54 lines
1.7 KiB
Go
54 lines
1.7 KiB
Go
package httpdl
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import "sync/atomic"
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// seg is one contiguous byte range of the output file, downloaded by a single
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// ranged GET. A segment IS a byte range — a plain HTTP downloader does not need
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// the Piece/Segment/block layering that exists only to share code with
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// BitTorrent. written is updated with atomic ops so Stat() can read it while a
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// worker advances it.
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type seg struct {
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index int
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start int64 // first byte offset, inclusive
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end int64 // last byte offset, inclusive
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written int64 // bytes already written into this segment (the resume point)
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}
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func (s *seg) length() int64 { return s.end - s.start + 1 }
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func (s *seg) done() bool { return atomic.LoadInt64(&s.written) >= s.length() }
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func (s *seg) advance(n int64) { atomic.AddInt64(&s.written, n) }
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func (s *seg) progress() int64 { return atomic.LoadInt64(&s.written) }
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func (s *seg) offset() int64 { return s.start + atomic.LoadInt64(&s.written) }
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func (s *seg) remaining() int64 { return s.length() - atomic.LoadInt64(&s.written) }
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// makeSegments divides a file of total bytes into contiguous segments, using at
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// most conns of them and never splitting below minSplit. The remainder lands in
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// the last segment. With conns==1 (the default) this yields one segment.
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func makeSegments(total, minSplit int64, conns int) []seg {
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if conns < 1 {
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conns = 1
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}
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if minSplit < 1 {
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minSplit = 1
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}
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n := int64(conns)
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if max := total / minSplit; max < n {
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n = max
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}
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if n < 1 {
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n = 1
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}
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chunk := total / n
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segs := make([]seg, n)
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var start int64
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for i := int64(0); i < n; i++ {
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end := start + chunk - 1
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if i == n-1 {
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end = total - 1
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}
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segs[i] = seg{index: int(i), start: start, end: end}
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start = end + 1
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}
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return segs
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}
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