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