Support MultipartBody uploads with declarative HTTP client

[goeh]

Upload MultipartBody with declarative HTTP @client seems to be unsupported. It would be nice if it was.

Steps to Reproduce

1. Create a HTTP @client that takes a MultipartBody as request body
2. Call the client method
3. A serialization exception is thrown

Expected Behaviour

A multipart request should be sent to the destination

Actual Behaviour

| 08:35:06.552 [nioEventLoopGroup-1-9] WARN  i.n.util.concurrent.DefaultPromise - An exception was thrown by io.micronaut.http.client.DefaultHttpClient$$Lambda$475/670393269.operationComplete()
| io.micronaut.http.codec.CodecException: Error encoding object [io.micronaut.http.client.multipart.MultipartBody@740893f4] to JSON: No serializer found for class io.micronaut.http.client.multipart.MultipartBody and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS)
| 	at io.micronaut.jackson.codec.JsonMediaTypeCodec.encode(JsonMediaTypeCodec.java:174)
| 	at io.micronaut.jackson.codec.JsonMediaTypeCodec.encode(JsonMediaTypeCodec.java:180)
| 	at io.micronaut.http.client.DefaultHttpClient.lambda$buildNettyRequest$36(DefaultHttpClient.java:1474)
| 	at java.util.Optional.map(Optional.java:215)
| 	at io.micronaut.http.client.DefaultHttpClient.buildNettyRequest(DefaultHttpClient.java:1474)
| 	at io.micronaut.http.client.DefaultHttpClient.prepareRequest(DefaultHttpClient.java:1910)
| 	at io.micronaut.http.client.DefaultHttpClient.streamRequestThroughChannel(DefaultHttpClient.java:1547)
| 	at io.micronaut.http.client.DefaultHttpClient.lambda$null$20(DefaultHttpClient.java:938)

Environment Information

• Operating System: MacOS 10.14
• Micronaut Version: 1.0.0.RC2
• JDK Version: 1.8.0_162-b12

Example Application

• https://github.com/goeh/micronaut-multipart-body

[goeh]

The sample application includes a test with the standard HTTP client and that test passes but with a warning. I don't know if I'm guilty or if the framework does something wrong. Maybe it's related to issue #721

13:09:23.282 [nioEventLoopGroup-1-3] WARN  i.n.channel.DefaultChannelPipeline - An exceptionCaught() event was fired, and it reached at the tail of the pipeline. It usually means the last handler in the pipeline did not handle the exception.
io.netty.util.IllegalReferenceCountException: refCnt: 0, decrement: 1
	at io.netty.buffer.AbstractReferenceCountedByteBuf.release0(AbstractReferenceCountedByteBuf.java:100)
	at io.netty.buffer.AbstractReferenceCountedByteBuf.release(AbstractReferenceCountedByteBuf.java:84)
	at io.netty.handler.codec.http.HttpObjectAggregator$AggregatedFullHttpMessage.release(HttpObjectAggregator.java:386)
	at io.netty.util.ReferenceCountUtil.release(ReferenceCountUtil.java:88)
	at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:112)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
	at io.netty.channel.ChannelInboundHandlerAdapter.channelRead(ChannelInboundHandlerAdapter.java:86)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
	at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:102)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
	at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:102)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
	at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:438)
	at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:310)
	at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:284)
	at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:253)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
	at io.netty.handler.timeout.IdleStateHandler.channelRead(IdleStateHandler.java:286)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340)
	at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1434)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348)
	at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:965)
	at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:163)
	at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:628)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:563)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:480)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:442)
	at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.lang.Thread.run(Thread.java:748)

[goeh]

I created issue #726 for the IllegalReferenceCountException problem.

[jameskleeh]

@goeh You have to set the correct content type. The test passes with
@Post(produces = MediaType.MULTIPART_FORM_DATA)

[jameskleeh]

@goeh I noticed that the same warning occurs when the declarative client is used. This is a different issue than 726 and I'm going to push the fix soon

[goeh]

@jameskleeh I just added produces = "...." and you are correct, it works. That's awesome, thanks!
Could the documentation be more specific about this or did I miss it?

[jameskleeh]

@goeh Perhaps it could, I'm not sure. If you think the docs could be made more clear please submit a PR.