Question

I am trying to create a UrlFetchApp() payload from multiple documents for a third-party service. If I follow their example for multiple inline documents, the UrlFetchApp() payload should contain both binary (for each file) and text (to separate the two pieces of content). How to I supply this mixed content to the payload advanced argument?

I have successfully done binary only using .getBytes() on a blob as follows:

function testfax() {
  var faxnum = '12125551234';
  var url = 'https://rest.interfax.net/outbound/faxes?faxNumber=+'+faxnum;
  Logger.log('url='+url)
  Logger.log(" ")

  var varAuthString = AuthString();  //user function to create HTTP simple authorization header
  //Logger.log(varAuthString)
  //Logger.log(" ")

  var accept = "application/xml";
  var meth = 'POST';

  var payloadBlob = testDocBlob("For-Testing-Fax");   //user function returns GAS blob mime type "application/pdf"
  var payload = [];
  payload = payloadBlob.getBytes();
  Logger.log(payload.length)
  var contentType = "application/pdf"
  var ContentLen = 0;
  var headers = 
    {
      "Accept": accept ,
      "Authorization": "Basic " + varAuthString
    }
  //Logger.log("headers= ")
  //Logger.log(headers)
  //Logger.log(" ")
  var options =
    {
      "method" : meth,
      "headers" : headers,
      "contentType":contentType,
      "contentLength": ContentLen,
      "payload" : payload
    };
  //Logger.log("options= ")
  //Logger.log(options)
  //Logger.log(" ")
  var r = UrlFetchApp.fetch(url,options);
  Logger.log(r.getResponseCode());
  Logger.log(r.getContentText());
  Logger.log(r.getHeaders());
}

Answer 1

You’ve got most of the code you need already, you just need to re-arrange it a bit and build in the multi-part handling.

I suggest you modify your fax sending function to deal with an array of file blobs.
Here’s what the code of your test function would look like, building up the array and calling your testfax() function:

function testtestfax() {
  // Build an array with files for faxing.
  var files = [];
  // Repeat push line for multiple files.
  files.push(testDocBlob("For-Testing-Fax"));   //user function returns GAS blob mime type "application/pdf"
  testfax(files);
}

This way, you can set contentType depending on the length of the file array. If it’s a single file, take contentType=fileBlob.getContentType(), otherwise contentType=multipart/mixed... with an appropriate boundary parameter.

  if (files.length == 1) {
    var contentType = "application/pdf"
  }
  else {
    var boundary="265001916915724"
    var contentType = 'multipart/mixed; boundary="'+boundary+'"';
  }

You can choose to use a hard-coded boundary like this – it’s interesting how often the one in this example shows up in searches. Better if you can generate your own random string. This is all described in Section 5.1 of RFC2046, Multipurpose Internet Mail Extensions.

Once your contentType is set, build the payload of your message. If it’s a single file, payload consists only of files[0].getBytes(). Otherwise, loop through files, appending to payload for each one.

The multipart payload for each file will consist of:

• a blank line (CRLF), followed by..
• the boundary string prepended by double-hyphens, followed by…
• the content-type tag for the file. files[i].getContentType(), followed by…
• files[i].getBytes()

The multipart payload is then finalized by:

• a blank line (CRLF), followed by…
• the boundary string enclosed front and back with double-hyphens, signifying the end.

The last part of your existing function remains as-is, setting up the options with the payload that has been constructed above, and using fetch() to send it off. You should now have a function that can handle single or multiple faxes.