Change MultipartFile.contentType from dart:io's ContentType type to http_parser's MediaType type.
Exceptions are now of type ClientException rather than dart:io's HttpException.
Make BaseRequest.contentLength and BaseResponse.contentLength use null to indicate an unknown content length rather than -1.
The contentLength parameter to new BaseResponse is now named rather than positional.
Make request headers case-insensitive.
Make MultipartRequest more closely adhere to browsers' encoding conventions.