From 1346784b013f7ee2338fb748e88b30d220e2264c Mon Sep 17 00:00:00 2001
From: whr819987540 <819987540@qq.com>
Date: Sat, 6 May 2023 11:44:23 +0800
Subject: [PATCH] add comment, use announceList[0] to fullfille announce field

---
 peerconn.go | 17 ++++++++++++++++-
 torrent.go  |  3 ++-
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/peerconn.go b/peerconn.go
index 0318cb6e..5170a749 100644
--- a/peerconn.go
+++ b/peerconn.go
@@ -269,6 +269,8 @@ func (cn *PeerConn) fillWriteBuffer() {
 			return
 		}
 	}
+	// write负责将msg写入缓冲区
+	// upload负责send
 	cn.upload(cn.write)
 }
 
@@ -481,6 +483,7 @@ func (c *PeerConn) maximumPeerRequestChunkLength() (_ Option[int]) {
 // startFetch is for testing purposes currently.
 func (c *PeerConn) onReadRequest(r Request, startFetch bool) error {
 	requestedChunkLengths.Add(strconv.FormatUint(r.Length.Uint64(), 10), 1)
+	// 来自某个peer的重复请求
 	if _, ok := c.peerRequests[r]; ok {
 		torrent.Add("duplicate requests received", 1)
 		if c.fastEnabled() {
@@ -488,6 +491,7 @@ func (c *PeerConn) onReadRequest(r Request, startFetch bool) error {
 		}
 		return nil
 	}
+	// 当前peer choking, 无法返回chunk
 	if c.choking {
 		torrent.Add("requests received while choking", 1)
 		if c.fastEnabled() {
@@ -505,6 +509,7 @@ func (c *PeerConn) onReadRequest(r Request, startFetch bool) error {
 		// BEP 6 says we may close here if we choose.
 		return nil
 	}
+	// chunk size is usually 16 KiB
 	if opt := c.maximumPeerRequestChunkLength(); opt.Ok && int(r.Length) > opt.Value {
 		err := fmt.Errorf("peer requested chunk too long (%v)", r.Length)
 		c.logger.Levelf(log.Warning, err.Error())
@@ -515,11 +520,13 @@ func (c *PeerConn) onReadRequest(r Request, startFetch bool) error {
 			return err
 		}
 	}
+	// 当前peer没有该piece, 因此没有该chunk
 	if !c.t.havePiece(pieceIndex(r.Index)) {
 		// TODO: Tell the peer we don't have the piece, and reject this request.
 		requestsReceivedForMissingPieces.Add(1)
 		return fmt.Errorf("peer requested piece we don't have: %v", r.Index.Int())
 	}
+	// 检查chunk是否超过piece的范围
 	pieceLength := c.t.pieceLength(pieceIndex(r.Index))
 	// Check this after we know we have the piece, so that the piece length will be known.
 	if chunkOverflowsPiece(r.ChunkSpec, pieceLength) {
@@ -541,7 +548,7 @@ func (c *PeerConn) onReadRequest(r Request, startFetch bool) error {
 }
 
 func (c *PeerConn) peerRequestDataReader(r Request, prs *peerRequestState) {
-	b, err := c.readPeerRequestData(r, prs)
+	b, err := c.readPeerRequestData(r, prs) // 读取数据(读取方式与该torrent的storage有关)
 	c.locker().Lock()
 	defer c.locker().Unlock()
 	if err != nil {
@@ -598,6 +605,7 @@ func (c *PeerConn) peerRequestDataReadFailed(err error, r Request) {
 	}
 }
 
+// 利用 torrent.Piece.Storage().ReadAt() 读取数据到b
 func (c *PeerConn) readPeerRequestData(r Request, prs *peerRequestState) ([]byte, error) {
 	// Should we depend on Torrent closure here? I think it's okay to get cancelled from elsewhere,
 	// or fail to read and then cleanup.
@@ -735,12 +743,14 @@ func (c *PeerConn) mainReadLoop() (err error) {
 			err = c.peerSentHave(pieceIndex(msg.Index))
 		case pp.Bitfield:
 			err = c.peerSentBitfield(msg.Bitfield)
+		// peer对chunk的请求(需要发送chunk, load from memory)
 		case pp.Request:
 			r := newRequestFromMessage(&msg)
 			err = c.onReadRequest(r, true)
 			if err != nil {
 				err = fmt.Errorf("on reading request %v: %w", r, err)
 			}
+		// 收到peer的chunk(需要接收chunk, store into memory)
 		case pp.Piece:
 			c.doChunkReadStats(int64(len(msg.Piece)))
 			err = c.receiveChunk(&msg)
@@ -939,6 +949,8 @@ another:
 			if !more {
 				return false
 			}
+			// 完成一次写入, 打印日志
+			log.Printf("write %d to %s",len(state.data),c.RemoteAddr)
 			goto another
 		}
 		return true
@@ -960,6 +972,9 @@ func (c *PeerConn) tickleWriter() {
 	c.messageWriter.writeCond.Broadcast()
 }
 
+// 函数式编程
+// fillWriteBuffer => cn.upload(cn.write)
+// msg即cn.write负责将数据写入缓冲区(套接字的缓冲区)
 func (c *PeerConn) sendChunk(r Request, msg func(pp.Message) bool, state *peerRequestState) (more bool) {
 	c.lastChunkSent = time.Now()
 	state.allocReservation.Release()
diff --git a/torrent.go b/torrent.go
index b5cda964..e80a4657 100644
--- a/torrent.go
+++ b/torrent.go
@@ -749,7 +749,7 @@ func (t *Torrent) writeStatus(w io.Writer) {
 			ml.StrictNext(lu.String() == ru.String(), lu.String() < ru.String())
 			return ml.Less()
 		}).([]torrentTrackerAnnouncer) {
-			fmt.Fprintf(tw, "    %q\t%v\n", ta.URL(), ta.statusLine())
+			fmt.Fprintf(tw, "    %q\t%v\n", ta.URL(), ta.statusLine()) // tracker的状态
 		}
 		tw.Flush()
 	}()
@@ -1447,6 +1447,7 @@ func appendMissingTrackerTiers(existing [][]string, minNumTiers int) (ret [][]st
 func (t *Torrent) addTrackers(announceList [][]string) {
 	fullAnnounceList := &t.metainfo.AnnounceList
 	t.metainfo.AnnounceList = appendMissingTrackerTiers(*fullAnnounceList, len(announceList))
+	t.metainfo.Announce = announceList[0][0]
 	for tierIndex, trackerURLs := range announceList {
 		(*fullAnnounceList)[tierIndex] = appendMissingStrings((*fullAnnounceList)[tierIndex], trackerURLs)
 	}