Fix regression introduced in a7bfb9f76b,
where busy loop can be started with a request for following logs with a
range header set with num_skip value pointing beyond the end of the
journal. In that case the reader callback returns 0 and is called
immediately again, usually causing an endless loop that is not recovered
even when new journal events are added.
The bug does not occur if num_skip is not set - in that case if no
journal entries matching the filters are added, the tight loop is
avoided by the sd_journal_wait().
To fix the issue, when no matching journal events are available, set a
flag and reuse the backoff mechanism using the sd_journal_wait().
Link: https://github.com/home-assistant/operating-system/issues/4190
When `num_skip` is supplied to the `Range` header, journal-gatewayd
always returns the very last record even though it should have been
skipped. This is because the `sd_journal_next_skip` always returns
non-zero value on the first call, leading to one iteration of the
`request_reader_entries` returning the last record.
To avoid this unexpected behavior, check that the number of lines we
have skipped by is not lower than the requested skip value. If it is,
then it means there are lines which should not be returned now -
decrement the n_skip counter then and return from the function, closing
the stream if follow flag is not set.
Fixes#37954
Since 435c372ce5 added in v256,
num_entries part of the Range header is mandatory and error is returned
when it's not filled in. This makes using the "follow" argument clumsy,
because for an indefinite following of the logs, arbitrary high number
must be specified. This change makes it possible to omit it again and
documents this behavior in the man page.
Moreover, as the cursor part of the header was never mandatory, enclose
it in square brackets in the documentation as well and elaborate how
indexing works.
Following are some concrete examples of the Range header which are now
accepted:
entries= (or entries=:)
- everything starting from the first event
entries=cursor
- everything starting from `cursor`
entries=:-9:10
- last 10 events and close the connection
If the follow flag is set:
entries=:-4:10
- last 5 events, wait for 5 new and close connection
entries=:-9:
- last 10 events and keep streaming
Note that only the very last one is changing current behavior, but
reintroduces pre-v256 compatibility.
Fixes#37172
Jan Čermák