mini proxy to debug requests from Claude Code to Datadog's agentless OTLP intake endpoint

otlp-debug.ts

// OTLP Debug Proxy
// tweak datadog site url as necessary
const DATADOG_OTLP_METRICS_ENDPOINT = `https://api.us5.datadoghq.com/api/intake/otlp/v1/metrics`;

console.log(`Starting OTLP Debug Proxy on port 8080...`);
console.log(`Forwarding OTLP/HTTP metrics to: ${DATADOG_OTLP_METRICS_ENDPOINT}`);

Bun.serve({
  port: 8080,
  async fetch(claudeRequest) {
    const claudeRequestUrl = new URL(claudeRequest.url);
    console.log(`\n--- [${new Date().toISOString()}] Received Request from Claude ---`);
    console.log(`Claude Method: ${claudeRequest.method}`);
    console.log(`Claude Path: ${claudeRequestUrl.pathname}${claudeRequestUrl.search}`);

    console.log("Claude Request Headers:");
    const originalClaudeHeaders = new Headers(claudeRequest.headers);
    for (const [key, value] of originalClaudeHeaders) {
      console.log(`  ${key}: ${value}`);
    }

    let claudeRequestBodyBuffer: ArrayBuffer | null = null;
    if (claudeRequest.method === "POST" && claudeRequest.body) {
      try {
        claudeRequestBodyBuffer = await claudeRequest.arrayBuffer();
        console.log(`Claude Request Body received, ${claudeRequestBodyBuffer.byteLength} bytes.`);
        const firstBytes = new Uint8Array(claudeRequestBodyBuffer.slice(0, 64));
        const hexDump = Array.from(firstBytes).map(b => b.toString(16).padStart(2, '0')).join('');
        console.log(`  Claude Body HEX (first 64 bytes): ${hexDump}${claudeRequestBodyBuffer.byteLength > 64 ? '...' : ''}`);
      } catch (e: any) {
        console.error("  Error reading Claude request body:", e.message);
        return new Response("Error reading client request body\n", { status: 500 });
      }
    } else {
      console.log("No body in Claude request or method not POST. Not forwarding.");
      return new Response("Request not forwarded (no body or not POST)\n", { status: 400 });
    }

    console.log(`\n--- [${new Date().toISOString()}] Forwarding Request to Datadog ---`);

    const headersToForward = new Headers();
    // Forward essential headers
    if (originalClaudeHeaders.has("content-type")) {
      headersToForward.set("content-type", originalClaudeHeaders.get("content-type")!);
    }
    if (originalClaudeHeaders.has("dd-api-key")) {
      headersToForward.set("dd-api-key", originalClaudeHeaders.get("dd-api-key")!);
    }
    if (originalClaudeHeaders.has("user-agent")) {
      headersToForward.set("user-agent", originalClaudeHeaders.get("user-agent")!);
    }
    if (originalClaudeHeaders.has("content-encoding")) {
        headersToForward.set("content-encoding", originalClaudeHeaders.get("content-encoding")!);
    }

    console.log("Forwarding these headers to Datadog:");
    for (const [key, value] of headersToForward) {
        console.log(`  ${key}: ${value}`);
    }

    try {
      const datadogResponse = await fetch(DATADOG_OTLP_METRICS_ENDPOINT, {
        method: claudeRequest.method,
        headers: headersToForward,
        body: claudeRequestBodyBuffer,
      });

      console.log(`\n--- [${new Date().toISOString()}] Received Response from Datadog ---`);
      console.log(`Datadog Status: ${datadogResponse.status} ${datadogResponse.statusText}`);

      const ddResponseHeaders = new Headers(datadogResponse.headers);
      console.log("Datadog Response Headers:");
      for (const [key, value] of ddResponseHeaders) {
        console.log(`  ${key}: ${value}`);
      }

      const datadogResponseBodyText = await datadogResponse.text();
      console.log("Datadog Response Body:");
      console.log(datadogResponseBodyText || "[No body content]");

      console.log("--- End of Datadog Interaction ---");

      return new Response(datadogResponseBodyText || null, {
        status: datadogResponse.status,
        statusText: datadogResponse.statusText,
        headers: ddResponseHeaders,
      });

    } catch (fetchError: any) {
      console.error(`\n--- [${new Date().toISOString()}] Error Fetching from Datadog ---`);
      console.error(fetchError.message);
      if (fetchError.cause) console.error("Cause:", fetchError.cause);
      console.log("--- End of Datadog Interaction (Fetch Error) ---");
      return new Response(`Error forwarding request to Datadog: ${fetchError.message}\n`, {
        status: 502,
        headers: { "Content-Type": "text/plain" },
      });
    }
  },
  error(bunServeError: Error) {
    console.error(`\n--- [${new Date().toISOString()}] Bun Serve Error (Proxy Level) ---`);
    console.error(bunServeError);
    return new Response("Internal Server Error in Proxy\n", {
      status: 500,
      headers: { "Content-Type": "text/plain" },
    });
  },
});

console.log("OTLP Debug Proxy is listening on http://localhost:8080");