Can I change the headers in a MultipartBody part? - okhttp

Question

I'm trying to send a MultipartBody payload with OkHttp3.
Here's a MWE for creating the payload (plus getting it as a String):
MediaType JSON = MediaType.get("application/json");
RequestBody requestBody = new MultipartBody.Builder()
.setType(MultipartBody.MIXED)
.addPart(RequestBody.create(JSON, "{\"foo\": true, \"bar\": \"some string\"}"))
.build();
Buffer buffer = new Buffer();
requestBody.writeTo(buffer);
String requestBodyAsString = buffer.readUtf8();
That automatically adds headers and the result is this:
--8d863b3b-72a0-4b29-b4f4-5cc0b68d8117
Content-Type: application/json; charset=utf-8
Content-Length: 35
{"foo": true, "bar": "some string"}
--8d863b3b-72a0-4b29-b4f4-5cc0b68d8117
The server I am sending against requires that the character encoding and Content-Length header are removed as in the following:
--8d863b3b-72a0-4b29-b4f4-5cc0b68d8117
Content-Type: application/json
{"foo": true, "bar": "some string"}
--8d863b3b-72a0-4b29-b4f4-5cc0b68d8117
The MultipartBody.Builder() has .addPart(Headers headers, RequestBody body) but I cannot use that to remove headers or override the Content-Type header. Is there a way to change these via the OkHttp API or would I have to edit the payload string directly?

Answer 1

Here's my hacked solution, directly modifying the payload with an interceptor. Note that it's important to adjust the Content-Length header of the overall request as well.
public class MultipartHeaderInterceptor implements Interceptor {
#Override public Response intercept(Interceptor.Chain chain) throws IOException {
Request originalRequest = chain.request();
String requestBody = requestBodyToString(originalRequest.body());
String modified = stripHeadersFromMultipart(requestBody);
Request targetRequest = originalRequest.newBuilder()
.post(RequestBody.create(MediaType.get("text/plain"), modified))
.header("Content-Length", String.valueOf(modified.length()))
.build();
return chain.proceed(targetRequest);
}
private String stripHeadersFromMultipart(String requestBody) {
String regexToStrip = "; charset=utf-8\r\nContent-Length: \\d*";
return requestBody.replaceAll(regexToStrip, "");
}
private String requestBodyToString(RequestBody body) {
String bodyAsString = "";
try (Buffer buffer = new Buffer()) {
if (body != null) {
body.writeTo(buffer);
bodyAsString = buffer.readUtf8();
}
} catch (IOException e) {
log.info(e);
}
return bodyAsString;
}
}
Would be nice to have a less hacky solution though.