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fix: buffer stdout in SimpleStdioMcpClient for split/batched JSON-RPC messages #277

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fix: buffer stdout in SimpleStdioMcpClient for split/batched JSON-RPC messages #277

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32 changes: 22 additions & 10 deletions packages/eko-nodejs/src/mcp/stdio.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ export class SimpleStdioMcpClient implements IMcpClient {
private options?: SpawnOptionsWithoutStdio;
private process: ChildProcessWithoutNullStreams | null = null;
private requestMap: Map<string, (messageData: any) => void>;
private stdoutBuffer: string = "";

constructor(
command: string,
Expand All @@ -38,18 +39,29 @@ export class SimpleStdioMcpClient implements IMcpClient {
this.process.kill();
} catch (e) {}
}
this.stdoutBuffer = "";
this.process = spawn(this.command, this.args, this.options);
this.process.stdout.on("data", (data) => {
const response = data.toString().trim();
Log.debug("MCP Client, onmessage", this.command, this.args, response);
if (!response.startsWith("{")) {
return;
}
const message = JSON.parse(response);
if (message.id) {
const callback = this.requestMap.get(message.id);
if (callback) {
callback(message);
this.stdoutBuffer += data.toString();
const lines = this.stdoutBuffer.split("\n");
// Keep the last (possibly incomplete) segment in the buffer
this.stdoutBuffer = lines.pop() || "";
for (const line of lines) {
const trimmed = line.trim();
if (!trimmed || !trimmed.startsWith("{")) {
continue;
}
Log.debug("MCP Client, onmessage", this.command, this.args, trimmed);
try {
const message = JSON.parse(trimmed);
if (message.id) {
const callback = this.requestMap.get(message.id);
if (callback) {
callback(message);
}
}
} catch (e) {
Log.warn("MCP Client, failed to parse JSON message:", trimmed, e);
}
}
});
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