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[o11y] Add undefined to tailStream return types #7436

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[o11y] Add undefined to tailStream return types #7436

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2 changes: 1 addition & 1 deletion src/workerd/api/global-scope.h
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Expand Up @@ -565,7 +565,7 @@ struct ExportedHandler {
type ExportedHandlerConnectHandler<Env = unknown, Props = unknown> = (socket: Socket, env: Env, ctx: ExecutionContext<Props>) => void | Promise<void>;
type ExportedHandlerTailHandler<Env = unknown, Props = unknown> = (events: TraceItem[], env: Env, ctx: ExecutionContext<Props>) => void | Promise<void>;
type ExportedHandlerTraceHandler<Env = unknown, Props = unknown> = (traces: TraceItem[], env: Env, ctx: ExecutionContext<Props>) => void | Promise<void>;
type ExportedHandlerTailStreamHandler<Env = unknown, Props = unknown> = (event : TailStream.TailEvent<TailStream.Onset>, env: Env, ctx: ExecutionContext<Props>) => TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType>;
type ExportedHandlerTailStreamHandler<Env = unknown, Props = unknown> = (event : TailStream.TailEvent<TailStream.Onset>, env: Env, ctx: ExecutionContext<Props>) => TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType> | undefined;
type ExportedHandlerScheduledHandler<Env = unknown, Props = unknown> = (controller: ScheduledController, env: Env, ctx: ExecutionContext<Props>) => void | Promise<void>;
type ExportedHandlerQueueHandler<Env = unknown, Message = unknown, Props = unknown> = (batch: MessageBatch<Message>, env: Env, ctx: ExecutionContext<Props>) => void | Promise<void>;
type ExportedHandlerTestHandler<Env = unknown, Props = unknown> = (controller: TestController, env: Env, ctx: ExecutionContext<Props>) => void | Promise<void>;
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2 changes: 1 addition & 1 deletion types/defines/rpc.d.ts
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Expand Up @@ -243,7 +243,7 @@ declare namespace CloudflareWorkersModule {
queue?(batch: MessageBatch): void | Promise<void>;
scheduled?(controller: ScheduledController): void | Promise<void>;
tail?(events: TraceItem[]): void | Promise<void>;
tailStream?(event: TailStream.TailEvent<TailStream.Onset>): TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType>;
tailStream?(event: TailStream.TailEvent<TailStream.Onset>): TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType> | undefined;

@ask-bonk ask-bonk Bot Sep 18, 2026

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async tailStream() { return undefined; } produces Promise<undefined>, which this signature still rejects because undefined is only outside the promise. The runtime explicitly awaits promises and treats a fulfilled undefined as the early-stop signal. Please also apply this same return contract to ExportedHandlerTailStreamHandler in src/workerd/api/global-scope.h and regenerate the snapshots; otherwise ordinary default-module tail workers remain unable to use the optimization.

Suggested change
tailStream?(event: TailStream.TailEvent<TailStream.Onset>): TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType> | undefined;
tailStream?(event: TailStream.TailEvent<TailStream.Onset>): TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType | undefined> | undefined;

test?(controller: TestController): void | Promise<void>;
trace?(traces: TraceItem[]): void | Promise<void>;
}
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8 changes: 6 additions & 2 deletions types/generated-snapshot/experimental/index.d.ts
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Expand Up @@ -532,7 +532,10 @@ type ExportedHandlerTailStreamHandler<Env = unknown, Props = unknown> = (
event: TailStream.TailEvent<TailStream.Onset>,
env: Env,
ctx: ExecutionContext<Props>,
) => TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType>;
) =>
| TailStream.TailEventHandlerType
| Promise<TailStream.TailEventHandlerType>
| undefined;
type ExportedHandlerScheduledHandler<Env = unknown, Props = unknown> = (
controller: ScheduledController,
env: Env,
Expand Down Expand Up @@ -16196,7 +16199,8 @@ declare namespace CloudflareWorkersModule {
event: TailStream.TailEvent<TailStream.Onset>,
):
| TailStream.TailEventHandlerType
| Promise<TailStream.TailEventHandlerType>;
| Promise<TailStream.TailEventHandlerType>
| undefined;
test?(controller: TestController): void | Promise<void>;
trace?(traces: TraceItem[]): void | Promise<void>;
}
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8 changes: 6 additions & 2 deletions types/generated-snapshot/experimental/index.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -534,7 +534,10 @@ export type ExportedHandlerTailStreamHandler<Env = unknown, Props = unknown> = (
event: TailStream.TailEvent<TailStream.Onset>,
env: Env,
ctx: ExecutionContext<Props>,
) => TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType>;
) =>
| TailStream.TailEventHandlerType
| Promise<TailStream.TailEventHandlerType>
| undefined;
export type ExportedHandlerScheduledHandler<Env = unknown, Props = unknown> = (
controller: ScheduledController,
env: Env,
Expand Down Expand Up @@ -16137,7 +16140,8 @@ export declare namespace CloudflareWorkersModule {
event: TailStream.TailEvent<TailStream.Onset>,
):
| TailStream.TailEventHandlerType
| Promise<TailStream.TailEventHandlerType>;
| Promise<TailStream.TailEventHandlerType>
| undefined;
test?(controller: TestController): void | Promise<void>;
trace?(traces: TraceItem[]): void | Promise<void>;
}
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8 changes: 6 additions & 2 deletions types/generated-snapshot/index.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -531,7 +531,10 @@ type ExportedHandlerTailStreamHandler<Env = unknown, Props = unknown> = (
event: TailStream.TailEvent<TailStream.Onset>,
env: Env,
ctx: ExecutionContext<Props>,
) => TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType>;
) =>
| TailStream.TailEventHandlerType
| Promise<TailStream.TailEventHandlerType>
| undefined;
type ExportedHandlerScheduledHandler<Env = unknown, Props = unknown> = (
controller: ScheduledController,
env: Env,
Expand Down Expand Up @@ -15913,7 +15916,8 @@ declare namespace CloudflareWorkersModule {
event: TailStream.TailEvent<TailStream.Onset>,
):
| TailStream.TailEventHandlerType
| Promise<TailStream.TailEventHandlerType>;
| Promise<TailStream.TailEventHandlerType>
| undefined;
test?(controller: TestController): void | Promise<void>;
trace?(traces: TraceItem[]): void | Promise<void>;
}
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8 changes: 6 additions & 2 deletions types/generated-snapshot/index.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -533,7 +533,10 @@ export type ExportedHandlerTailStreamHandler<Env = unknown, Props = unknown> = (
event: TailStream.TailEvent<TailStream.Onset>,
env: Env,
ctx: ExecutionContext<Props>,
) => TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType>;
) =>
| TailStream.TailEventHandlerType
| Promise<TailStream.TailEventHandlerType>
| undefined;
export type ExportedHandlerScheduledHandler<Env = unknown, Props = unknown> = (
controller: ScheduledController,
env: Env,
Expand Down Expand Up @@ -15854,7 +15857,8 @@ export declare namespace CloudflareWorkersModule {
event: TailStream.TailEvent<TailStream.Onset>,
):
| TailStream.TailEventHandlerType
| Promise<TailStream.TailEventHandlerType>;
| Promise<TailStream.TailEventHandlerType>
| undefined;
test?(controller: TestController): void | Promise<void>;
trace?(traces: TraceItem[]): void | Promise<void>;
}
Expand Down
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