Update object Put to avoid loosing last chunk

[tinou98]

The old code might miss the last object if Reader return both a value and EOF

Extract from Reader doc :

When Read encounters an error or end-of-file condition after successfully reading n > 0 bytes, it returns the number of bytes read. It may return the (non-nil) error from the same call or return the error (and n == 0) from a subsequent call. An instance of this general case is that a Reader returning a non-zero number of bytes at the end of the input stream may return either err == EOF or err == nil. The next Read should return 0, EOF.

Callers should always process the n > 0 bytes returned before considering the error err. Doing so correctly handles I/O errors that happen after reading some bytes and also both of the allowed EOF behaviors.

[piotrpio]

Hello @tinou98 , thank you for the contribution! While you're right in that we should process the leftover bytes in case of EOF, I have a couple of comments:

1. We definitely should not be sending an empty message if we get an EOF error and n == 0 - so this check would have to be added before publishing the message (you can run TestObjectHistory in test/object_test.go to verify).
2. I think we can safely return immediately if err != nil && err != io.EOF - in that case we don't really care about any processed bytes, as we purge the subject anyway with purgePartial().

After those changes, the flow would look something like this:

1. Call n, err := r.Read(chunk)
2. Check if err != nil && err != io.EOF
   • if true, purge and return
3. Check if n > 0
   • if true, publish message and update counters
4. Check if err == io.EOF

WDYT?

[tinou98]

Updated to match the flow you described.
It also improves the handling of a weird Reader that could return n == 0, but no error.

[coveralls]

Coverage decreased (-0.04%) to 83.915% when pulling 9654d96 on tinou98:patch-1 into 69f0e65 on nats-io:main.

[piotrpio]

LGTM

[derekcollison]

Can we squash this done to one CL?

[tinou98]

You should be able to Squash & Merge from GitHub UI, otherwise I can Squash & Force Push on my branch

[derekcollison]

Would you mind squashing and force push?

[tinou98]

Squashed

[derekcollison]

LGTM! Thanks for the contribution.