[New API Proposal] TSHttpTxnGetClientRequestBody

[CrazyCow <zh...@gmail.com>]

Hi, ATS devs,

As a part of https://github.com/apache/trafficserver/pull/2335, I'd like to
introduce a new API that the plugin can get the entire post body.

The current signature of it is
"tsapi char *
TSHttpTxnGetClientRequestBody(TSHttpTxn txnp, int *len)"

In the implementation, it will get a clone of the buffer reader, malloc new
memory, read the content to the memory and return the address. It's not
good as it requires the caller free the memory. Probably it's better
to return a string, which is also kind of sketchy.

The PR itself is enabling request buffering in ATS before we connecting to
the origin server. Once it's done, the plugin can call this API to get the
entire body.

Docs will be added later in the PR.

Any ideas about the API design and the PR would be much appreciated!



Thanks,
Zizhong