reader.mx raw

   1  // Copyright 2023 The Go Authors. All rights reserved.
   2  // Use of this source code is governed by a BSD-style
   3  // license that can be found in the LICENSE file.
   4  
   5  package raw
   6  
   7  import (
   8  	"bufio"
   9  	"encoding/binary"
  10  	"fmt"
  11  	"io"
  12  
  13  	"internal/trace/tracev2"
  14  	"internal/trace/version"
  15  )
  16  
  17  // Reader parses trace bytes with only very basic validation
  18  // into an event stream.
  19  type Reader struct {
  20  	r     *bufio.Reader
  21  	v     version.Version
  22  	specs []tracev2.EventSpec
  23  }
  24  
  25  // NewReader creates a new reader for the trace wire format.
  26  func NewReader(r io.Reader) (*Reader, error) {
  27  	br := bufio.NewReader(r)
  28  	v, err := version.ReadHeader(br)
  29  	if err != nil {
  30  		return nil, err
  31  	}
  32  	return &Reader{r: br, v: v, specs: v.Specs()}, nil
  33  }
  34  
  35  // Version returns the version of the trace that we're reading.
  36  func (r *Reader) Version() version.Version {
  37  	return r.v
  38  }
  39  
  40  // ReadEvent reads and returns the next trace event in the byte stream.
  41  func (r *Reader) ReadEvent() (Event, error) {
  42  	evb, err := r.r.ReadByte()
  43  	if err == io.EOF {
  44  		return Event{}, io.EOF
  45  	}
  46  	if err != nil {
  47  		return Event{}, err
  48  	}
  49  	if int(evb) >= len(r.specs) || evb == 0 {
  50  		return Event{}, fmt.Errorf("invalid event type: %d", evb)
  51  	}
  52  	ev := tracev2.EventType(evb)
  53  	spec := r.specs[ev]
  54  	args, err := r.readArgs(len(spec.Args))
  55  	if err != nil {
  56  		return Event{}, err
  57  	}
  58  	if spec.IsStack {
  59  		len := int(args[1])
  60  		for i := 0; i < len; i++ {
  61  			// Each stack frame has four args: pc, func ID, file ID, line number.
  62  			frame, err := r.readArgs(4)
  63  			if err != nil {
  64  				return Event{}, err
  65  			}
  66  			args = append(args, frame...)
  67  		}
  68  	}
  69  	var data []byte
  70  	if spec.HasData {
  71  		data, err = r.readData()
  72  		if err != nil {
  73  			return Event{}, err
  74  		}
  75  	}
  76  	return Event{
  77  		Version: r.v,
  78  		Ev:      ev,
  79  		Args:    args,
  80  		Data:    data,
  81  	}, nil
  82  }
  83  
  84  func (r *Reader) readArgs(n int) ([]uint64, error) {
  85  	var args []uint64
  86  	for i := 0; i < n; i++ {
  87  		val, err := binary.ReadUvarint(r.r)
  88  		if err != nil {
  89  			return nil, err
  90  		}
  91  		args = append(args, val)
  92  	}
  93  	return args, nil
  94  }
  95  
  96  func (r *Reader) readData() ([]byte, error) {
  97  	len, err := binary.ReadUvarint(r.r)
  98  	if err != nil {
  99  		return nil, err
 100  	}
 101  	var data []byte
 102  	for i := 0; i < int(len); i++ {
 103  		b, err := r.r.ReadByte()
 104  		if err != nil {
 105  			return nil, err
 106  		}
 107  		data = append(data, b)
 108  	}
 109  	return data, nil
 110  }
 111