MastraAI•2d ago

using `writer.custom()` for UI framework integration

Hey team! 👋 I'm trying to implement tool streaming with custom events following the docs here: https://mastra.ai/en/docs/streaming/tool-streaming#using-the-writer-argument The docs show using writer.custom() for UI framework integration:

await writer?.custom({
  type: "data-tool-progress",
  status: "pending"
});

await writer?.custom({
  type: "data-tool-progress",
  status: "pending"
});

However, I'm getting TypeError: writer?.custom is not a function at runtime. Environment: - @mastra/core@0.21.1 (all Mastra packages on 0.21.x) - Verified with npm list @mastra/core - all dependencies properly deduplicated What I found: Looking at node_modules/@mastra/core/dist/tools/stream.d.ts, the ToolStream class only has a write() method, not custom():

export declare class ToolStream<T> extends WritableStream<T> {
    write(data: any): Promise<void>;
    // ❌ No custom() method
}

export declare class ToolStream<T> extends WritableStream<T> {
    write(data: any): Promise<void>;
    // ❌ No custom() method
}

Questions: 1. Is writer.custom() available in 0.21.1, or is this a docs issue? 2. If it's coming in a future release, when can we expect it? (0.21.2, 0.22.0?) Thanks! 🙏

Tool Streaming | Streaming | Mastra

Learn how to use tool streaming in Mastra, including handling tool calls, tool results, and tool execution events during streaming.

5 Replies

! .kinderjaje•2d ago

I dont know if its related, but I think its similiar to the issue I reported over here https://discord.com/channels/1309558646228779139/1427185080144498709 . In short, try with alpha for all Mastra packages and see if its gonna work. But keep in mind maybe its unrelated. @spo0nman

spo0nmanOP•this hour

I see that @mastra/core 0.22.0 • Public • Published 7 minutes ago ... it seems to have writer.custom()

! .kinderjaje•this hour

yeah, seems the released new package

spo0nmanOP•22h ago

here are full details. Ward's Finding: transformNetwork() filters custom events (network routing issue) AgentStreamToAISDKTransformer does preserve custom events my Issue: using agent.stream() (not network), so I should hit the good transformer BUT crashing with: Cannot use 'in' operator to search for 'type' in undefined This happens before it can check for data- prefix

DISCORD_ARTIFACT_ISS...

Mastra Triager•20h ago

📝 Created GitHub issue: https://github.com/mastra-ai/mastra/issues/9120

GitHub

[DISCORD:1430420806990561311] using writer.custom() for UI framew...

This issue was created from Discord post: https://discord.com/channels/1309558646228779139/1430420806990561311 Hey team! 👋 I'm trying to implement tool streaming with custom events following th...

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Programming

using `writer.custom()` for UI framework integration

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