@ func loadControl(out, url string, total int64, etag, lastmod string) *control {
 	if (lastmod != "" || c.LastModified != "") && c.LastModified != lastmod {
 		return nil
 	}
+	// Reject a control file whose segments do not exactly tile [0,total): a
+	// truncated/corrupted/hand-edited sidecar that still parses as JSON could
+	// otherwise mark a segment done() without its bytes on disk (inflated Written)
+	// or leave an un-downloaded hole, both of which would be reported as a complete
+	// file. We restart cleanly instead of trusting it.
+	if !validSegs(c.Segs, c.Total) {
+		return nil
+	}
 	return &c
 }
 
+// validSegs reports whether segs cover [0,total) with no gap or overlap and a
+// sane written count for each. The recorded order is not sorted (a steal appends
+// a tail), so we check coverage on a sorted copy.
+func validSegs(segs []segState, total int64) bool {
+	if total <= 0 || len(segs) == 0 {
+		return false
+	}
+	sorted := append([]segState(nil), segs...)
+	sort.Slice(sorted, func(i, j int) bool { return sorted[i].Start < sorted[j].Start })
+	var next int64
+	for _, s := range sorted {
+		length := s.End - s.Start + 1
+		if s.Start != next || s.End < s.Start || s.Written < 0 || s.Written > length {
+			return false
+		}
+		next = s.End + 1
+	}
+	return next == total
+}
+
 func removeControl(out string) { os.Remove(controlPath(out)) }

httpdl/httpdl.go

@@ -1,6 +1,6 @@
 // Package httpdl downloads a single HTTP(S) resource over one or more
 // connections. The model is deliberately flat: split the file into byte-range
-// segments, hand them to a pool of worker goroutines, and have each worker
+// segments, give each segment its own worker goroutine, and have each worker
 // stream its range straight to disk with WriteAt (safe for concurrent,
 // non-overlapping writes — no shared seek, no mutex). Goroutines blocking on
 // real I/O keep the model simple: no segment manager, no piece storage, no
@@ -119,19 +119,20 @@ type Config struct {
 // connections.
 type Download struct {
 	uris     []string // mirror list; uris[0] is the primary (naming + resume key)
-	maxConns int      // segment workers = min(split, len(uris)*max-connection-per-server)
+	maxConns int      // segment-worker cap = min(split, len(uris)*max-connection-per-server)
 	cfg      Config
 	client   *http.Client
 	limit    []*rate.Limiter
 	jar      *cookiejar.Jar // non-nil when cookies are in use, for save-cookies
 
 	// name and out are resolved in Run after the probe response is known (the
-	// final post-redirect URL and any Content-Disposition can change them), then
-	// never mutated again, so Stat can read name from another goroutine without a
-	// lock once Run has set it. They are seeded in New so a Stat before Run still
-	// has a sensible best-effort name.
-	name    string
-	out     string
+	// final post-redirect URL and any Content-Disposition can change them). The
+	// engine publishes a Download to the progress reporter before Run starts, so
+	// Stat reads these from the reporter goroutine while resolveName writes them;
+	// they are atomic.Pointer[string] (exactly like bt.Download.name) to keep that
+	// read/write race-free. Seeded in New so a Stat before Run has a best-effort name.
+	name    atomic.Pointer[string]
+	out     atomic.Pointer[string]
 	initErr error
 
 	// mu guards seenURLs, which records every URL we sent a request to so
@@ -224,7 +225,21 @@ func New(uris []string, cfg Config) *Download {
 		TLSClientConfig:       tlsCfg,
 	}
 	if cfg.Proxy != "" {
-		if pu, err := url.Parse(cfg.Proxy); err == nil {
+		pu, err := url.Parse(cfg.Proxy)
+		switch {
+		case err != nil:
+			// A malformed proxy must fail loudly, not silently fall back to the
+			// environment proxy (or a direct connection) and leak the real IP.
+			if initErr == nil {
+				initErr = fmt.Errorf("proxy %q: %w", cfg.Proxy, err)
+			}
+		case pu.Host == "":
+			// "host:port" with no scheme parses to an opaque URL with no Host, which
+			// http.ProxyURL would route nowhere; require an explicit scheme.
+			if initErr == nil {
+				initErr = fmt.Errorf("proxy %q: missing scheme (use scheme://host:port)", cfg.Proxy)
+			}
+		default:
 			tr.Proxy = http.ProxyURL(pu)
 		}
 	}
@@ -286,29 +301,47 @@ func New(uris []string, cfg Config) *Download {
 		client.Jar = jar
 	}
 
-	return &Download{
+	d := &Download{
 		uris:     uris,
 		maxConns: maxConns,
 		cfg:      cfg,
 		client:   client,
 		limit:    limit,
 		jar:      jar,
-		name:     name,
-		out:      out,
 		total:    -1,
 		initErr:  initErr,
 	}
+	d.setName(name)
+	d.setOut(out)
+	return d
 }
 
-func (d *Download) Name() string { return d.name }
+func (d *Download) Name() string { return d.loadName() }
 
 // Path returns the resolved output file path (used by --follow-torrent).
-func (d *Download) Path() string { return d.out }
+func (d *Download) Path() string { return d.loadOut() }
+
+// name and out are read by Stat from the reporter goroutine while Run resolves
+// them, so they are stored atomically (mirroring bt.Download.name).
+func (d *Download) setName(s string) { d.name.Store(&s) }
+func (d *Download) setOut(s string)  { d.out.Store(&s) }
+func (d *Download) loadName() string {
+	if p := d.name.Load(); p != nil {
+		return *p
+	}
+	return ""
+}
+func (d *Download) loadOut() string {
+	if p := d.out.Load(); p != nil {
+		return *p
+	}
+	return ""
+}
 
 func (d *Download) Stat() download.Stat {
 	return download.Stat{
-		Name:      d.name,
-		ID:        d.out, // resolved output path; stable per process (CONTRACT)
+		Name:      d.loadName(),
+		ID:        d.loadOut(), // resolved output path; stable per process (CONTRACT)
 		IsBT:      false,
 		Status:    download.Status(atomic.LoadInt32(&d.status)),
 		Total:     atomic.LoadInt64(&d.total),
@@ -392,15 +425,19 @@ func (d *Download) Run(ctx context.Context) (err error) {
 	// the limit past a startup grace. The watcher cancels xferCtx and sets a
 	// flag so we can return the distinct "too slow" error rather than a bare
 	// cancellation.
+	out := d.loadOut()
 	xferCtx, stopGuard, tooSlow := d.speedGuard(ctx)
 	if !pr.ranged || pr.total <= 0 {
-		err = d.single(xferCtx, d.out)
+		err = d.single(xferCtx, out)
 	} else {
-		err = d.segmented(xferCtx, d.out, pr.total, pr.etag, pr.lastmod)
+		err = d.segmented(xferCtx, out, pr.total, pr.etag, pr.lastmod)
 	}
 	stopGuard()
 	if err != nil {
-		if tooSlow() {
+		// Only translate to ErrTooSlow when the transfer actually ended in the
+		// guard's cancellation; a write error or mirror exhaustion that merely
+		// raced the guard firing keeps its own (real) cause and exit code.
+		if tooSlow() && errors.Is(err, context.Canceled) {
 			return fmt.Errorf("%s: %w (<= %d bytes/sec)", d.primary(), ErrTooSlow, d.cfg.LowestSpeedLimit)
 		}
 		return err
@@ -408,14 +445,14 @@ func (d *Download) Run(ctx context.Context) (err error) {
 	// --checksum: verify the finished file before declaring success, so a
 	// corrupted or tampered download fails (--checksum, exit code 32).
 	if newSum != nil {
-		if err = verifyFile(d.out, newSum, sumWant); err != nil {
+		if err = verifyFile(out, newSum, sumWant); err != nil {
 			return err
 		}
 	}
 	// -R / --remote-time: stamp the finished file with the server's mtime.
 	if d.cfg.RemoteTime && pr.lastmod != "" {
 		if t, err := http.ParseTime(pr.lastmod); err == nil {
-			os.Chtimes(d.out, t, t)
+			os.Chtimes(out, t, t)
 		}
 	}
 	d.setStatus(download.Complete)
@@ -427,6 +464,7 @@ func (d *Download) Run(ctx context.Context) (err error) {
 // the original URL. Overwrite / auto-rename is then resolved against the final
 // path, honouring -c so a resumable file is never renamed (items [2],[8],[13]).
 func (d *Download) resolveName(pr probeResult) error {
+	out := d.loadOut()
 	if d.cfg.Out == "" {
 		name := ""
 		if cd := pr.cdisp; cd != "" {
@@ -438,8 +476,9 @@ func (d *Download) resolveName(pr probeResult) error {
 		if name == "" {
 			name = nameFromURL(d.primary())
 		}
-		d.name = name
-		d.out = filepath.Join(d.cfg.Dir, name)
+		out = filepath.Join(d.cfg.Dir, name)
+		d.setName(name)
+		d.setOut(out)
 	}
 
 	// --dry-run writes nothing, so skip overwrite/auto-rename resolution; the name
@@ -450,20 +489,20 @@ func (d *Download) resolveName(pr probeResult) error {
 
 	// -c resumes either our own .got sidecar or a foreign/browser partial file,
 	// so an existing file is never auto-renamed under -c (item [2]).
-	if d.cfg.Continue && fileExists(d.out) {
+	if d.cfg.Continue && fileExists(out) {
 		return nil
 	}
-	if fileExists(d.out) && !d.cfg.AllowOverwrite {
+	if fileExists(out) && !d.cfg.AllowOverwrite {
 		if d.cfg.AutoRename {
-			u, err := uniqueName(d.out)
+			u, err := uniqueName(out)
 			if err != nil {
 				return err
 			}
-			d.out = u
-			d.name = filepath.Base(u)
+			d.setOut(u)
+			d.setName(filepath.Base(u))
 			return nil
 		}
-		return fmt.Errorf("%s: %w (use --allow-overwrite or -c)", d.out, ErrOutputExists)
+		return fmt.Errorf("%s: %w (use --allow-overwrite or -c)", out, ErrOutputExists)
 	}
 	return nil
 }
@@ -528,30 +567,44 @@ func (d *Download) withRetries(ctx context.Context, what string, attempt func()
 	return retriesExhausted(what, tries, lastErr)
 }
 
+// overMirrors calls fn against each mirror URL in turn, starting at offset start
+// so callers can spread work across mirrors (segment index) and rotate on retry.
+// It returns nil on the first success, ctx.Err() if cancelled between mirrors, or
+// the last error once every mirror is spent.
+func (d *Download) overMirrors(ctx context.Context, start int, fn func(uri string) error) error {
+	var lastErr error
+	for i := range d.uris {
+		if ctx.Err() != nil {
+			return ctx.Err()
+		}
+		if err := fn(d.mirror(start + i)); err != nil {
+			lastErr = err
+			continue
+		}
+		return nil
+	}
+	return lastErr
+}
+
 // probeRetry runs probe within the shared retry policy (item [18]). The probe
 // result is captured through pr because withRetries only carries an error.
 func (d *Download) probeRetry(ctx context.Context) (probeResult, error) {
 	// Probe mirrors in order (primary first); the first that answers anchors the
 	// size and validators for the whole download. A dead/404 primary falls over
 	// to the next mirror.
-	var lastErr error
-	for _, u := range d.uris {
-		if ctx.Err() != nil {
-			return probeResult{}, ctx.Err()
-		}
 	var pr probeResult
-		err := d.withRetries(ctx, u, func() error {
+	err := d.overMirrors(ctx, 0, func(uri string) error {
+		return d.withRetries(ctx, uri, func() error {
 			var perr error
-			pr, perr = d.probe(ctx, u)
+			pr, perr = d.probe(ctx, uri)
 			return perr
 		})
-		if err == nil {
+	})
+	if err != nil {
+		return probeResult{}, err
+	}
 	return pr, nil
 }
-		lastErr = err
-	}
-	return probeResult{}, lastErr
-}
 
 // probe issues a one-byte ranged GET to learn the total size, whether the
 // server honours ranges, and the validator headers used for safe resume. It
@@ -565,8 +618,8 @@ func (d *Download) probe(ctx context.Context, uri string) (probeResult, error) {
 	// is already current. Only done when there is no .got control file (an
 	// in-progress resume must not be short-circuited), using the local file's
 	// mtime for If-Modified-Since.
-	if d.cfg.ConditionalGet && !fileExists(controlPath(d.out)) {
-		if fi, err := os.Stat(d.out); err == nil {
+	if out := d.loadOut(); d.cfg.ConditionalGet && !fileExists(controlPath(out)) {
+		if fi, err := os.Stat(out); err == nil {
 			req.Header.Set("If-Modified-Since", fi.ModTime().UTC().Format(http.TimeFormat))
 		}
 	}
@@ -652,37 +705,23 @@ func (d *Download) segmented(ctx context.Context, out string, total int64, etag,
 	saveDone := make(chan struct{})
 	go d.saveLoop(ctx, out, total, etag, lastmod, segs, saveDone)
 
-	jobs := make(chan *seg)
-	go func() {
-		defer close(jobs)
-		for i := range segs {
-			if segs[i].done() {
-				continue
-			}
-			select {
-			case jobs <- &segs[i]:
-			case <-ctx.Done(): // stop feeding once we're tearing down
-				return
-			}
-		}
-	}()
-
+	// One worker per segment. Segments are non-overlapping byte ranges written
+	// with WriteAt, so the workers share no cursor and need no coordination — a
+	// finished worker simply exits. The division (makeSegments / a resumed
+	// control) fixes the parallelism up front; there is no rebalancing.
 	var (
 		wg      sync.WaitGroup
 		errOnce sync.Once
 		runErr  error
 	)
-	for w := 0; w < d.maxConns; w++ {
+	for i := range segs {
 		wg.Add(1)
-		go func() {
+		go func(s *seg) {
 			defer wg.Done()
-			for s := range jobs {
 			if err := d.fetchSeg(ctx, f, s, total); err != nil {
 				errOnce.Do(func() { runErr = err; cancel() })
-					return
 			}
-			}
-		}()
+		}(&segs[i])
 	}
 	wg.Wait()
 	cancel()
@@ -706,30 +745,20 @@ func (d *Download) fetchSeg(ctx context.Context, f *os.File, s *seg, total int64
 	// The segment fails only once every mirror is spent. Starting at s.index
 	// spreads the segments across mirrors round-robin, and each attempt resumes
 	// from s.offset().
-	var lastErr error
-	for i := range d.uris {
-		if ctx.Err() != nil {
-			return ctx.Err()
-		}
-		uri := d.mirror(s.index + i)
-		err := d.withRetries(ctx, fmt.Sprintf("segment %d", s.index), func() error {
+	return d.overMirrors(ctx, s.index, func(uri string) error {
+		return d.withRetries(ctx, fmt.Sprintf("segment %d", s.index), func() error {
 			if s.done() {
 				return nil
 			}
 			return d.fetchOnce(ctx, f, s, uri, total)
 		})
-		if err == nil {
-			return nil
-		}
-		lastErr = err
-	}
-	return lastErr
+	})
 }
 
 func (d *Download) fetchOnce(ctx context.Context, f *os.File, s *seg, uri string, total int64) error {
 	reqCtx, cancel := context.WithCancel(ctx)
 	defer cancel()
-	req, err := d.request(reqCtx, uri, fmt.Sprintf("bytes=%d-%d", s.offset(), s.end))
+	req, err := d.request(reqCtx, uri, fmt.Sprintf("bytes=%d-%d", s.offset(), s.endOff()))
 	if err != nil {
 		return err
 	}
@@ -744,60 +773,95 @@ func (d *Download) fetchOnce(ctx context.Context, f *os.File, s *seg, uri string
 		atomic.AddInt32(&d.conns, -1)
 	}()
 	if resp.StatusCode != http.StatusPartialContent {
-		return statusError(fmt.Sprintf("segment %d: expected 206, got %s", s.index, resp.Status), resp.StatusCode)
+		err := statusError(fmt.Sprintf("segment %d: expected 206, got %s", s.index, resp.Status), resp.StatusCode)
+		// A 200 means this mirror ignores Range entirely; retrying it only burns the
+		// budget, so make it fatal and let fetchSeg fail over to the next mirror.
+		if resp.StatusCode == http.StatusOK {
+			err = fatal{err}
+		}
+		return err
 	}
 	// A mirror must serve the same file as the primary, or its bytes written at
-	// this offset would corrupt the output. Reject a 206 whose total length
-	// disagrees with the probe (validate the total length); fatal so withRetries
-	// stops and fetchSeg falls over to the next mirror instead of writing it.
-	if _, _, t, ok := parseContentRange(resp.Header.Get("Content-Range")); ok && t != total {
-		return fatal{fmt.Errorf("segment %d: %s reports length %d, want %d", s.index, uri, t, total)}
+	// this offset would corrupt the output. Require a Content-Range that confirms
+	// both the offset we asked for and the total length the probe saw; a missing,
+	// unparseable, or divergent range is fatal so withRetries stops and fetchSeg
+	// falls over to the next mirror instead of writing unverified bytes.
+	if start, _, t, ok := parseContentRange(resp.Header.Get("Content-Range")); !ok || t != total || start != s.offset() {
+		return fatal{fmt.Errorf("segment %d: %s returned an unverifiable range %q (want start %d, length %d)",
+			s.index, uri, resp.Header.Get("Content-Range"), s.offset(), total)}
 	}
 	body, stop := d.idleGuard(resp.Body, cancel)
 	defer stop()
 	return d.pump(ctx, f, s, body)
 }
 
-// errIdleTimeout marks a read that stalled past the idle window, so callers can
-// report a distinct "timed out" instead of the bare "context canceled" that the
-// cancelled request would otherwise surface (item [39]).
-var errIdleTimeout = errors.New("idle timeout: no data received")
+// ErrTimeout marks a transfer that stalled past the idle window (--timeout): a
+// distinct "timed out" instead of the bare "context canceled" the cancelled
+// request would otherwise surface (item [39]). main maps it to exit code 2 via
+// errors.Is, so it must stay on the error chain (CONTRACT).
+var ErrTimeout = errors.New("idle timeout: no data received")
 
-// idleReader resets a watchdog timer on every read; if a read stalls longer
-// than the idle window the timer fires and cancels the request, so the blocked
-// Read returns an error instead of hanging forever on a wedged connection.
+// idleReader records the time of the last byte received; a background watcher
+// (idleGuard) cancels the request once a full idle window passes with no
+// progress. Tracking progress by timestamp — rather than arming a per-read timer
+// — means a slow-but-advancing transfer is never aborted, and there is no
+// Reset/Stop race that could poison a connection that was still delivering data.
 type idleReader struct {
 	r        io.Reader
-	timer *time.Timer
 	idle     time.Duration
-	fired atomic.Bool // set when the watchdog cancelled the request
+	last     atomic.Int64 // UnixNano of the last byte received
+	timedOut atomic.Bool  // set when the watcher cancelled the request
 }
 
 func (ir *idleReader) Read(p []byte) (int, error) {
-	ir.timer.Reset(ir.idle)
 	n, err := ir.r.Read(p)
-	ir.timer.Stop() // only the Read itself counts as idle, not write/throttle gaps
-	if err != nil && ir.fired.Load() {
-		// The cancellation came from our watchdog, not the caller's ctx, so
+	if n > 0 {
+		ir.last.Store(time.Now().UnixNano())
+	}
+	if err != nil && ir.timedOut.Load() {
+		// The cancellation came from our watcher, not the caller's ctx, so
 		// translate the read error into the distinct idle-timeout sentinel.
-		return n, fmt.Errorf("%w (after %s)", errIdleTimeout, ir.idle)
+		return n, fmt.Errorf("%w (after %s)", ErrTimeout, ir.idle)
 	}
 	return n, err
 }
 
-// idleGuard wraps body with an idle timeout of d.cfg.Timeout, cancelling the
-// request if no data arrives in that window. It returns the reader to use and a
-// stop func to call when the transfer is done.
+// watch cancels the request once idle passes with no byte received. It polls a
+// few times per window so a stall is caught within ~idle of the last byte,
+// without a shared timer that Read would have to Reset/Stop.
+func (ir *idleReader) watch(stop <-chan struct{}, cancel context.CancelFunc) {
+	tick := ir.idle / 4
+	if tick <= 0 {
+		tick = ir.idle
+	}
+	t := time.NewTicker(tick)
+	defer t.Stop()
+	for {
+		select {
+		case <-stop:
+			return
+		case now := <-t.C:
+			if now.UnixNano()-ir.last.Load() >= int64(ir.idle) {
+				ir.timedOut.Store(true)
+				cancel()
+				return
+			}
+		}
+	}
+}
+
+// idleGuard wraps body with an idle timeout of d.cfg.Timeout: a watcher goroutine
+// cancels the request when no byte arrives for that long. It returns the reader to
+// use and a stop func to call (exactly once) when the transfer is done.
 func (d *Download) idleGuard(body io.Reader, cancel context.CancelFunc) (io.Reader, func()) {
 	if d.cfg.Timeout <= 0 {
 		return body, func() {}
 	}
 	ir := &idleReader{r: body, idle: d.cfg.Timeout}
-	ir.timer = time.AfterFunc(d.cfg.Timeout, func() {
-		ir.fired.Store(true)
-		cancel()
-	})
-	return ir, func() { ir.timer.Stop() }
+	ir.last.Store(time.Now().UnixNano())
+	stop := make(chan struct{})
+	go ir.watch(stop, cancel)
+	return ir, func() { close(stop) }
 }
 
 // speedStartupGrace is how long a download may stay slow before the
@@ -807,10 +871,9 @@ const speedStartupGrace = 10 * time.Second
 
 // belowSpeed reports whether the bytes transferred between two cumulative
 // d.completed samples (prev -> now over one window) put the download at or
-// below limit. A negative delta is not a slow second: d.completed is not
-// strictly monotonic — singleOnce rewrites it with an absolute StoreInt64 and a
-// resumed Range answered by a 200 resets the offset to 0, so the counter can
-// jump backward on a retry. Treating that backward jump as "below limit" would
+// below limit. A negative delta is not a slow second: when a resumed Range is
+// answered by a 200 the transfer restarts from offset 0, so d.completed jumps
+// backward on that retry. Treating that backward jump as "below limit" would
 // false-abort a healthy download, so a reset (delta < 0) reports false; the
 // caller has already advanced its baseline, so the next full window measures the
 // real speed. Only a genuine non-negative delta at or under the limit aborts.
@@ -901,7 +964,9 @@ func statusError(ctxMsg string, code int) error {
 }
 
 // pump copies the response body into the file at the segment's running offset,
-// stopping at the segment end and respecting rate limits.
+// stopping at the segment end and respecting rate limits. Only this worker writes
+// s.written, so the advance is a plain atomic add (Stat and the snapshot read it
+// atomically); the loop ends when the range is filled.
 func (d *Download) pump(ctx context.Context, f *os.File, s *seg, body io.Reader) error {
 	buf := make([]byte, readBuf)
 	for s.remaining() > 0 {
@@ -914,7 +979,7 @@ func (d *Download) pump(ctx context.Context, f *os.File, s *seg, body io.Reader)
 			if _, werr := f.WriteAt(buf[:rd], s.offset()); werr != nil {
 				return werr
 			}
-			s.advance(int64(rd))
+			s.addWritten(int64(rd))
 			atomic.AddInt64(&d.completed, int64(rd))
 			d.throttle(ctx, rd)
 		}
@@ -953,23 +1018,13 @@ func (d *Download) single(ctx context.Context, out string) error {
 	first := true
 	// One connection at a time, but try each mirror: a mirror that fails its
 	// retry budget falls over to the next (resuming from what's already on disk).
-	var lastErr error
-	for i := range d.uris {
-		if ctx.Err() != nil {
-			return ctx.Err()
-		}
-		uri := d.mirror(i)
-		err := d.withRetries(ctx, uri, func() error {
+	return d.overMirrors(ctx, 0, func(uri string) error {
+		return d.withRetries(ctx, uri, func() error {
 			resumeFromDisk := !first || foreignResume
 			first = false
 			return d.singleOnce(ctx, out, uri, resumeFromDisk)
 		})
-		if err == nil {
-			return nil
-		}
-		lastErr = err
-	}
-	return lastErr
+	})
 }
 
 // singleOnce performs one single-stream transfer attempt. When resumeFromDisk is
@@ -1005,6 +1060,19 @@ func (d *Download) singleOnce(ctx context.Context, out, uri string, resumeFromDi
 	if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusPartialContent {
 		return statusError(fmt.Sprintf("%s: %s", uri, resp.Status), resp.StatusCode)
 	}
+	// On failover, resumeAt is the prefix a previous mirror wrote. If this mirror
+	// honours the range, make sure it serves the same file before we append to that
+	// prefix — a divergent total or start means different content, and writing it
+	// past the existing bytes would corrupt the output. Mirror the segmented guard
+	// (fatal, so we fall over rather than append unverified bytes). A same-mirror
+	// retry compares against its own earlier total, so it never false-trips.
+	if resp.StatusCode == http.StatusPartialContent && resumeAt > 0 {
+		if prev := atomic.LoadInt64(&d.total); prev > 0 {
+			if start, _, t, ok := parseContentRange(resp.Header.Get("Content-Range")); ok && (t != prev || start != resumeAt) {
+				return fatal{fmt.Errorf("%s: returned a divergent range %q (want start %d, length %d)", uri, resp.Header.Get("Content-Range"), resumeAt, prev)}
+			}
+		}
+	}
 	// If we asked to resume but the server replied 200 (no range honoured), start
 	// over from the top rather than appending past the existing bytes.
 	if resp.StatusCode == http.StatusOK {
@@ -1047,7 +1115,7 @@ func (d *Download) singleOnce(ctx context.Context, out, uri string, resumeFromDi
 			}
 			off += int64(rd)
 			got += int64(rd)
-			atomic.StoreInt64(&d.completed, off)
+			atomic.AddInt64(&d.completed, int64(rd)) // add deltas, as pump does
 			d.throttle(ctx, rd)
 		}
 		if err == io.EOF {

httpdl/segment.go

@@ -5,8 +5,9 @@ import "sync/atomic"
 // seg is one contiguous byte range of the output file, downloaded by a single
 // ranged GET. A segment IS a byte range — a plain HTTP downloader does not need
 // the Piece/Segment/block layering that exists only to share code with
-// BitTorrent. written is updated with atomic ops so Stat() can read it while a
-// worker advances it.
+// BitTorrent. start and end are fixed when the file is divided; written is
+// advanced (atomically) by the segment's one worker, so Stat() and the resume
+// snapshot can read its frontier while it downloads.
 type seg struct {
 	index   int
 	start   int64 // first byte offset, inclusive
@@ -15,15 +16,18 @@ type seg struct {
 }
 
 func (s *seg) length() int64      { return s.end - s.start + 1 }
+func (s *seg) endOff() int64      { return s.end }
 func (s *seg) done() bool         { return atomic.LoadInt64(&s.written) >= s.length() }
-func (s *seg) advance(n int64)  { atomic.AddInt64(&s.written, n) }
+func (s *seg) addWritten(n int64) { atomic.AddInt64(&s.written, n) }
 func (s *seg) progress() int64    { return atomic.LoadInt64(&s.written) }
 func (s *seg) offset() int64      { return s.start + atomic.LoadInt64(&s.written) }
 func (s *seg) remaining() int64   { return s.length() - atomic.LoadInt64(&s.written) }
 
 // makeSegments divides a file of total bytes into contiguous segments, using at
 // most conns of them and never splitting below minSplit. The remainder lands in
-// the last segment. With conns==1 (the default) this yields one segment.
+// the last segment. With conns==1 (the default) this yields one segment. Each
+// segment gets its own worker, so the division here fixes the parallelism: there
+// is no later rebalancing.
 func makeSegments(total, minSplit int64, conns int) []seg {
 	if conns < 1 {
 		conns = 1

httpdl/segment_test.go

@@ -3,6 +3,9 @@ package httpdl
 import (
 	"os"
 	"path/filepath"
+	"sort"
+	"sync"
+	"sync/atomic"
 	"testing"
 )
 
@@ -52,14 +55,14 @@ func TestSegProgress(t *testing.T) {
 	if s.done() {
 		t.Fatalf("new segment should not be done")
 	}
-	s.advance(60)
+	s.addWritten(60)
 	if s.offset() != 160 {
 		t.Errorf("offset = %d, want 160", s.offset())
 	}
 	if s.remaining() != 40 {
 		t.Errorf("remaining = %d, want 40", s.remaining())
 	}
-	s.advance(40)
+	s.addWritten(40)
 	if !s.done() {
 		t.Errorf("segment should be done after writing full length")
 	}
@@ -186,3 +189,107 @@ func TestParseContentRange(t *testing.T) {
 		t.Errorf("parseContentRange(garbage) ok = true, want false")
 	}
 }
+
+// tilesCover checks that segs cover [0,total) exactly: sorted by start they must
+// be contiguous with no gap and no overlap.
+func tilesCover(t *testing.T, segs []seg, total int64) {
+	t.Helper()
+	sorted := append([]seg(nil), segs...)
+	sort.Slice(sorted, func(i, j int) bool { return sorted[i].start < sorted[j].start })
+	var next int64
+	for _, s := range sorted {
+		if s.start != next {
+			t.Fatalf("segment gap/overlap: next byte %d, got start %d", next, s.start)
+		}
+		next = s.endOff() + 1
+	}
+	if next != total {
+		t.Fatalf("segments cover %d bytes, want %d", next, total)
+	}
+}
+
+// TestSegmentsConcurrentCoverage drives the segments the way real workers do —
+// one worker per segment, each copying its range in small chunks and committing
+// with addWritten. The coverage array proves the core invariant: every byte is
+// written exactly once, with no gap or overlap between adjacent segments.
+func TestSegmentsConcurrentCoverage(t *testing.T) {
+	const (
+		total    = int64(64 * readBuf) // 2 MiB
+		minSplit = int64(readBuf)
+		chunk    = int64(readBuf / 4) // one "read"
+		conns    = 8
+	)
+	segs := makeSegments(total, minSplit, conns)
+	if len(segs) < 2 {
+		t.Fatalf("expected several segments, got %d", len(segs))
+	}
+	cover := make([]uint32, total)
+
+	var wg sync.WaitGroup
+	for i := range segs {
+		wg.Add(1)
+		go func(s *seg) {
+			defer wg.Done()
+			for s.remaining() > 0 {
+				n := chunk
+				if s.remaining() < n {
+					n = s.remaining()
+				}
+				off := s.offset()
+				for j := off; j < off+n; j++ {
+					atomic.AddUint32(&cover[j], 1)
+				}
+				s.addWritten(n)
+			}
+		}(&segs[i])
+	}
+	wg.Wait()
+
+	for i, c := range cover {
+		if c != 1 {
+			t.Fatalf("byte %d written %d times, want exactly 1", i, c)
+		}
+	}
+	tilesCover(t, segs, total)
+}
+
+// TestSnapshotRoundTrips checks the persistence path an interrupt-and-resume
+// relies on: a snapshot of partially-written segments records each frontier, and
+// segsFromControl rebuilds a set that still tiles the file and keeps the bytes
+// already written.
+func TestSnapshotRoundTrips(t *testing.T) {
+	const (
+		total    = int64(8 * readBuf)
+		minSplit = int64(readBuf)
+	)
+	segs := makeSegments(total, minSplit, 4)
+	if len(segs) < 2 {
+		t.Fatalf("expected several segments, got %d", len(segs))
+	}
+	// Each segment makes some progress, so the snapshot has a real frontier to
+	// carry across the round trip.
+	var want int64
+	for i := range segs {
+		n := int64(readBuf)
+		if n > segs[i].length() {
+			n = segs[i].length()
+		}
+		segs[i].addWritten(n)
+		want += n
+	}
+
+	c := snapshot("http://x", total, "", "", segs)
+	if len(c.Segs) != len(segs) {
+		t.Fatalf("snapshot has %d segments, want %d", len(c.Segs), len(segs))
+	}
+
+	rebuilt := segsFromControl(&c)
+	tilesCover(t, rebuilt, total)
+	var written int64
+	for _, s := range rebuilt {
+		written += s.progress()
+	}
+	if written != want {
+		t.Errorf("rebuilt written = %d, want %d (bytes must survive the round trip)", written, want)
+	}
+}

main.go

@@ -100,9 +100,15 @@ func run(args []string) int {
 	eng := download.NewEngine(opts.Int("max-concurrent-downloads"))
 
 	uiCtx, uiCancel := context.WithCancel(context.Background())
+	uiDone := make(chan struct{})
 	if !opts.Bool("quiet") && !opts.Bool("dry-run") {
 		rep := progress.New(eng.Snapshot, opts.Bool("human-readable"))
-		go rep.Run(uiCtx)
+		go func() {
+			rep.Run(uiCtx)
+			close(uiDone)
+		}()
+	} else {
+		close(uiDone)
 	}
 
 	jobsRef.set(jobs)
@@ -129,7 +135,7 @@ func run(args []string) int {
 	}
 
 	uiCancel()
-	time.Sleep(20 * time.Millisecond) // let the renderer clear its line
+	<-uiDone // wait for the renderer's final frame before printing the OK/FAIL lines
 
 	saveCookies(jobs)
 
@@ -190,9 +196,9 @@ type failedDownload struct {
 	err  error
 }
 
-func (f failedDownload) Name() string              { return f.name }
-func (f failedDownload) Run(context.Context) error { return f.err }
-func (f failedDownload) Stat() download.Stat {
+func (f *failedDownload) Name() string              { return f.name }
+func (f *failedDownload) Run(context.Context) error { return f.err }
+func (f *failedDownload) Stat() download.Stat {
 	return download.Stat{Name: f.name, Status: download.Errored, Total: -1}
 }
 
@@ -224,6 +230,24 @@ func dedupeTorrents(uris []string, follow bool) map[string]string {
 	return dup
 }
 
+// markInfoHash records the v1 infohash of the .torrent at path in seen and
+// reports whether it repeats one already seen, returning the path first recorded
+// under that infohash. Callers fail the duplicate rather than let two jobs share
+// one torrent on the client (see bt.SourceInfoHash for why that aliasing is
+// unsafe). A v2-only or unreadable infohash is never a duplicate — the dedup
+// can't see it, so it runs.
+func markInfoHash(seen map[metainfo.Hash]string, path string) (first string, dup bool) {
+	h, ok := bt.SourceInfoHash(path, true)
+	if !ok {
+		return "", false
+	}
+	if first, dup = seen[h]; dup {
+		return first, true
+	}
+	seen[h] = path
+	return "", false
+}
+
 func build(opts *cli.Options, targets []target) ([]job, *torrent.Client, error) {
 	flat := allURIs(targets)
 	// Two sources naming the same torrent (a magnet and its own .torrent, say)
@@ -263,7 +287,7 @@ func build(opts *cli.Options, targets []target) ([]job, *torrent.Client, error)
 		u := t.uris[0] // primary: classifies the target and names the session source
 		src := strings.Join(t.uris, "\t")
 		if first, isDup := dups[u]; isDup {
-			out = append(out, job{source: src, dl: failedDownload{
+			out = append(out, job{source: src, dl: &failedDownload{
 				name: u,
 				err:  fmt.Errorf("%w: same torrent as %s", errDuplicate, first),
 			}})
@@ -358,6 +382,7 @@ func runJobs(ctx context.Context, eng *download.Engine, jobs []job) []download.R
 // so a regular download that merely ends in ".torrent" is left alone.
 func followUps(jobs []job, client *torrent.Client, bo bt.Options) []job {
 	var out []job
+	seen := map[metainfo.Hash]string{}
 	for _, j := range jobs {
 		h, ok := j.dl.(*httpdl.Download)
 		if !ok || j.dl.Stat().Status != download.Complete {
@@ -373,6 +398,17 @@ func followUps(jobs []job, client *torrent.Client, bo bt.Options) []job {
 		if _, err := bt.Files(path); err != nil {
 			continue // downloaded file is not a valid torrent
 		}
+		// Two fetched .torrent files that name the same torrent would share one
+		// torrent on the refcount-less client: the first to finish Drops it out
+		// from under the other, stranding it at 0%. build() dedupes pass-1 sources
+		// but cannot reach a not-yet-fetched HTTP .torrent, so dedupe here too.
+		if first, dup := markInfoHash(seen, path); dup {
+			out = append(out, job{source: path, dl: &failedDownload{
+				name: path,
+				err:  fmt.Errorf("%w: same torrent as %s", errDuplicate, first),
+			}})
+			continue
+		}
 		out = append(out, job{source: path, dl: bt.New(client, path, true, bo)})
 	}
 	return out
@@ -408,22 +444,23 @@ func allURIs(ts []target) []string {
 // gatherURIs collects download targets from the command line, --torrent-file,
 // and --input-file. Plain command-line http/https URIs are grouped into ONE
 // mirrored download by default (every command-line URI names the same file);
-// -Z/--force-sequential makes each its own download. Torrents and magnets
-// are always one target each; --input-file groups TAB-separated URIs per line.
+// -Z/--force-sequential makes each its own download. Torrents, magnets, and
+// .torrent URLs (fetched over HTTP then followed) are always one target each,
+// since distinct torrents are not mirrors of one another; --input-file groups
+// TAB-separated URIs per line.
 func gatherURIs(opts *cli.Options, cmdURIs []string) []target {
 	var ts []target
 	follow := opts.Bool("follow-torrent")
 	seq := opts.Bool("force-sequential")
 	var httpGroup []string
 	for _, u := range cmdURIs {
-		switch uriKind(u, follow) {
-		case kindHTTP, kindFollow:
-			if seq {
-				ts = append(ts, target{uris: []string{u}})
-			} else {
+		// Only plain HTTP URLs collapse into one mirror download (alternate sources
+		// for the same file); -Z opts out. A .torrent URL (kindFollow), like a
+		// torrent or magnet, is its own download — distinct torrents are never
+		// mirrors of one another.
+		if uriKind(u, follow) == kindHTTP && !seq {
 			httpGroup = append(httpGroup, u)
-			}
-		default:
+		} else {
 			ts = append(ts, target{uris: []string{u}})
 		}
 	}
@@ -679,42 +716,29 @@ func exitCode(err error) int {
 
 // isNameResolution reports whether err is (or wraps) a DNS lookup failure —
 // "name resolution failed" (19), which usually points at the user's own
-// network or resolver rather than a dead remote.
+// network or resolver rather than a dead remote. The stdlib reports every such
+// failure (no-such-host, server-misbehaving) as *net.DNSError.
 func isNameResolution(err error) bool {
 	var de *net.DNSError
-	if errors.As(err, &de) {
-		return true
-	}
-	msg := strings.ToLower(err.Error())
-	return strings.Contains(msg, "no such host") || strings.Contains(msg, "server misbehaving")
+	return errors.As(err, &de)
 }
 
 // isNetwork reports whether err is a connection-level failure — refused, reset,
-// or an unreachable host/network — a "network problem" (6).
+// or an unreachable host/network — a "network problem" (6). A dial error from
+// net/http wraps the syscall errno, so the typed check sees through it.
 func isNetwork(err error) bool {
-	if errors.Is(err, syscall.ECONNREFUSED) || errors.Is(err, syscall.ECONNRESET) ||
-		errors.Is(err, syscall.ENETUNREACH) || errors.Is(err, syscall.EHOSTUNREACH) {
-		return true
-	}
-	msg := strings.ToLower(err.Error())
-	return strings.Contains(msg, "connection refused") ||
-		strings.Contains(msg, "connection reset") ||
-		strings.Contains(msg, "network is unreachable") ||
-		strings.Contains(msg, "no route to host")
+	return errors.Is(err, syscall.ECONNREFUSED) || errors.Is(err, syscall.ECONNRESET) ||
+		errors.Is(err, syscall.ENETUNREACH) || errors.Is(err, syscall.EHOSTUNREACH)
 }
 
 // isTimeout reports whether err is (or wraps) a timeout: a deadline exceeded, a
-// net.Error that timed out, or an idle-read timeout reported as such.
+// net.Error that timed out, or our own idle-read timeout (httpdl.ErrTimeout).
 func isTimeout(err error) bool {
-	if errors.Is(err, context.DeadlineExceeded) {
+	if errors.Is(err, context.DeadlineExceeded) || errors.Is(err, httpdl.ErrTimeout) {
 		return true
 	}
 	var ne net.Error
-	if errors.As(err, &ne) && ne.Timeout() {
-		return true
-	}
-	msg := strings.ToLower(err.Error())
-	return strings.Contains(msg, "timeout") || strings.Contains(msg, "timed out")
+	return errors.As(err, &ne) && ne.Timeout()
 }
 
 // saveSession writes the sources of every download that did not finish to path,
@@ -799,6 +823,11 @@ func makeLimiter(bps int64) *rate.Limiter {
 	return rate.NewLimiter(rate.Limit(bps), download.LimiterBurst(bps))
 }
 
+// maxSelectIndex bounds how far a --select-file range is expanded: a torrent has
+// at most a few thousand files, so a degenerate spec like "1-9999999999" must not
+// spin or balloon the map. Indexes past the real file count are ignored anyway.
+const maxSelectIndex = 1 << 20
+
 // parseSelect parses "1,3-5" into a set of 1-based file indexes.
 func parseSelect(s string) map[int]bool {
 	s = strings.TrimSpace(s)
@@ -816,10 +845,14 @@ func parseSelect(s string) map[int]bool {
 			continue
 		}
 		b, _ := strconv.Atoi(strings.TrimSpace(hi))
-		for i := a; i <= b; i++ {
-			if i > 0 {
-				out[i] = true
+		if a < 1 {
+			a = 1
 		}
+		if b > maxSelectIndex {
+			b = maxSelectIndex
+		}
+		for i := a; i <= b; i++ {
+			out[i] = true
 		}
 	}
 	return out

main_test.go

@@ -11,6 +11,9 @@ import (
 	"syscall"
 	"testing"
 
+	"github.com/anacrolix/torrent/bencode"
+	"github.com/anacrolix/torrent/metainfo"
+	"github.com/hanbok/got/bt"
 	"github.com/hanbok/got/cli"
 	"github.com/hanbok/got/download"
 	"github.com/hanbok/got/httpdl"
@@ -66,16 +69,14 @@ func TestExitCode(t *testing.T) {
 		err  error
 		want int
 	}{
-		{"idle timeout", errors.New("idle timeout: no data received"), 2},
-		{"metadata timed out", errors.New("timed out fetching metadata after 3s"), 2},
+		{"idle timeout", fmt.Errorf("segment 0: %w (after 1m0s)", httpdl.ErrTimeout), 2},
+		{"metadata timed out", fmt.Errorf("timed out fetching metadata after 3s: %w", context.DeadlineExceeded), 2},
 		{"deadline", context.DeadlineExceeded, 2},
 		{"file exists", fmt.Errorf("/tmp/x: %w (use --allow-overwrite or -c)", httpdl.ErrOutputExists), 13},
 		{"dns typed", dnsErr, 19},
 		{"dns wrapped through retries", fmt.Errorf("http://x: %w (after 5 tries)", dnsErr), 19},
-		{"dns by message", errors.New("dial tcp: lookup nope.invalid: no such host"), 19},
 		{"refused typed", refused, 6},
 		{"refused wrapped through retries", fmt.Errorf("http://x: %w (after 5 tries)", refused), 6},
-		{"refused by message", errors.New("dial tcp 127.0.0.1:1: connect: connection refused"), 6},
 		{"not found", fmt.Errorf("%w: http://x/y: 404 Not Found", httpdl.ErrNotFound), 3},
 		{"too slow", fmt.Errorf("http://x: %w (<= %d bytes/sec)", httpdl.ErrTooSlow, 1024), 5},
 		{"checksum", fmt.Errorf("/tmp/x: %w (want a, got b)", httpdl.ErrChecksum), 32},
@@ -112,8 +113,8 @@ func TestDedupeTorrents(t *testing.T) {
 }
 
 // TestGatherURIsGrouping checks the command-line grouping: plain http URIs
-// become one mirrored download by default, -Z splits them, and torrents/magnets
-// stay separate.
+// become one mirrored download by default, -Z splits them, and torrents,
+// magnets, and .torrent URLs stay separate.
 func TestGatherURIsGrouping(t *testing.T) {
 	parse := func(args ...string) []target {
 		res, err := cli.Parse(append([]string{"--no-conf"}, args...))
@@ -131,6 +132,16 @@ func TestGatherURIsGrouping(t *testing.T) {
 	if ts := parse("http://a/x", "magnet:?xt=urn:btih:abc"); len(ts) != 2 {
 		t.Errorf("http + magnet: got %d targets, want 2 (magnet never mirrors)", len(ts))
 	}
+	// Distinct .torrent URLs are separate downloads, not mirrors of one file
+	// (follow-torrent defaults on, so each is fetched then followed).
+	if ts := parse("http://a/x.torrent", "http://b/y.torrent", "http://c/z.torrent"); len(ts) != 3 {
+		t.Errorf(".torrent URLs: got %d targets, want 3 separate downloads", len(ts))
+	}
+	// A plain http URL still mirror-groups even alongside a .torrent URL: one
+	// http group of 1 + one torrent target = 2.
+	if ts := parse("http://a/x", "http://b/y.torrent"); len(ts) != 2 {
+		t.Errorf("http + .torrent: got %d targets, want 2", len(ts))
+	}
 }
 
 // TestReadInputFileTAB checks the input-file grouping: TAB-separated URIs on
@@ -152,10 +163,69 @@ func TestReadInputFileTAB(t *testing.T) {
 	}
 }
 
+// writeTorrent creates a .torrent file at dir/name whose info dict is built from
+// a file of the given content and internal name. Two calls with the same
+// internalName and content produce the same infohash regardless of the output
+// filename, so the test can make two .torrent files that name one torrent.
+func writeTorrent(t *testing.T, dir, name, internalName string, content []byte) string {
+	t.Helper()
+	data := filepath.Join(dir, internalName)
+	if err := os.WriteFile(data, content, 0o644); err != nil {
+		t.Fatal(err)
+	}
+	info := metainfo.Info{PieceLength: 32 * 1024}
+	if err := info.BuildFromFilePath(data); err != nil {
+		t.Fatal(err)
+	}
+	b, err := bencode.Marshal(info)
+	if err != nil {
+		t.Fatal(err)
+	}
+	tp := filepath.Join(dir, name)
+	f, err := os.Create(tp)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+	if err := (&metainfo.MetaInfo{InfoBytes: b}).Write(f); err != nil {
+		t.Fatal(err)
+	}
+	return tp
+}
+
+// TestFollowUpInfoHashDedup covers the fix for two fetched .torrent files that
+// name the same torrent: the second must be flagged a duplicate so followUps
+// fails it rather than letting both share — and Drop — one torrent on the client.
+func TestFollowUpInfoHashDedup(t *testing.T) {
+	dir := t.TempDir()
+	a := writeTorrent(t, dir, "a.torrent", "same", []byte("AAAAAAAA"))
+	b := writeTorrent(t, dir, "b.torrent", "same", []byte("AAAAAAAA")) // same infohash as a
+	c := writeTorrent(t, dir, "c.torrent", "diff", []byte("BBBBBBBB")) // a distinct torrent
+
+	// Sanity-check the fixture: a and b really share an infohash, c differs.
+	ha, _ := bt.SourceInfoHash(a, true)
+	hb, _ := bt.SourceInfoHash(b, true)
+	hc, _ := bt.SourceInfoHash(c, true)
+	if ha != hb || ha == hc {
+		t.Fatalf("fixture: want a==b!=c infohashes, got a=%v b=%v c=%v", ha, hb, hc)
+	}
+
+	seen := map[metainfo.Hash]string{}
+	if first, dup := markInfoHash(seen, a); dup {
+		t.Fatalf("a is the first occurrence, wrongly flagged a duplicate of %s", first)
+	}
+	if first, dup := markInfoHash(seen, b); !dup || first != a {
+		t.Errorf("b should duplicate a: got first=%q dup=%v, want %q true", first, dup, a)
+	}
+	if _, dup := markInfoHash(seen, c); dup {
+		t.Errorf("c is a distinct torrent, wrongly flagged a duplicate")
+	}
+}
+
 func TestReportExit(t *testing.T) {
 	canceled := download.Result{Name: "a", Err: context.Canceled}
 	done := download.Result{Name: "b", Err: nil}
-	timeout := download.Result{Name: "c", Err: errors.New("idle timeout")}
+	timeout := download.Result{Name: "c", Err: httpdl.ErrTimeout}
 
 	tests := []struct {
 		name    string

progress/progress.go

@@ -25,8 +25,10 @@ type Reporter struct {
 	w        io.Writer
 	tty      bool
 	width    int
+	height   int
 
 	win       map[string]*speedWindow // keyed by Stat.ID
+	prevLines int                     // lines drawn in the previous TTY frame, redrawn in place
 	lastLog   time.Time               // last non-TTY line emitted
 }
 
@@ -62,6 +64,7 @@ func New(snap func() []download.Stat, human bool) *Reporter {
 		w:        os.Stdout,
 		tty:      term.IsTerminal(int(os.Stdout.Fd())),
 		width:    80,
+		height:   24,
 		win:      map[string]*speedWindow{},
 	}
 }
@@ -103,29 +106,21 @@ func (r *Reporter) render(final bool) {
 		}
 	}
 
-	var line string
-	switch len(stats) {
-	case 0:
-		if !final && r.tty {
-			return // nothing active; leave the line as-is
-		}
-	case 1:
-		line = r.lineOne(stats[0])
-	default:
-		line = r.lineMany(stats)
-	}
-
 	if r.tty {
 		r.width = termWidth(r.width)
-		line = clampRunes(line, r.width)
-		fmt.Fprint(r.w, "\r"+line+"\x1b[K")
-		if final {
-			fmt.Fprintln(r.w)
-		}
+		r.height = termHeight(r.height)
+		r.redraw(r.block(stats), final)
 		return
 	}
-	// Not a TTY: can't redraw one line, so print sparingly (and always the
-	// final line) to keep redirected output and logs readable.
+	// Not a TTY: no cursor control, so emit a single line sparingly (and always
+	// the final one) to keep redirected output and logs readable.
+	var line string
+	switch {
+	case len(stats) == 1:
+		line = r.lineOne(stats[0])
+	case len(stats) > 1:
+		line = r.summary(stats)
+	}
 	if line != "" && (final || now.Sub(r.lastLog) >= logEvery) {
 		fmt.Fprintln(r.w, line)
 		r.lastLog = now
@@ -158,34 +153,189 @@ func (r *Reporter) lineOne(s download.Stat) string {
 		fmt.Fprintf(&b, " UL:%s", speed(ul, r.human))
 	}
 	if !seeding && s.Total > 0 && dl > 0 {
-		eta := time.Duration(float64(s.Total-s.Completed)/float64(dl)) * time.Second
-		fmt.Fprintf(&b, " ETA:%s", secfmt(eta))
+		fmt.Fprintf(&b, " ETA:%s", secfmt(etaDuration(s.Total-s.Completed, dl)))
 	}
 	b.WriteByte(']')
 	return b.String()
 }
 
-func (r *Reporter) lineMany(stats []download.Stat) string {
+// nameW is the fixed rune width of the name column in the table, matching
+// shortName's cap so a padded name lines the columns up.
+const nameW = 20
+
+// block builds the lines of the live display: the single-download dashboard for
+// one download, a name/bar/speed/ETA table for several, or a one-line summary
+// when the table would not fit the window.
+func (r *Reporter) block(stats []download.Stat) []string {
+	switch {
+	case len(stats) == 0:
+		return nil
+	case len(stats) == 1:
+		return []string{r.lineOne(stats[0])}
+	case len(stats)+1 > r.height: // header + one row each would overflow the screen
+		return []string{r.summary(stats)}
+	default:
+		out := make([]string, 0, len(stats)+1)
+		out = append(out, r.summary(stats))
+		for _, s := range stats {
+			out = append(out, r.tableRow(s))
+		}
+		return out
+	}
+}
+
+// redraw repaints the block in place: move to the top of the previous frame,
+// clear it, and print the new lines clamped to the terminal width. A stray line
+// from stderr that lands in the block is painted over on the next tick.
+func (r *Reporter) redraw(lines []string, final bool) {
+	if r.prevLines > 0 {
+		if r.prevLines > 1 {
+			fmt.Fprintf(r.w, "\x1b[%dA", r.prevLines-1) // up to the first line
+		}
+		fmt.Fprint(r.w, "\r\x1b[J") // column 0, clear to end of screen
+	}
+	for i, ln := range lines {
+		if i > 0 {
+			fmt.Fprint(r.w, "\n")
+		}
+		fmt.Fprint(r.w, clampRunes(ln, r.width))
+	}
+	r.prevLines = len(lines)
+	if final && len(lines) > 0 {
+		fmt.Fprintln(r.w) // leave the cursor below the block for the OK/FAIL lines
+		r.prevLines = 0
+	}
+}
+
+// summary is the header/aggregate line: the active count and total down/up
+// speed, plus a stalled count when any download has gone quiet.
+func (r *Reporter) summary(stats []download.Stat) string {
+	if len(stats) == 0 {
+		return ""
+	}
 	var totDL, totUL int64
+	stalled, waiting := 0, 0
 	for _, s := range stats {
 		dl, ul := r.rates(s)
 		totDL += dl
 		totUL += ul
+		if s.Status == download.Waiting {
+			waiting++
+			continue
 		}
-	var b strings.Builder
-	fmt.Fprintf(&b, "[%d active DL:%s UL:%s]", len(stats), speed(totDL, r.human), speed(totUL, r.human))
-	for i, s := range stats {
-		if i >= 4 {
-			fmt.Fprintf(&b, "[+%d]", len(stats)-i)
-			break
-		}
-		if s.Total > 0 {
-			fmt.Fprintf(&b, "[%s %d%%]", shortName(s.Name), percent(s.Completed, s.Total))
-		} else {
-			fmt.Fprintf(&b, "[%s %s]", shortName(s.Name), humanSize(s.Completed, r.human))
+		if r.isStalled(s, dl) {
+			stalled++
 		}
 	}
-	return b.String()
+	line := fmt.Sprintf("%d active   DL:%s UL:%s", len(stats)-waiting, speed(totDL, r.human), speed(totUL, r.human))
+	if waiting > 0 {
+		line += fmt.Sprintf("  (%d waiting)", waiting)
+	}
+	if stalled > 0 {
+		line += fmt.Sprintf("  (%d stalled)", stalled)
+	}
+	return line
+}
+
+// tableRow renders one download as "name |bar| pct metric tail": the bar and
+// percent for progress, then the field that answers "stalled or fast" (DL speed
+// or seeding) and a tail (ETA, upload rate, or a stalled flag).
+func (r *Reporter) tableRow(s download.Stat) string {
+	dl, ul := r.rates(s)
+	metric, tail := r.rowMetric(s, dl, ul)
+	return fmt.Sprintf("  %s  %s %s  %-9s %s", padRune(shortName(s.Name), nameW), barOf(s), pctField(s), metric, tail)
+}
+
+// rowMetric returns a table row's two trailing fields for the download's state:
+// the primary metric (DL speed, "seeding", "done", "failed") and a tail (ETA,
+// upload rate, or a "stalled" flag).
+func (r *Reporter) rowMetric(s download.Stat, dl, ul int64) (metric, tail string) {
+	switch s.Status {
+	case download.Waiting:
+		return "queued", ""
+	case download.Seeding:
+		return "seeding", "UL:" + speed(ul, r.human)
+	case download.Complete:
+		return "done", ""
+	case download.Errored:
+		return "failed", ""
+	default:
+		metric = "DL:" + speed(dl, r.human)
+		switch {
+		case dl > 0 && s.Total > 0:
+			tail = secfmt(etaDuration(s.Total-s.Completed, dl))
+		case r.isStalled(s, dl):
+			tail = "stalled"
+		}
+		return metric, tail
+	}
+}
+
+// maxETASeconds caps an ETA before it becomes a Duration: a near-stalled download
+// yields an astronomically large seconds value, and time.Duration(secs) *
+// time.Second would overflow int64 and wrap to a bogus tiny ETA. secfmt renders
+// anything past 99h as "--", so clamping to 100h loses nothing.
+const maxETASeconds = 100 * 3600
+
+func etaDuration(remaining, dl int64) time.Duration {
+	secs := float64(remaining) / float64(dl)
+	if secs > maxETASeconds {
+		secs = maxETASeconds
+	}
+	return time.Duration(secs) * time.Second
+}
+
+// isStalled reports an active download that has gone a while with no new bytes,
+// so the table can flag it rather than leave the eye to read DL:0B. A download
+// too young to have a rate yet is not stalled.
+func (r *Reporter) isStalled(s download.Stat, dl int64) bool {
+	if s.Status != download.Active || dl > 0 {
+		return false
+	}
+	w := r.win[s.ID]
+	if w == nil || len(w.samples) < 2 {
+		return false
+	}
+	return w.samples[len(w.samples)-1].t.Sub(w.samples[0].t) >= 4*time.Second
+}
+
+// barOf renders a fixed-width progress bar. A seeding or complete download is
+// full; an unknown total (no Content-Length, or pre-metadata) shows empty.
+func barOf(s download.Stat) string {
+	const cells = 12
+	k := 0
+	switch {
+	case s.Status == download.Seeding || s.Status == download.Complete:
+		k = cells
+	case s.Total > 0:
+		k = int(int64(cells) * s.Completed / s.Total)
+		if k > cells {
+			k = cells
+		}
+	}
+	return "|" + strings.Repeat("#", k) + strings.Repeat("-", cells-k) + "|"
+}
+
+// pctField is the percent column: a number, full for seeding/complete, or "--"
+// when the total is unknown.
+func pctField(s download.Stat) string {
+	switch {
+	case s.Status == download.Seeding || s.Status == download.Complete:
+		return "100%"
+	case s.Total > 0:
+		return fmt.Sprintf("%3d%%", percent(s.Completed, s.Total))
+	default:
+		return "  --"
+	}
+}
+
+// padRune right-pads s with spaces to w runes (it is never longer, having been
+// through shortName) so table columns line up on rune count.
+func padRune(s string, w int) string {
+	if n := utf8.RuneCountInString(s); n < w {
+		return s + strings.Repeat(" ", w-n)
+	}
+	return s
 }
 
 // add records a sample and drops any that have fallen out of the window. A
@@ -272,3 +422,13 @@ func termWidth(prev int) int {
 	}
 	return 80
 }
+
+func termHeight(prev int) int {
+	if _, h, err := term.GetSize(int(os.Stdout.Fd())); err == nil && h > 0 {
+		return h
+	}
+	if prev > 0 {
+		return prev
+	}
+	return 24
+}

progress/progress_test.go

@@ -1,6 +1,7 @@
 package progress
 
 import (
+	"bytes"
 	"strings"
 	"testing"
 	"time"
@@ -112,6 +113,100 @@ func TestLineOneCNSD(t *testing.T) {
 	}
 }
 
+func TestBarOf(t *testing.T) {
+	tests := []struct {
+		name string
+		s    download.Stat
+		want string
+	}{
+		{"empty", download.Stat{Status: download.Active, Total: 100, Completed: 0}, "|------------|"},
+		{"half", download.Stat{Status: download.Active, Total: 100, Completed: 50}, "|######------|"},
+		{"full by complete", download.Stat{Status: download.Complete}, "|############|"},
+		{"full by seeding", download.Stat{Status: download.Seeding}, "|############|"},
+		{"unknown total is empty", download.Stat{Status: download.Active, Total: -1, Completed: 9}, "|------------|"},
+	}
+	for _, tc := range tests {
+		if got := barOf(tc.s); got != tc.want {
+			t.Errorf("%s: barOf = %q, want %q", tc.name, got, tc.want)
+		}
+	}
+}
+
+func TestPctField(t *testing.T) {
+	if got := pctField(download.Stat{Status: download.Active, Total: 100, Completed: 50}); got != " 50%" {
+		t.Errorf("active 50%% = %q, want ' 50%%'", got)
+	}
+	if got := pctField(download.Stat{Status: download.Seeding}); got != "100%" {
+		t.Errorf("seeding = %q, want 100%%", got)
+	}
+	if got := pctField(download.Stat{Status: download.Active, Total: -1}); got != "  --" {
+		t.Errorf("unknown total = %q, want '  --'", got)
+	}
+}
+
+// TestRowMetric: the two trailing fields per download state.
+func TestRowMetric(t *testing.T) {
+	r := newReporter(true)
+	if m, tail := r.rowMetric(download.Stat{Status: download.Active, Total: 100, Completed: 50}, 10, 0); !strings.HasPrefix(m, "DL:") || tail == "" {
+		t.Errorf("active downloading: metric=%q tail=%q, want DL:… + an ETA", m, tail)
+	}
+	if m, tail := r.rowMetric(download.Stat{Status: download.Seeding}, 0, 128<<10); m != "seeding" || !strings.HasPrefix(tail, "UL:") {
+		t.Errorf("seeding: metric=%q tail=%q, want seeding + UL:…", m, tail)
+	}
+	if m, _ := r.rowMetric(download.Stat{Status: download.Complete}, 0, 0); m != "done" {
+		t.Errorf("complete metric=%q, want done", m)
+	}
+}
+
+// TestBlockTableAndFallback: several downloads render as header+rows when they
+// fit, and collapse to a single summary line when the window is too short.
+func TestBlockTableAndFallback(t *testing.T) {
+	r := newReporter(true)
+	stats := []download.Stat{
+		{ID: "a", Name: "a", Status: download.Active, Total: 100, Completed: 50},
+		{ID: "b", Name: "b", Status: download.Active, Total: 100, Completed: 10},
+	}
+	r.height = 24
+	if got := r.block(stats); len(got) != 3 { // header + 2 rows
+		t.Errorf("table block = %d lines, want 3:\n%v", len(got), got)
+	}
+	r.height = 2 // header + 2 rows = 3 > 2
+	if got := r.block(stats); len(got) != 1 {
+		t.Errorf("overflow block = %d lines, want 1 summary:\n%v", len(got), got)
+	}
+}
+
+// TestRenderRedraw: the TTY path draws the block, then on the next frame moves
+// the cursor up over the previous frame and clears it before repainting.
+func TestRenderRedraw(t *testing.T) {
+	snap := []download.Stat{
+		{ID: "a", Name: "alpha", IsBT: true, Status: download.Active, Total: 100, Completed: 50},
+		{ID: "b", Name: "beta", IsBT: true, Status: download.Seeding, Total: 100, Completed: 100, Uploaded: 200},
+	}
+	var buf bytes.Buffer
+	r := &Reporter{
+		snap:  func() []download.Stat { return snap },
+		human: true, w: &buf, tty: true, width: 200, height: 24,
+		win: map[string]*speedWindow{},
+	}
+	r.render(false)
+	first := buf.String()
+	for _, want := range []string{"2 active", "alpha", "seeding", "|"} {
+		if !strings.Contains(first, want) {
+			t.Fatalf("first frame missing %q:\n%q", want, first)
+		}
+	}
+	buf.Reset()
+	r.render(false)
+	second := buf.String()
+	if !strings.Contains(second, "\x1b[2A") { // up prevLines-1 = 3-1
+		t.Errorf("second frame should move cursor up 2 lines:\n%q", second)
+	}
+	if !strings.Contains(second, "\x1b[J") {
+		t.Errorf("second frame should clear to end of screen:\n%q", second)
+	}
+}
+
 // TestShortNameRune ensures CJK names are truncated on runes, not bytes.
 func TestShortNameRune(t *testing.T) {
 	name := strings.Repeat("あ", 30) // 30 runes, 90 bytes