fix: make ping conform with the spec

Author: seuros

src/transports/http/server.ts

@@ -21,6 +21,7 @@ import { logger } from "../../core/Logger.js";
 import { getRequestHeader, setResponseHeaders } from "../../utils/headers.js";
 import { DEFAULT_CORS_CONFIG } from "../sse/types.js";
 import { CORSConfig } from "../sse/types.js";
+import { PING_SSE_MESSAGE } from "../utils/ping-message.js";
 
 function isRequest(msg: JsonRpcMessage): msg is JsonRpcRequest {
   return msg && 
@@ -645,8 +646,7 @@ export class HttpStreamTransport extends AbstractTransport {
   private sendPing(connection: ActiveSseConnection): void {
       if (!connection || !connection.res || connection.res.writableEnded) return;
       try {
-          const pingMessage = { jsonrpc: "2.0", method: "ping", params: { timestamp: Date.now() } };
-          connection.res.write(`data: ${JSON.stringify(pingMessage)}\n\n`);
+          connection.res.write(PING_SSE_MESSAGE);
           logger.debug(`Sent keep-alive ping to stream ${connection.streamId}`);
       } catch (error: any) {
           logger.error(`Error sending ping to stream ${connection.streamId}: ${error.message}`);

src/transports/sse/server.ts

@@ -9,6 +9,7 @@ import { AbstractTransport } from "../base.js"
 import { DEFAULT_SSE_CONFIG, SSETransportConfig, SSETransportConfigInternal, DEFAULT_CORS_CONFIG, CORSConfig } from "./types.js"
 import { logger } from "../../core/Logger.js"
 import { getRequestHeader, setResponseHeaders } from "../../utils/headers.js"
+import { PING_SSE_MESSAGE } from "../utils/ping-message.js";
 
 interface ExtendedIncomingMessage extends IncomingMessage {
   body?: ClientRequest
@@ -225,21 +226,11 @@ export class SSEServerTransport extends AbstractTransport {
     res.write(`event: endpoint\ndata: ${endpointUrl}\n\n`)
 
     logger.debug('Sending initial keep-alive')
-    // Removed initial keep-alive: res.write(": keep-alive\n\n")
 
     this._keepAliveInterval = setInterval(() => {
       if (this._sseResponse && !this._sseResponse.writableEnded) {
         try {
-          // Sending proper JSON-RPC ping instead of ': keep-alive' comment
-          // logger.debug('Sending keep-alive ping')
-          // this._sseResponse.write(": keep-alive\n\n")
-          
-          const pingMessage = {
-            jsonrpc: "2.0",
-            method: "ping",
-            params: { timestamp: Date.now() }
-          }
-          this._sseResponse.write(`data: ${JSON.stringify(pingMessage)}\n\n`)
+          this._sseResponse.write(PING_SSE_MESSAGE);
         } catch (error) {
           logger.error(`Error sending keep-alive: ${error}`)
           this.cleanupConnection()

src/transports/utils/ping-message.ts

@@ -0,0 +1,5 @@
+/**
+ * Pre-stringified JSON-RPC ping message formatted for Server-Sent Events (SSE).
+ * Includes the 'data: ' prefix and trailing newlines.
+ */
+export const PING_SSE_MESSAGE = 'data: {"jsonrpc":"2.0","method":"ping"}\n\n';