http: fixed race condition in persist.go

R=rsc, bradfitzgo, bradfitzwork
CC=golang-dev
https://golang.org/cl/4266042

src/pkg/http/persist.go

@@ -25,15 +25,15 @@ var (
 // i.e. requests can be read out of sync (but in the same order) while the
 // respective responses are sent.
 type ServerConn struct {
+	lk              sync.Mutex // read-write protects the following fields
 	c               net.Conn
 	r               *bufio.Reader
-	clsd            bool     // indicates a graceful close
 	re, we          os.Error // read/write errors
 	lastbody        io.ReadCloser
 	nread, nwritten int
-	pipe            textproto.Pipeline
 	pipereq         map[*Request]uint
-	lk              sync.Mutex // protected read/write to re,we
+
+	pipe textproto.Pipeline
 }
 
 // NewServerConn returns a new ServerConn reading and writing c.  If r is not
@@ -90,15 +90,21 @@ func (sc *ServerConn) Read() (req *Request, err os.Error) {
 		defer sc.lk.Unlock()
 		return nil, sc.re
 	}
+	if sc.r == nil { // connection closed by user in the meantime
+		defer sc.lk.Unlock()
+		return nil, os.EBADF
+	}
+	r := sc.r
+	lastbody := sc.lastbody
+	sc.lastbody = nil
 	sc.lk.Unlock()
 
 	// Make sure body is fully consumed, even if user does not call body.Close
-	if sc.lastbody != nil {
+	if lastbody != nil {
 		// body.Close is assumed to be idempotent and multiple calls to
 		// it should return the error that its first invokation
 		// returned.
-		err = sc.lastbody.Close()
-		sc.lastbody = nil
+		err = lastbody.Close()
 		if err != nil {
 			sc.lk.Lock()
 			defer sc.lk.Unlock()
@@ -107,10 +113,10 @@ func (sc *ServerConn) Read() (req *Request, err os.Error) {
 		}
 	}
 
-	req, err = ReadRequest(sc.r)
-	if err != nil {
+	req, err = ReadRequest(r)
 	sc.lk.Lock()
 	defer sc.lk.Unlock()
+	if err != nil {
 		if err == io.ErrUnexpectedEOF {
 			// A close from the opposing client is treated as a
 			// graceful close, even if there was some unparse-able
@@ -119,18 +125,16 @@ func (sc *ServerConn) Read() (req *Request, err os.Error) {
 			return nil, sc.re
 		} else {
 			sc.re = err
-			return
+			return req, err
 		}
 	}
 	sc.lastbody = req.Body
 	sc.nread++
 	if req.Close {
-		sc.lk.Lock()
-		defer sc.lk.Unlock()
 		sc.re = ErrPersistEOF
 		return req, sc.re
 	}
-	return
+	return req, err
 }
 
 // Pending returns the number of unanswered requests
@@ -165,24 +169,27 @@ func (sc *ServerConn) Write(req *Request, resp *Response) os.Error {
 		defer sc.lk.Unlock()
 		return sc.we
 	}
-	sc.lk.Unlock()
+	if sc.c == nil { // connection closed by user in the meantime
+		defer sc.lk.Unlock()
+		return os.EBADF
+	}
+	c := sc.c
 	if sc.nread <= sc.nwritten {
+		defer sc.lk.Unlock()
 		return os.NewError("persist server pipe count")
 	}
-
 	if resp.Close {
 		// After signaling a keep-alive close, any pipelined unread
 		// requests will be lost. It is up to the user to drain them
 		// before signaling.
-		sc.lk.Lock()
 		sc.re = ErrPersistEOF
-		sc.lk.Unlock()
 	}
+	sc.lk.Unlock()
 
-	err := resp.Write(sc.c)
-	if err != nil {
+	err := resp.Write(c)
 	sc.lk.Lock()
 	defer sc.lk.Unlock()
+	if err != nil {
 		sc.we = err
 		return err
 	}
@@ -196,14 +203,15 @@ func (sc *ServerConn) Write(req *Request, resp *Response) os.Error {
 // responsible for closing the underlying connection. One must call Close to
 // regain control of that connection and deal with it as desired.
 type ClientConn struct {
+	lk              sync.Mutex // read-write protects the following fields
 	c               net.Conn
 	r               *bufio.Reader
 	re, we          os.Error // read/write errors
 	lastbody        io.ReadCloser
 	nread, nwritten int
-	pipe            textproto.Pipeline
 	pipereq         map[*Request]uint
-	lk              sync.Mutex // protects read/write to re,we,pipereq,etc.
+
+	pipe textproto.Pipeline
 }
 
 // NewClientConn returns a new ClientConn reading and writing c.  If r is not
@@ -221,11 +229,11 @@ func NewClientConn(c net.Conn, r *bufio.Reader) *ClientConn {
 // logic. The user should not call Close while Read or Write is in progress.
 func (cc *ClientConn) Close() (c net.Conn, r *bufio.Reader) {
 	cc.lk.Lock()
+	defer cc.lk.Unlock()
 	c = cc.c
 	r = cc.r
 	cc.c = nil
 	cc.r = nil
-	cc.lk.Unlock()
 	return
 }
 
@@ -261,20 +269,22 @@ func (cc *ClientConn) Write(req *Request) (err os.Error) {
 		defer cc.lk.Unlock()
 		return cc.we
 	}
-	cc.lk.Unlock()
-
+	if cc.c == nil { // connection closed by user in the meantime
+		defer cc.lk.Unlock()
+		return os.EBADF
+	}
+	c := cc.c
 	if req.Close {
 		// We write the EOF to the write-side error, because there
 		// still might be some pipelined reads
-		cc.lk.Lock()
 		cc.we = ErrPersistEOF
-		cc.lk.Unlock()
 	}
+	cc.lk.Unlock()
 
-	err = req.Write(cc.c)
-	if err != nil {
+	err = req.Write(c)
 	cc.lk.Lock()
 	defer cc.lk.Unlock()
+	if err != nil {
 		cc.we = err
 		return err
 	}
@@ -316,15 +326,21 @@ func (cc *ClientConn) Read(req *Request) (resp *Response, err os.Error) {
 		defer cc.lk.Unlock()
 		return nil, cc.re
 	}
+	if cc.r == nil { // connection closed by user in the meantime
+		defer cc.lk.Unlock()
+		return nil, os.EBADF
+	}
+	r := cc.r
+	lastbody := cc.lastbody
+	cc.lastbody = nil
 	cc.lk.Unlock()
 
 	// Make sure body is fully consumed, even if user does not call body.Close
-	if cc.lastbody != nil {
+	if lastbody != nil {
 		// body.Close is assumed to be idempotent and multiple calls to
 		// it should return the error that its first invokation
 		// returned.
-		err = cc.lastbody.Close()
-		cc.lastbody = nil
+		err = lastbody.Close()
 		if err != nil {
 			cc.lk.Lock()
 			defer cc.lk.Unlock()
@@ -333,24 +349,22 @@ func (cc *ClientConn) Read(req *Request) (resp *Response, err os.Error) {
 		}
 	}
 
-	resp, err = ReadResponse(cc.r, req.Method)
-	if err != nil {
+	resp, err = ReadResponse(r, req.Method)
 	cc.lk.Lock()
 	defer cc.lk.Unlock()
+	if err != nil {
 		cc.re = err
-		return
+		return resp, err
 	}
 	cc.lastbody = resp.Body
 
 	cc.nread++
 
 	if resp.Close {
-		cc.lk.Lock()
-		defer cc.lk.Unlock()
 		cc.re = ErrPersistEOF // don't send any more requests
 		return resp, cc.re
 	}
-	return
+	return resp, err
 }
 
 // Do is convenience method that writes a request and reads a response.