1// Go support for leveled logs, analogous to https://code.google.com/p/google-glog/
2//
3// Copyright 2013 Google Inc. All Rights Reserved.
4//
5// Licensed under the Apache License, Version 2.0 (the "License");
6// you may not use this file except in compliance with the License.
7// You may obtain a copy of the License at
8//
9//     http://www.apache.org/licenses/LICENSE-2.0
10//
11// Unless required by applicable law or agreed to in writing, software
12// distributed under the License is distributed on an "AS IS" BASIS,
13// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14// See the License for the specific language governing permissions and
15// limitations under the License.
16
17// File I/O for logs.
18
19package klog
20
21import (
22	"errors"
23	"fmt"
24	"os"
25	"os/user"
26	"path/filepath"
27	"strings"
28	"sync"
29	"time"
30)
31
32// MaxSize is the maximum size of a log file in bytes.
33var MaxSize uint64 = 1024 * 1024 * 1800
34
35// logDirs lists the candidate directories for new log files.
36var logDirs []string
37
38func createLogDirs() {
39	if logging.logDir != "" {
40		logDirs = append(logDirs, logging.logDir)
41	}
42	logDirs = append(logDirs, os.TempDir())
43}
44
45var (
46	pid      = os.Getpid()
47	program  = filepath.Base(os.Args[0])
48	host     = "unknownhost"
49	userName = "unknownuser"
50)
51
52func init() {
53	h, err := os.Hostname()
54	if err == nil {
55		host = shortHostname(h)
56	}
57
58	current, err := user.Current()
59	if err == nil {
60		userName = current.Username
61	}
62
63	// Sanitize userName since it may contain filepath separators on Windows.
64	userName = strings.Replace(userName, `\`, "_", -1)
65}
66
67// shortHostname returns its argument, truncating at the first period.
68// For instance, given "www.google.com" it returns "www".
69func shortHostname(hostname string) string {
70	if i := strings.Index(hostname, "."); i >= 0 {
71		return hostname[:i]
72	}
73	return hostname
74}
75
76// logName returns a new log file name containing tag, with start time t, and
77// the name for the symlink for tag.
78func logName(tag string, t time.Time) (name, link string) {
79	name = fmt.Sprintf("%s.%s.%s.log.%s.%04d%02d%02d-%02d%02d%02d.%d",
80		program,
81		host,
82		userName,
83		tag,
84		t.Year(),
85		t.Month(),
86		t.Day(),
87		t.Hour(),
88		t.Minute(),
89		t.Second(),
90		pid)
91	return name, program + "." + tag
92}
93
94var onceLogDirs sync.Once
95
96// create creates a new log file and returns the file and its filename, which
97// contains tag ("INFO", "FATAL", etc.) and t.  If the file is created
98// successfully, create also attempts to update the symlink for that tag, ignoring
99// errors.
100// The startup argument indicates whether this is the initial startup of klog.
101// If startup is true, existing files are opened for appending instead of truncated.
102func create(tag string, t time.Time, startup bool) (f *os.File, filename string, err error) {
103	if logging.logFile != "" {
104		f, err := openOrCreate(logging.logFile, startup)
105		if err == nil {
106			return f, logging.logFile, nil
107		}
108		return nil, "", fmt.Errorf("log: unable to create log: %v", err)
109	}
110	onceLogDirs.Do(createLogDirs)
111	if len(logDirs) == 0 {
112		return nil, "", errors.New("log: no log dirs")
113	}
114	name, link := logName(tag, t)
115	var lastErr error
116	for _, dir := range logDirs {
117		fname := filepath.Join(dir, name)
118		f, err := openOrCreate(fname, startup)
119		if err == nil {
120			symlink := filepath.Join(dir, link)
121			os.Remove(symlink)        // ignore err
122			os.Symlink(name, symlink) // ignore err
123			return f, fname, nil
124		}
125		lastErr = err
126	}
127	return nil, "", fmt.Errorf("log: cannot create log: %v", lastErr)
128}
129
130// The startup argument indicates whether this is the initial startup of klog.
131// If startup is true, existing files are opened for appending instead of truncated.
132func openOrCreate(name string, startup bool) (*os.File, error) {
133	if startup {
134		f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
135		return f, err
136	}
137	f, err := os.Create(name)
138	return f, err
139}
140