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fix: avoid quadratic memory growth in streamText text() without breaking chunk streaming #14119

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fix: avoid quadratic memory growth in streamText text() without breaking chunk streaming #14119

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12 changes: 12 additions & 0 deletions packages/ai/src/generate-text/stream-text.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -629,6 +629,7 @@ function createOutputTransformStream<
let textChunk = '';
let textProviderMetadata: ProviderMetadata | undefined = undefined;
let lastPublishedJson = '';
const isTextOutput = output.name === 'text';

function publishTextChunk({
controller,
Expand Down Expand Up @@ -696,6 +697,17 @@ function createOutputTransformStream<
textChunk += chunk.text;
textProviderMetadata = chunk.providerMetadata ?? textProviderMetadata;

// For text output, every text-delta always changes the partial output,
// so we can publish immediately and avoid the expensive JSON.stringify
// comparison that causes O(n²) memory growth with large responses.
if (isTextOutput) {
publishTextChunk({
controller,
partialOutput: text as InferPartialOutput<OUTPUT>,
});
return;
}

// only publish if partial json can be parsed:
const result = await output.parsePartialOutput({ text });

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