37 lines
1.4 KiB
TypeScript
37 lines
1.4 KiB
TypeScript
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/** JSON string-prefix accounting for the outer-output ledger. @module @deepseek-ai/dsh-code-runtime-worker/output-json */
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/** Control characters with a two-byte short JSON escape instead of `\u00XX`. */
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const SHORT_ESCAPE_CODES = new Set([0x08, 0x09, 0x0a, 0x0c, 0x0d])
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/** Serialized bytes contributed by one complete Unicode code point inside JSON quotes. */
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function serializedCharacterBytes(character: string): number {
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if (character.length === 2) return 4
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if (character === '"' || character === '\\') return 2
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const code = character.charCodeAt(0)
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if (code >= 0xd800 && code <= 0xdfff) return 6
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if (code < 0x20) return SHORT_ESCAPE_CODES.has(code) ? 2 : 6
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return Buffer.byteLength(character, 'utf8')
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}
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/**
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* Return the longest code-point-aligned prefix whose JSON string encoding,
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* including its surrounding quotes, fits `maxBytes`.
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*
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* @param text - the candidate string.
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* @param maxBytes - serialized JSON-string bytes available.
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* @returns the fitting prefix, or an empty string when even useful content cannot fit.
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*/
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export function truncateJsonStringBytes(text: string, maxBytes: number): string {
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if (maxBytes < 2) return ''
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if (Buffer.byteLength(JSON.stringify(text), 'utf8') <= maxBytes) return text
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let bytes = 2
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let end = 0
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for (const character of text) {
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const cost = serializedCharacterBytes(character)
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if (bytes + cost > maxBytes) break
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bytes += cost
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end += character.length
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}
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return text.slice(0, end)
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}
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