client: support printing cURL command

client/client.go

@@ -256,6 +256,10 @@ type simpleHTTPClient struct {
 func (c *simpleHTTPClient) Do(ctx context.Context, act httpAction) (*http.Response, []byte, error) {
 	req := act.HTTPRequest(c.endpoint)
 
+	if err := printcURL(req); err != nil {
+		return nil, nil, err
+	}
+
 	rtchan := make(chan roundTripResponse, 1)
 	go func() {
 		resp, err := c.transport.RoundTrip(req)

client/curl.go

@@ -0,0 +1,70 @@
+// Copyright 2015 CoreOS, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package client
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"os"
+)
+
+var (
+	cURLDebug = false
+)
+
+func EnablecURLDebug() {
+	cURLDebug = true
+}
+
+func DisablecURLDebug() {
+	cURLDebug = false
+}
+
+// printcURL prints the cURL equivalent request to stderr.
+// It returns an error if the body of the request cannot
+// be read.
+// The caller MUST cancel the request if there is an error.
+func printcURL(req *http.Request) error {
+	if !cURLDebug {
+		return nil
+	}
+	var (
+		command string
+		b       []byte
+		err     error
+	)
+
+	if req.URL != nil {
+		command = fmt.Sprintf("curl -X %s %s", req.Method, req.URL.String())
+	}
+
+	if req.Body != nil {
+		b, err = ioutil.ReadAll(req.Body)
+		if err != nil {
+			return err
+		}
+		command += fmt.Sprintf(" -d %q", string(b))
+	}
+
+	fmt.Fprintf(os.Stderr, "cURL Command: %s\n", command)
+
+	// reset body
+	body := bytes.NewBuffer(b)
+	req.Body = ioutil.NopCloser(body)
+
+	return nil
+}