You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: buffer.go
    path of file: ./repos/kubeedge/vendor/k8s.io/klog/v2/internal/buffer
    
    the code of the file until where you have to start completion: // Copyright 2013 Google Inc. All Rights Reserved.
// Copyright 2022 The Kubernetes Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package buffer provides a cache for byte.Buffer instances that can be reused
// to avoid frequent allocation and deallo
    
func (buf *Buffer) FormatHeader(s severity.Severity, file string, line int, now time.Time) {
	if line < 0 {
		line = 0 // not a real line number, but acceptable to someDigits
	}
	if s > severity.FatalLog {
		s = severity.InfoLog // for safety.
	}

	// 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] = severity.Char[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])
}