From d3fcddb18ae3a2a8bdafd09686ab7cbcdd0b6f33 Mon Sep 17 00:00:00 2001
From: Chiran Fernando <pcnfernando@gmail.com>
Date: Sat, 5 Apr 2025 08:23:29 +0530
Subject: [PATCH] Intercept and modify SSE response

---
 internal/proxy/sse.go | 74 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)

diff --git a/internal/proxy/sse.go b/internal/proxy/sse.go
index 44d6558..cd168ce 100644
--- a/internal/proxy/sse.go
+++ b/internal/proxy/sse.go
@@ -1,10 +1,14 @@
 package proxy
 
 import (
+	"bufio"
 	"context"
+	"fmt"
+	"io"
 	"log"
 	"net/http"
 	"net/http/httputil"
+	"strings"
 	"time"
 )
 
@@ -32,3 +36,73 @@ func HandleSSE(w http.ResponseWriter, r *http.Request, rp *httputil.ReverseProxy
 func NewShutdownContext(timeout time.Duration) (context.Context, context.CancelFunc) {
 	return context.WithTimeout(context.Background(), timeout)
 }
+
+// sseTransport is a custom http.RoundTripper that intercepts and modifies SSE responses
+type sseTransport struct {
+	Transport  http.RoundTripper
+	proxyHost  string
+	targetHost string
+}
+
+func (t *sseTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	// Call the underlying transport
+	resp, err := t.Transport.RoundTrip(req)
+	if err != nil {
+		return nil, err
+	}
+	
+	// Check if this is an SSE response
+	contentType := resp.Header.Get("Content-Type")
+	if !strings.Contains(contentType, "text/event-stream") {
+		return resp, nil
+	}
+	
+	log.Printf("INFO: Intercepting SSE response to modify endpoint events")
+	
+	// Create a response wrapper that modifies the response body
+	originalBody := resp.Body
+	pr, pw := io.Pipe()
+	
+	go func() {
+		defer originalBody.Close()
+		defer pw.Close()
+		
+		scanner := bufio.NewScanner(originalBody)
+		for scanner.Scan() {
+			line := scanner.Text()
+			
+			// Check if this line contains an endpoint event
+			if strings.HasPrefix(line, "event: endpoint") {
+				// Read the data line
+				if scanner.Scan() {
+					dataLine := scanner.Text()
+					if strings.HasPrefix(dataLine, "data: ") {
+						// Extract the endpoint URL
+						endpoint := strings.TrimPrefix(dataLine, "data: ")
+						
+						// Replace the host in the endpoint
+						log.Printf("DEBUG: Original endpoint: %s", endpoint)
+						endpoint = strings.Replace(endpoint, t.targetHost, t.proxyHost, 1)
+						log.Printf("DEBUG: Modified endpoint: %s", endpoint)
+						
+						// Write the modified event lines
+						fmt.Fprintln(pw, line)
+						fmt.Fprintln(pw, "data: "+endpoint)
+						continue
+					}
+				}
+			}
+			
+			// Write the original line for non-endpoint events
+			fmt.Fprintln(pw, line)
+		}
+		
+		if err := scanner.Err(); err != nil {
+			log.Printf("Error reading SSE stream: %v", err)
+		}
+	}()
+	
+	// Replace the response body with our modified pipe
+	resp.Body = pr
+	return resp, nil
+}
\ No newline at end of file