dnscrypt-proxy/vendor/github.com/hashicorp/go-syslog/builtin.go

// 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", "/var/run/log"}
	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")
}