Before this series, the "system.clients" virtual table lists active connections (and their various properties, like client address, logged in username and client version) only for CQL requests. This series adds also Alternator clients to system.clients. One of the interesting use cases of this new feature is understanding exactly which SDK a user is using -without inspecting their application code. Different SDKs pass different "User-Agent" headers in requests, and that User-Agent will be visible in the system.clients entries for Alternator requests as the "driver_name" field.
Unlike CQL where logged in username, driver name, etc. applies to a complete connection, in the Alternator API, different requests can theoretically be signed by different users and carry different headers but still arrive over the same HTTP connection. So instead of listing the currently open Alternator *connections*, we will list the currently active *requests*.
The first three patches introduce utilities that will be useful in the implementation. The fourth patch is the implementation itself (which is quite simple with the utility introduced in the second patch), and the fifth patch a regression test for the new feature. The sixth patch adds documentation, the seventh patch refactors generic_server to use the newly introduced utility class and reduce code duplication, and the eighth patch adds a small check to an existing check of CQL's system.clients.
Fixes#24993
This patch adds a new feature, so doesn't require a backport. Nevertheless, if we want it to get to existing customers more quickly to allow us to better understand their use case by reading the system.clients table, we may want to consider backporting this patch to existing branches. There is some risk involved in this patch, because it adds code that gets run on every Alternator request, so a bug on it can cause problems for every Alternator request.
Closesscylladb/scylladb#25178
* github.com:scylladb/scylladb:
test/cqlpy: slightly strengthen test for system.clients
generic_server: use utils::scoped_item_list
docs/alternator: document the system.clients system table in Alternator
alternator: add test for Alternator clients in system.clients
alternator: list active Alternator requests in system.clients
utils: unit test for utils::scoped_item_list
utils: add a scoped_item_list utility class
utils: add "fatal" version of utils::on_internal_error()
4c785b31c7