open-consul/vendor/github.com/hashicorp/go-syslog/builtin.go

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// This file is taken from the log/syslog in the standard lib.
// However, there is a bug with overwhelming syslog that causes writes
// to block indefinitely. This is fixed by adding a write deadline.
//
// +build !windows,!nacl,!plan9
package gsyslog
import (
"errors"
"fmt"
"log/syslog"
"net"
"os"
"strings"
"sync"
"time"
)
const severityMask = 0x07
const facilityMask = 0xf8
const localDeadline = 20 * time.Millisecond
const remoteDeadline = 50 * time.Millisecond
// A builtinWriter is a connection to a syslog server.
type builtinWriter struct {
priority syslog.Priority
tag string
hostname string
network string
raddr string
mu sync.Mutex // guards conn
conn serverConn
}
// This interface and the separate syslog_unix.go file exist for
// Solaris support as implemented by gccgo. On Solaris you can not
// simply open a TCP connection to the syslog daemon. The gccgo
// sources have a syslog_solaris.go file that implements unixSyslog to
// return a type that satisfies this interface and simply calls the C
// library syslog function.
type serverConn interface {
writeString(p syslog.Priority, hostname, tag, s, nl string) error
close() error
}
type netConn struct {
local bool
conn net.Conn
}
// New establishes a new connection to the system log daemon. Each
// write to the returned writer sends a log message with the given
// priority and prefix.
func newBuiltin(priority syslog.Priority, tag string) (w *builtinWriter, err error) {
return dialBuiltin("", "", priority, tag)
}
// Dial establishes a connection to a log daemon by connecting to
// address raddr on the specified network. Each write to the returned
// writer sends a log message with the given facility, severity and
// tag.
// If network is empty, Dial will connect to the local syslog server.
func dialBuiltin(network, raddr string, priority syslog.Priority, tag string) (*builtinWriter, error) {
if priority < 0 || priority > syslog.LOG_LOCAL7|syslog.LOG_DEBUG {
return nil, errors.New("log/syslog: invalid priority")
}
if tag == "" {
tag = os.Args[0]
}
hostname, _ := os.Hostname()
w := &builtinWriter{
priority: priority,
tag: tag,
hostname: hostname,
network: network,
raddr: raddr,
}
w.mu.Lock()
defer w.mu.Unlock()
err := w.connect()
if err != nil {
return nil, err
}
return w, err
}
// connect makes a connection to the syslog server.
// It must be called with w.mu held.
func (w *builtinWriter) connect() (err error) {
if w.conn != nil {
// ignore err from close, it makes sense to continue anyway
w.conn.close()
w.conn = nil
}
if w.network == "" {
w.conn, err = unixSyslog()
if w.hostname == "" {
w.hostname = "localhost"
}
} else {
var c net.Conn
c, err = net.DialTimeout(w.network, w.raddr, remoteDeadline)
if err == nil {
w.conn = &netConn{conn: c}
if w.hostname == "" {
w.hostname = c.LocalAddr().String()
}
}
}
return
}
// Write sends a log message to the syslog daemon.
func (w *builtinWriter) Write(b []byte) (int, error) {
return w.writeAndRetry(w.priority, string(b))
}
// Close closes a connection to the syslog daemon.
func (w *builtinWriter) Close() error {
w.mu.Lock()
defer w.mu.Unlock()
if w.conn != nil {
err := w.conn.close()
w.conn = nil
return err
}
return nil
}
func (w *builtinWriter) writeAndRetry(p syslog.Priority, s string) (int, error) {
pr := (w.priority & facilityMask) | (p & severityMask)
w.mu.Lock()
defer w.mu.Unlock()
if w.conn != nil {
if n, err := w.write(pr, s); err == nil {
return n, err
}
}
if err := w.connect(); err != nil {
return 0, err
}
return w.write(pr, s)
}
// write generates and writes a syslog formatted string. The
// format is as follows: <PRI>TIMESTAMP HOSTNAME TAG[PID]: MSG
func (w *builtinWriter) write(p syslog.Priority, msg string) (int, error) {
// ensure it ends in a \n
nl := ""
if !strings.HasSuffix(msg, "\n") {
nl = "\n"
}
err := w.conn.writeString(p, w.hostname, w.tag, msg, nl)
if err != nil {
return 0, err
}
// Note: return the length of the input, not the number of
// bytes printed by Fprintf, because this must behave like
// an io.Writer.
return len(msg), nil
}
func (n *netConn) writeString(p syslog.Priority, hostname, tag, msg, nl string) error {
if n.local {
// Compared to the network form below, the changes are:
// 1. Use time.Stamp instead of time.RFC3339.
// 2. Drop the hostname field from the Fprintf.
timestamp := time.Now().Format(time.Stamp)
n.conn.SetWriteDeadline(time.Now().Add(localDeadline))
_, err := fmt.Fprintf(n.conn, "<%d>%s %s[%d]: %s%s",
p, timestamp,
tag, os.Getpid(), msg, nl)
return err
}
timestamp := time.Now().Format(time.RFC3339)
n.conn.SetWriteDeadline(time.Now().Add(remoteDeadline))
_, err := fmt.Fprintf(n.conn, "<%d>%s %s %s[%d]: %s%s",
p, timestamp, hostname,
tag, os.Getpid(), msg, nl)
return err
}
func (n *netConn) close() error {
return n.conn.Close()
}
// unixSyslog opens a connection to the syslog daemon running on the
// local machine using a Unix domain socket.
func unixSyslog() (conn serverConn, err error) {
logTypes := []string{"unixgram", "unix"}
logPaths := []string{"/dev/log", "/var/run/syslog"}
for _, network := range logTypes {
for _, path := range logPaths {
conn, err := net.DialTimeout(network, path, localDeadline)
if err != nil {
continue
} else {
return &netConn{conn: conn, local: true}, nil
}
}
}
return nil, errors.New("Unix syslog delivery error")
}