All files / csv / parse.ts

// Copyright 2018-2025 the Deno authors. MIT license.
// This module is browser compatible.

import {
  convertRowToObject,
  createBareQuoteErrorMessage,
  createQuoteErrorMessage,
  type ParseResult,
  type ReadOptions,
  type RecordWithColumn,
} from "./_io.ts";
import { codePointLength } from "./_shared.ts";

export type { ParseResult, RecordWithColumn };

const BYTE_ORDER_MARK = "\ufeff";

class Parser {
  #input = "";
  #cursor = 0;
  #options: {
    separator: string;
    trimLeadingSpace: boolean;
    comment: string | undefined;
    lazyQuotes: boolean | undefined;
    fieldsPerRecord: number | undefined;
  };
  constructor({
    separator = ",",
    trimLeadingSpace = false,
    comment,
    lazyQuotes,
    fieldsPerRecord,
  }: ReadOptions = {}) {
    this.#options = {
      separator,
      trimLeadingSpace,
      comment,
      lazyQuotes,
      fieldsPerRecord,
    };
  }
  #readLine(): string | null {
    if (this.#isEOF()) return null;

    let buffer = "";
    let hadNewline = false;
    while (this.#cursor < this.#input.length) {
      if (this.#input.startsWith("\r\n", this.#cursor)) {
        hadNewline = true;
        this.#cursor += 2;
        break;
      }
      if (
        this.#input.startsWith("\n", this.#cursor)
      ) {
        hadNewline = true;
        this.#cursor += 1;
        break;
      }
      buffer += this.#input[this.#cursor];
      this.#cursor += 1;
    }
    if (!hadNewline && buffer.endsWith("\r")) {
      buffer = buffer.slice(0, -1);
    }

    return buffer;
  }
  #isEOF(): boolean {
    return this.#cursor >= this.#input.length;
  }
  #parseRecord(zeroBasedStartLine: number): string[] | null {
    let fullLine = this.#readLine();
    if (fullLine === null) return null;
    if (fullLine.length === 0) {
      return [];
    }

    let zeroBasedLine = zeroBasedStartLine;

    // line starting with comment character is ignored
    if (this.#options.comment && fullLine[0] === this.#options.comment) {
      return [];
    }

    let line = fullLine;
    const quote = '"';
    const quoteLen = quote.length;
    const separatorLen = this.#options.separator.length;
    let recordBuffer = "";
    const fieldIndexes = [] as number[];
    parseField: while (true) {
      if (this.#options.trimLeadingSpace) {
        line = line.trimStart();
      }

      if (line.length === 0 || !line.startsWith(quote)) {
        // Non-quoted string field
        const i = line.indexOf(this.#options.separator);
        let field = line;
        if (i >= 0) {
          field = field.substring(0, i);
        }
        // Check to make sure a quote does not appear in field.
        if (!this.#options.lazyQuotes) {
          const j = field.indexOf(quote);
          if (j >= 0) {
            const col = codePointLength(
              fullLine.slice(0, fullLine.length - line.slice(j).length),
            );
            throw new SyntaxError(
              createBareQuoteErrorMessage(
                zeroBasedStartLine,
                zeroBasedLine,
                col,
              ),
            );
          }
        }
        recordBuffer += field;
        fieldIndexes.push(recordBuffer.length);
        if (i >= 0) {
          line = line.substring(i + separatorLen);
          continue parseField;
        }
        break parseField;
      } else {
        // Quoted string field
        line = line.substring(quoteLen);
        while (true) {
          const i = line.indexOf(quote);
          if (i >= 0) {
            // Hit next quote.
            recordBuffer += line.substring(0, i);
            line = line.substring(i + quoteLen);
            if (line.startsWith(quote)) {
              // `""` sequence (append quote).
              recordBuffer += quote;
              line = line.substring(quoteLen);
            } else if (line.startsWith(this.#options.separator)) {
              // `","` sequence (end of field).
              line = line.substring(separatorLen);
              fieldIndexes.push(recordBuffer.length);
              continue parseField;
            } else if (0 === line.length) {
              // `"\n` sequence (end of line).
              fieldIndexes.push(recordBuffer.length);
              break parseField;
            } else if (this.#options.lazyQuotes) {
              // `"` sequence (bare quote).
              recordBuffer += quote;
            } else {
              // `"*` sequence (invalid non-escaped quote).
              const col = codePointLength(
                fullLine.slice(0, fullLine.length - line.length - quoteLen),
              );
              throw new SyntaxError(
                createQuoteErrorMessage(zeroBasedStartLine, zeroBasedLine, col),
              );
            }
          } else if (line.length > 0 || !(this.#isEOF())) {
            // Hit end of line (copy all data so far).
            recordBuffer += line;
            const r = this.#readLine();
            line = r ?? ""; // This is a workaround for making this module behave similarly to the encoding/csv/reader.go.
            fullLine = line;
            if (r === null) {
              // Abrupt end of file (EOF or error).
              if (!this.#options.lazyQuotes) {
                const col = codePointLength(fullLine);
                throw new SyntaxError(
                  createQuoteErrorMessage(
                    zeroBasedStartLine,
                    zeroBasedLine,
                    col,
                  ),
                );
              }
              fieldIndexes.push(recordBuffer.length);
              break parseField;
            }
            zeroBasedLine++;
            recordBuffer += "\n"; // preserve line feed (This is because TextProtoReader removes it.)
          } else {
            // Abrupt end of file (EOF on error).
            if (!this.#options.lazyQuotes) {
              const col = codePointLength(fullLine);
              throw new SyntaxError(
                createQuoteErrorMessage(zeroBasedStartLine, zeroBasedLine, col),
              );
            }
            fieldIndexes.push(recordBuffer.length);
            break parseField;
          }
        }
      }
    }
    const result = [] as string[];
    let preIdx = 0;
    for (const i of fieldIndexes) {
      result.push(recordBuffer.slice(preIdx, i));
      preIdx = i;
    }
    return result;
  }
  parse(input: string): string[][] {
    this.#input = input.startsWith(BYTE_ORDER_MARK) ? input.slice(1) : input;
    this.#cursor = 0;
    const result: string[][] = [];

    let lineResult: string[];
    let first = true;
    let lineIndex = 0;

    const INVALID_RUNE = ["\r", "\n", '"'];

    const options = this.#options;
    if (
      INVALID_RUNE.includes(options.separator) ||
      (typeof options.comment === "string" &&
        INVALID_RUNE.includes(options.comment)) ||
      options.separator === options.comment
    ) {
      throw new Error("Cannot parse input: invalid delimiter");
    }

    // The number of fields per record that is either inferred from the first
    // row (when options.fieldsPerRecord = 0), or set by the caller (when
    // options.fieldsPerRecord > 0).
    //
    // Each possible variant means the following:
    // "ANY": Variable number of fields is allowed.
    // "UNINITIALIZED": The first row has not been read yet. Once it's read, the
    //                  number of fields will be set.
    // <number>: The number of fields per record that every record must follow.
    let _nbFields: "ANY" | "UNINITIALIZED" | number;
    if (options.fieldsPerRecord === undefined || options.fieldsPerRecord < 0) {
      _nbFields = "ANY";
    } else if (options.fieldsPerRecord === 0) {
      _nbFields = "UNINITIALIZED";
    } else {
      // TODO: Should we check if it's a valid integer?
      _nbFields = options.fieldsPerRecord;
    }

    while (true) {
      const r = this.#parseRecord(lineIndex);
      if (r === null) break;
      lineResult = r;
      lineIndex++;
      // If fieldsPerRecord is 0, Read sets it to
      // the number of fields in the first record
      if (first) {
        first = false;
        if (_nbFields === "UNINITIALIZED") {
          _nbFields = lineResult.length;
        }
      }

      if (lineResult.length > 0) {
        if (typeof _nbFields === "number" && _nbFields !== lineResult.length) {
          throw new SyntaxError(
            `Syntax error on line ${lineIndex}: expected ${_nbFields} fields but got ${lineResult.length}`,
          );
        }
        result.push(lineResult);
      }
    }
    return result;
  }
}

/** Options for {@linkcode parse}. */
export interface ParseOptions {
  /** Character which separates values.
   *
   * @default {","}
   */
  separator?: string;
  /** Character to start a comment.
   *
   * Lines beginning with the comment character without preceding whitespace
   * are ignored. With leading whitespace the comment character becomes part of
   * the field, even you provide `trimLeadingSpace: true`.
   *
   * By default, no character is considered to be a start of a comment.
   */
  comment?: string;
  /** Flag to trim the leading space of the value.
   *
   * This is done even if the field delimiter, `separator`, is white space.
   *
   * @default {false}
   */
  trimLeadingSpace?: boolean;
  /**
   * Allow unquoted quote in a quoted field or non-double-quoted quotes in
   * quoted field.
   *
   * @default {false}
   */
  lazyQuotes?: boolean;
  /**
   * Enabling checking number of expected fields for each row.
   *
   * If positive, each record is required to have the given number of fields.
   * If 0, it will be set to the number of fields in the first row, so that
   * future rows must have the same field count.
   * If negative, no check is made and records may have a variable number of
   * fields.
   *
   * If the wrong number of fields is in a row, a {@linkcode SyntaxError} is
   * thrown.
   */
  fieldsPerRecord?: number;
  /**
   * If you provide `skipFirstRow: true` and `columns`, the first line will be
   * skipped.
   * If you provide `skipFirstRow: true` but not `columns`, the first line will
   * be skipped and used as header definitions.
   *
   * @default {false}
   */
  skipFirstRow?: boolean;

  /** List of names used for header definition. */
  columns?: readonly string[];
}

/**
 * Parses CSV string into an array of arrays of strings.
 *
 * @example Usage
 * ```ts
 * import { parse } from "@std/csv/parse";
 * import { assertEquals } from "@std/assert/equals";
 *
 * const string = "a,b,c\n#d,e,f";
 *
 * assertEquals(parse(string), [["a", "b", "c"], ["#d", "e", "f"]]);
 * ```
 *
 * @example Quoted fields
 * ```ts
 * import { parse } from "@std/csv/parse";
 * import { assertEquals } from "@std/assert/equals";
 *
 * const string = `"a ""word""","comma,","newline\n"\nfoo,bar,baz`;
 * const result = parse(string);
 *
 * assertEquals(result, [
 *   ['a "word"', "comma,", "newline\n"],
 *   ["foo", "bar", "baz"]
 * ]);
 * ```
 *
 * @param input The input to parse.
 * @returns The parsed data.
 */
export function parse(input: string): string[][];
/**
 * Parses CSV string into an array of objects or an array of arrays of strings.
 *
 * If `columns` or `skipFirstRow` option is provided, it returns an array of
 * objects, otherwise it returns an array of arrays of string.
 *
 * @example Don't skip first row with `skipFirstRow: false`
 * ```ts
 * import { parse } from "@std/csv/parse";
 * import { assertEquals } from "@std/assert/equals";
 * import { assertType, IsExact } from "@std/testing/types"
 *
 * const string = "a,b,c\nd,e,f";
 * const result = parse(string, { skipFirstRow: false });
 *
 * assertEquals(result, [["a", "b", "c"], ["d", "e", "f"]]);
 * assertType<IsExact<typeof result, string[][]>>(true);
 * ```
 *
 * @example Skip first row with `skipFirstRow: true`
 * ```ts
 * import { parse } from "@std/csv/parse";
 * import { assertEquals } from "@std/assert/equals";
 * import { assertType, IsExact } from "@std/testing/types"
 *
 * const string = "a,b,c\nd,e,f";
 * const result = parse(string, { skipFirstRow: true });
 *
 * assertEquals(result, [{ a: "d", b: "e", c: "f" }]);
 * assertType<IsExact<typeof result, Record<string, string>[]>>(true);
 * ```
 *
 * @example Specify columns with `columns` option
 * ```ts
 * import { parse } from "@std/csv/parse";
 * import { assertEquals } from "@std/assert/equals";
 * import { assertType, IsExact } from "@std/testing/types"
 *
 * const string = "a,b,c\nd,e,f";
 * const result = parse(string, { columns: ["x", "y", "z"] });
 *
 * assertEquals(result, [{ x: "a", y: "b", z: "c" }, { x: "d", y: "e", z: "f" }]);
 * assertType<IsExact<typeof result, Record<"x" | "y" | "z", string>[]>>(true);
 * ```
 *
 * @example Specify columns with `columns` option and skip first row with
 * `skipFirstRow: true`
 * ```ts
 * import { parse } from "@std/csv/parse";
 * import { assertEquals } from "@std/assert/equals";
 * import { assertType, IsExact } from "@std/testing/types"
 *
 * const string = "a,b,c\nd,e,f";
 * const result = parse(string, { columns: ["x", "y", "z"], skipFirstRow: true });
 *
 * assertEquals(result, [{ x: "d", y: "e", z: "f" }]);
 * assertType<IsExact<typeof result, Record<"x" | "y" | "z", string>[]>>(true);
 * ```
 *
 * @example TSV (tab-separated values) with `separator: "\t"`
 * ```ts
 * import { parse } from "@std/csv/parse";
 * import { assertEquals } from "@std/assert/equals";
 *
 * const string = "a\tb\tc\nd\te\tf";
 * const result = parse(string, { separator: "\t" });
 *
 * assertEquals(result, [["a", "b", "c"], ["d", "e", "f"]]);
 * ```
 *
 * @example Trim leading space with `trimLeadingSpace: true`
 * ```ts
 * import { parse } from "@std/csv/parse";
 * import { assertEquals } from "@std/assert/equals";
 *
 * const string = " a,  b,    c\n";
 * const result = parse(string, { trimLeadingSpace: true });
 *
 * assertEquals(result, [["a", "b", "c"]]);
 * ```
 *
 * @example Lazy quotes with `lazyQuotes: true`
 * ```ts
 * import { parse } from "@std/csv/parse";
 * import { assertEquals } from "@std/assert/equals";
 *
 * const string = `a "word","1"2",a","b`;
 * const result = parse(string, { lazyQuotes: true });
 *
 * assertEquals(result, [['a "word"', '1"2', 'a"', 'b']]);
 * ```
 *
 * @example Set comment prefix with `comment` option
 * ```ts
 * import { parse } from "@std/csv/parse";
 * import { assertEquals } from "@std/assert/equals";
 *
 * const string = "a,b,c\n# THIS IS A COMMENT LINE\nd,e,f";
 * const result = parse(string, { comment: "#" });
 *
 * assertEquals(result, [["a", "b", "c"], ["d", "e", "f"]]);
 * ```
 *
 * @example Infer the number of fields from the first row with `fieldsPerRecord: 0`
 *  ```ts
 * import { parse } from "@std/csv/parse";
 * import { assertThrows } from "@std/assert/throws";
 *
 * // Note that the second row has more fields than the first row
 * const string = "a,b\nc,d,e";
 * assertThrows(
 *   () => parse(string, { fieldsPerRecord: 0 }),
 *   SyntaxError,
 *   "Syntax error on line 2: expected 2 fields but got 3",
 * );
 * ```
 *
 * @example Enforce the number of fields for each row with `fieldsPerRecord: 2`
 *  ```ts
 * import { parse } from "@std/csv/parse";
 * import { assertThrows } from "@std/assert/throws";
 *
 * const string = "a,b\nc,d,e";
 * assertThrows(
 *   () => parse(string, { fieldsPerRecord: 2 }),
 *   SyntaxError,
 *   "Syntax error on line 2: expected 2 fields but got 3",
 * );
 * ```
 *
 * @typeParam T The options' type for parsing.
 * @param input The input to parse.
 * @param options The options for parsing.
 * @returns If you don't provide `options.skipFirstRow` or `options.columns`, it
 * returns `string[][]`. If you provide `options.skipFirstRow` or
 * `options.columns`, it returns `Record<string, string>[]`.
 */
export function parse<const T extends ParseOptions>(
  input: string,
  options: T,
): ParseResult<ParseOptions, T>;
export function parse<const T extends ParseOptions>(
  input: string,
  options: T = { skipFirstRow: false } as T,
): ParseResult<ParseOptions, T> {
  const parser = new Parser(options);
  const r = parser.parse(input);

  if (options.skipFirstRow || options.columns) {
    let headers: readonly string[] = [];

    if (options.skipFirstRow) {
      const head = r.shift();
      if (head === undefined) {
        throw new TypeError("Cannot parse input: headers must be defined");
      }
      headers = head;
    }

    if (options.columns) {
      headers = options.columns;
    }

    const zeroBasedFirstLineIndex = options.skipFirstRow ? 1 : 0;
    return r.map((row, i) => {
      return convertRowToObject(row, headers, zeroBasedFirstLineIndex + i);
    }) as ParseResult<ParseOptions, T>;
  }
  return r as ParseResult<ParseOptions, T>;
}