net/http: wrap client errors

Fixes #50856

Change-Id: I7fe89fcce223e1571debb73436f8aeb3bfbe4b9f
GitHub-Last-Rev: be570e7883be06adbd227a1dfe63a80e384d96f6
GitHub-Pull-Request: golang/go#63448
Reviewed-on: https://go-review.googlesource.com/c/go/+/533119
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: qiulaidongfeng <2645477756@qq.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

src/net/http/client.go

@@ -726,7 +726,7 @@ func (c *Client) do(req *Request) (retres *Response, reterr error) {
 			reqBodyClosed = true
 			if !deadline.IsZero() && didTimeout() {
 				err = &httpError{
-					err:     err.Error() + " (Client.Timeout exceeded while awaiting headers)",
+					err:     fmt.Errorf("%w (Client.Timeout exceeded while awaiting headers)", err),
 					timeout: true,
 				}
 			}
@@ -969,7 +969,7 @@ func (b *cancelTimerBody) Read(p []byte) (n int, err error) {
 	}
 	if b.reqDidTimeout() {
 		err = &httpError{
-			err:     err.Error() + " (Client.Timeout or context cancellation while reading body)",
+			err:     fmt.Errorf("%w (Client.Timeout exceeded or context cancellation while reading body)", err),
 			timeout: true,
 		}
 	}

src/net/http/client_test.go

@@ -2127,3 +2127,22 @@ func testProbeZeroLengthBody(t *testing.T, mode testMode) {
 		t.Fatalf("server got body %q, want %q", gotBody, content)
 	}
 }
+
+func TestClientTimeoutReturnsContextDeadlineExceeded(t *testing.T) {
+	run(t, testClientTimeoutReturnsContextDeadlineExceeded)
+}
+func testClientTimeoutReturnsContextDeadlineExceeded(t *testing.T, mode testMode) {
+	doneCh := make(chan struct{})
+	defer close(doneCh)
+	cst := newClientServerTest(t, mode, HandlerFunc(func(w ResponseWriter, r *Request) {
+		<-doneCh
+		w.WriteHeader(200)
+	}))
+	// check that, upon exceeding Client.Timeout, the returned error is context.DeadlineExceeded.
+	cst.c.Timeout = 1 * time.Millisecond
+	req, _ := NewRequest("GET", cst.ts.URL, nil)
+	_, err := cst.c.Do(req)
+	if !errors.Is(err, context.DeadlineExceeded) {
+		t.Fatalf("expected context.DeadlineExceeded, got %v", err)
+	}
+}

src/net/http/transport.go

@@ -2556,15 +2556,17 @@ type writeRequest struct {
 }
 
 type httpError struct {
-	err     string
+	err     error
 	timeout bool
 }
 
-func (e *httpError) Error() string   { return e.err }
+func (e *httpError) Error() string        { return e.err.Error() }
 func (e *httpError) Timeout() bool        { return e.timeout }
 func (e *httpError) Temporary() bool      { return true }
+func (e *httpError) Is(target error) bool { return errors.Is(e.err, target) }
+func (e *httpError) Unwrap() error        { return e.err }
 
-var errTimeout error = &httpError{err: "net/http: timeout awaiting response headers", timeout: true}
+var errTimeout error = &httpError{err: errors.New("net/http: timeout awaiting response headers"), timeout: true}
 
 // errRequestCanceled is set to be identical to the one from h2 to facilitate
 // testing.