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scanner.go
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scanner.go
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package logd
import (
"bufio"
"bytes"
stderrors "errors"
"io"
"time"
"github.com/jeffrom/logd/internal"
"github.com/jeffrom/logd/protocol"
"github.com/pkg/errors"
)
// ErrStopped indicates the scanner was stopped
var ErrStopped = stderrors.New("stopped")
// Scanner is used to read batches from the log, scanning message by message
type Scanner struct {
Client *Client
conf *Config
topic []byte
s *protocol.BatchScanner
batch *protocol.Batch
msg *protocol.Message
batchBuf *bytes.Buffer
batchBufBr *bufio.Reader
batchRead int
batchesRead int
nbatches int
messagesRead int
totalMessagesRead int
statem StatePuller
currLocal uint64
currRemote uint64
err error
done chan struct{}
pollC chan error
usetail bool
startoff uint64
limit int
}
// NewScanner returns a new instance of *Scanner.
func NewScanner(conf *Config, topic string) *Scanner {
s := &Scanner{
conf: conf,
batchBuf: &bytes.Buffer{},
msg: protocol.NewMessage(conf.BatchSize),
done: make(chan struct{}),
pollC: make(chan error),
usetail: conf.UseTail,
startoff: conf.Offset,
limit: conf.Limit,
statem: NoopStatePuller(0),
}
if topic != "" {
s.Client = New(conf)
s.topic = []byte(topic)
}
return s
}
// ScannerForClient returns a new scanner from a Client
func ScannerForClient(c *Client) *Scanner {
s := NewScanner(c.conf, "")
s.Client = c
return s
}
// DialScannerConfig returns a new writer with a connection to addr
func DialScannerConfig(addr string, conf *Config) (*Scanner, error) {
if addr == "" {
addr = conf.Host
}
c, err := DialConfig(addr, conf)
if err != nil {
return nil, err
}
return ScannerForClient(c), nil
}
// DialScanner returns a new scanner with a default configuration
func DialScanner(addr string) (*Scanner, error) {
return DialScannerConfig(addr, DefaultConfig)
}
// Reset sets the scanner to it's initial values so it can be reused.
func (s *Scanner) Reset() {
s.msg.Reset()
s.currLocal = 0
s.currRemote = 0
s.messagesRead = 0
s.totalMessagesRead = 0
if s.batch != nil {
s.batch.Reset()
}
s.batchBuf.Reset()
s.batchBufBr = bufio.NewReader(s.batchBuf)
s.msg.Reset()
s.batchRead = 0
s.batchesRead = 0
s.nbatches = 0
s.s = nil
s.usetail = s.conf.UseTail
s.startoff = s.conf.Offset
s.limit = s.conf.Limit
select {
case <-s.done:
default:
}
}
func (s *Scanner) resetDoneC() {
select {
case <-s.done: // if it's closed, this will recreate it
s.done = make(chan struct{})
default:
}
}
// WithSetStatePuller sets the StatePuller on the Scanner.
func (s *Scanner) WithStateHandler(statem StatePuller) *Scanner {
s.statem = statem
return s
}
// SetTopic sets the topic for the scanner.
func (s *Scanner) SetTopic(topic string) {
s.topic = []byte(topic)
}
// Topic returns the topic for the scanner.
func (s *Scanner) Topic() string {
return string(s.topic)
}
func (s *Scanner) UseTail() {
if s.messagesRead > 0 {
panic("attempted to set offset while already scanning")
}
s.usetail = true
}
func (s *Scanner) SetOffset(off uint64) {
if s.messagesRead > 0 {
panic("attempted to set offset while already scanning")
}
s.usetail = false
s.startoff = off
}
func (s *Scanner) SetLimit(n int) {
s.limit = n
}
// Scan reads the next message. If it encounters an error, it returns false.
func (s *Scanner) Scan() bool {
if !s.conf.ReadForever && s.totalMessagesRead >= s.limit {
return s.scanErr(nil)
}
if s.s == nil { // initial state
s.resetDoneC()
if err := s.doInitialRead(); err != nil {
return s.scanErr(err)
}
} else if err := s.scanNextBatch(); err != nil {
return s.scanErr(err)
}
// read the next message in the batch
if err := s.readMessage(); err != nil {
return s.scanErr(err)
}
return true
}
// Start marks the current message as processing. It will return ErrProcessing
// if the message is already being processed.
func (s *Scanner) Start() error {
return s.statem.Start(s.currRemote, uint64(s.batchRead))
}
// Complete marks the current message processing completed. It will panic if no
// StatePuller exists on the scanner.
func (s *Scanner) Complete(err error) error {
off := s.currRemote
delta := s.batchRead
if s.batch != nil && s.batchRead >= s.batch.Size {
fullsize, _ := s.batch.FullSize()
off = s.currRemote + uint64(fullsize)
delta = 0
}
if err == nil {
err = s.Error()
}
internal.Debugf(s.Client.gconf, "completing to offset %d, delta %d (err: %+v)", off, delta, err)
return s.statem.Complete(off, uint64(delta), err)
}
func (s *Scanner) readMessage() error {
s.msg.Reset()
n, err := s.msg.ReadFrom(s.batchBufBr)
if err != nil {
return err
}
s.msg.Offset = s.currLocal
s.msg.Delta = uint64(s.batchRead)
s.batchRead += int(n)
s.messagesRead++
s.totalMessagesRead++
return err
}
func (s *Scanner) doInitialRead() error {
var bs *protocol.BatchScanner
var err error
var nbatches int
var hasState bool
var delta uint64
if s.statem != nil {
_, _, err := s.statem.Get()
if err == nil {
hasState = true
}
}
if s.usetail { // offset was not explicitly set
if hasState {
off, delt, err := s.statem.Get()
delta = delt
if err != nil {
return err
}
s.currRemote = off
internal.Debugf(s.Client.gconf, "starting from previous state: offset %d, delta %d", off, delta)
nbatches, bs, err = s.Client.ReadOffset(s.topic, s.currRemote, s.limit)
if err != nil {
return err
}
} else {
s.currRemote, nbatches, bs, err = s.Client.Tail(s.topic, s.limit)
internal.Debugf(s.Client.gconf, "starting with %d batches from log tail at %d (err: %+v)", nbatches, s.currRemote, err)
}
} else {
s.currRemote = s.startoff
nbatches, bs, err = s.Client.ReadOffset(s.topic, s.currRemote, s.limit)
internal.Debugf(s.Client.gconf, "starting with %d batches from offset %d (err: %+v)", nbatches, s.currRemote, err)
}
if err != nil {
return err
}
s.currLocal = s.currRemote
s.s = bs
s.nbatches = nbatches
internal.Debugf(s.Client.gconf, "started reading from %d", s.currRemote)
if !s.s.Scan() {
return s.s.Error()
}
if err := s.setNextBatch(); err != nil {
return err
}
for uint64(s.batchRead) < delta {
if err := s.readMessage(); err != nil {
return err
}
}
return err
}
func (s *Scanner) scanNextBatch() error {
if s.batchRead >= s.batch.Size {
if s.batchesRead >= s.nbatches {
err := s.requestMoreBatches(false)
if err == protocol.ErrNotFound {
if !s.conf.ReadForever {
return protocol.ErrNotFound
}
if perr := s.pollBatch(); perr != nil {
return perr
}
} else if err != nil {
return err
}
}
if !s.s.Scan() {
err := s.s.Error()
if err != nil && err != io.EOF {
return err
}
}
if err := s.setNextBatch(); err != nil {
return err
}
}
return nil
}
// Stop causes the scanner to stop making requests and returns ErrStopped
func (s *Scanner) Stop() {
close(s.done)
s.s = nil
}
func (s *Scanner) requestMoreBatches(poll bool) error {
select {
case <-s.done:
return ErrStopped
default:
}
if !poll {
s.currRemote += uint64(s.Client.bs.Scanned())
}
nbatches, bs, err := s.Client.ReadOffset(s.topic, s.currRemote, s.limit)
internal.Debugf(s.Client.gconf,
"requested more batches from %d. read %d messages (%d/%d bytes) (err: %+v)",
s.currRemote, s.messagesRead, s.batchRead, s.batch.Size, err)
if err != nil {
return err
}
s.s = bs
s.messagesRead = 0
s.batchesRead = 0
s.nbatches = nbatches
return nil
}
func (s *Scanner) setNextBatch() error {
if size, ok := s.batch.FullSize(); ok {
s.currLocal += uint64(size)
}
s.batch = s.s.Batch()
s.batchRead = 0
s.batchesRead++
s.batchBuf.Reset()
s.batchBufBr = bufio.NewReader(s.batchBuf)
_, err := s.batchBuf.Write(s.batch.MessageBytes())
return err
}
func (s *Scanner) pollBatch() error {
go func() {
for {
select {
case <-time.After(s.conf.WaitInterval):
err := s.requestMoreBatches(true)
if err != nil {
if err == protocol.ErrNotFound {
continue
}
s.pollC <- err
return
}
s.pollC <- nil
return
case <-s.done:
s.pollC <- ErrStopped
return
}
}
}()
return <-s.pollC
}
func (s *Scanner) scanErr(err error) bool {
if err != nil {
if errors.Cause(err) == protocol.ErrNotFound {
internal.Debugf(s.Client.gconf, "scan: %+v", err)
} else {
internal.Logf("scan: %+v", err)
}
}
s.err = err
return false
}
// Message returns the current message
func (s *Scanner) Message() *protocol.Message {
return s.msg
}
func (s *Scanner) Error() error {
return s.err
}
func (s *Scanner) Close() error {
internal.IgnoreError(s.conf.Verbose, s.Client.Close())
if m, ok := s.statem.(internal.LifecycleManager); ok {
internal.LogError(m.Shutdown())
}
return nil
}