perf(ai-chat-ui): skip doomed JSON.parse on streaming tool arguments - #17975
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perf(ai-chat-ui): skip doomed JSON.parse on streaming tool arguments#17975safisa wants to merge 1 commit into
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extractJsonStringField attempted JSON.parse on every call even while tool call arguments were still streaming, where the truncated JSON always throws after scanning the whole string - quadratic as arguments grow. Only attempt the parse once the arguments object can be complete (ends with '}') and use the regex extraction otherwise. Fixes eclipse-theia#17974
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What it does
Fixes #17974.
extractJsonStringFieldtriedJSON.parsefirst and used its regex fallback only when the parse threw. While tool call arguments stream in, the JSON is truncated, so the parse always throws — after scanning the entire string. Called per render from the tool-call label, this gets quadratic as the arguments grow (measured ~27 s of CPU for 2 MB of arguments at 64-char deltas).Now the full parse is only attempted once the arguments object can actually be complete (trimmed string ends with
}); otherwise the regex extraction runs directly. Complete JSON still goes throughJSON.parse, so proper unescaping (e.g.\", Windows paths with\\) is preserved — pinned by the existing tests. Inputs that never start with{behave exactly as before.How to test
cd packages/ai-chat-ui && npx mocha --config ../../configs/mocharc.yml "./lib/**/*.spec.js"— 278 passing, including 3 new boundary tests.writeFileContentwith a largecontentargument and profile the frontend while the arguments stream:JSON.parseunderextractJsonStringFieldno longer shows up.Follow-ups
The regex still matches the first
"<field>": "..."occurrence anywhere in the string, so acontentvalue that itself contains e.g. a"path"property can show a wrong label mid-stream (cosmetic, pre-existing; noted in #17974).Breaking changes
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