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feat(cdp-proxy): add /json endpoint for Playwright connectOverCDP support #139

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feat(cdp-proxy): add /json endpoint for Playwright connectOverCDP support #139

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c62b34c
feat(cdp-proxy): add /json endpoint for Playwright connectOverCDP sup…
rgarcia Jan 31, 2026
a1171a1
test(e2e): add agent-browser CDP proxy connectivity tests
rgarcia Feb 1, 2026
3ae8d73
fix(e2e): rewrite test to properly validate CDP proxy JSON endpoints
rgarcia Feb 1, 2026
bcba715
fix(test): use stdbuf to prevent flaky UpstreamManager test
rgarcia Feb 1, 2026
1cfe0c1
fix(cdp-proxy): address bot review comments
rgarcia Feb 1, 2026
d2ec4e3
Add trailing slash support for CDP JSON endpoints and agent-browser e…
rgarcia Feb 2, 2026
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110 changes: 105 additions & 5 deletions server/cmd/api/main.go
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@ import (
"os"
"os/exec"
"os/signal"
"strings"
"syscall"
"time"

Expand Down Expand Up @@ -157,10 +158,12 @@ func main() {
},
scaletozero.Middleware(stz),
)
// Expose a minimal /json/version endpoint so clients that attempt to
// resolve a browser websocket URL via HTTP can succeed. We map the
// upstream path onto this proxy's host:port so clients connect back to us.
rDevtools.Get("/json/version", func(w http.ResponseWriter, r *http.Request) {
// Expose /json/version endpoint so clients that attempt to resolve a browser
// websocket URL via HTTP can succeed. We map the upstream path onto this
// proxy's host:port so clients connect back to us.
// Note: Playwright's connectOverCDP requests /json/version/ with trailing slash,
// so we register both variants to avoid 426 errors from the WebSocket handler.
jsonVersionHandler := func(w http.ResponseWriter, r *http.Request) {
current := upstreamMgr.Current()
if current == "" {
http.Error(w, "upstream not ready", http.StatusServiceUnavailable)
Expand All @@ -171,7 +174,73 @@ func main() {
_ = json.NewEncoder(w).Encode(map[string]string{
"webSocketDebuggerUrl": proxyWSURL,
})
})
}
rDevtools.Get("/json/version", jsonVersionHandler)
rDevtools.Get("/json/version/", jsonVersionHandler)

// Handler for /json and /json/list - proxies to Chrome and rewrites URLs.
// This is needed for Playwright's connectOverCDP which fetches /json for target discovery.
jsonTargetHandler := func(w http.ResponseWriter, r *http.Request) {
current := upstreamMgr.Current()
if current == "" {
http.Error(w, "upstream not ready", http.StatusServiceUnavailable)
return
}

// Parse upstream URL to get Chrome's host (e.g., ws://127.0.0.1:9223/...)
parsed, err := url.Parse(current)
if err != nil {
http.Error(w, "invalid upstream URL", http.StatusInternalServerError)
return
}

// Fetch /json from Chrome
chromeJSONURL := fmt.Sprintf("http://%s/json", parsed.Host)
resp, err := http.Get(chromeJSONURL)
if err != nil {
slogger.Error("failed to fetch /json from Chrome", "err", err, "url", chromeJSONURL)
http.Error(w, "failed to fetch target list from browser", http.StatusBadGateway)
return
}
defer resp.Body.Close()

// Verify Chrome returned a successful response
if resp.StatusCode != http.StatusOK {
slogger.Error("Chrome /json returned non-200 status", "status", resp.StatusCode, "url", chromeJSONURL)
http.Error(w, fmt.Sprintf("browser returned status %d", resp.StatusCode), http.StatusBadGateway)
return
}

// Read and parse the JSON response
var targets []map[string]interface{}
if err := json.NewDecoder(resp.Body).Decode(&targets); err != nil {
slogger.Error("failed to decode /json response", "err", err)
http.Error(w, "failed to parse target list", http.StatusBadGateway)
return
}

// Rewrite URLs to use this proxy's host instead of Chrome's
proxyHost := r.Host
chromeHost := parsed.Host
for i := range targets {
// Rewrite webSocketDebuggerUrl
if wsURL, ok := targets[i]["webSocketDebuggerUrl"].(string); ok {
targets[i]["webSocketDebuggerUrl"] = rewriteWSURL(wsURL, chromeHost, proxyHost)
}
// Rewrite devtoolsFrontendUrl if present
if frontendURL, ok := targets[i]["devtoolsFrontendUrl"].(string); ok {
targets[i]["devtoolsFrontendUrl"] = rewriteWSURL(frontendURL, chromeHost, proxyHost)
}
}

w.Header().Set("Content-Type", "application/json")
_ = json.NewEncoder(w).Encode(targets)
}
rDevtools.Get("/json", jsonTargetHandler)
rDevtools.Get("/json/", jsonTargetHandler)
rDevtools.Get("/json/list", jsonTargetHandler)
rDevtools.Get("/json/list/", jsonTargetHandler)

rDevtools.Get("/*", func(w http.ResponseWriter, r *http.Request) {
devtoolsproxy.WebSocketProxyHandler(upstreamMgr, slogger, config.LogCDPMessages, stz).ServeHTTP(w, r)
})
Expand Down Expand Up @@ -227,3 +296,34 @@ func mustFFmpeg() {
panic(fmt.Errorf("ffmpeg not found or not executable: %w", err))
}
}

// rewriteWSURL replaces the Chrome host with the proxy host in WebSocket URLs.
// It handles two cases:
// 1. Direct WebSocket URLs: "ws://127.0.0.1:9223/devtools/page/..." -> "ws://127.0.0.1:9222/devtools/page/..."
// 2. DevTools frontend URLs with ws= query param: "https://...?ws=127.0.0.1:9223/..." -> "https://...?ws=127.0.0.1:9222/..."
func rewriteWSURL(urlStr, chromeHost, proxyHost string) string {
parsed, err := url.Parse(urlStr)
if err != nil {
return urlStr
}

// Case 1: Direct replacement if the URL's host matches Chrome's host
if parsed.Host == chromeHost {
parsed.Host = proxyHost
}

// Case 2: Check for ws= query parameter (used in devtoolsFrontendUrl)
// e.g., https://chrome-devtools-frontend.appspot.com/.../inspector.html?ws=127.0.0.1:9223/devtools/page/...
if wsParam := parsed.Query().Get("ws"); wsParam != "" {
// The ws param value is like "127.0.0.1:9223/devtools/page/..."
// We need to replace the host portion
if strings.HasPrefix(wsParam, chromeHost) {
newWsParam := strings.Replace(wsParam, chromeHost, proxyHost, 1)
q := parsed.Query()
q.Set("ws", newWsParam)
parsed.RawQuery = q.Encode()
}
}

return parsed.String()
}
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