From a01644c0ae5f9340807aff97d489faa98aed8a37 Mon Sep 17 00:00:00 2001
From: "Han Verstraete (OpenFaaS Ltd)" <han@openfaas.com>
Date: Thu, 19 Jun 2025 16:51:43 +0200
Subject: [PATCH] Support ndjson streams for function invocations

Additional fixes:
- Support Accept headers with multiple Accept values
- Accept header values should be mathced case insensitive.
  As stated in RFC 7321: https://datatracker.ietf.org/doc/html/rfc7231#section-3.1.1.1
  Media Types are case-insensitive

Signed-off-by: Han Verstraete (OpenFaaS Ltd) <han@openfaas.com>
---
 proxy/proxy.go      | 14 ++++++--
 proxy/proxy_test.go | 80 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 92 insertions(+), 2 deletions(-)

diff --git a/proxy/proxy.go b/proxy/proxy.go
index 2a7ab1e..284a9d2 100644
--- a/proxy/proxy.go
+++ b/proxy/proxy.go
@@ -28,6 +28,7 @@ import (
 	"net/http"
 	"net/http/httputil"
 	"net/url"
+	"strings"
 	"time"
 
 	"github.com/gorilla/mux"
@@ -189,8 +190,7 @@ func proxyRequest(w http.ResponseWriter, originalReq *http.Request, proxyClient
 		}()
 	}
 
-	if v := originalReq.Header.Get("Accept"); v == "text/event-stream" ||
-		originalReq.Header.Get("Upgrade") == "websocket" {
+	if requiresStdlibProxy(originalReq) {
 		originalReq.URL = proxyReq.URL
 
 		reverseProxy.ServeHTTP(w, originalReq)
@@ -222,6 +222,16 @@ func proxyRequest(w http.ResponseWriter, originalReq *http.Request, proxyClient
 	}
 }
 
+// requiresStdlibProxy checks if the request should be proxied using the standard library reverse proxy.
+// Support SSE, NDSJON and WebSockets through the stdlib reverse proxy
+func requiresStdlibProxy(req *http.Request) bool {
+	acceptHeader := strings.ToLower(req.Header.Get("Accept"))
+
+	return strings.Contains(acceptHeader, "text/event-stream") ||
+		strings.Contains(acceptHeader, "application/x-ndjson") ||
+		req.Header.Get("Upgrade") == "websocket"
+}
+
 // buildProxyRequest creates a request object for the proxy request, it will ensure that
 // the original request headers are preserved as well as setting openfaas system headers
 func buildProxyRequest(originalReq *http.Request, baseURL url.URL, extraPath string) (*http.Request, error) {
diff --git a/proxy/proxy_test.go b/proxy/proxy_test.go
index d9a57d3..d14c2ab 100644
--- a/proxy/proxy_test.go
+++ b/proxy/proxy_test.go
@@ -528,3 +528,83 @@ func Test_NewProxyClientConfig(t *testing.T) {
 		})
 	}
 }
+
+func Test_requiresStdlibProxy(t *testing.T) {
+	testCases := []struct {
+		name    string
+		headers map[string]string
+		want    bool
+	}{
+		{
+			name:    "SSE request",
+			headers: map[string]string{"Accept": "text/event-stream"},
+			want:    true,
+		},
+		{
+			name:    "SSE request with multiple accept values",
+			headers: map[string]string{"Accept": "application/json, text/event-stream;q=0.9, text/plain"},
+			want:    true,
+		},
+		{
+			name:    "NDJSON request",
+			headers: map[string]string{"Accept": "application/x-ndjson"},
+			want:    true,
+		},
+		{
+			name:    "NDJSON request with multiple accept values",
+			headers: map[string]string{"Accept": "text/plain, application/x-ndjson;q=0.9, application/json;q=0.8"},
+			want:    true,
+		},
+		{
+			name:    "WebSocket request",
+			headers: map[string]string{"Upgrade": "websocket"},
+			want:    true,
+		},
+		{
+			name:    "Regular JSON request",
+			headers: map[string]string{"Accept": "application/json"},
+			want:    false,
+		},
+		{
+			name:    "Regular request with multiple values",
+			headers: map[string]string{"Accept": "text/plain, application/json;q=0.9"},
+			want:    false,
+		},
+		{
+			name:    "Request without headers",
+			headers: map[string]string{},
+			want:    false,
+		},
+		{
+			name:    "Request with non-websocket Upgrade header",
+			headers: map[string]string{"Accept": "application/json", "Upgrade": "h2c"},
+			want:    false,
+		},
+
+		{
+			name:    "Case insensitive headers",
+			headers: map[string]string{"Accept": "APPLICATION/X-NDJSON"},
+			want:    true,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			req, err := http.NewRequest("GET", "/function/test", nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			// Set headers from test case
+			for key, value := range tc.headers {
+				req.Header.Set(key, value)
+			}
+
+			got := requiresStdlibProxy(req)
+
+			if got != tc.want {
+				t.Errorf("Want %t, got %t", tc.want, got)
+			}
+		})
+	}
+}