Fix allow_cors: true returning two Access-Control-Allow-Origin headers (#489)

* fix: `allow_cors: true` returning two `Access-Control-Allow-Origin` headers

Fixes #93.
The `Access-Control-Allow-Origin` was set before on the response before the proxy call,
and ClickHouse was returning the response with its own `Access-Control-Allow-Origin` (in my case, "*").
So, having `allow_cors: true` was eventually returning two `Access-Control-Allow-Origin`, one from chproxy and one from ClickHouse.

This commit just move the `"Access-Control-Allow-Origin` after the proxy call, overriding the value returned by ClickHouse.
If `allow_cors: false`, chproxy does not change the value (so it can be, I believe, any value set by ClickHouse), else, with `allow_cors: true`,
it will override to either the value of `Origin` request if any or else `*`.

* fix: add tests for allow CORS behavior

* fix failing tests

* add failing test

* fix failing tests

* add TODO

---------

Co-authored-by: Christophe Kalenzaga <mgachka@aol.com>

Author: matthieugouel

main_test.go

@@ -896,6 +896,64 @@ func TestServe(t *testing.T) {
 			},
 			startHTTP,
 		},
+		{
+			"http allow CORS false",
+			"testdata/http.yml",
+			func(t *testing.T) {
+				// TODO: rework this test because it doesn't fails when it should
+				// cf the discussion in https://github.com/ContentSquare/chproxy/pull/489
+				q := "cors"
+				req, err := http.NewRequest("GET", "http://127.0.0.1:9090?query="+url.QueryEscape(q), nil)
+				checkErr(t, err)
+				resp, err := http.DefaultClient.Do(req)
+				checkErr(t, err)
+				if resp.StatusCode != http.StatusOK {
+					t.Fatalf("unexpected status code: %d; expected: %d", resp.StatusCode, http.StatusOK)
+				}
+				defer resp.Body.Close()
+				checkHeader(t, resp, "Access-Control-Allow-Origin", "*")
+			},
+			startHTTP,
+		},
+		{
+			"http allow CORS true without request Origin header",
+			"testdata/http.allow.cors.yml",
+			func(t *testing.T) {
+				// TODO: rework this test because it doesn't fails when it should
+				// cf the discussion in https://github.com/ContentSquare/chproxy/pull/489
+				q := "cors"
+				req, err := http.NewRequest("GET", "http://127.0.0.1:9090?query="+url.QueryEscape(q), nil)
+				checkErr(t, err)
+				resp, err := http.DefaultClient.Do(req)
+				checkErr(t, err)
+				if resp.StatusCode != http.StatusOK {
+					t.Fatalf("unexpected status code: %d; expected: %d", resp.StatusCode, http.StatusOK)
+				}
+				defer resp.Body.Close()
+				checkHeader(t, resp, "Access-Control-Allow-Origin", "*")
+			},
+			startHTTP,
+		},
+		{
+			"http allow CORS true with request Origin header",
+			"testdata/http.allow.cors.yml",
+			func(t *testing.T) {
+				// TODO: rework this test because it doesn't fails when it should
+				// cf the discussion in https://github.com/ContentSquare/chproxy/pull/489
+				q := "cors"
+				req, err := http.NewRequest("GET", "http://127.0.0.1:9090?query="+url.QueryEscape(q), nil)
+				checkErr(t, err)
+				req.Header.Set("Origin", "http://example.com")
+				resp, err := http.DefaultClient.Do(req)
+				checkErr(t, err)
+				if resp.StatusCode != http.StatusOK {
+					t.Fatalf("unexpected status code: %d; expected: %d", resp.StatusCode, http.StatusOK)
+				}
+				defer resp.Body.Close()
+				checkHeader(t, resp, "Access-Control-Allow-Origin", "http://example.com")
+			},
+			startHTTP,
+		},
 	}
 
 	// Wait until CHServer starts.
@@ -1108,6 +1166,8 @@ func fakeCHHandler(w http.ResponseWriter, r *http.Request) {
 		// execute sleep 1.5 sec
 		time.Sleep(1500 * time.Millisecond)
 		fmt.Fprint(w, b)
+	case q == "cors":
+		w.Header().Set("Access-Control-Allow-Origin", "*")
 	default:
 		if strings.Contains(string(query), killQueryPattern) {
 			fakeCHState.kill()

proxy.go

@@ -107,14 +107,6 @@ func (rp *reverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 	log.Debugf("%s: request start", s)
 	requestSum.With(s.labels).Inc()
 
-	if s.user.allowCORS {
-		origin := req.Header.Get("Origin")
-		if len(origin) == 0 {
-			origin = "*"
-		}
-		rw.Header().Set("Access-Control-Allow-Origin", origin)
-	}
-
 	req.Body = &statReadCloser{
 		ReadCloser: req.Body,
 		bytesRead:  requestBodyBytes.With(s.labels),
@@ -149,6 +141,14 @@ func (rp *reverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 		rp.proxyRequest(s, srw, srw, req)
 	}
 
+	if s.user.allowCORS {
+		origin := req.Header.Get("Origin")
+		if len(origin) == 0 {
+			origin = "*"
+		}
+		rw.Header().Set("Access-Control-Allow-Origin", origin)
+	}
+
 	// It is safe calling getQuerySnippet here, since the request
 	// has been already read in proxyRequest or serveFromCache.
 	query := getQuerySnippet(req)

testdata/http.allow.cors.yml

@@ -0,0 +1,15 @@
+log_debug: true
+server:
+  http:
+      listen_addr: ":9090"
+      allowed_networks: ["127.0.0.1/24"]
+
+users:
+  - name: "default"
+    to_cluster: "default"
+    to_user: "default"
+    allow_cors: true
+
+clusters:
+  - name: "default"
+    nodes: ["127.0.0.1:18124"]