writer.go

// Copyright 2012 SocialCode. All rights reserved.
// Use of this source code is governed by the MIT
// license that can be found in the LICENSE file.

package gelf

import (
	"bytes"
	"compress/flate"
	"compress/gzip"
	"compress/zlib"
	"crypto/rand"
	"encoding/json"
	"fmt"
	"io"
	"net"
	"os"
	"path"
	"runtime"
	"strings"
	"sync"
	"time"
)

// Writer implements io.Writer and is used to send both discrete
// messages to a graylog2 server, or data from a stream-oriented
// interface (like the functions in log).
type Writer struct {
	mu               sync.Mutex
	conn             net.Conn
	hostname         string
	Facility         string // defaults to current process name
	CompressionLevel int    // one of the consts from compress/flate
	CompressionType  CompressType
}

// What compression type the writer should use when sending messages
// to the graylog2 server
type CompressType int

const (
	CompressGzip CompressType = iota
	CompressZlib
	CompressNone
)

// Message represents the contents of the GELF message.  It is gzipped
// before sending.
type Message struct {
	Version  string                 `json:"version"`
	Host     string                 `json:"host"`
	Short    string                 `json:"short_message"`
	Full     string                 `json:"full_message,omitempty"`
	TimeUnix float64                `json:"timestamp"`
	Level    int32                  `json:"level,omitempty"`
	Facility string                 `json:"facility,omitempty"`
	Extra    map[string]interface{} `json:"extra,omitempty"`
	File     string                 `json:"file,omitempty"`
	Line     int32                  `json:"line,omitempty"`
	RawExtra json.RawMessage        `json:"-"`
}

// Used to control GELF chunking.  Should be less than (MTU - len(UDP
// header)).
//
// TODO: generate dynamically using Path MTU Discovery?
const (
	ChunkSize        = 1420
	chunkedHeaderLen = 12
	chunkedDataLen   = ChunkSize - chunkedHeaderLen
)

var (
	magicChunked = []byte{0x1e, 0x0f}
	magicZlib    = []byte{0x78}
	magicGzip    = []byte{0x1f, 0x8b}
)

// Syslog severity levels
const (
	LOG_EMERG   = int32(0)
	LOG_ALERT   = int32(1)
	LOG_CRIT    = int32(2)
	LOG_ERR     = int32(3)
	LOG_WARNING = int32(4)
	LOG_NOTICE  = int32(5)
	LOG_INFO    = int32(6)
	LOG_DEBUG   = int32(7)
)

// numChunks returns the number of GELF chunks necessary to transmit
// the given compressed buffer.
func numChunks(b []byte) int {
	lenB := len(b)
	if lenB <= ChunkSize {
		return 1
	}
	return len(b)/chunkedDataLen + 1
}

// New returns a new GELF Writer.  This writer can be used to send the
// output of the standard Go log functions to a central GELF server by
// passing it to log.SetOutput()
func NewWriter(addr string) (*Writer, error) {
	var err error
	w := new(Writer)
	w.CompressionLevel = flate.BestSpeed

	if w.conn, err = net.Dial("udp", addr); err != nil {
		return nil, err
	}
	if w.hostname, err = os.Hostname(); err != nil {
		return nil, err
	}

	w.Facility = path.Base(os.Args[0])

	return w, nil
}

// writes the gzip compressed byte array to the connection as a series
// of GELF chunked messages.  The header format is documented at
// https://github.com/Graylog2/graylog2-docs/wiki/GELF as:
//
//     2-byte magic (0x1e 0x0f), 8 byte id, 1 byte sequence id, 1 byte
//     total, chunk-data
func (w *Writer) writeChunked(zBytes []byte) (err error) {
	b := make([]byte, 0, ChunkSize)
	buf := bytes.NewBuffer(b)
	nChunksI := numChunks(zBytes)
	if nChunksI > 128 {
		return fmt.Errorf("msg too large, would need %d chunks", nChunksI)
	}
	nChunks := uint8(nChunksI)
	// use urandom to get a unique message id
	msgId := make([]byte, 8)
	n, err := io.ReadFull(rand.Reader, msgId)
	if err != nil || n != 8 {
		return fmt.Errorf("rand.Reader: %d/%s", n, err)
	}

	bytesLeft := len(zBytes)
	for i := uint8(0); i < nChunks; i++ {
		buf.Reset()
		// manually write header.  Don't care about
		// host/network byte order, because the spec only
		// deals in individual bytes.
		buf.Write(magicChunked) //magic
		buf.Write(msgId)
		buf.WriteByte(i)
		buf.WriteByte(nChunks)
		// slice out our chunk from zBytes
		chunkLen := chunkedDataLen
		if chunkLen > bytesLeft {
			chunkLen = bytesLeft
		}
		off := int(i) * chunkedDataLen
		chunk := zBytes[off : off+chunkLen]
		buf.Write(chunk)

		// write this chunk, and make sure the write was good
		n, err := w.conn.Write(buf.Bytes())
		if err != nil {
			return fmt.Errorf("Write (chunk %d/%d): %s", i,
				nChunks, err)
		}
		if n != len(buf.Bytes()) {
			return fmt.Errorf("Write len: (chunk %d/%d) (%d/%d)",
				i, nChunks, n, len(buf.Bytes()))
		}

		bytesLeft -= chunkLen
	}

	if bytesLeft != 0 {
		return fmt.Errorf("error: %d bytes left after sending", bytesLeft)
	}
	return nil
}

// 1k bytes buffer by default
var bufPool = sync.Pool{
	New: func() interface{} {
		return bytes.NewBuffer(make([]byte, 0, 1024))
	},
}

func newBuffer() *bytes.Buffer {
	b := bufPool.Get().(*bytes.Buffer)
	if b != nil {
		b.Reset()
		return b
	}
	return bytes.NewBuffer(nil)
}

// WriteMessage sends the specified message to the GELF server
// specified in the call to New().  It assumes all the fields are
// filled out appropriately.  In general, clients will want to use
// Write, rather than WriteMessage.
func (w *Writer) WriteMessage(m *Message) (err error) {
	mBuf := newBuffer()
	defer bufPool.Put(mBuf)
	if err = m.MarshalJSONBuf(mBuf); err != nil {
		return err
	}
	mBytes := mBuf.Bytes()

	var (
		zBuf   *bytes.Buffer
		zBytes []byte
	)

	var zw io.WriteCloser
	switch w.CompressionType {
	case CompressGzip:
		zBuf = newBuffer()
		defer bufPool.Put(zBuf)
		zw, err = gzip.NewWriterLevel(zBuf, w.CompressionLevel)
	case CompressZlib:
		zBuf = newBuffer()
		defer bufPool.Put(zBuf)
		zw, err = zlib.NewWriterLevel(zBuf, w.CompressionLevel)
	case CompressNone:
		zBytes = mBytes
	default:
		panic(fmt.Sprintf("unknown compression type %d",
			w.CompressionType))
	}
	if zw != nil {
		if err != nil {
			return
		}
		if _, err = zw.Write(mBytes); err != nil {
			zw.Close()
			return
		}
		zw.Close()
		zBytes = zBuf.Bytes()
	}

	if numChunks(zBytes) > 1 {
		return w.writeChunked(zBytes)
	}
	n, err := w.conn.Write(zBytes)
	if err != nil {
		return
	}
	if n != len(zBytes) {
		return fmt.Errorf("bad write (%d/%d)", n, len(zBytes))
	}

	return nil
}

// Close connection and interrupt blocked Read or Write operations
func (w *Writer) Close() error {
	return w.conn.Close()
}

/*
func (w *Writer) Alert(m string) (err error)
func (w *Writer) Close() error
func (w *Writer) Crit(m string) (err error)
func (w *Writer) Debug(m string) (err error)
func (w *Writer) Emerg(m string) (err error)
func (w *Writer) Err(m string) (err error)
func (w *Writer) Info(m string) (err error)
func (w *Writer) Notice(m string) (err error)
func (w *Writer) Warning(m string) (err error)
*/

// getCaller returns the filename and the line info of a function
// further down in the call stack.  Passing 0 in as callDepth would
// return info on the function calling getCallerIgnoringLog, 1 the
// parent function, and so on.  Any suffixes passed to getCaller are
// path fragments like "/pkg/log/log.go", and functions in the call
// stack from that file are ignored.
func getCaller(callDepth int, suffixesToIgnore ...string) (file string, line int) {
	// bump by 1 to ignore the getCaller (this) stackframe
	callDepth++
outer:
	for {
		var ok bool
		_, file, line, ok = runtime.Caller(callDepth)
		if !ok {
			file = "???"
			line = 0
			break
		}

		for _, s := range suffixesToIgnore {
			if strings.HasSuffix(file, s) {
				callDepth++
				continue outer
			}
		}
		break
	}
	return
}

func getCallerIgnoringLogMulti(callDepth int) (string, int) {
	// the +1 is to ignore this (getCallerIgnoringLogMulti) frame
	return getCaller(callDepth+1, "/pkg/log/log.go", "/pkg/io/multi.go")
}

// Write encodes the given string in a GELF message and sends it to
// the server specified in New().
func (w *Writer) Write(p []byte) (n int, err error) {

	// 1 for the function that called us.
	file, line := getCallerIgnoringLogMulti(1)

	// remove trailing and leading whitespace
	p = bytes.TrimSpace(p)

	// If there are newlines in the message, use the first line
	// for the short message and set the full message to the
	// original input.  If the input has no newlines, stick the
	// whole thing in Short.
	short := p
	full := []byte("")
	if i := bytes.IndexRune(p, '\n'); i > 0 {
		short = p[:i]
		full = p
	}

	m := Message{
		Version:  "1.1",
		Host:     w.hostname,
		Short:    string(short),
		Full:     string(full),
		TimeUnix: float64(time.Now().Unix()),
		Level:    6, // info
		Facility: w.Facility,
		Extra: map[string]interface{}{
			"_file": file,
			"_line": line,
		},
	}

	if err = w.WriteMessage(&m); err != nil {
		return 0, err
	}

	return len(p), nil
}

func (m *Message) MarshalJSONBuf(buf *bytes.Buffer) error {
	b, err := json.Marshal(m)
	if err != nil {
		return err
	}
	// write up until the final }
	if _, err = buf.Write(b[:len(b)-1]); err != nil {
		return err
	}
	if len(m.Extra) > 0 {
		eb, err := json.Marshal(m.Extra)
		if err != nil {
			return err
		}
		// merge serialized message + serialized extra map
		if err = buf.WriteByte(','); err != nil {
			return err
		}
		// write serialized extra bytes, without enclosing quotes
		if _, err = buf.Write(eb[1 : len(eb)-1]); err != nil {
			return err
		}
	}

	if len(m.RawExtra) > 0 {
		if err := buf.WriteByte(','); err != nil {
			return err
		}

		// write serialized extra bytes, without enclosing quotes
		if _, err = buf.Write(m.RawExtra[1 : len(m.RawExtra)-1]); err != nil {
			return err
		}
	}

	// write final closing quotes
	return buf.WriteByte('}')
}

func (m *Message) UnmarshalJSON(data []byte) error {
	i := make(map[string]interface{}, 16)
	if err := json.Unmarshal(data, &i); err != nil {
		return err
	}
	for k, v := range i {
		if k[0] == '_' {
			if m.Extra == nil {
				m.Extra = make(map[string]interface{}, 1)
			}
			m.Extra[k] = v
			continue
		}
		switch k {
		case "version":
			m.Version = v.(string)
		case "host":
			m.Host = v.(string)
		case "short_message":
			m.Short = v.(string)
		case "full_message":
			m.Full = v.(string)
		case "timestamp":
			m.TimeUnix = v.(float64)
		case "level":
			m.Level = int32(v.(float64))
		case "facility":
			m.Facility = v.(string)
		case "file":
			m.File = v.(string)
		case "line":
			m.Line = int32(v.(float64))
		}
	}
	return nil
}