parse-data-url.js

const removeLeadingAndTrailingHTTPWhitespace = (string) =>
  string.replace(/^[ \t\n\r]+/, "").replace(/[ \t\n\r]+$/, "");

const removeTrailingHTTPWhitespace = (string) =>
  string.replace(/[ \t\n\r]+$/, "");

const isHTTPWhitespaceChar = (char) =>
  char === " " || char === "\t" || char === "\n" || char === "\r";

const solelyContainsHTTPTokenCodePoints = (string) =>
  /^[-!#$%&'*+.^_`|~A-Za-z0-9]*$/.test(string);

const soleyContainsHTTPQuotedStringTokenCodePoints = (string) =>
  /^[\t\u0020-\u007E\u0080-\u00FF]*$/.test(string);

const asciiLowercase = (string) =>
  string.replace(/[A-Z]/g, (l) => l.toLowerCase());

const collectAnHTTPQuotedString = (input, position) => {
  let value = "";

  // eslint-disable-next-line no-param-reassign
  position += 1;

  // eslint-disable-next-line no-constant-condition
  while (true) {
    while (
      position < input.length &&
      input[position] !== '"' &&
      input[position] !== "\\"
    ) {
      value += input[position];
      // eslint-disable-next-line no-param-reassign
      position += 1;
    }

    if (position >= input.length) {
      break;
    }

    const quoteOrBackslash = input[position];

    // eslint-disable-next-line no-param-reassign
    position += 1;

    if (quoteOrBackslash === "\\") {
      if (position >= input.length) {
        value += "\\";
        break;
      }

      value += input[position];
      // eslint-disable-next-line no-param-reassign
      position += 1;
    } else {
      break;
    }
  }

  return [value, position];
};

function isASCIIHex(c) {
  return (
    (c >= 0x30 && c <= 0x39) ||
    (c >= 0x41 && c <= 0x46) ||
    (c >= 0x61 && c <= 0x66)
  );
}

function percentDecodeBytes(input) {
  const output = new Uint8Array(input.byteLength);
  let outputIndex = 0;

  for (let i = 0; i < input.byteLength; ++i) {
    const byte = input[i];

    if (byte !== 0x25) {
      output[outputIndex] = byte;
    } else if (
      byte === 0x25 &&
      (!isASCIIHex(input[i + 1]) || !isASCIIHex(input[i + 2]))
    ) {
      output[outputIndex] = byte;
    } else {
      output[outputIndex] = parseInt(
        String.fromCodePoint(input[i + 1], input[i + 2]),
        16,
      );
      i += 2;
    }

    outputIndex += 1;
  }

  return output.slice(0, outputIndex);
}

/**
 * A lookup table for atob(), which converts an ASCII character to the
 * corresponding six-bit number.
 */

const characters =
  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

function atobLookup(chr) {
  const index = characters.indexOf(chr);
  // Throw exception if character is not in the lookup string; should not be hit in tests
  // eslint-disable-next-line no-undefined
  return index < 0 ? undefined : index;
}

/**
 * Implementation of atob() according to the HTML and Infra specs, except that
 * instead of throwing INVALID_CHARACTER_ERR we return null.
 */
function atob(input) {
  /* eslint-disable no-bitwise */
  // Web IDL requires DOMStrings to just be converted using ECMAScript
  // ToString, which in our case amounts to using a template literal.
  let data = `${input}`;

  // "Remove all ASCII whitespace from data."
  data = data.replace(/[ \t\n\f\r]/g, "");

  // "If data's length divides by 4 leaving no remainder, then: if data ends
  // with one or two U+003D (=) code points, then remove them from data."
  if (data.length % 4 === 0) {
    data = data.replace(/==?$/, "");
  }

  // "If data's length divides by 4 leaving a remainder of 1, then return
  // failure."
  //
  // "If data contains a code point that is not one of
  //
  // U+002B (+)
  // U+002F (/)
  // ASCII alphanumeric
  //
  // then return failure."
  if (data.length % 4 === 1 || /[^+/0-9A-Za-z]/.test(data)) {
    return null;
  }

  // "Let output be an empty byte sequence."
  let output = "";

  // "Let buffer be an empty buffer that can have bits appended to it."
  //
  // We append bits via left-shift and or.  accumulatedBits is used to track
  // when we've gotten to 24 bits.
  let buffer = 0;
  let accumulatedBits = 0;

  // "Let position be a position variable for data, initially pointing at the
  // start of data."
  //
  // "While position does not point past the end of data:"
  for (let i = 0; i < data.length; i++) {
    // "Find the code point pointed to by position in the second column of
    // Table 1: The Base 64 Alphabet of RFC 4648. Let n be the number given in
    // the first cell of the same row.
    //
    // "Append to buffer the six bits corresponding to n, most significant bit
    // first."
    //
    // atobLookup() implements the table from RFC 4648.
    // eslint-disable-next-line no-bitwise
    buffer <<= 6;

    // eslint-disable-next-line no-bitwise
    buffer |= atobLookup(data[i]);
    accumulatedBits += 6;

    // "If buffer has accumulated 24 bits, interpret them as three 8-bit
    // big-endian numbers. Append three bytes with values equal to those
    // numbers to output, in the same order, and then empty buffer."
    if (accumulatedBits === 24) {
      output += String.fromCharCode((buffer & 0xff0000) >> 16);
      output += String.fromCharCode((buffer & 0xff00) >> 8);
      output += String.fromCharCode(buffer & 0xff);
      accumulatedBits = 0;
      buffer = 0;
    }
    // "Advance position by 1."
  }

  // "If buffer is not empty, it contains either 12 or 18 bits. If it contains
  // 12 bits, then discard the last four and interpret the remaining eight as
  // an 8-bit big-endian number. If it contains 18 bits, then discard the last
  // two and interpret the remaining 16 as two 8-bit big-endian numbers. Append
  // the one or two bytes with values equal to those one or two numbers to
  // output, in the same order."
  if (accumulatedBits === 12) {
    buffer >>= 4;
    output += String.fromCharCode(buffer);
  } else if (accumulatedBits === 18) {
    buffer >>= 2;
    output += String.fromCharCode((buffer & 0xff00) >> 8);
    output += String.fromCharCode(buffer & 0xff);
  }
  /* eslint-enable no-bitwise */

  // "Return output."
  return output;
}

export default function parseDataUrl(stringInput) {
  let parsedUrl;

  try {
    parsedUrl = new URL(stringInput);
  } catch (error) {
    return null;
  }

  if (parsedUrl.protocol !== "data:") {
    return null;
  }

  parsedUrl.hash = "";

  // `5` is value of `'data:'.length`
  const input = parsedUrl.toString().substring(5);

  let position = 0;
  let mediaType = "";

  while (position < input.length && input[position] !== ",") {
    mediaType += input[position];
    position += 1;
  }

  mediaType = mediaType
    .replace(/^[ \t\n\f\r]+/, "")
    .replace(/[ \t\n\f\r]+$/, "");

  if (position === input.length) {
    return null;
  }

  position += 1;

  const encodedBody = input.substring(position);

  let body = Buffer.from(percentDecodeBytes(Buffer.from(encodedBody, "utf-8")));

  // Can't use /i regexp flag because it isn't restricted to ASCII.
  const mimeTypeBase64MatchResult = /(.*); *[Bb][Aa][Ss][Ee]64$/.exec(
    mediaType,
  );

  if (mimeTypeBase64MatchResult) {
    const stringBody = body.toString("binary");
    const asString = atob(stringBody);

    if (asString === null) {
      return null;
    }

    body = Buffer.from(asString, "binary");

    [, mediaType] = mimeTypeBase64MatchResult;
  }

  if (mediaType.startsWith(";")) {
    mediaType = `text/plain ${mediaType}`;
  }

  const result = {
    // eslint-disable-next-line no-undefined
    type: undefined,
    // eslint-disable-next-line no-undefined
    subtype: undefined,
    parameters: new Map(),
    isBase64: Boolean(mimeTypeBase64MatchResult),
    body,
  };

  if (!mediaType) {
    return result;
  }

  const inputMediaType = removeLeadingAndTrailingHTTPWhitespace(mediaType);

  let positionMediaType = 0;
  let type = "";

  while (
    positionMediaType < inputMediaType.length &&
    inputMediaType[positionMediaType] !== "/"
  ) {
    type += inputMediaType[positionMediaType];
    positionMediaType += 1;
  }

  if (type.length === 0 || !solelyContainsHTTPTokenCodePoints(type)) {
    return result;
  }

  if (positionMediaType >= inputMediaType.length) {
    return result;
  }

  // Skips past "/"
  positionMediaType += 1;

  let subtype = "";

  while (
    positionMediaType < inputMediaType.length &&
    inputMediaType[positionMediaType] !== ";"
  ) {
    subtype += inputMediaType[positionMediaType];
    positionMediaType += 1;
  }

  subtype = removeTrailingHTTPWhitespace(subtype);

  if (subtype.length === 0 || !solelyContainsHTTPTokenCodePoints(subtype)) {
    return result;
  }

  result.type = asciiLowercase(type);
  result.subtype = asciiLowercase(subtype);

  while (positionMediaType < inputMediaType.length) {
    // Skip past ";"
    positionMediaType += 1;

    while (isHTTPWhitespaceChar(inputMediaType[positionMediaType])) {
      positionMediaType += 1;
    }

    let parameterName = "";

    while (
      positionMediaType < inputMediaType.length &&
      inputMediaType[positionMediaType] !== ";" &&
      inputMediaType[positionMediaType] !== "="
    ) {
      parameterName += inputMediaType[positionMediaType];
      positionMediaType += 1;
    }

    parameterName = asciiLowercase(parameterName);

    if (positionMediaType < inputMediaType.length) {
      if (inputMediaType[positionMediaType] === ";") {
        // eslint-disable-next-line no-continue
        continue;
      }

      // Skip past "="
      positionMediaType += 1;
    }

    let parameterValue = "";

    if (inputMediaType[positionMediaType] === '"') {
      [parameterValue, positionMediaType] = collectAnHTTPQuotedString(
        inputMediaType,
        positionMediaType,
      );

      while (
        positionMediaType < inputMediaType.length &&
        inputMediaType[positionMediaType] !== ";"
      ) {
        positionMediaType += 1;
      }
    } else {
      while (
        positionMediaType < inputMediaType.length &&
        inputMediaType[positionMediaType] !== ";"
      ) {
        parameterValue += inputMediaType[positionMediaType];
        positionMediaType += 1;
      }

      parameterValue = removeTrailingHTTPWhitespace(parameterValue);

      if (parameterValue === "") {
        // eslint-disable-next-line no-continue
        continue;
      }
    }

    if (
      parameterName.length > 0 &&
      solelyContainsHTTPTokenCodePoints(parameterName) &&
      soleyContainsHTTPQuotedStringTokenCodePoints(parameterValue) &&
      !result.parameters.has(parameterName)
    ) {
      result.parameters.set(parameterName, parameterValue);
    }
  }

  return result;
}