Monorail client in Go

go/src/infra/httputil/httputil.go

Index: go/src/infra/httputil/httputil.go
diff --git a/go/src/infra/httputil/httputil.go b/go/src/infra/httputil/httputil.go
new file mode 100644
index 0000000000000000000000000000000000000000..c6073f1aee0b5f6e0e7069711302ccb7117f7774
--- /dev/null
+++ b/go/src/infra/httputil/httputil.go
@@ -0,0 +1,56 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Package httputil contains HTTP utility functions.
+package httputil
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"time"
+
+	"golang.org/x/net/context"
+	"golang.org/x/net/context/ctxhttp"
+
+	"github.com/luci/luci-go/common/clock"
+	"github.com/luci/luci-go/common/errors"
+	"github.com/luci/luci-go/common/logging"
+	"github.com/luci/luci-go/common/retry"
+)
+
+// RetryRequest retires an HTTP request on transient errors,
+// calls fn on success and guarantees to close response body.
+// ctx deadline is limited to client's timeout.

[seanmccullough1, 2016/06/03 18:45:33]

Nice. Does this do exponential back-off?  

[nodir, 2016/06/03 18:56:12]

retry.Default does

updated docstring

+func RetryRequest(ctx context.Context, client *http.Client, req *http.Request, requestBody []byte, fn func(*http.Response) error) error {
+	if client == nil {
+		client = http.DefaultClient
+	}
+	return retry.Retry(
+		ctx,
+		retry.TransientOnly(retry.Default),
+		func() error {
+			ctx := ctx
+			if client.Timeout > 0 {
+				clientDeadline := clock.Now(ctx).Add(client.Timeout)
+				if deadline, ok := ctx.Deadline(); !ok || deadline.After(clientDeadline) {
+					ctx, _ = context.WithDeadline(ctx, clientDeadline)
+				}
+			}
+			req.Body = ioutil.NopCloser(bytes.NewReader(requestBody))
+			res, err := ctxhttp.Do(ctx, client, req)
+			if err != nil {
+				return errors.WrapTransient(err)
+			}
+			defer res.Body.Close()
+			if res.StatusCode >= 500 {
+				return errors.WrapTransient(fmt.Errorf("HTTP status %s", res.Status))
+			}
+			return fn(res)
+		},
+		func(err error, delay time.Duration) {
+			logging.Warningf(ctx, "failed transiently, will retry in %s: %s", delay, err)
+		})
+}