Upload binary file with retrofit 2 in Android

Just adding another solution, as I had to dig a bit to understand what happened in the question in the first place.

My solution is to get the binary file as a byte[] directly and then put it inside the RequestBody. So in the end, the code would look like this:

interface RetrofitService {
    @POST("api/v1/upload_file")
    Call<Void> uploadBinaryFile(@Body RequestBody body);
}

And to call it:

public void uploadBinaryFile(File fileToUpload) {
    retrofitService
        .uploadBinaryFile(RequestBody.create(MediaType.parse("application/octet"), 
            Files.readAllBytes(fileToUpload));
}

This is basically the same as OP's original question, but just for the sake of clarity I'll leave this answer as well for the next reader.

After hours of searching I found that there was an @Multipart annotation remains in API interface of my code from last example! which prevent to send binary data to the server and the solution in retrofit repository was OK!

I had same problem, I wanted to upload binary file(image). The API was of Wordpress

I followed the solution code which is given at the end of this issue

Here is my little modified code

@POST("wp-json/wp/v2/media/")
Call<ImagePostResult> postEventPhoto(
        @Header("Authorization") String accessToken,
        @Header("Content-Type") String contentType,
        @Header("Content-Disposition") String contentDisposition,
        @Body RequestBody photo);

Here is the request

        // For BasicAuth
        String authHeader = getAuthHeader();

        String contentType = "application/binary";
        String contentDisposition = "attachment; filename =  " + fileName;

        RequestBody requestBodyee = null;
        try {
            InputStream in = new FileInputStream(file);

            byte[] buf;
            buf = new byte[in.available()];
            while (in.read(buf) != -1) ;
            requestBodyee = RequestBody
                    .create(MediaType.parse("application/octet-stream"), buf);
        } catch (IOException e) {
            e.printStackTrace();
        }


        Call<ImagePostResult> imagePostResultCall = apiInterface.postEventPhoto(
                authHeader,
                contentType,
                contentDisposition,
                requestBodyee);
        imagePostResultCall.enqueue(new Callback<ImagePostResult>() {
            @Override
            public void onResponse(Call<ImagePostResult> call, Response<ImagePostResult> response) {
                // Response Success
                if (response.isSuccessful()) {
                  // yaay
                }
            }

            @Override
            public void onFailure(Call<ImagePostResult> call, Throwable t) {
                Log.d(TAG, "onFailure: " + t);
            }
        });

In Kotlin you can do this:

val file: File = retrieveMyJavaFile()
val requestBody: RequestBody = file.asRequestBody("application/octet-stream".toMediaTypeOrNull())
val response: MyResponse = myAPI.uploadPhoto(requestBody).body()!!