PartMap should add filename to each file part

[wesleywu]

PartMap should add filename to each file part, because many Java servlet container treat part as an upload file only by the filename attribute.

Also, the Content-Transfer-Encoding header is useless.

I hacked the PartMap impl

static final class PartMap extends RequestBuilderAction {
  private final Retrofit retrofit;
  private final String transferEncoding;
  private final Annotation[] annotations;

  PartMap(Retrofit retrofit, String transferEncoding, Annotation[] annotations) {
    this.retrofit = retrofit;
    this.transferEncoding = transferEncoding;
    this.annotations = annotations;
  }

  @Override void perform(RequestBuilder builder, Object value) {
    if (value == null) return; // Skip null values.

    Map<?, ?> map = (Map<?, ?>) value;
    for (Map.Entry<?, ?> entry : map.entrySet()) {
      Object entryKey = entry.getKey();
      if (entryKey == null) {
        throw new IllegalArgumentException("Part map contained null key.");
      }
      Object entryValue = entry.getValue();
      if (entryValue == null) {
        continue; // Skip null values.
      }

      // hack by wesley wu start
      // support multivaluemap
      if (entryValue instanceof Collection) {
        Collection valueCollection = (Collection) entryValue;
        for (Object valueOne : valueCollection) {
          addPart(builder, entryKey, valueOne);
        }
      } else {
        addPart(builder, entryKey, entryValue);
      }
      // hack by wesley wu end
    }
  }

  private void addPart(RequestBuilder builder, Object entryKey, Object entryValue) {
    Headers headers;

    Class<?> entryClass = entryValue.getClass();
    //noinspection unchecked
    Converter<Object, RequestBody> converter =
            retrofit.requestConverter(entryClass, annotations);
    RequestBody body;
    try {
      body = converter.convert(entryValue);
    } catch (IOException e) {
      throw new RuntimeException("Unable to convert " + entryValue + " to RequestBody", e);
    }
    // dirty hack by wesley wu start
    if (BINARY_TYPE.contains(body.contentType().type())) {
      headers = Headers.of(
              "Content-Disposition", "form-data; name=\"" + entryKey + "\"; filename=\"" + entryKey + "\"",
              "Content-Transfer-Encoding", transferEncoding);
    } else {
      headers = Headers.of(
              "Content-Disposition", "form-data; name=\"" + entryKey + "\"");
    }
    // dirty hack by wesley wu end
    builder.addPart(headers, body);
  }
}

[wesleywu]

duplicated with #1140. Please ignore this :)

[JakeWharton]

Dupe #1140.