How to build Multipart request with binary file content?

Google Cloud Apigee
1

Hi All,

when i upload a image as “multipart/form-data” directly to the backend i’m getting success response. But i have a requirement to upload the image as binary and then build a “multipart/form-data” request with the binary content, i tried building the request in JavaScript and send it to the backend but i’m getting an error response.

Please find the below code:

function getMultipartPayload(content, boundary){
    var formPayload = "";
    formPayload  = formPayload + boundary+"\r\n"+"Content-Disposition: form-data; name=\"file\"; filename=\"Sideview.jpg\"\r\nContent-Type: image/jpeg\r\n\r\n"+content+"\r\n";
    formPayload+= boundary+"--\r\n";
    return formPayload;
}
var content = context.getVariable("request.content");
var boundary = "--------------------------703350424384203211386545";
var multipartPayload = getMultipartPayload(content, boundary);
context.setVariable("boundary",boundary);
context.setVariable("multipartPayload",multipartPayload);

I used the above set variables in an Assign Message policy to form the request.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<AssignMessage async="false" continueOnError="false" enabled="true" name="AM.Build.Request">
    <DisplayName>AM.Build.Request</DisplayName>
    <Properties/>
    <Set>
        <Headers>
            <Header name="Content-Type">multipart/form-data; boundary={boundary}</Header>
        </Headers>
        <Payload variablePrefix="@" variableSuffix="#">@multipartPayload#</Payload>
        <Verb>POST</Verb>
    </Set>
    <IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
    <AssignTo createNew="false" transport="http" type="request"/>
</AssignMessage>

and i observed that Content-Length is different from what i received in the request header and when printed in JavaScript. Does Apigee alter the content when we do context.getVariable(“request.content”) in a multipart/form-data or binary, file upload request?

9132-capture.png
9132-capture.png506×299 7.68 KB

I saw these related discussions:

https://community.apigee.com/questions/13135/how-do-i-send-multipart-data-to-my-request.html

https://community.apigee.com/questions/34311/how-do-i-calculate-the-content-length-for-a-multip.html

Any suggestions what can be done here?

2

I don’t think you can do what you want in a JS callout. The JS callout does not have good facilities for handling byte streams (aka “binary content”). If the multipart form contains only text, it’s easy. But if you want non-UTF-8 byte streams, then JS won’t satisfy.

You could do what you want in

  • a Java callout
  • maybe a Python callout
  • a Hosted Target
3

Thanks @Dino-at-Google for the quick response. Yes, i figured out, i was losing some data in JS, so i used a Java callout and it worked.

https://community.apigee.com/articles/60050/multipart-multipartform-data-creation-and-parsing.html

This article is really helpful.

1 Like