[API] Propagation: fix for hex conversion to binary for odd hex strings

[karusher]

The conversion of hex to binary did not handle odd-length inputs correctly.

The output was zero-padded on the right rather than the left. On little endian machines, the second to last entry received the 0.

For example, "78cfcfec62ae9e9" would result in:

0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x78 0xcf 0xcf 0xec 0x62 0xae 0x9e 0x09

The desired output is:

0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x07 0x8c 0xfc 0xfe 0xc6 0x2a 0xe9 0xe9

I have attached a toy program to reproduce the problem:

test_program.txt

Changes

Please provide a brief description of the changes here.

Corrected conversion of hex to binary for propagation

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

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[lalitb]

Thanks for the fix. While this method is always used for converting even-length hex strings (trace_id and span_id) to binary, I believe the additional check for odd lengths should not significantly affect performance.

[marcalff]

LGTM, thanks for the fix.