deno.land / std@0.166.0 / encoding / json / _parse.ts
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import { toTransformStream } from "../../streams/conversion.ts";
/** The type of the result of parsing JSON. */export type JsonValue = | { [key: string]: JsonValue | undefined } | JsonValue[] | string | number | boolean | null;
/** Optional object interface for `JSONParseStream` and `ConcatenatedJsonParseStream`. */export interface ParseStreamOptions { /** Controls the buffer of the TransformStream used internally. Check https://developer.mozilla.org/en-US/docs/Web/API/TransformStream/TransformStream. */ readonly writableStrategy?: QueuingStrategy<string>; /** Controls the buffer of the TransformStream used internally. Check https://developer.mozilla.org/en-US/docs/Web/API/TransformStream/TransformStream. */ readonly readableStrategy?: QueuingStrategy<JsonValue>;}
/** * Parse each chunk as JSON. * * This can be used to parse [JSON lines](https://jsonlines.org/), [NDJSON](http://ndjson.org/) and [JSON Text Sequences](https://datatracker.ietf.org/doc/html/rfc7464). * Chunks consisting of spaces, tab characters, or newline characters will be ignored. * * ```ts * import { TextLineStream } from "https://deno.land/std@$STD_VERSION/streams/mod.ts"; * import { JsonParseStream } from "https://deno.land/std@$STD_VERSION/encoding/json/stream.ts"; * * const url = "https://deno.land/std@$STD_VERSION/encoding/testdata/json/test.jsonl"; * const { body } = await fetch(url); * * const readable = body! * .pipeThrough(new TextDecoderStream()) * .pipeThrough(new TextLineStream()) // or `new TextDelimiterStream(delimiter)` * .pipeThrough(new JsonParseStream()); * * for await (const data of readable) { * console.log(data); * } * ``` */export class JsonParseStream extends TransformStream<string, JsonValue> { /** * @param options * @param options.writableStrategy Controls the buffer of the TransformStream used internally. Check https://developer.mozilla.org/en-US/docs/Web/API/TransformStream/TransformStream. * @param options.readableStrategy Controls the buffer of the TransformStream used internally. Check https://developer.mozilla.org/en-US/docs/Web/API/TransformStream/TransformStream. */ constructor({ writableStrategy, readableStrategy }: ParseStreamOptions = {}) { super( { transform(chunk, controller) { if (!isBrankString(chunk)) { controller.enqueue(parse(chunk)); } }, }, writableStrategy, readableStrategy, ); }}
const branks = /^[ \t\r\n]*$/;function isBrankString(str: string) { return branks.test(str);}
/** * stream to parse [Concatenated JSON](https://en.wikipedia.org/wiki/JSON_streaming#Concatenated_JSON). * * ```ts * import { ConcatenatedJsonParseStream } from "https://deno.land/std@$STD_VERSION/encoding/json/stream.ts"; * * const url = "https://deno.land/std@$STD_VERSION/encoding/testdata/json/test.concatenated-json"; * const { body } = await fetch(url); * * const readable = body! * .pipeThrough(new TextDecoderStream()) * .pipeThrough(new ConcatenatedJsonParseStream()); * * for await (const data of readable) { * console.log(data); * } * ``` */export class ConcatenatedJsonParseStream implements TransformStream<string, JsonValue> { readonly writable: WritableStream<string>; readonly readable: ReadableStream<JsonValue>; /** * @param options * @param options.writableStrategy Controls the buffer of the TransformStream used internally. Check https://developer.mozilla.org/en-US/docs/Web/API/TransformStream/TransformStream. * @param options.readableStrategy Controls the buffer of the TransformStream used internally. Check https://developer.mozilla.org/en-US/docs/Web/API/TransformStream/TransformStream. */ constructor({ writableStrategy, readableStrategy }: ParseStreamOptions = {}) { const { writable, readable } = toTransformStream( this.#concatenatedJSONIterator, writableStrategy, readableStrategy, ); this.writable = writable; this.readable = readable; }
async *#concatenatedJSONIterator(src: AsyncIterable<string>) { // Counts the number of '{', '}', '[', ']', and when the nesting level reaches 0, concatenates and returns the string. let targetString = ""; let hasValue = false; let nestCount = 0; let readingString = false; let escapeNext = false; for await (const string of src) { let sliceStart = 0; for (let i = 0; i < string.length; i++) { const char = string[i];
if (readingString) { if (char === '"' && !escapeNext) { readingString = false;
// When the nesting level is 0, it returns a string when '"' comes. if (nestCount === 0 && hasValue) { yield parse(targetString + string.slice(sliceStart, i + 1)); hasValue = false; targetString = ""; sliceStart = i + 1; } } escapeNext = !escapeNext && char === "\\"; continue; }
// Parses number, true, false, null with a nesting level of 0. // example: 'null["foo"]' => null, ["foo"] // example: 'false{"foo": "bar"}' => false, {foo: "bar"} if ( hasValue && nestCount === 0 && (char === "{" || char === "[" || char === '"' || char === " ") ) { yield parse(targetString + string.slice(sliceStart, i)); hasValue = false; readingString = false; targetString = ""; sliceStart = i; i--; continue; }
switch (char) { case '"': readingString = true; escapeNext = false; break; case "{": case "[": nestCount++; break; case "}": case "]": nestCount--; break; }
// parse object or array if ( hasValue && nestCount === 0 && (char === "}" || char === "]") ) { yield parse(targetString + string.slice(sliceStart, i + 1)); hasValue = false; targetString = ""; sliceStart = i + 1; continue; }
if (!hasValue && !isBrankChar(char)) { // We want to ignore the character string with only blank, so if there is a character other than blank, record it. hasValue = true; } } targetString += string.slice(sliceStart); } if (hasValue) { yield parse(targetString); } }}
const blank = new Set(" \t\r\n");function isBrankChar(char: string) { return blank.has(char);}
/** JSON.parse with detailed error message. */function parse(text: string): JsonValue { try { return JSON.parse(text); } catch (error: unknown) { if (error instanceof Error) { // Truncate the string so that it is within 30 lengths. const truncatedText = 30 < text.length ? `${text.slice(0, 30)}...` : text; throw new (error.constructor as ErrorConstructor)( `${error.message} (parsing: '${truncatedText}')`, ); } throw error; }}
std
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