RFR: 8329829: HttpClient: Add a BodyPublishers.ofFileChannel method [v2]

[Daniel Fuchs]

On Mon, 7 Jul 2025 09:32:33 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:
> 
>   Implement review feedback

src/java.net.http/share/classes/java/net/http/HttpRequest.java line 743:

> 741:          * @throws IndexOutOfBoundsException if the specified byte range is
> 742:          * found to be out of bounds compared with the size of the file
> 743:          * referred by the channel

So we accept length = 0 (OK though not very useful?) and we reject length < 0 (which is good). Maybe we should say:
Suggestion:

         * @throws IndexOutOfBoundsException if the specified byte range is
         * found to be {@linkplain Objects.checkFromIndexSize(long, long, long) out of bounds}
         * compared with the size of the file referred by the channel

to clarify that.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/26155#discussion_r2189525585