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log.go
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log.go
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package oncecache
import (
"context"
"fmt"
"log/slog"
"strings"
)
// LogConfig is used by [oncecache.Log] to configure log output.
// See also: [oncecache.Event.LogValue], [oncecache.Entry.LogValue].
var LogConfig = struct {
Msg string
AttrEvent string
AttrCache string
AttrOp string
AttrKey string
AttrVal string
AttrErr string
}{
Msg: "Cache event",
AttrEvent: "ev",
AttrCache: "cache",
AttrOp: "op",
AttrKey: "k",
AttrVal: "v",
AttrErr: "err",
}
// Log is an [Opt] for [oncecache.New] that logs each [Event] to log, where
// [Event.Op] is in ops. If ops is empty, all events are logged. If log is nil,
// Log is a no-op. If lvl is nil, [slog.LevelInfo] is used. Example usage:
//
// c := oncecache.New[int, int](
// calcFibonacci,
// oncecache.Name("fibs"),
// oncecache.Log(log, slog.LevelInfo, oncecache.OpFill, oncecache.OpEvict),
// oncecache.Log(log, slog.LevelDebug, oncecache.OpHit, oncecache.OpMiss),
// )
//
// Log is intended to handle basic logging needs. Some configuration is possible
// via [oncecache.LogConfig]. If you require more control, you can roll your own
// logging mechanism using an [OnEvent] channel or the On* callbacks. If doing
// so, note that [Event], [Entry] and [Cache] each implement [slog.LogValuer].
func Log(log *slog.Logger, lvl slog.Leveler, ops ...Op) Opt {
if log == nil {
return nil
}
if isNil(lvl) {
lvl = slog.LevelInfo
}
if len(ops) == 0 {
ops = []Op{OpHit, OpMiss, OpFill, OpEvict}
} else {
ops = uniq(ops)
}
return logOptConfig{
log: log,
lvl: lvl,
ops: ops,
}
}
var _ Opt = logOptConfig{}
type logOptConfig struct {
log *slog.Logger
lvl slog.Leveler
ops []Op
}
func (o logOptConfig) optioner() {}
var _ Opt = &logOpt[any, any]{}
type logOpt[K comparable, V any] logOptConfig
func (o *logOpt[K, V]) optioner() {}
func (o *logOpt[K, V]) apply(c *Cache[K, V]) {
for _, op := range o.ops {
switch op {
case OpFill:
c.onFill = append(c.onFill, o.logFill)
case OpEvict:
c.onEvict = append(c.onEvict, o.logEvict)
case OpHit:
c.onHit = append(c.onHit, o.logHit)
case OpMiss:
c.onMiss = append(c.onMiss, o.logMiss)
default:
// Shouldn't happen.
panic(fmt.Sprintf("oncecache: unknown op[%d]: %s", op, op))
}
}
}
func (o *logOpt[K, V]) logEvent(ev Event[K, V]) {
o.log.LogAttrs(context.Background(), o.lvl.Level(), LogConfig.Msg, slog.Any(LogConfig.AttrEvent, ev))
}
func (o *logOpt[K, V]) logHit(ctx context.Context, key K, val V, err error) {
ev := Event[K, V]{
Op: OpHit,
Entry: Entry[K, V]{Cache: FromContext[K, V](ctx), Key: key, Val: val, Err: err},
}
o.logEvent(ev)
}
func (o *logOpt[K, V]) logMiss(ctx context.Context, key K, val V, err error) {
ev := Event[K, V]{
Op: OpMiss,
Entry: Entry[K, V]{Cache: FromContext[K, V](ctx), Key: key, Val: val, Err: err},
}
o.logEvent(ev)
}
func (o *logOpt[K, V]) logFill(ctx context.Context, key K, val V, err error) {
ev := Event[K, V]{
Op: OpFill,
Entry: Entry[K, V]{Cache: FromContext[K, V](ctx), Key: key, Val: val, Err: err},
}
o.logEvent(ev)
}
func (o *logOpt[K, V]) logEvict(ctx context.Context, key K, val V, err error) {
ev := Event[K, V]{
Op: OpEvict,
Entry: Entry[K, V]{Cache: FromContext[K, V](ctx), Key: key, Val: val, Err: err},
}
o.logEvent(ev)
}
// LogValue implements [slog.LogValuer], logging according to [Entry.LogValue],
// but also logging [Event.Op].
func (e Event[K, V]) LogValue() slog.Value {
attrs := make([]slog.Attr, 3, 5)
attrs[0] = slog.String(LogConfig.AttrCache, e.Cache.name)
attrs[1] = slog.String(LogConfig.AttrOp, e.Op.String())
attrs[2] = slog.Any(LogConfig.AttrKey, e.Key)
if e.Op != OpMiss {
if e.isValLogged() {
attrs = append(attrs, slog.Any(LogConfig.AttrVal, e.Val))
}
if e.Err != nil {
attrs = append(attrs, slog.Any(LogConfig.AttrErr, e.Err))
}
}
return slog.GroupValue(attrs...)
}
// String returns a string representation of the event. The event's Val field
// is not incorporated. For logging, note [Event.LogValue].
func (e Event[K, V]) String() string {
var sb strings.Builder
sb.WriteString(e.Cache.name)
sb.WriteRune('.')
sb.WriteString(e.Op.String())
sb.WriteRune('[')
sb.WriteString(fmt.Sprintf("%v", e.Key))
sb.WriteRune(']')
if e.Err != nil {
sb.WriteString("[! ")
sb.WriteString(e.Err.Error())
sb.WriteRune(']')
}
return sb.String()
}
// String returns a string representation of the entry. The entry's Val field
// is not incorporated. For logging, note [Entry.LogValue].
func (e Entry[K, V]) String() string {
sb := strings.Builder{}
sb.WriteString(e.Cache.name)
sb.WriteRune('[')
sb.WriteString(fmt.Sprintf("%v", e.Key))
sb.WriteRune(']')
if e.Err != nil {
sb.WriteString("[! ")
sb.WriteString(e.Err.Error())
sb.WriteRune(']')
}
return sb.String()
}
// LogValue implements [slog.LogValuer], logging Val if it implements
// [slog.LogValuer] or is a primitive type such as int or bool (but not string),
// logging Err if non-nil, and always logging Key and [Cache.Name].
func (e Entry[K, V]) LogValue() slog.Value {
attrs := make([]slog.Attr, 2, 4)
attrs[0] = slog.String(LogConfig.AttrCache, e.Cache.name)
attrs[1] = slog.Any(LogConfig.AttrKey, e.Key)
if e.isValLogged() {
attrs = append(attrs, slog.Any(LogConfig.AttrVal, e.Val))
}
if e.Err != nil {
attrs = append(attrs, slog.Any(LogConfig.AttrErr, e.Err))
}
return slog.GroupValue(attrs...)
}
// isValLogged returns true if the Entry's Val field should be logged. Only
// primitive types and [slog.LogValuer] are logged. In particular, note that
// string is not logged.
func (e Entry[K, V]) isValLogged() bool {
switch any(e.Val).(type) {
case slog.LogValuer, bool, nil, int, int8, int16, int32, int64,
uint, uint8, uint16, uint32, uint64,
float32, float64, complex64, complex128:
return true
default:
return false
}
}