From 623d9e0e0627c3ac2d8ef0f750746a5714d4d28a Mon Sep 17 00:00:00 2001
From: Matt Joiner <anacrolix@gmail.com>
Date: Sun, 7 Feb 2016 21:58:48 +1100
Subject: [PATCH] Rework requesting of shuffled pending pieces

---
 piece.go   | 34 ++++++++++------------------------
 torrent.go | 14 ++++++++------
 2 files changed, 18 insertions(+), 30 deletions(-)

diff --git a/piece.go b/piece.go
index 9f22d718..bcc09546 100644
--- a/piece.go
+++ b/piece.go
@@ -1,11 +1,9 @@
 package torrent
 
 import (
-	"math/rand"
 	"sync"
 
 	"github.com/anacrolix/missinggo/bitmap"
-	"github.com/bradfitz/iter"
 
 	pp "github.com/anacrolix/torrent/peer_protocol"
 )
@@ -30,7 +28,9 @@ const (
 
 type piece struct {
 	// The completed piece SHA1 hash, from the metainfo "pieces" field.
-	Hash pieceSum
+	Hash  pieceSum
+	t     *torrent
+	index int
 	// Chunks we've written to since the last check. The chunk offset and
 	// length can be determined by the request chunkSize in use.
 	DirtyChunks      bitmap.Bitmap
@@ -77,27 +77,13 @@ func chunkIndexSpec(index int, pieceLength, chunkSize pp.Integer) chunkSpec {
 	return ret
 }
 
-func (p *piece) shuffledPendingChunkSpecs(t *torrent, piece int) (css []chunkSpec) {
-	// defer func() {
-	// 	log.Println(piece, css)
-	// }()
-	numPending := t.pieceNumPendingChunks(piece)
-	if numPending == 0 {
-		return
-	}
-	css = make([]chunkSpec, 0, numPending)
-	for ci := range iter.N(t.pieceNumChunks(piece)) {
-		if !p.DirtyChunks.Contains(ci) {
-			css = append(css, t.chunkIndexSpec(ci, piece))
-		}
-	}
-	if len(css) <= 1 {
-		return
-	}
-	for i := range css {
-		j := rand.Intn(i + 1)
-		css[i], css[j] = css[j], css[i]
-	}
+func (p *piece) numChunks() int {
+	return p.t.pieceNumChunks(p.index)
+}
+
+func (p *piece) undirtiedChunkIndices() (ret bitmap.Bitmap) {
+	ret = p.DirtyChunks.Copy()
+	ret.FlipRange(0, p.numChunks())
 	return
 }
 
diff --git a/torrent.go b/torrent.go
index d1764875..5f7807c8 100644
--- a/torrent.go
+++ b/torrent.go
@@ -14,6 +14,7 @@ import (
 
 	"github.com/anacrolix/missinggo"
 	"github.com/anacrolix/missinggo/bitmap"
+	"github.com/anacrolix/missinggo/itertools"
 	"github.com/anacrolix/missinggo/perf"
 	"github.com/anacrolix/missinggo/pubsub"
 	"github.com/bradfitz/iter"
@@ -252,6 +253,8 @@ func (t *torrent) setMetadata(md *metainfo.Info, infoBytes []byte) (err error) {
 	t.Pieces = make([]piece, len(hashes))
 	for i, hash := range hashes {
 		piece := &t.Pieces[i]
+		piece.t = t
+		piece.index = i
 		piece.noPendingWrites.L = &piece.pendingWritesMutex
 		missinggo.CopyExact(piece.Hash[:], hash)
 	}
@@ -997,12 +1000,11 @@ func (t *torrent) connRequestPiecePendingChunks(c *connection, piece int) (more
 	if !c.PeerHasPiece(piece) {
 		return true
 	}
-	for _, cs := range t.Pieces[piece].shuffledPendingChunkSpecs(t, piece) {
-		req := request{pp.Integer(piece), cs}
-		if !c.Request(req) {
-			return false
-		}
-	}
+	chunkIndices := t.Pieces[piece].undirtiedChunkIndices().ToSortedSlice()
+	return itertools.ForPerm(len(chunkIndices), func(i int) bool {
+		req := request{pp.Integer(piece), t.chunkIndexSpec(chunkIndices[i], piece)}
+		return c.Request(req)
+	})
 	return true
 }
 
-- 
2.48.1