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developing: Add ResponseBuffer explanation

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Daniel Oaks 2018-02-11 17:21:13 +10:00
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@ -99,3 +99,23 @@ In consequence, there is a lot of state (in particular, server and channel state
There are some mutexes that are "tier 0": anything in a subpackage of `irc` (e.g., `irc/logger` or `irc/connection_limits`) shouldn't acquire mutexes defined in `irc`. There are some mutexes that are "tier 0": anything in a subpackage of `irc` (e.g., `irc/logger` or `irc/connection_limits`) shouldn't acquire mutexes defined in `irc`.
We are using `buntdb` for persistence; a `buntdb.DB` has an `RWMutex` inside it, with read-write transactions getting the `Lock()` and read-only transactions getting the `RLock()`. We haven't completely decided where this lock fits into the overall lock model. For now, it's probably better to err on the side of caution: if possible, don't acquire new locks inside the `buntdb` transaction, and be careful about what locks are held around the transaction as well. We are using `buntdb` for persistence; a `buntdb.DB` has an `RWMutex` inside it, with read-write transactions getting the `Lock()` and read-only transactions getting the `RLock()`. We haven't completely decided where this lock fits into the overall lock model. For now, it's probably better to err on the side of caution: if possible, don't acquire new locks inside the `buntdb` transaction, and be careful about what locks are held around the transaction as well.
## Command handlers and ResponseBuffer
We support a lot of IRCv3 specs. Pretty much all of them, in fact. And a lot of proposed/draft ones. One of the draft specifications that we support is called ["labeled responses"](https://ircv3.net/specs/extensions/labeled-response.html).
With labeled responses, when a client sends a label along with their command, they are assured that they will receive the response messages with that same label.
For example, if the client sends this to the server:
@label=pQraCjj82e PRIVMSG #channel :hi!
They will expect to receive this (with echo-message also enabled):
@label=pQraCjj82e :nick!user@host PRIVMSG #channel :hi!
They receive the response with the same label, so they can match the sent command to the received response. They can also do the same with any other command.
In order to allow this, in command handlers we don't send responses directly back to the user. Instead, we buffer the responses in an object called a ResponseBuffer. When the command handler returns, the contents of the ResponseBuffer is sent to the user with the appropriate label (and batches, if they're required).
Basically, if you're in a command handler and you're sending a response back to the requesting client, use `rb.Add*` instead of `client.Send*`. Doing this makes sure the labeled responses feature above works as expected. The handling around `PRIVMSG`/`NOTICE`/`TAGMSG` is strange, so simply defer to [irctest](https://github.com/DanielOaks/irctest)'s judgement about whether that's correct for the most part.