Salesoforce Apex parse RestRequest into multipart

RestRequestMultipart.cls

public with sharing class RestRequestMultipart
{
	public List<RestRequest> requests;
	public Map<String, String> headers;
	public String httpMethod;
	public Map<String, String> params;
	public String remoteAddress;
	public String requestURI;
	public String resourcePath;

	private RestRequest originalRequest;

	public RestRequestMultipart(RestRequest req)
	{
		this.setAttributes(req);

		this.buildRequestList(req);
	}

	/**
	 * Parse original request into its mutliparts
	 */
	private void buildRequestList(RestRequest req)
	{
		this.requests = new List<RestRequest>();
		String boundary = req.headers.get('boundary');

		List<String> parts = req.requestBody.toString().split('--'+boundary);

		for(String part : parts) {

			if(part.length() == 0) {
				continue;
			}

			Integer splitter = part.indexOf('\n\n');

			String headersString = part.substring(0, splitter);
			String body = part.substring(splitter+2, part.length()-1);

			RestRequest newRequest = new RestRequest();

			Map<String, String> headerMap = this.buildHeaders(headersString);
			for(String key : headerMap.keySet()) {
				newRequest.addHeader(key, headerMap.get(key));
			}

			newRequest.requestBody = Blob.valueOf(body);

			this.requests.add(newRequest);
		}
	}

	@TestVisible
	private Map<String, String> buildHeaders(String headerString)
	{
		Map<String, String> headerMap = new Map<String, String>();
		List<String> headerList = headerString.split('\n');

		for(String headerLine : headerList) {

			if(headerLine.length() == 0) {
				continue;
			}

			Integer colon = headerLine.indexOf(':');

			headerMap.put(
				headerLine.substring(0, colon).trim(),
				headerLine.substring(colon+1).trim()
			);
		}

		return headerMap;
	}

	private void setAttributes(RestRequest req)
	{
		this.originalRequest = req;

		this.headers = req.headers;
		this.httpMethod = req.httpMethod;
		this.params = req.params;
		this.remoteAddress = req.remoteAddress;
		this.requestURI = req.requestURI;
		this.resourcePath = req.resourcePath;
	}
}

RestRequestMultipartTest.cls

@isTest
public with sharing class RestRequestMultipartTest
{
	@isTest
	public static void test_parsing_mutlipart_request()
	{
		String body = '--83ff53821b7c' +'\n'+
'Content-Disposition: form-data; name="img"; filename="a.png"' +'\n'+
'Content-Type: application/octet-stream' +'\n'+
+'\n'+
'testcontent1\n'+
'--83ff53821b7c' +'\n'+
'Content-Disposition: form-data; name="foo"' +'\n'+
+'\n'+
'testcontent2' +'\n'+
'--83ff53821b7c';

		RestRequest req = new RestRequest();
		req.addHeader('boundary', '83ff53821b7c');
		req.requestBody = Blob.valueOf(body);

		RestRequestMultipart multipart = new RestRequestMultipart(req);

		System.assertEquals(2, multipart.requests.size());
		System.assertEquals('testcontent2', multipart.requests.get(1).requestBody.toString());
	}

	@isTest
	public static void test_header_builder()
	{
		RestRequest req = new RestRequest();
		req.requestBody = Blob.valueOf('');
		RestRequestMultipart multipart = new RestRequestMultipart(req);

		String headString =
			'Content-Disposition: form-data; name="img"; filename="a.png"' +'\n'+
			'Content-Type: application/octet-stream' +'\n' +
			'Some : thing\n' +
			'Content-Length:22'
		;

		Map<String, String> headers = multipart.buildHeaders(headString);

		System.assertEquals(headers.get('Content-Length'), '22');
		System.assertEquals(headers.get('Some'), 'thing');
		System.assertEquals(4, headers.size());
	}

}