How to upload an audio file in apex code via MultiPart FormData - apex

Question

I am working on a project in which I need to upload an audio file to the External webservice via Apex code. So I am using multipart form data to do the same but every time I am getting an error i.e ActionController::UnknownFormat
I am trying to do the same via multipart form data in apex.
String body = '--' + boundary + '\r\n';
body += 'Content-Disposition: form-data; name="recording[s3_location]"; filename="abc.mp3"\r\nContent-Type: audio/mpeg\r\n\r\n';
body += 'F:\Test.mp3\r\n';
body += '--' + boundary + '--';
Expected result code: 201(success)
Actual Result Code: 500(ActionController::UnknownFormat)
I tried with postman its working fine but whenever i am trying with my code i am getting the exception. Please help me. Thanks in advance :)

Answer 1

Here is a working solution for sending one file at a time:
// form boundary must be a string that will very likely never appear again in the form
public static final String BOUNDARY = '----FormBoundary4Amf13kZd';
public static final String EXTRABOUNDARY = '--' + BOUNDARY;
/**
*
*
* #param file The file that will be uploaded.
* #param contentType The content-type of the file. Will default to application/octet-stream.
* #param filename Name to give the file.
* #param formDataMap Any extra metadata that you want to send.
*
* #return Blob of the complete multipart form.
*/
public static Blob multiPartFormDataBody(Blob file, String contentType, String filename, Map<String, String> metadataMap) {
contentType = contentType == '' ? 'application/octet-stream' : contentType;
String bodyStartHex = EncodingUtil.convertToHex(Blob.valueOf(EXTRABOUNDARY + '\r\nContent-Disposition: form-data; name=\"file\"; filename="' + filename + '"\r\nContent-Type: ' + contentType + '\r\n\r\n'));
String bodyEndHex = EncodingUtil.convertToHex(Blob.valueOf(EXTRABOUNDARY + '--\r\n'));
bodyStartHex += EncodingUtil.convertToHex(file);
if (metadataMap != null && metadataMap.size() != 0) {
String formElements = '\r\n';
for (String key : metadataMap.keySet()) {
formElements += EXTRABOUNDARY + '\r\nContent-Disposition: form-data; name=\"' + key + '\"\r\n\r\n' + metadataMap.get(key) + '\r\n';
}
bodyStartHex += EncodingUtil.convertToHex(Blob.valueOf(formElements));
} else {
// the extra '--' at the end is crucial
bodyEndHex = EncodingUtil.convertToHex(Blob.valueOf('\r\n' + EXTRABOUNDARY + '--'));
}
return EncodingUtil.convertFromHex(bodyStartHex + bodyEndHex);
}
The important thing to note here is that you MUST convert your entire mutltipart-form string to a hexidecimal string and then back to Blob before sending to an external webservice, because you cannot mix the file binary and the UTF-8 boundary strings. You first get the Blob of the boundaries and metadata and convert them to hex. Then you take your input file Blob and convert it to hex. Then you combine the hex strings together and convert them back to a Blob to be sent via HttpRequest:
public static HttpResponse sendMultiPartForm(Blob file, String contentType, String filename, Map<String, String> metadataMap) {
HttpRequest request = new HttpRequest();
Http http = new Http();
request.setEndpoint('https://example.com/api/upload');
request.setMethod('POST');
// Boundary must be set to exactly what was set before
request.setHeader('Content-Type', 'multipart/form-data; boundary=' + BOUNDARY);
request.setBodyAsBlob(multiPartFormDataBody(file, contentType, filename, metadataMap));
request.setHeader('Content-Length', String.valueOf(request.getBodyAsBlob().size()));
return http.send(request);
}
I left out explanation for the carriage returns and newlines, because they need to be so exact here that honestly everyone should just copy and paste them. It took a lot of trial and error to get it right.