Dump request when daemon is set to debug

Uses a new middleware which calls httputils.DumpRequest which is output
to `logrus.Debug`.
This is implemented in a separate middleare so that we only have to
check the logging level when the router is instantiated rather than at
every request.
If this was just `logrus.Debug(httputil.DumpRequest(...))`, the
DumpRequest would be called on each request requardless of logging
level set on the daemon.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

api/server/middleware.go

@@ -1,6 +1,9 @@
 package server
 
 import (
+	"bytes"
+	"encoding/json"
+	"io/ioutil"
 	"net/http"
 	"runtime"
 	"strings"
@@ -28,6 +31,32 @@ func (s *Server) loggingMiddleware(handler httputils.APIFunc) httputils.APIFunc
 	}
 }
 
+// debugRequestMiddleware dumps the request to logger
+// This is implemented separately from `loggingMiddleware` so that we don't have to
+// check the logging level or have httputil.DumpRequest called on each request.
+// Instead the middleware is only injected when the logging level is set to debug
+func (s *Server) debugRequestMiddleware(handler httputils.APIFunc) httputils.APIFunc {
+	return func(ctx context.Context, w http.ResponseWriter, r *http.Request, vars map[string]string) error {
+		if s.cfg.Logging && r.Method == "POST" {
+			if err := httputils.CheckForJSON(r); err == nil {
+				var buf bytes.Buffer
+				if _, err := buf.ReadFrom(r.Body); err == nil {
+					r.Body.Close()
+					r.Body = ioutil.NopCloser(&buf)
+					var postForm map[string]interface{}
+					if err := json.Unmarshal(buf.Bytes(), &postForm); err == nil {
+						if _, exists := postForm["password"]; exists {
+							postForm["password"] = "*****"
+						}
+						logrus.Debugf("form data: %q", postForm)
+					}
+				}
+			}
+		}
+		return handler(ctx, w, r, vars)
+	}
+}
+
 // userAgentMiddleware checks the User-Agent header looking for a valid docker client spec.
 func (s *Server) userAgentMiddleware(handler httputils.APIFunc) httputils.APIFunc {
 	return func(ctx context.Context, w http.ResponseWriter, r *http.Request, vars map[string]string) error {
@@ -110,6 +139,13 @@ func (s *Server) handleWithGlobalMiddlewares(handler httputils.APIFunc) httputil
 		s.loggingMiddleware,
 	}
 
+	// Only want this on debug level
+	// this is separate from the logging middleware so that we can do this check here once,
+	// rather than for each request.
+	if logrus.GetLevel() == logrus.DebugLevel {
+		middlewares = append(middlewares, s.debugRequestMiddleware)
+	}
+
 	h := handler
 	for _, m := range middlewares {
 		h = m(h)