Attempt to identify remote IP addresses for requests which come

through proxies.

Add a function to examine X-Forward-For and X-Real-Ip headers for
originating IP addresses.  Use RemoteAddr for notification request
record and HTTP request context.

context/http_test.go

@@ -2,6 +2,9 @@ package context
 
 import (
 	"net/http"
+	"net/http/httptest"
+	"net/http/httputil"
+	"net/url"
 	"reflect"
 	"testing"
 	"time"
@@ -205,3 +208,47 @@ func TestWithVars(t *testing.T) {
 		}
 	}
 }
+
+// SingleHostReverseProxy will insert an X-Forwarded-For header, and can be used to test
+// RemoteAddr().  A fake RemoteAddr cannot be set on the HTTP request - it is overwritten
+// at the transport layer to 127.0.0.1:<port> .  However, as the X-Forwarded-For header
+// just contains the IP address, it is different enough for testing.
+func TestRemoteAddr(t *testing.T) {
+	expectedRemote := "127.0.0.1"
+	var actualRemote string
+	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		defer r.Body.Close()
+
+		if r.RemoteAddr == expectedRemote {
+			t.Errorf("Unexpected matching remote addresses")
+		}
+		actualRemote = RemoteAddr(r)
+
+		if expectedRemote != actualRemote {
+			t.Errorf("Mismatching remote hosts: %v != %v", expectedRemote, actualRemote)
+		}
+
+		w.WriteHeader(200)
+	}))
+
+	defer backend.Close()
+	backendURL, err := url.Parse(backend.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	proxy := httputil.NewSingleHostReverseProxy(backendURL)
+	frontend := httptest.NewServer(proxy)
+	defer frontend.Close()
+
+	getReq, err := http.NewRequest("GET", frontend.URL, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = http.DefaultClient.Do(getReq)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+}