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Add new follow method #386

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Add new follow method #386

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d644ef3
Add new follow method to follow entries from next to tail
Dec 17, 2021
92cdb09
Update method description
Dec 17, 2021
9ceb5b8
Add SkipN method to allow follow-decoupled entry skipping
Dec 17, 2021
325976a
Improve error handling, refactor loop, add context to FollowTail
Mar 31, 2022
1d77cbd
Merge branch 'coreos:main' into follow_tail
maGitty Mar 31, 2022
7c68517
Add basic test case for FollowTail
May 13, 2022
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42 changes: 42 additions & 0 deletions sdjournal/read.go
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Original file line number Diff line number Diff line change
Expand Up @@ -256,6 +256,48 @@ process:
}
}

// SkipN skips the next n entries and returns the number of skipped entries and an eventual error.
func (r *JournalReader) SkipN(n int) (int, error) {
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I think it may be useful here to check that n >= 0.

var i int
for i := 1; i <= n; i++ {
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Just curious, why doesn't this start at i := 0? Let's maybe change to that, as it may be less surprising to read, right?

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Didn't notice until you mentioned it, but it really looks kind of messy! Thanks.

c, err := r.journal.Next()
if err != nil {
return i, err
} else if c == 0 {
return i, nil
}
}
return i, nil
}

// FollowTail synchronously follows the JournalReader, writing each new journal entry to entries.
// It will start from the next unread entry.
func (r *JournalReader) FollowTail(entries chan *JournalEntry) error {
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I'm not overly positive with this proposed signature, as it lacks at least a Context to cancel the inner looping logic.
Additionally, I'm wondering whether it is better to return two channels (entries and err) so that the whole follow-tailing logic can be handled asynchronously.

defer close(entries)

for {
status := r.journal.Wait(200 * time.Millisecond)
if status != SD_JOURNAL_APPEND && status != SD_JOURNAL_INVALIDATE {
continue
}

for {
if c, err := r.journal.Next(); err != nil {
return err
} else if c == 0 {
// EOF, should mean we're at the tail
break
}

if entry, err := r.journal.GetEntry(); err != nil {
return err
} else {
entries <- entry
}
}
}
}

// simpleMessageFormatter is the default formatter.
// It returns a string representing the current journal entry in a simple format which
// includes the entry timestamp and MESSAGE field.
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