The architecture of SQLServer is currently such that it sends results
over IPC one row at a time. After the rows are exhausted, it sends a
completion IPC. However, it does not wait for the client to finish
processing a row before sending another row or the completion signal.
This can result in clients hanging if the completion comes in while a
row is being processed. At least in the case of WebView::Database, the
result is that the completion signal is dropped, and the browser then
hangs forever waiting for that signal (after it finishes processing the
row).
This patch makes SQLServer asynchronously wait for the client to tell it
that the row has been processed and the next row (or completion) may be
sent. We repurpose the `m_ongoing_executions` in SQLStatement for this
purpose (this member was oddly being written to, but otherwise unused).
If a statement is executed multiple times in quick succession, we may
overwrite the results of a previous execution. Instead of storing the
result, pass it around as it is sent to the client.
In order to execute a prepared statement multiple times, and track each
execution's results, clients will need to be provided an execution ID.
This will create a monotonically increasing ID each time a prepared
statement is executed for this purpose.
When storing IDs and sending values over IPC, this changes SQLServer to:
1. Stop using -1 as a nominal "bad" ID. Store the IDs as unsigned, and
use Optional in the one place that the IPC needs to indicate an ID
was not allocated.
2. Let LibIPC encode/decode enumerations (SQLErrorCode) on our behalf.
3. Use size_t for array sizes.
One of the benefits of prepared statements is that the SQL string is
parsed just once and re-used. This updates SQLStatement to do just that
and store the parsed result.
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
The result of a SQL statement execution is either:
1. An error.
2. The list of rows inserted, deleted, selected, etc.
(2) is currently represented by a combination of the Result class and
the ResultSet list it holds. This worked okay, but issues start to
arise when trying to use Result in non-statement contexts (for example,
when introducing Result to SQL expression execution).
What we really need is for Result to be a thin wrapper that represents
both (1) and (2), and to not have any explicit members like a ResultSet.
So this commit removes ResultSet from Result, and introduces ResultOr,
which is just an alias for AK::ErrorOrr. Statement execution now returns
ResultOr<ResultSet> instead of Result. This further opens the door for
expression execution to return ResultOr<Value> in the future.
Lastly, this moves some other context held by Result over to ResultSet.
This includes the row count (which is really just the size of ResultSet)
and the command for which the result is for.
Derivatives of Core::Object should be constructed through
ClassName::construct(), to avoid handling ref-counted objects with
refcount zero. Fixing the visibility means that misuses like this are
more difficult.
This patch introduces the SQLServer system server. This service is
supposed to be the only process/application talking to database storage.
This makes things like locking and caching more reliable, easier to
implement, and more efficient.
In LibSQL we added a client component that does the ugly IPC nitty-
gritty for you. All that's needed is setting a number of event handler
lambdas and you can connect to databases and execute statements on them.
Applications that wish to use this SQLClient class obviously need to
link LibSQL and LibIPC.
