Handle text protocol COM_QUERY response

[jdangerx]

The MySQL text protocol COM_QUERY response is not supported. I needed to communicated with a MySQL-like implementation that only supported the text protocol, so I was running into #132.

This is my implementation of the text query response protocol. The difference between the binary and text protocols is that the text protocol converts all the row data to length encoded strings. I've made Query.decode dispatch on the query type, added more function clauses to handle_text_query, and added a bunch of string parsing for the decode_text_rows function.

I also have a few questions/concerns about my code:

• It seems like the handle_text_query function should be able to have more overlap with the handle_binary_query functions, but I'm not sure how that would work. It sure would be nice to DRY it up a bit.
• It would be nice for my use case to pass query type (and whether or not to prepare the query) into Mariaex.query - does that seem like something that we could or should insert into the API?

[coveralls]

Coverage decreased (-9.2%) to 53.318% when pulling 31b34de on TeachersPayTeachers:text-protocol into 566ece4 on xerions:master.

[jdangerx]

Hm. Not sure why my changes messed with the existing unit tests. I'll fix them and update.

[coveralls]

Coverage increased (+1.9%) to 64.411% when pulling 0a56b59 on TeachersPayTeachers:text-protocol into 566ece4 on xerions:master.

[coveralls]

Coverage increased (+1.7%) to 64.286% when pulling b325c05 on TeachersPayTeachers:text-protocol into a0aa98b on xerions:master.

[coveralls]

Coverage increased (+2.1%) to 64.651% when pulling 39887ff on TeachersPayTeachers:text-protocol into a0aa98b on xerions:master.

[coveralls]

Coverage increased (+2.6%) to 65.146% when pulling ba54e00 on TeachersPayTeachers:text-protocol into a0aa98b on xerions:master.

[coveralls]

Coverage decreased (-1.4%) to 61.154% when pulling 94e95d5 on TeachersPayTeachers:text-protocol into a0aa98b on xerions:master.

[coveralls]

Coverage increased (+3.7%) to 66.202% when pulling 9b17906 on TeachersPayTeachers:text-protocol into a0aa98b on xerions:master.

[coveralls]

Coverage increased (+3.7%) to 66.202% when pulling 9b17906 on TeachersPayTeachers:text-protocol into a0aa98b on xerions:master.

[coveralls]

Coverage increased (+3.7%) to 66.202% when pulling 04cacbd on TeachersPayTeachers:text-protocol into a0aa98b on xerions:master.

[coveralls]

Coverage increased (+3.7%) to 66.202% when pulling 04cacbd on TeachersPayTeachers:text-protocol into a0aa98b on xerions:master.

[jdangerx]

Sorry about the coveralls/travis noise - I was having issues getting the Elixir 1.1 build to work. Tests pass everywhere now :)

[jdangerx]

Ping @liveforeverx - tests pass, so the question is, is this functionality something we want to have around?

[liveforeverx]

Pong, sorry for late answer.

[liveforeverx]

What use case, do you need it for?

[liveforeverx]

Is there some query or database, which didn't support prepared statements?

[jdangerx]

Yes, as far as I can tell the Sphinx search MySQL protocol does not support prepared statements.

[jdangerx]

I guess an alternative could be that we can add optional client side preparation of statements :\

[jdangerx]

@liveforeverx I forgot about this PR for a couple weeks. Revisiting this - what do you think of adding this functionality?

[fishcakez]

I would like to implement cursor support so results of queries can be streamed with memory efficiency inside a transaction but this is prohibitively difficult if the text protocol is supported. Is it possible to drop text query support? I realise this is the opposite of the request in this PR.

[shantiii]

@fishcakez Hi there, I'm a coworker of @jdangerx, and I think dropping text protocol support is infeasible given the large number of mysql commands that are unable to be executed through the prepared statement/binary protocol. Currently, this is impacting us when we attempt to connect to Sphinx, which doesn't seem to have support for the binary protocol.

[fishcakez]

@shantiii thanks for letting me. In that case I won't implement cursors but just do a standard query. I'll let someone else pick it up if they need it.

[liveforeverx]

@fishcakez : Is it possible to support cursor only for prepared queries?

[fishcakez]

@liveforeverx yeah I managed it here: #145.

[liveforeverx]

@shantiii @jdangerx So, I would rebase your work and merge this week.

Do you need it working with elixir < 1.2?

[jdangerx]

That's great news! We don't need it to work with elixir < 1.2. Are you planning on doing the rebasing or should I?

[liveforeverx]

@jdangerx Thanks for the work! Merged now. If you have further enhancements for text protocol, welcome.

[jdangerx]

Thanks @liveforeverx! There are likely a few more enhancements in the pipeline, courtesy of @shantiii.