net/http: set the Request context for incoming server requests

Updates #13021
Updates #15224

Change-Id: Ia3cd608bb887fcfd8d81b035fa57bd5eb8edf09b
Reviewed-on: https://go-review.googlesource.com/21810
Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/request.go

@@ -266,9 +266,13 @@ type Request struct {
 //
 // The returned context is always non-nil; it defaults to the
 // background context.
+//
+// For outgoing client requests, the context controls cancelation.
+//
+// For incoming server requests, the context is canceled when either
+// the client's connection closes, or when the ServeHTTP method
+// returns.
 func (r *Request) Context() context.Context {
-	// TODO(bradfitz): document above what Context means for server and client
-	// requests, once implemented.
 	if r.ctx != nil {
 		return r.ctx
 	}

src/net/http/serve_test.go

@@ -9,6 +9,7 @@ package http_test
 import (
 	"bufio"
 	"bytes"
+	"context"
 	"crypto/tls"
 	"errors"
 	"fmt"
@@ -3989,6 +3990,72 @@ func TestServerValidatesHeaders(t *testing.T) {
 	}
 }
 
+func TestServerRequestContextCancel_ServeHTTPDone(t *testing.T) {
+	defer afterTest(t)
+	ctxc := make(chan context.Context, 1)
+	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+		ctx := r.Context()
+		select {
+		case <-ctx.Done():
+			t.Error("should not be Done in ServeHTTP")
+		default:
+		}
+		ctxc <- ctx
+	}))
+	defer ts.Close()
+	res, err := Get(ts.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+	res.Body.Close()
+	ctx := <-ctxc
+	select {
+	case <-ctx.Done():
+	default:
+		t.Error("context should be done after ServeHTTP completes")
+	}
+}
+
+func TestServerRequestContextCancel_ConnClose(t *testing.T) {
+	// Currently the context is not canceled when the connection
+	// is closed because we're not reading from the connection
+	// until after ServeHTTP for the previous handler is done.
+	// Until the server code is modified to always be in a read
+	// (Issue 15224), this test doesn't work yet.
+	t.Skip("TODO(bradfitz): this test doesn't yet work; golang.org/issue/15224")
+	defer afterTest(t)
+	inHandler := make(chan struct{})
+	handlerDone := make(chan struct{})
+	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+		close(inHandler)
+		select {
+		case <-r.Context().Done():
+		case <-time.After(3 * time.Second):
+			t.Errorf("timeout waiting for context to be done")
+		}
+		close(handlerDone)
+	}))
+	defer ts.Close()
+	c, err := net.Dial("tcp", ts.Listener.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer c.Close()
+	io.WriteString(c, "GET / HTTP/1.1\r\nHost: foo\r\n\r\n")
+	select {
+	case <-inHandler:
+	case <-time.After(3 * time.Second):
+		t.Fatalf("timeout waiting to see ServeHTTP get called")
+	}
+	c.Close() // this should trigger the context being done
+
+	select {
+	case <-handlerDone:
+	case <-time.After(3 * time.Second):
+		t.Fatalf("timeout waiting to see ServeHTTP exit")
+	}
+}
+
 func BenchmarkClientServer(b *testing.B) {
 	b.ReportAllocs()
 	b.StopTimer()

src/net/http/server.go

@@ -9,6 +9,7 @@ package http
 import (
 	"bufio"
 	"bytes"
+	"context"
 	"crypto/tls"
 	"errors"
 	"fmt"
@@ -312,10 +313,11 @@ type response struct {
 	conn             *conn
 	req              *Request // request for this response
 	reqBody          io.ReadCloser
-	wroteHeader      bool // reply header has been (logically) written
-	wroteContinue    bool // 100 Continue response was written
-	wants10KeepAlive bool // HTTP/1.0 w/ Connection "keep-alive"
-	wantsClose       bool // HTTP request has Connection "close"
+	cancelCtx        context.CancelFunc // when ServeHTTP exits
+	wroteHeader      bool               // reply header has been (logically) written
+	wroteContinue    bool               // 100 Continue response was written
+	wants10KeepAlive bool               // HTTP/1.0 w/ Connection "keep-alive"
+	wantsClose       bool               // HTTP request has Connection "close"
 
 	w  *bufio.Writer // buffers output in chunks to chunkWriter
 	cw chunkWriter
@@ -686,7 +688,7 @@ func appendTime(b []byte, t time.Time) []byte {
 var errTooLarge = errors.New("http: request too large")
 
 // Read next request from connection.
-func (c *conn) readRequest() (w *response, err error) {
+func (c *conn) readRequest(ctx context.Context) (w *response, err error) {
 	if c.hijacked() {
 		return nil, ErrHijacked
 	}
@@ -715,6 +717,10 @@ func (c *conn) readRequest() (w *response, err error) {
 		}
 		return nil, err
 	}
+
+	ctx, cancelCtx := context.WithCancel(ctx)
+	req.ctx = ctx
+
 	c.lastMethod = req.Method
 	c.r.setInfiniteReadLimit()
 
@@ -749,6 +755,7 @@ func (c *conn) readRequest() (w *response, err error) {
 
 	w = &response{
 		conn:          c,
+		cancelCtx:     cancelCtx,
 		req:           req,
 		reqBody:       req.Body,
 		handlerHeader: make(Header),
@@ -1432,12 +1439,20 @@ func (c *conn) serve() {
 		}
 	}
 
+	// HTTP/1.x from here on.
+
 	c.r = &connReader{r: c.rwc}
 	c.bufr = newBufioReader(c.r)
 	c.bufw = newBufioWriterSize(checkConnErrorWriter{c}, 4<<10)
 
+	// TODO: allow changing base context? can't imagine concrete
+	// use cases yet.
+	baseCtx := context.Background()
+	ctx, cancelCtx := context.WithCancel(baseCtx)
+	defer cancelCtx()
+
 	for {
-		w, err := c.readRequest()
+		w, err := c.readRequest(ctx)
 		if c.r.remain != c.server.initialReadLimitSize() {
 			// If we read any bytes off the wire, we're active.
 			c.setState(c.rwc, StateActive)
@@ -1485,6 +1500,7 @@ func (c *conn) serve() {
 		// [*] Not strictly true: HTTP pipelining. We could let them all process
 		// in parallel even if their responses need to be serialized.
 		serverHandler{c.server}.ServeHTTP(w, w.req)
+		w.cancelCtx()
 		if c.hijacked() {
 			return
 		}