Improve support for tracing REST API processing

[bobbingwide]

REST API requests are similar to AJAX requests.

• They are expected to return JSON
• So the client end is likely to fail if it sees non JSON output.

When, for any reason, oik-bwtrace fails to open the trace output file Warning message is produced from fopen(). The documentation suggests that it's OK to suppress this warning with a preceding @. We should do this regardless of the type of request. I'll raise a separate issue.

It would be nice if REST requests could be traced to separate files. This depends on how early in the processing the REST_REQUEST constant is set to true. define( 'REST_REQUEST', true );

[bobbingwide]

With regards to tracing to separate files. REST_REQUEST is not defined until the end of processing for parse_request. This is well after trace has started. We could implement some code to pre-detect a REST request, by looking at $_SERVER['REQUEST_URI'], taking into account sub-directory installs,

• /index.php?rest_route
• /wp-json/wp/v2/
• a user defined string

The only thing we'll do differently at this stage is to start tracing to the 'rest' set of trace files instead of the normal set.

[bobbingwide]

At the end of REST processing, the filter rest_pre_echo_response allows us to see what's being returned to the client.

If rest tracing is enabled we can hook into this and simply call bw_trace2().

[bobbingwide]

Now doucmented: https://www.oik-plugins.com/wordpress-plugins-from-oik-plugins/free-oik-plugins/oik-trace-plugin/viewing-trace-files/viewing-rest-request-trace-files/