proxy: Add SRV support for proxy upstream (#1915)

* Simplify parseUpstream function

* Add SRV support for proxy upstream

caddyhttp/proxy/proxy.go

@@ -82,7 +82,8 @@ type UpstreamHost struct {
 	// This is an int32 so that we can use atomic operations to do concurrent
 	// reads & writes to this value.  The default value of 0 indicates that it
 	// is healthy and any non-zero value indicates unhealthy.
-	Unhealthy int32
+	Unhealthy         int32
+	HealthCheckResult atomic.Value
 }
 
 // Down checks whether the upstream host is down or not.

caddyhttp/proxy/reverseproxy.go

@@ -26,7 +26,9 @@
 package proxy
 
 import (
+	"context"
 	"crypto/tls"
+	"fmt"
 	"io"
 	"net"
 	"net/http"
@@ -91,6 +93,8 @@ type ReverseProxy struct {
 	// response body.
 	// If zero, no periodic flushing is done.
 	FlushInterval time.Duration
+
+	srvResolver srvResolver
 }
 
 // Though the relevant directive prefix is just "unix:", url.Parse
@@ -105,6 +109,23 @@ func socketDial(hostName string) func(network, addr string) (conn net.Conn, err
 	}
 }
 
+func (rp *ReverseProxy) srvDialerFunc(locator string) func(network, addr string) (conn net.Conn, err error) {
+	service := locator
+	if strings.HasPrefix(locator, "srv://") {
+		service = locator[6:]
+	} else if strings.HasPrefix(locator, "srv+https://") {
+		service = locator[12:]
+	}
+
+	return func(network, addr string) (conn net.Conn, err error) {
+		_, addrs, err := rp.srvResolver.LookupSRV(context.Background(), "", "", service)
+		if err != nil {
+			return nil, err
+		}
+		return net.Dial("tcp", fmt.Sprintf("%s:%d", addrs[0].Target, addrs[0].Port))
+	}
+}
+
 func singleJoiningSlash(a, b string) string {
 	aslash := strings.HasSuffix(a, "/")
 	bslash := strings.HasPrefix(b, "/")
@@ -131,6 +152,12 @@ func NewSingleHostReverseProxy(target *url.URL, without string, keepalive int) *
 			// scheme and host have to be faked
 			req.URL.Scheme = "http"
 			req.URL.Host = "socket"
+		} else if target.Scheme == "srv" {
+			req.URL.Scheme = "http"
+			req.URL.Host = target.Host
+		} else if target.Scheme == "srv+https" {
+			req.URL.Scheme = "https"
+			req.URL.Host = target.Host
 		} else {
 			req.URL.Scheme = target.Scheme
 			req.URL.Host = target.Host
@@ -199,7 +226,12 @@ func NewSingleHostReverseProxy(target *url.URL, without string, keepalive int) *
 		}
 	}
 
-	rp := &ReverseProxy{Director: director, FlushInterval: 250 * time.Millisecond} // flushing good for streaming & server-sent events
+	rp := &ReverseProxy{
+		Director:      director,
+		FlushInterval: 250 * time.Millisecond, // flushing good for streaming & server-sent events
+		srvResolver:   net.DefaultResolver,
+	}
+
 	if target.Scheme == "unix" {
 		rp.Transport = &http.Transport{
 			Dial: socketDial(target.String()),
@@ -210,13 +242,15 @@ func NewSingleHostReverseProxy(target *url.URL, without string, keepalive int) *
 				HandshakeTimeout: defaultCryptoHandshakeTimeout,
 			},
 		}
-	} else if keepalive != http.DefaultMaxIdleConnsPerHost {
-		// if keepalive is equal to the default,
-		// just use default transport, to avoid creating
-		// a brand new transport
+	} else if keepalive != http.DefaultMaxIdleConnsPerHost || strings.HasPrefix(target.Scheme, "srv") {
+		dialFunc := defaultDialer.Dial
+		if strings.HasPrefix(target.Scheme, "srv") {
+			dialFunc = rp.srvDialerFunc(target.String())
+		}
+
 		transport := &http.Transport{
 			Proxy:                 http.ProxyFromEnvironment,
-			Dial:                  defaultDialer.Dial,
+			Dial:                  dialFunc,
 			TLSHandshakeTimeout:   defaultCryptoHandshakeTimeout,
 			ExpectContinueTimeout: 1 * time.Second,
 		}

caddyhttp/proxy/reverseproxy_test.go

@@ -0,0 +1,94 @@
+// Copyright 2015 Light Code Labs, LLC
+//
+// 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 proxy
+
+import (
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strconv"
+	"testing"
+)
+
+const (
+	expectedResponse = "response from request proxied to upstream"
+	expectedStatus   = http.StatusOK
+)
+
+var upstreamHost *httptest.Server
+
+func setupTest() {
+	upstreamHost = httptest.NewServer(http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			if r.URL.Path == "/test-path" {
+				w.WriteHeader(expectedStatus)
+				w.Write([]byte(expectedResponse))
+			} else {
+				w.WriteHeader(404)
+				w.Write([]byte("Not found"))
+			}
+		}))
+}
+
+func tearDownTest() {
+	upstreamHost.Close()
+}
+
+func TestSingleSRVHostReverseProxy(t *testing.T) {
+	setupTest()
+	defer tearDownTest()
+
+	target, err := url.Parse("srv://test.upstream.service")
+	if err != nil {
+		t.Errorf("Failed to parse target URL. %s", err.Error())
+	}
+
+	upstream, err := url.Parse(upstreamHost.URL)
+	if err != nil {
+		t.Errorf("Failed to parse test server URL [%s]. %s", upstreamHost.URL, err.Error())
+	}
+	pp, err := strconv.Atoi(upstream.Port())
+	if err != nil {
+		t.Errorf("Failed to parse upstream server port [%s]. %s", upstream.Port(), err.Error())
+	}
+	port := uint16(pp)
+
+	rp := NewSingleHostReverseProxy(target, "", http.DefaultMaxIdleConnsPerHost)
+	rp.srvResolver = testResolver{
+		result: []*net.SRV{
+			{Target: upstream.Hostname(), Port: port, Priority: 1, Weight: 1},
+		},
+	}
+
+	resp := httptest.NewRecorder()
+	req, err := http.NewRequest("GET", "http://test.host/test-path", nil)
+	if err != nil {
+		t.Errorf("Failed to create new request. %s", err.Error())
+	}
+
+	err = rp.ServeHTTP(resp, req, nil)
+	if err != nil {
+		t.Errorf("Failed to perform reverse proxy to upstream host. %s", err.Error())
+	}
+
+	if resp.Body.String() != expectedResponse {
+		t.Errorf("Unexpected proxy response received. Expected: '%s', Got: '%s'", expectedResponse, resp.Body.String())
+	}
+
+	if resp.Code != expectedStatus {
+		t.Errorf("Unexpected proxy status. Expected: '%d', Got: '%d'", expectedStatus, resp.Code)
+	}
+}