input_chunk: express specific errors using negative encoded numerical error values.

[pwhelan]

Summary

Change some internal flb_input_chunk APIs to return a negative value encoding specific errno codes in them instead of just return -1.

The semantics of the calls should not change but it does force callers of the relevant functions to check for negative values instead of -1.

This PR also has a fix for in_emitter to accept negative values as errors instead of just the value -1.

Description

This PR includes everal changes to the flb_input_chunk API so it is possible to know the nature of the error when a call to flb_log_append fails.

There is a refactor of the function input_chunk_get to return a negative value encoded with an errno number to specify the following possible errors:

• ENOMEM: unable to allocate memory.
• ENOSPC: have reached a space limit.
• EAGAIN: buffer is paused, try again.
• EIO: I/O error when creating a chunk.

The function input_chunk_append_raw has been refactored to return the negative value of errno if it is set during the call if there is an error or the negative value of EIO if not.

These changes are necessary for a forth-coming change in in_http which uses these errors and others to generate more verbose HTTP error response codes.

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Testing
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• Example configuration file for the change
• Debug log output from testing the change

• Attached Valgrind output that shows no leaks or memory corruption was found

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• Run local packaging test showing all targets (including any new ones) build.
• Set ok-package-test label to test for all targets (requires maintainer to do).

Documentation

• Documentation required for this feature

Backporting

• Backport to latest stable release.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.