Update bulidbucket client

buildbucket/client/cmd/buildbucket/client.go

Index: buildbucket/client/cmd/buildbucket/client.go
diff --git a/buildbucket/client/cmd/buildbucket/client.go b/buildbucket/client/cmd/buildbucket/client.go
new file mode 100644
index 0000000000000000000000000000000000000000..64ca76a963bc8224c26886c87c643a72616d06da
--- /dev/null
+++ b/buildbucket/client/cmd/buildbucket/client.go
@@ -0,0 +1,79 @@
+// Copyright 2016 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+	"time"
+
+	"golang.org/x/net/context"
+
+	"github.com/luci/luci-go/common/errors"
+	"github.com/luci/luci-go/common/logging"
+	"github.com/luci/luci-go/common/retry"
+	"golang.org/x/net/context/ctxhttp"
+)
+
+type client struct {
+	HTTP    *http.Client
+	baseURL *url.URL
+}
+
+// call makes an HTTP call with exponential back-off on transient errors.
+// if urlStr is relative, rebases it on c.baseURL.
+func (c *client) call(ctx context.Context, method, urlStr string, body interface{}) (response []byte, err error) {
+	if !c.baseURL.IsAbs() {
+		panic("baseURL is not absolute")
+	}
+
+	var bodyBytes []byte
+	if body != nil {
+		var err error
+		if bodyBytes, err = json.Marshal(body); err != nil {
+			return nil, err
+		}
+	}
+
+	u, err := url.Parse(urlStr)
+	if err != nil {
+		return nil, fmt.Errorf("invalid urlStr: %s", err)
+	}
+	u = c.baseURL.ResolveReference(u)
+	logging.Infof(ctx, "%s %s", method, u)
+
+	err = retry.Retry(
+		ctx,
+		retry.TransientOnly(retry.Default),
+		func() error {
+			req := &http.Request{Method: method, URL: u}
+			if bodyBytes != nil {
+				req.Body = ioutil.NopCloser(bytes.NewReader(bodyBytes))
+			}
+			res, err := ctxhttp.Do(ctx, c.HTTP, req)
+			if err != nil {
+				return errors.WrapTransient(err)
+			}
+
+			defer res.Body.Close()
+			if res.StatusCode >= 500 {
+				bodyBytes, _ := ioutil.ReadAll(res.Body)
+				return errors.WrapTransient(fmt.Errorf(
+					"status %s: %s", res.Status, bodyBytes))
+			}
+
+			response, err = ioutil.ReadAll(res.Body)
+			return err
+		},
+		func(err error, wait time.Duration) {
+			logging.WithError(err).Warningf(ctx, "API request failed transiently, will retry in %s", wait)
+		},
+	)
+	return
+}