Rework handshake parsing

go.mod

@@ -11,13 +11,13 @@ require (
 	github.com/anacrolix/dht/v2 v2.19.2-0.20221121215055-066ad8494444
 	github.com/anacrolix/envpprof v1.3.0
 	github.com/anacrolix/fuse v0.2.0
-	github.com/anacrolix/generics v0.0.2-0.20240227122613-f95486179cab
+	github.com/anacrolix/generics v0.0.3-0.20240902042256-7fb2702ef0ca
 	github.com/anacrolix/go-libutp v1.3.1
 	github.com/anacrolix/gostdapp v0.1.0
 	github.com/anacrolix/log v0.15.3-0.20240627045001-cd912c641d83
 	github.com/anacrolix/missinggo v1.3.0
 	github.com/anacrolix/missinggo/perf v1.0.0
-	github.com/anacrolix/missinggo/v2 v2.7.3
+	github.com/anacrolix/missinggo/v2 v2.7.5-0.20240913034152-5da762c29f00
 	github.com/anacrolix/multiless v0.3.0
 	github.com/anacrolix/possum/go v0.1.1-0.20240321122240-a01f3a22f2d1
 	github.com/anacrolix/squirrel v0.6.4
@@ -53,8 +53,8 @@ require (
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.11.1
 	go.opentelemetry.io/otel/sdk v1.11.1
 	go.opentelemetry.io/otel/trace v1.11.1
-	golang.org/x/exp v0.0.0-20240506185415-9bf2ced13842
-	golang.org/x/sync v0.7.0
+	golang.org/x/exp v0.0.0-20240823005443-9b4947da3948
+	golang.org/x/sync v0.8.0
 	golang.org/x/sys v0.18.0
 	golang.org/x/time v0.0.0-20220609170525-579cf78fd858
 )

go.sum

@@ -80,8 +80,8 @@ github.com/anacrolix/envpprof v1.3.0/go.mod h1:7QIG4CaX1uexQ3tqd5+BRa/9e2D02Wcer
 github.com/anacrolix/fuse v0.2.0 h1:pc+To78kI2d/WUjIyrsdqeJQAesuwpGxlI3h1nAv3Do=
 github.com/anacrolix/fuse v0.2.0/go.mod h1:Kfu02xBwnySDpH3N23BmrP3MDfwAQGRLUCj6XyeOvBQ=
 github.com/anacrolix/generics v0.0.0-20230113004304-d6428d516633/go.mod h1:ff2rHB/joTV03aMSSn/AZNnaIpUw0h3njetGsaXcMy8=
-github.com/anacrolix/generics v0.0.2-0.20240227122613-f95486179cab h1:MvuAC/UJtcohN6xWc8zYXSZfllh1LVNepQ0R3BCX5I4=
-github.com/anacrolix/generics v0.0.2-0.20240227122613-f95486179cab/go.mod h1:ff2rHB/joTV03aMSSn/AZNnaIpUw0h3njetGsaXcMy8=
+github.com/anacrolix/generics v0.0.3-0.20240902042256-7fb2702ef0ca h1:aiiGqSQWjtVNdi8zUMfA//IrM8fPkv2bWwZVPbDe0wg=
+github.com/anacrolix/generics v0.0.3-0.20240902042256-7fb2702ef0ca/go.mod h1:MN3ve08Z3zSV/rTuX/ouI4lNdlfTxgdafQJiLzyNRB8=
 github.com/anacrolix/go-libutp v1.3.1 h1:idJzreNLl+hNjGC3ZnUOjujEaryeOGgkwHLqSGoige0=
 github.com/anacrolix/go-libutp v1.3.1/go.mod h1:heF41EC8kN0qCLMokLBVkB8NXiLwx3t8R8810MTNI5o=
 github.com/anacrolix/gostdapp v0.1.0 h1:sZC+gSLhA7Hdalak5rPCkhO0YSEl0tt/lsovxh6qka4=
@@ -104,8 +104,8 @@ github.com/anacrolix/missinggo/perf v1.0.0 h1:7ZOGYziGEBytW49+KmYGTaNfnwUqP1HBsy
 github.com/anacrolix/missinggo/perf v1.0.0/go.mod h1:ljAFWkBuzkO12MQclXzZrosP5urunoLS0Cbvb4V0uMQ=
 github.com/anacrolix/missinggo/v2 v2.2.0/go.mod h1:o0jgJoYOyaoYQ4E2ZMISVa9c88BbUBVQQW4QeRkNCGY=
 github.com/anacrolix/missinggo/v2 v2.5.1/go.mod h1:WEjqh2rmKECd0t1VhQkLGTdIWXO6f6NLjp5GlMZ+6FA=
-github.com/anacrolix/missinggo/v2 v2.7.3 h1:Ee//CmZBMadeNiYB/hHo9ly2PFOEZ4Fhsbnug3rDAIE=
-github.com/anacrolix/missinggo/v2 v2.7.3/go.mod h1:mIEtp9pgaXqt8VQ3NQxFOod/eQ1H0D1XsZzKUQfwtac=
+github.com/anacrolix/missinggo/v2 v2.7.5-0.20240913034152-5da762c29f00 h1:tKJ0RqnJPWEjnBZNxaMKglMb61Jp/DpHF6h5iNp1Lsk=
+github.com/anacrolix/missinggo/v2 v2.7.5-0.20240913034152-5da762c29f00/go.mod h1:vVO5FEziQm+NFmJesc7StpkquZk+WJFCaL0Wp//2sa0=
 github.com/anacrolix/mmsg v0.0.0-20180515031531-a4a3ba1fc8bb/go.mod h1:x2/ErsYUmT77kezS63+wzZp8E3byYB0gzirM/WMBLfw=
 github.com/anacrolix/mmsg v1.0.0 h1:btC7YLjOn29aTUAExJiVUhQOuf/8rhm+/nWCMAnL3Hg=
 github.com/anacrolix/mmsg v1.0.0/go.mod h1:x8kRaJY/dCrY9Al0PEcj1mb/uFHwP6GCJ9fLl4thEPc=
@@ -633,8 +633,8 @@ golang.org/x/exp v0.0.0-20200119233911-0405dc783f0a/go.mod h1:2RIsYlXP63K8oxa1u0
 golang.org/x/exp v0.0.0-20200207192155-f17229e696bd/go.mod h1:J/WKrq2StrnmMY6+EHIKF9dgMWnmCNThgcyBT1FY9mM=
 golang.org/x/exp v0.0.0-20200224162631-6cc2880d07d6/go.mod h1:3jZMyOhIsHpP37uCMkUooju7aAi5cS1Q23tOzKc+0MU=
 golang.org/x/exp v0.0.0-20220428152302-39d4317da171/go.mod h1:lgLbSvA5ygNOMpwM/9anMpWVlVJ7Z+cHWq/eFuinpGE=
-golang.org/x/exp v0.0.0-20240506185415-9bf2ced13842 h1:vr/HnozRka3pE4EsMEg1lgkXJkTFJCVUX+S/ZT6wYzM=
-golang.org/x/exp v0.0.0-20240506185415-9bf2ced13842/go.mod h1:XtvwrStGgqGPLc4cjQfWqZHG1YFdYs6swckp8vpsjnc=
+golang.org/x/exp v0.0.0-20240823005443-9b4947da3948 h1:kx6Ds3MlpiUHKj7syVnbp57++8WpuKPcR5yjLBjvLEA=
+golang.org/x/exp v0.0.0-20240823005443-9b4947da3948/go.mod h1:akd2r19cwCdwSwWeIdzYQGa/EZZyqcOdwWiwj5L5eKQ=
 golang.org/x/image v0.0.0-20190227222117-0694c2d4d067/go.mod h1:kZ7UVZpmo3dzQBMxlp+ypCbDeSB+sBbTgSJuh5dn5js=
 golang.org/x/image v0.0.0-20190802002840-cff245a6509b/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
 golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
@@ -730,8 +730,8 @@ golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sync v0.0.0-20201207232520-09787c993a3a/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.7.0 h1:YsImfSBoP9QPYL0xyKJPq0gcaJdG3rInoqxTWbfQu9M=
-golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
+golang.org/x/sync v0.8.0 h1:3NFvSEYkUoMifnESzZl15y791HH1qU2xm6eCJU5ZPXQ=
+golang.org/x/sync v0.8.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20180909124046-d0be0721c37e/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=

peer_protocol/handshake.go

@@ -3,12 +3,11 @@ package peer_protocol
 import (
 	"context"
 	"encoding/hex"
-	"errors"
 	"fmt"
+	"github.com/anacrolix/missinggo/v2/panicif"
 	"github.com/anacrolix/torrent/internal/ctxrw"
 	"io"
 	"math/bits"
-	"strconv"
 	"strings"
 	"unsafe"
 
@@ -153,37 +152,39 @@ func Handshake(
 	}()
 
 	post := func(bb []byte) {
-		select {
-		case postCh <- bb:
-		default:
-			panic("mustn't block while posting")
-		}
+		panicif.SendBlocks(postCh, bb)
 	}
 
-	post([]byte(Protocol))
+	post(protocolBytes())
 	post(extensions[:])
 	if ih != nil { // We already know what we want.
 		post(ih[:])
 		post(peerID[:])
 	}
-	var b [68]byte
-	_, err = io.ReadFull(sock, b[:68])
+
+	// Putting an array on the heap still escapes.
+	b := make([]byte, 68)
+	// Read in one hit to avoid potential overhead in underlying reader.
+	_, err = io.ReadFull(sock, b[:])
 	if err != nil {
 		return res, fmt.Errorf("while reading: %w", err)
 	}
-	if string(b[:20]) != Protocol {
-		return res, errors.New("unexpected protocol string")
-	}
 
-	copyExact := func(dst, src []byte) {
-		if dstLen, srcLen := uint64(len(dst)), uint64(len(src)); dstLen != srcLen {
-			panic("dst len " + strconv.FormatUint(dstLen, 10) + " != src len " + strconv.FormatUint(srcLen, 10))
-		}
-		copy(dst, src)
+	p := b[:len(Protocol)]
+	// This gets optimized to runtime.memequal
+	if string(p) != Protocol {
+		return res, fmt.Errorf("unexpected protocol string %q", string(p))
+	}
+	b = b[len(p):]
+	read := func(dst []byte) {
+		n := copy(dst, b)
+		panicif.NotEq(n, len(dst))
+		b = b[n:]
 	}
-	copyExact(res.PeerExtensionBits[:], b[20:28])
-	copyExact(res.Hash[:], b[28:48])
-	copyExact(res.PeerID[:], b[48:68])
+	read(res.PeerExtensionBits[:])
+	read(res.Hash[:])
+	read(res.PeerID[:])
+	panicif.NotEq(len(b), 0)
 	// peerExtensions.Add(res.PeerExtensionBits.String(), 1)
 
 	// TODO: Maybe we can just drop peers here if we're not interested. This

peer_protocol/protocol.go

@@ -1,9 +1,19 @@
 package peer_protocol
 
+import (
+	"unsafe"
+)
+
 const (
 	Protocol = "\x13BitTorrent protocol"
 )
 
+var protocolStr = Protocol
+
+func protocolBytes() []byte {
+	return unsafe.Slice(unsafe.StringData(Protocol), len(Protocol))
+}
+
 type MessageType byte
 
 // golang.org/x/tools/cmd/stringer