IBM API Connect - GatewayScript Code example: Transform application/json to multipart/form-data

Posted on September 05, 2016

IBM API Connect GatewayScripts are a great possibility to transform a message up to everyones needs within a API Assembly. Unfortunately the GatewayScript API is not documented very well yet. So just to get some ideas how it works: The following example shows how to transform an application/json message body to a multipart/form-data message.

Assembly Screenshot

var boundary = "--VFCPlauenIstSuper";
var crlf = String.fromCharCode(13) + String.fromCharCode(10);

var json = apim.getvariable('message.body');
var keys = Object.keys(json);
var output = '';

for (var i = 0; i < keys.length; i++) {
  output += "--" + boundary + crlf;
  output += 'Content-Disposition: form-data; name="' + keys[i] + '"' + crlf + crlf;
  output += json[keys[i]] + crlf;

console.alert("this should end up in DataPower system log at alert level");

output += "--" + boundary + "--";

apim.setvariable('message.body', output);
apim.output("multipart/form-data; boundary=" + boundary);

Some notes on that code snippet:

  • var crlf = String.fromCharCode(13) + String.fromCharCode(10) is a replacement for var crlf = "\r\n" which won't work. During my tests I saw often problems when using escape characters in GatewayScript.

  • apim.setvariable('message.body', output) sets the message body as string. When using a string as body the Invoke policy didn't work for me - I replaced it with a Proxy policy.

  • apim.output("multipart/form-data; boundary=" + boundary) sets the message's content type.

Michael Wellner

by Michael Wellner

Merzig, Saarland