[MCP] fix: stray token leak when early-exit is triggered (#1508)

hanouticelina · web-flow · commit 6e5ac81363cd · 2025-06-03T11:27:40.000+02:00
similar PR to huggingface/huggingface_hub#3132. as explained by @danielholanda in the PR, when `opts.exitIfFirstChunkNoTool` is `True`, the CLI is supposed to abort streaming if the first chunk contains no tool call. However, we currently yield the first chunk before checking the exit condition, so a "vestigial" token still reached the user. This PR fixes this behavior.
diff --git a/packages/mcp-client/src/McpClient.ts b/packages/mcp-client/src/McpClient.ts
@@ -145,7 +145,6 @@ export class McpClient {
 			if (opts.abortSignal?.aborted) {
 				throw new Error("AbortError");
 			}
-			yield chunk;
 			debug(chunk.choices[0]);
 			numOfChunks++;
 			const delta = chunk.choices[0]?.delta;
@@ -174,6 +173,7 @@ export class McpClient {
 				//github.com/ If no tool is present in chunk number 1 or 2, exit.
 				return;
 			}
+			yield chunk;
 		}
 
 		messages.push(message);

Original file line number	Diff line number	Diff line change
`@@ -145,7 +145,6 @@ export class McpClient {`
`145`	`145`	`if (opts.abortSignal?.aborted) {`
`146`	`146`	`throw new Error("AbortError");`
`147`	`147`	`}`
`148`		`- yield chunk;`
`149`	`148`	`debug(chunk.choices[0]);`
`150`	`149`	`numOfChunks++;`
`151`	`150`	`const delta = chunk.choices[0]?.delta;`
`@@ -174,6 +173,7 @@ export class McpClient {`
`174`	`173`	`//github.com/ If no tool is present in chunk number 1 or 2, exit.`
`175`	`174`	`return;`
`176`	`175`	`}`
	`176`	`+ yield chunk;`
`177`	`177`	`}`
`178`	`178`
`179`	`179`	`messages.push(message);`