98 lines
2.4 KiB
Go
98 lines
2.4 KiB
Go
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package journslog
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import (
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_ "log/slog"
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"strings"
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"sync"
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"src.lwithers.me.uk/go/journal"
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)
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// KeyMapper maps [slog.Attr] keys onto [journal.AttrKey] objects. Such a mapper
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// is necessary because systemd-journald is very restrictive about suitable
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// attribute keys.
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type KeyMapper interface {
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KeyMap(slogAttrKey string) journal.AttrKey
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}
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// DefaultKeyMapper returns a [KeyMapper] with the package's default behaviour.
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// The returned mapper contains an internal, persistent map and a [sync.RWMutex]
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// to cache map results.
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//
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// The default behaviour is to strip leading underscores; to turn lowercase
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// ASCII ‘a’–‘z’ chars into uppercase ‘A’–‘Z’ (uppercase is passed through
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// verbatim), to accept underscores, and to map all other chars to underscores.
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// If the result is an empty string, it instead returns the key "BAD_ATTR_KEY".
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func DefaultKeyMapper() KeyMapper {
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return &defaultKeyMapper{
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badKey: journal.MustAttrKey("BAD_ATTR_KEY"),
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keys: make(map[string]journal.AttrKey),
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}
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}
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type defaultKeyMapper struct {
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badKey journal.AttrKey
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keys map[string]journal.AttrKey
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lock sync.RWMutex
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}
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func (dkm *defaultKeyMapper) KeyMap(slogAttrKey string) journal.AttrKey {
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if key, ok := dkm.mapFast(slogAttrKey); ok {
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return key
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}
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return dkm.mapSlow(slogAttrKey)
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}
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func (dkm *defaultKeyMapper) mapFast(slogAttrKey string) (journal.AttrKey, bool) {
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dkm.lock.RLock()
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defer dkm.lock.RUnlock()
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key, ok := dkm.keys[slogAttrKey]
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return key, ok
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}
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func (dkm *defaultKeyMapper) mapSlow(slogAttrKey string) journal.AttrKey {
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key := dkm.mapFunc(slogAttrKey)
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// it's OK if another goroutine in the slow path just wrote the key, we
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// will overwrite its result but the result will still be correct
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dkm.lock.Lock()
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defer dkm.lock.Unlock()
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dkm.keys[slogAttrKey] = key
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return key
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}
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func (dkm *defaultKeyMapper) mapFunc(slogAttrKey string) journal.AttrKey {
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key, err := journal.NewAttrKey(slogAttrKey)
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if err == nil {
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return key
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}
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var s strings.Builder
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for _, r := range slogAttrKey {
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switch {
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case r >= 'a' && r <= 'z':
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s.WriteRune(r - 'a' + 'A')
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case r >= '0' && r <= '9',
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r >= 'A' && r <= 'Z':
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s.WriteRune(r)
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default:
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if s.Len() > 0 {
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s.WriteRune('_')
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}
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}
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}
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if s.Len() == 0 {
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return dkm.badKey
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}
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skey := s.String()
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if len(skey) > 255 {
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skey = skey[:255] // known to only contain ASCII chars
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}
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if key, err = journal.NewAttrKey(skey); err != nil {
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return dkm.badKey
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}
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return key
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}
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