RFR: 8329829: HttpClient: Add a BodyPublishers.ofFileChannel method [v3]

[Jaikiran Pai]

On Mon, 7 Jul 2025 10:41:58 GMT, Volkan Yazici <vyazici at openjdk.org> wrote:

>> Adds a new `ofFileChannel(FileChannel channel, long offset, long length)` method to `java.net.HttpRequest.BodyPublishers` to provide an `HttpClient` publisher to upload a certain region of a file. The new publisher does not modify the state of the passed `FileChannel`, streams the file channel bytes as it publishes (i.e., avoids reading the entire file into the memory), and can be leveraged to implement sliced uploads. As noted in the Javadoc:
>> 
>>> The file channel will not be closed upon completion. The caller is
>>> expected to manage the life cycle of the channel, and close it
>>> appropriately when not needed anymore.
>> 
>> ### Implementation notes
>> 
>> - `FileChannel` is preferred over `{Readable,Seekable}ByteChannel`, since the latter does not provide a positional read without modifying the state of the `FileChannel`, which is necessary to use a single `FileChannel` instance to implement sliced uploads.
>> - `ofFileChannel(FileChannel,long,long)` is preferred over `ofPath(Path,long,long)` to avoid overloading the maximum file descriptor limit of the platform.
>
> Volkan Yazici has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Improve docs on `IndexOutOfBoundsException` thrown
>   
>   Co-authored-by: Daniel Fuchs <67001856+dfuch at users.noreply.github.com>

src/java.net.http/share/classes/jdk/internal/net/http/RequestPublishers.java line 492:

> 490:                 if (readLength < 0) {
> 491:                     // We *must* throw to signal that the request needs to be cancelled.
> 492:                     // Otherwise, the server will continue waiting data.

The comment itself is a good idea but i think we should leave out the reference to a "server" from this comment. Perhaps something like: "Throw to signal that the request needs to be cancelled"?

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/26155#discussion_r2213382091