8235761: (httpclient) Investigate support for multipart/form-data in BodyPublishers

[Chris Hegarty]

Thanks for posting here Moataz,

I am busy with other work at the moment, but just to say that providing some level of support for multipart has come up a number of times (it is very useful). The built-in body publishers and subscribers are deliberately minimal, but it does seem that, at least, some level of support to more easy build multipart (if not multipart itself) would be desirable.

-Chris.

> On 11 May 2020, at 22:56, Moataz Abdelnasser <moataz.nasser20 at gmail.com> wrote:
> 
> Email was unintentionally sent in HTML, causing it to be scrubbed.
> This is plain text form:
> 
> Hi all!
> 
> I tackled with the multipart issue in a library I wrote that provides
> extensions to the HTTP client including multipart
> support (please see https://github.com/mizosoft/methanol). I was
> wondering if I could provide a patch for this issue in
> the light of https://github.com/mizosoft/methanol/blob/master/methanol/src/main/java/com/github/mizosoft/methanol/MultipartBodyPublisher.java
> to be included in java.net.http. Flow control can be rewritten against
> the module using jdk.internal.net.http.common.SequentialScheduler.
> I haven’t found any of the available RequestPublishers impls that can
> be efficiently reused for such flow control.
> 
> If that is possible, please consider if I could also provide other
> complementary patches such as:
> 
>  - FormBodyPublisher (similarly in the light of
>    https://github.com/mizosoft/methanol/blob/master/methanol/src/main/java/com/github/mizosoft/methanol/FormBodyPublisher.java).
>    This implements the application/x-www-form-urlencoded format. As
> with the linked class, this can make use of the already
>    available jdk.internal.net.http.RequestPublishers.StringPublisher.
> 
>  - Add an internal trusted MimeBodyPublisher interface that attaches
> the correct media type info to the body:
> 
>    public interface MimeBodyPublisher extends BodyPublisher {
>      String contentType();
>    }
> 
> The HttpClient can use that to transparently add a Content-Type header
> for the request. In case of MultipartBodyPublisher,
> this ensures a Content-Type header with the correct boundary (which
> might be randomly generated) is used instead of being
> explicitly specified by the user. Similarly, this ensures the correct
> Content-Type is used in case of FormBodyPublisher.
> 
> Please tell me which patches I can start working on. If any, this will
> be my first contribution so I believe I will need a sponsor.
> 
> Thanks in advance!
> Moataz