http: don't use ClientConn in Transport

ClientConn's main feature (pipelining support)
wasn't being used anyway.  Ends up simpler to
just not use it.

This is prep for the http diet, moving ClientConn,
ServerConn, etc into http/httputil.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5305088

src/pkg/http/transport.go

@@ -372,7 +372,7 @@ func (t *Transport) getConn(cm *connectMethod) (*persistConn, error) {
 	}
 
 	pconn.br = bufio.NewReader(pconn.conn)
-	pconn.cc = NewClientConn(conn, pconn.br)
+	pconn.bw = bufio.NewWriter(pconn.conn)
 	go pconn.readLoop()
 	return pconn, nil
 }
@@ -474,8 +474,8 @@ type persistConn struct {
 	t        *Transport
 	cacheKey string // its connectMethod.String()
 	conn     net.Conn
-	cc       *ClientConn
-	br       *bufio.Reader
+	br       *bufio.Reader       // from conn
+	bw       *bufio.Writer       // to conn
 	reqch    chan requestAndChan // written by roundTrip(); read by readLoop()
 	isProxy  bool
 
@@ -515,6 +515,8 @@ func remoteSideClosed(err error) bool {
 
 func (pc *persistConn) readLoop() {
 	alive := true
+	var lastbody io.ReadCloser // last response body, if any, read on this connection
+
 	for alive {
 		pb, err := pc.br.Peek(1)
 		if err != nil {
@@ -533,33 +535,32 @@ func (pc *persistConn) readLoop() {
 		}
 
 		rc := <-pc.reqch
-		resp, err := pc.cc.readUsing(rc.req, func(buf *bufio.Reader, forReq *Request) (*Response, error) {
-			resp, err := ReadResponse(buf, forReq)
-			if err != nil || resp.ContentLength == 0 {
-				return resp, err
-			}
+
+		// Advance past the previous response's body, if the
+		// caller hasn't done so.
+		if lastbody != nil {
+			lastbody.Close() // assumed idempotent
+			lastbody = nil
+		}
+		resp, err := ReadResponse(pc.br, rc.req)
+
+		if err == nil {
 			if rc.addedGzip && resp.Header.Get("Content-Encoding") == "gzip" {
 				resp.Header.Del("Content-Encoding")
 				resp.Header.Del("Content-Length")
 				resp.ContentLength = -1
-				gzReader, err := gzip.NewReader(resp.Body)
+				gzReader, zerr := gzip.NewReader(resp.Body)
 				if err != nil {
 					pc.close()
-					return nil, err
+					err = zerr
+				} else {
+					resp.Body = &readFirstCloseBoth{&discardOnCloseReadCloser{gzReader}, resp.Body}
 				}
-				resp.Body = &readFirstCloseBoth{&discardOnCloseReadCloser{gzReader}, resp.Body}
 			}
 			resp.Body = &bodyEOFSignal{body: resp.Body}
-			return resp, err
-		})
+		}
 
-		if err == ErrPersistEOF {
-			// Succeeded, but we can't send any more
-			// persistent connections on this again.  We
-			// hide this error to upstream callers.
-			alive = false
-			err = nil
-		} else if err != nil || rc.req.Close {
+		if err != nil || resp.Close || rc.req.Close {
 			alive = false
 		}
 
@@ -567,6 +568,7 @@ func (pc *persistConn) readLoop() {
 		var waitForBodyRead chan bool
 		if alive {
 			if hasBody {
+				lastbody = resp.Body
 				waitForBodyRead = make(chan bool)
 				resp.Body.(*bodyEOFSignal).fn = func() {
 					pc.t.putIdleConn(pc)
@@ -580,9 +582,7 @@ func (pc *persistConn) readLoop() {
 				// loop, otherwise it might close the body
 				// before the client code has had a chance to
 				// read it (even though it'll just be 0, EOF).
-				pc.cc.lk.Lock()
-				pc.cc.lastbody = nil
-				pc.cc.lk.Unlock()
+				lastbody = nil
 
 				pc.t.putIdleConn(pc)
 			}
@@ -635,15 +635,12 @@ func (pc *persistConn) roundTrip(req *transportRequest) (resp *Response, err err
 	pc.numExpectedResponses++
 	pc.lk.Unlock()
 
-	pc.cc.writeReq = func(r *Request, w io.Writer) error {
-		return r.write(w, pc.isProxy, req.extra)
-	}
-
-	err = pc.cc.Write(req.Request)
+	err = req.Request.write(pc.bw, pc.isProxy, req.extra)
 	if err != nil {
 		pc.close()
 		return
 	}
+	pc.bw.Flush()
 
 	ch := make(chan responseAndError, 1)
 	pc.reqch <- requestAndChan{req.Request, ch, requestedGzip}
@@ -659,7 +656,6 @@ func (pc *persistConn) close() {
 	pc.lk.Lock()
 	defer pc.lk.Unlock()
 	pc.broken = true
-	pc.cc.Close()
 	pc.conn.Close()
 	pc.mutateHeaderFunc = nil
 }