[EXPORTER] Refactor ElasticSearchRecordable

[sjinks]

Changes

• Simplify ElasticSearchRecordable::WriteValue() by using the ADL Serializer;
• Simplify ElasticSearchRecordable::SetTimestamp();
• Refactor ElasticSearchRecordable::SetTraceId() and ElasticSearchRecordable::SetSpanId() by using constants for array sizes instead of hardcoded values.

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

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

[netlify]

✅ Deploy Preview for opentelemetry-cpp-api-docs canceled.

Name	Link
🔨 Latest commit	b72c41b
🔍 Latest deploy log	https://app.netlify.com/sites/opentelemetry-cpp-api-docs/deploys/6744171d3f2e7100087c5e2d

[sjinks]

A possible breaking change here is that the original WriteValue() did not handle spans. If this is important, I can add an if condition to follow the old behavior.

[sjinks]

This approach is safer: should kSize change someday, the buffer's size will be automatically updated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.86%. Comparing base (31956f8) to head (b72c41b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3164   +/-   ##
=======================================
  Coverage   87.86%   87.86%           
=======================================
  Files         195      195           
  Lines        6151     6151           
=======================================
  Hits         5404     5404           
  Misses        747      747           

---- 🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests

[owent]

Why change it to put_time and ostringstream? In my understandarding, using strftime and snprintf with just one static buffer block will have better performence than using ostringstream and put_time with dynamic memory allocation. And there are also some compatiblity problems with put_time and old compiler's STL.

[sjinks]

A newer version of gcc complained:

warning: ‘__builtin___snprintf_chk’ output may be truncated before the last format character [-Wformat-truncation=]
   47 |     std::snprintf(bufferMilliseconds, sizeof(bufferMilliseconds), ".%06ld",
      |                                                                          ^
In function ‘int snprintf(char*, size_t, const char*, ...)’,
/usr/include/x86_64-linux-gnu/bits/stdio2.h:54:35: note: ‘__builtin___snprintf_chk’ output between 8 and 9 bytes into a destination of size 8
   54 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
      |          ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   55 |                                    __glibc_objsize (__s), __fmt,
      |                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   56 |                                    __va_arg_pack ());
      |                                    ~~~~~~~~~~~~~~~~~

so I tried to come up with something safe that does not involve hardcoded sizes, compiles cleanly, does not have a potential for buffer overflows, and is as fast as std::format("{:%FT%T%Ez}", timePoint).

For example, in

  const static int dateToSecondsSize = 19;
  const static int millisecondsSize  = 8;

it was not immediately evident that millisecondsSize reserves one byte for the null terminator (.123456 is seven bytes, not eight), and it felt like dateSize = dateToSecondsSize + millisecondsSize + timeZoneSize; char bufferDate[dateSize]; could lead to a buffer overflow.

Anyway, I think I have found a faster solution not involving strcat and hardcoded buffer sizes.