Source file src/pkg/internal/trace/writer.go

     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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