addMultipartHeaders.ts

/**
 * Creates multipart body for files with additional headers
 * @param formData native FormData
 * @param headers object: key - field name, value - object with header: value pairs
 * @returns contentType and body
 */

function createMultipartBody(
  formData: FormData,
  headers: Record<string, AdditionalHeaders> = {},
) {
  const boundary = `----WebKitFormBoundary${Math.random()
    .toString(36)
    .substring(2)}`;
  let body = "";

  // Create a Blob array to handle binary data properly
  const blobs = [];

  [...formData.entries()].forEach(([key, value]) => {
    body += `--${boundary}\r\n`;
    if (value instanceof File) {
      body += `Content-Disposition: form-data; name="${key}"; filename="${value.name}"\r\n`;
      body += `Content-Type: ${value.type || "application/octet-stream"}\r\n`;
      if (headers[key]) {
        const customHeaders = headers[key];
        const headersString = Object.keys(customHeaders).reduce((acc, curr) => {
          return `${acc}${curr}: ${customHeaders[curr]}\r\n`;
        }, "");
        body += headersString;
      }
      body += "\r\n";
      blobs.push(new Blob([body], { type: value.type || "text/plain" }));
      blobs.push(value);
      body = "\r\n";
    } else {
      body += `Content-Disposition: form-data; name="${key}"\r\n\r\n`;
      body += `${value}\r\n`;
      blobs.push(new Blob([body], { type: "text/plain" }));
      body = "";
    }
  });
  body = `\r\n--${boundary}--\r\n`;
  blobs.push(new Blob([body], { type: "text/plain" }));

  const multipartBlob = new Blob(blobs, {
    type: `multipart/form-data; boundary=${boundary}`,
  });
  return {
    contentType: `multipart/form-data; boundary=${boundary}`,
    body: multipartBlob,
  };
}