Fix gin-gonic#723

context.go

@@ -353,9 +353,17 @@ func (c *Context) ClientIP() string {
 			return clientIP
 		}
 	}
+
+	if c.engine.AppEngine {
+		if addr := c.Request.Header.Get("X-Appengine-Remote-Addr"); addr != "" {
+			return addr
+		}
+	}
+
 	if ip, _, err := net.SplitHostPort(strings.TrimSpace(c.Request.RemoteAddr)); err == nil {
 		return ip
 	}
+
 	return ""
 }
 

context_appengine.go

@@ -0,0 +1,7 @@
+// +build appengine
+
+package gin
+
+func init() {
+	defaultAppEngine = true
+}

context_test.go

@@ -650,6 +650,7 @@ func TestContextClientIP(t *testing.T) {
 
 	c.Request.Header.Set("X-Real-IP", " 10.10.10.10  ")
 	c.Request.Header.Set("X-Forwarded-For", "  20.20.20.20, 30.30.30.30")
+	c.Request.Header.Set("X-Appengine-Remote-Addr", "50.50.50.50")
 	c.Request.RemoteAddr = "  40.40.40.40:42123 "
 
 	assert.Equal(t, c.ClientIP(), "10.10.10.10")
@@ -661,7 +662,15 @@ func TestContextClientIP(t *testing.T) {
 	assert.Equal(t, c.ClientIP(), "30.30.30.30")
 
 	c.Request.Header.Del("X-Forwarded-For")
+	c.engine.AppEngine = true
+	assert.Equal(t, c.ClientIP(), "50.50.50.50")
+
+	c.Request.Header.Del("X-Appengine-Remote-Addr")
 	assert.Equal(t, c.ClientIP(), "40.40.40.40")
+
+	// no port
+	c.Request.RemoteAddr = "50.50.50.50"
+	assert.Equal(t, c.ClientIP(), "")
 }
 
 func TestContextContentType(t *testing.T) {

gin.go

@@ -19,6 +19,7 @@ const Version = "v1.0rc2"
 
 var default404Body = []byte("404 page not found")
 var default405Body = []byte("405 method not allowed")
+var defaultAppEngine bool
 
 type HandlerFunc func(*Context)
 type HandlersChain []HandlerFunc
@@ -78,6 +79,10 @@ type (
 		// handler.
 		HandleMethodNotAllowed bool
 		ForwardedByClientIP    bool
+
+		// #726 #755 If enabled, it will thrust some headers starting with
+		// 'X-AppEngine...' for better integration with that PaaS.
+		AppEngine bool
 	}
 )
 
@@ -101,6 +106,7 @@ func New() *Engine {
 		RedirectFixedPath:      false,
 		HandleMethodNotAllowed: false,
 		ForwardedByClientIP:    true,
+		AppEngine:              defaultAppEngine,
 		trees:                  make(methodTrees, 0, 9),
 	}
 	engine.RouterGroup.engine = engine