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Source file src/internal/trace/writer.go

Documentation: internal/trace

     1  package trace
     2  
     3  import "bytes"
     4  
     5  // Writer is a test trace writer.
     6  type Writer struct {
     7  	bytes.Buffer
     8  }
     9  
    10  func NewWriter() *Writer {
    11  	w := new(Writer)
    12  	w.Write([]byte("go 1.9 trace\x00\x00\x00\x00"))
    13  	return w
    14  }
    15  
    16  // Emit writes an event record to the trace.
    17  // See Event types for valid types and required arguments.
    18  func (w *Writer) Emit(typ byte, args ...uint64) {
    19  	nargs := byte(len(args)) - 1
    20  	if nargs > 3 {
    21  		nargs = 3
    22  	}
    23  	buf := []byte{typ | nargs<<6}
    24  	if nargs == 3 {
    25  		buf = append(buf, 0)
    26  	}
    27  	for _, a := range args {
    28  		buf = appendVarint(buf, a)
    29  	}
    30  	if nargs == 3 {
    31  		buf[1] = byte(len(buf) - 2)
    32  	}
    33  	n, err := w.Write(buf)
    34  	if n != len(buf) || err != nil {
    35  		panic("failed to write")
    36  	}
    37  }
    38  
    39  func appendVarint(buf []byte, v uint64) []byte {
    40  	for ; v >= 0x80; v >>= 7 {
    41  		buf = append(buf, 0x80|byte(v))
    42  	}
    43  	buf = append(buf, byte(v))
    44  	return buf
    45  }
    46  

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