聊聊klog的header

func (l *loggingT) println(s severity, logr logr.Logger, filter LogFilter, args ...interface{}) {
    buf, file, line := l.header(s, 0)
    // if logr is set, we clear the generated header as we rely on the backing
    // logr implementation to print headers
    if logr != nil {
        l.putBuffer(buf)
        buf = l.getBuffer()
    }
    if filter != nil {
        args = filter.Filter(args)
    }
    fmt.Fprintln(buf, args...)
    l.output(s, logr, buf, file, line, false)
}

func (l *loggingT) header(s severity, depth int) (*buffer, string, int) {
    _, file, line, ok := runtime.Caller(3 + depth)
    if !ok {
        file = "???"
        line = 1
    } else {
        if slash := strings.LastIndex(file, "/"); slash >= 0 {
            path := file
            file = path[slash+1:]
            if l.addDirHeader {
                if dirsep := strings.LastIndex(path[:slash], "/"); dirsep >= 0 {
                    file = path[dirsep+1:]
                }
            }
        }
    }
    return l.formatHeader(s, file, line), file, line
}

// formatHeader formats a log header using the provided file name and line number.
func (l *loggingT) formatHeader(s severity, file string, line int) *buffer {
    now := timeNow()
    if line < 0 {
        line = 0 // not a real line number, but acceptable to someDigits
    }
    if s > fatalLog {
        s = infoLog // for safety.
    }
    buf := l.getBuffer()
    if l.skipHeaders {
        return buf
    }

    // Avoid Fprintf, for speed. The format is so simple that we can do it quickly by hand.
    // It's worth about 3X. Fprintf is hard.
    _, month, day := now.Date()
    hour, minute, second := now.Clock()
    // Lmmdd hh:mm:ss.uuuuuu threadid file:line]
    buf.tmp[0] = severityChar[s]
    buf.twoDigits(1, int(month))
    buf.twoDigits(3, day)
    buf.tmp[5] = ' '
    buf.twoDigits(6, hour)
    buf.tmp[8] = ':'
    buf.twoDigits(9, minute)
    buf.tmp[11] = ':'
    buf.twoDigits(12, second)
    buf.tmp[14] = '.'
    buf.nDigits(6, 15, now.Nanosecond()/1000, '0')
    buf.tmp[21] = ' '
    buf.nDigits(7, 22, pid, ' ') // TODO: should be TID
    buf.tmp[29] = ' '
    buf.Write(buf.tmp[:30])
    buf.WriteString(file)
    buf.tmp[0] = ':'
    n := buf.someDigits(1, line)
    buf.tmp[n+1] = ']'
    buf.tmp[n+2] = ' '
    buf.Write(buf.tmp[:n+3])
    return buf
}

func headerDemo() {
    flag.Set("skip_headers", "true")
    klog.Info("hello by Info")
    klog.InfoDepth(0, "hello by InfoDepth 0")
    klog.InfoDepth(1, "hello by InfoDepth 1")
    klog.Infoln("hello by Infoln")
    klog.Infof("hello by %s", "Infof")
    klog.InfoS("Pod status updated", "pod", "kubedns", "status", "ready")
}

hello by Info
hello by InfoDepth 0
hello by InfoDepth 1
hello by Infoln
hello by Infof
"Pod status updated" pod="kubedns" status="ready"

I1229 23:45:57.827487    2176 klog_demo.go:41] hello by Info
I1229 23:45:57.827591    2176 klog_demo.go:42] hello by InfoDepth 0
I1229 23:45:57.827600    2176 klog_demo.go:31] hello by InfoDepth 1
I1229 23:45:57.827605    2176 klog_demo.go:44] hello by Infoln
I1229 23:45:57.827608    2176 klog_demo.go:45] hello by Infof
I1229 23:45:57.827617    2176 klog_demo.go:46] "Pod status updated" pod="kubedns" status="ready"