feat: add more conversion methods for JVM streams

[ianbotsf]

Issue #

Closes awslabs/aws-sdk-kotlin#1352

Description of changes

This change adds new methods for converting to/from ByteStream and JVM streams:

• InputStream.asByteStream: Wrap an InputStream as a ByteStream
• ByteStream.fromInputStream: Alias for InputStream.asByteStream
• ByteStream.writeToOutputStream: Writes the contents of a ByteStream to an OutputStream

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[github-actions]

Affected Artifacts

Changed in size

Artifact	Pull Request (bytes)	Latest Release (bytes)	Delta (bytes)	Delta (percentage)
runtime-core-jvm.jar	888,946	883,520	5,426	0.61%

[0marperez]

question: just curious, why an alias for InputStream.asByteStream?

[ianbotsf]

We have a similar alias for File.asByteStream(..) so it seemed prudent to mirror the pattern.

[lauzadis]

After this PR I think the only operation we're missing is converting an OutputStream to a ByteStream. Is that something you think would be useful, should we add it for the sake of completion?

[ianbotsf]

After this PR I think the only operation we're missing is converting an OutputStream to a ByteStream. Is that something you think would be useful, should we add it for the sake of completion?

OutputStreams are meant for writing to, which makes them a natural counterpart to Okio's Sink or our SdkSink components. Using them as a Source may be possible but would be a slight inversion of the typical control flow. ByteStreams typically read from a source as opposed to being written to by a source so the use case is not super clear here. I can imagine users could use machinery like PipedOutputStream/PipedInputStream to bridge into something that could be a ByteStream source but even there the semantics are a little unclear—how does the ByteStream know when the OutputStream is "complete"? If it does know, does a hypothetical operation invocation simply block until the output stream is fully written?

I think we should wait for feature requests or user examples to put something concrete in place for OutputStream→ByteStream conversion.