parse multipart/form-data in JavaScript, for Apigee X

parse-multipart-form.js

function parseMultipartPart(part) {
  var lines = part.split(/\r\n|\n/);
  var name = null;
  var value = [];
  var state = 0;

  for (var i = 0; i < lines.length; i++) {
    var line = lines[i];

    switch (state) {
      case 0 /* awaiting content-disposition */:
        {
          var lowerCaseLine = line.toLowerCase();
          if (lowerCaseLine.startsWith("content-disposition:")) {
            var nameMatch = /name=\"([^\"]+)\"/.exec(line);
            if (nameMatch && nameMatch.length > 1) {
              name = nameMatch[1];
              state = 1;
            }
          }
        }
        break;
      case 1 /* awaiting end of headers */:
        if (line.trim() === "") {
          // Empty line, part content starts after this
          state = 2;
        }
        break;
      case 2 /*  Reading part content */:
        value.push(line);
        break;
      default:
        throw new Error("parse error");
    }
  }

  var resultValue = value.join("\n");
  if (resultValue.endsWith("\n")) {
    resultValue = resultValue.slice(0, -1);
  }

  return {
    name: name,
    value: resultValue,
  };
}

function parseMultiPart(eachPart) {
  var ctype = context.getVariable("request.header.content-type");
  // Example
  // Content-Type: multipart/form-data; boundary=---------------------------1837170403803086655542689190
  var parts = ctype.split(";").map((p) => p.trim());
  // print("examining part0: (" + parts[0] + ")");
  if (parts[0] != "multipart/form-data") {
    throw new Error("Not a multipart/form-data message");
  }
  var boundaryPart = parts.find((v) => v.startsWith("boundary="));
  var boundary =
    boundaryPart && boundaryPart.split("=").map((p) => p.trim())[1];
  var payload = context.getVariable("request.content");

  parts = payload.split("--" + boundary).map((p) => p.trim());
  if (parts && parts.length) {
    var L = parts.length;
    if (parts[L - 1] == "--") {
      // end of all parts marker
      var count = 0;
      parts.forEach((part, ix) => {
        if (part && part != "--") {
          var parsed = parseMultipartPart(part);
          eachPart(parsed, ix);
          count++;
        }
      });
      context.setVariable("formpart.count", String(count));
    } else {
      throw new Error("Could not find the final part delimiter");
    }
  } else {
    context.setVariable("formpart.count", "0");
  }
}

parseMultiPart((parsed, ix) => {
  context.setVariable("formpart." + ix + ".name", parsed.name);
  context.setVariable("formpart." + ix + ".value", parsed.value);
});