PLT-2058 Debugging incoming web hook content (#3150)

* PLT-2058 Debugging incoming web hook content

This change debugs contents of incoming webhooks using l4g.

The problem is that in order to debug the request body, it neads to be
read. And a Reader can only be read once. Hence, the body is only read
for Debugging if it is actually enabled. Furthermore, a new reader is
created from the content of the old reader in order for the rest of the
method to work as usual (with or without debugging).

The debug statement is wrapped in a closure, so that the content is
only copied if Debug is actually enabled.

It is not possible to return `(string, string)` from the closure to
`l4g.Debug()`. That is the reason the debugging is not done with `=%v`,
but the translations strings end with a space.

I tested the change with a `application/json` HTTP header as well as
`payload=`

The debug method is extracted into util/log.go in order to be re-usable
for debugging `io.Reader`

* Added a config flag to turn off incoming webhook debugging

Setting `EnableWebhookDebugging` to false in the `config.json` will
disable the printing of the content of incoming webhooks to the console

* Defaulting webhook debugging to true

* Added the setting of debugging incoming webhooks to the system console

1 files changed, 33 insertions, 0 deletions

diff --git a/utils/log.go b/utils/log.go
new file mode 100644
index 000000000..360c785d0
--- /dev/null
+++ b/utils/log.go
@@ -0,0 +1,33 @@
+// Copyright (c) 2015 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package utils
+
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+
+	l4g "github.com/alecthomas/log4go"
+)
+
+// DebugReader logs the content of the io.Reader and returns a new io.Reader
+// with the same content as the received io.Reader.
+// If you pass reader by reference, it won't be re-created unless the loglevel
+// includes Debug.
+// If an error is returned, the reader is consumed an cannot be read again.
+func DebugReader(reader io.Reader, message string) (io.Reader, error) {
+	var err error
+	l4g.Debug(func() string {
+		content, err := ioutil.ReadAll(reader)
+		if err != nil {
+			return ""
+		}
+
+		reader = bytes.NewReader(content)
+
+		return message + string(content)
+	})
+
+	return reader, err
+}