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level.go
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level.go
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// Package logutils augments the standard log package with levels.
package logutils
import (
"bytes"
"io"
"sync"
)
type LogLevel string
// LevelFilter is an io.Writer that can be used with a logger that
// will filter out log messages that aren't at least a certain level.
//
// Once the filter is in use somewhere, it is not safe to modify
// the structure.
type LevelFilter struct {
// Levels is the list of log levels, in increasing order of
// severity. Example might be: {"DEBUG", "WARN", "ERROR"}.
Levels []LogLevel
// MinLevel is the minimum level allowed through
MinLevel LogLevel
// The underlying io.Writer where log messages that pass the filter
// will be set.
Writer io.Writer
badLevels map[LogLevel]struct{}
once sync.Once
}
// Check will check a given line if it would be included in the level
// filter.
func (f *LevelFilter) Check(line []byte) bool {
f.once.Do(f.init)
// Check for a log level
var level LogLevel
x := bytes.IndexByte(line, '[')
if x >= 0 {
y := bytes.IndexByte(line[x:], ']')
if y >= 0 {
level = LogLevel(line[x+1 : x+y])
}
}
_, ok := f.badLevels[level]
return !ok
}
func (f *LevelFilter) Write(p []byte) (n int, err error) {
// Note in general that io.Writer can receive any byte sequence
// to write, but the "log" package always guarantees that we only
// get a single line. We use that as a slight optimization within
// this method, assuming we're dealing with a single, complete line
// of log data.
if !f.Check(p) {
return len(p), nil
}
return f.Writer.Write(p)
}
// SetMinLevel is used to update the minimum log level
func (f *LevelFilter) SetMinLevel(min LogLevel) {
f.MinLevel = min
f.init()
}
func (f *LevelFilter) init() {
badLevels := make(map[LogLevel]struct{})
for _, level := range f.Levels {
if level == f.MinLevel {
break
}
badLevels[level] = struct{}{}
}
f.badLevels = badLevels
}