simplify WriteShortstr

[bollhals]

Proposed Changes

Simplifying write of string values. GetBytes returns the number of bytes written, so there is no need to precalculate the length.

Types of Changes

• Bug fix (non-breaking change which fixes issue #NNNN)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
• Documentation improvements (corrections, new content, etc)
• Cosmetic change (whitespace, formatting, etc)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating
the PR. If you're unsure about any of them, don't hesitate to ask on the
mailing list. We're here to help! This is simply a reminder of what we are
going to look for before merging your code.

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

Further Comments

Question: There is a bug in the code (before this and also after this) that if you write a string resulting in more than 255 bytes, the length variable (byte) will be cut off and the resulting deserialized value will be different from the source. Shall I open an issue for this?

[michaelklishin]

Thank you!

[bollhals]

Question: There is a bug in the code (before this and also after this) that if you write a string resulting in more than 255 bytes, the length variable (byte) will be cut off and the resulting deserialized value will be different from the source.

Shall I open an issue for this or is this "as designed"?

[stebet]

An AMQP shortstr value can only contain 256 bytes: https://www.rabbitmq.com/amqp-0-9-1-reference.html#domain.shortstr

[bollhals]

Yes, that I understand, but the current code does the following for payload all 'A':

real length	length	payload
255	255	65, 65, ... (255 times)
256	0	65, 65, ... (256 times)

So when you read it back, it reads wrong values (due to the wrong ones sent).

There is nowhere a prevention built in to not being able to send more than 255 chars.

[michaelklishin]

We should fail early and visibly so yes @bollhals, this is worth changing, even though this is how the protocol is designed and not really a bug.

[michaelklishin]

Backported to 6.x.