net/http: use runtime.Stack instead of runtime/debug.Stack

Fixes #4060.

2012/11/21 19:51:34 http: panic serving 127.0.0.1:47139: Kaaarn!
goroutine 7 [running]:
net/http.func·004(0x7f330807ffb0, 0x7f330807f100)
	/home/dfc/go/src/pkg/net/http/server.go:615 +0xa7
----- stack segment boundary -----
main.(*httpHandler).ServeHTTP()
	/home/dfc/src/httppanic.go:16 +0x53
net/http.(*conn).serve(0xc200090240, 0x0)
	/home/dfc/go/src/pkg/net/http/server.go:695 +0x55d
created by net/http.(*Server).Serve
	/home/dfc/go/src/pkg/net/http/server.go:1119 +0x36d

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/6846085

src/pkg/net/http/server.go

@@ -11,7 +11,6 @@ package http
 
 import (
 	"bufio"
-	"bytes"
 	"crypto/tls"
 	"errors"
 	"fmt"
@@ -21,7 +20,7 @@ import (
 	"net"
 	"net/url"
 	"path"
-	"runtime/debug"
+	"runtime"
 	"strconv"
 	"strings"
 	"sync"
@@ -610,10 +609,10 @@ func (c *conn) serve() {
 			return
 		}
 
-		var buf bytes.Buffer
-		fmt.Fprintf(&buf, "http: panic serving %v: %v\n", c.remoteAddr, err)
-		buf.Write(debug.Stack())
-		log.Print(buf.String())
+		const size = 4096
+		buf := make([]byte, size)
+		buf = buf[:runtime.Stack(buf, false)]
+		log.Printf("http: panic serving %v: %v\n%s", c.remoteAddr, err, buf)
 
 		if c.rwc != nil { // may be nil if connection hijacked
 			c.rwc.Close()