Document required encoding of query parameters of search

[lucafavatella]

Solr

A note in the documented changes of Solr 4.1.0 regarding portability of Solr across Web containers points out that "Query strings passed in via the URL need to be properly-%-escaped, UTF-8 encoded bytes, otherwise Solr refuses to handle the request".
A note in the documented changes of Solr 4.5.0 mentions parametrization of encoding of query parameters by ie parameter (e.g. ie=iso-8859-1), parametrization of encoding of POST request body by Content-Type header (e.g. application/x-www-form-urlencoded; charset=iso-8859-1), and UTF-8 as the default encoding.
As of Solr 4.10.4 UTF-8 is still the default encoding for both query parameters and POST request body.

Riak Search

The version of yokozuna in riak kv 2.2.3 is 2.1.10
that integrates Solr 4.10.4
(see also basho/yokozuna@7f0d464)
whose documentation is available online.

Yokozuna 2.1.10 depends on riak_kv 2.1.7
that via riak_api 2.1.6 depends on basho/webmachine 1.10.8-basho1
that contains e.g. module wrq,
and
that depends on mochiweb v2.9.0p2
that contains e.g. module mochiweb_util.

When receiving a search request,
yokozuna calls the search function,
that extracts the query - percent-decoded but not further decoded e.g. Unicode -
then appends some distributed search related parameters
then percent-encodes (not further e.g. Unicode) the parameters
and contacts Solr via POST request
setting header content type to application/x-www-form-urlencoded.

As such content type header has no charset specified, Solr interprets the POST body as UTF-8.

[lucafavatella]

I did not mention percent-encoding as that is part of HTTP. Wanting to be extremely explicit and complete, and wanting to avoid any misunderstandings, this shall be e.g. "Query parameters must be UTF-8 encoded, before being percent-encoded (as required by HTTP)."