encodefile.go

Documentation: internal/coverage/encodemeta

     1  // Copyright 2021 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 encodemeta
     6  
     7  import (
     8  	"bufio"
     9  	"crypto/md5"
    10  	"encoding/binary"
    11  	"fmt"
    12  	"internal/coverage"
    13  	"internal/coverage/stringtab"
    14  	"io"
    15  	"os"
    16  	"unsafe"
    17  )
    18  
    19  // This package contains APIs and helpers for writing out a meta-data
    20  // file (composed of a file header, offsets/lengths, and then a series of
    21  // meta-data blobs emitted by the compiler, one per Go package).
    22  
    23  type CoverageMetaFileWriter struct {
    24  	stab   stringtab.Writer
    25  	mfname string
    26  	w      *bufio.Writer
    27  	tmp    []byte
    28  	debug  bool
    29  }
    30  
    31  func NewCoverageMetaFileWriter(mfname string, w io.Writer) *CoverageMetaFileWriter {
    32  	r := &CoverageMetaFileWriter{
    33  		mfname: mfname,
    34  		w:      bufio.NewWriter(w),
    35  		tmp:    make([]byte, 64),
    36  	}
    37  	r.stab.InitWriter()
    38  	r.stab.Lookup("")
    39  	return r
    40  }
    41  
    42  func (m *CoverageMetaFileWriter) Write(finalHash [16]byte, blobs [][]byte, mode coverage.CounterMode, granularity coverage.CounterGranularity) error {
    43  	mhsz := uint64(unsafe.Sizeof(coverage.MetaFileHeader{}))
    44  	stSize := m.stab.Size()
    45  	stOffset := mhsz + uint64(16*len(blobs))
    46  	preambleLength := stOffset + uint64(stSize)
    47  
    48  	if m.debug {
    49  		fmt.Fprintf(os.Stderr, "=+= sizeof(MetaFileHeader)=%d\n", mhsz)
    50  		fmt.Fprintf(os.Stderr, "=+= preambleLength=%d stSize=%d\n", preambleLength, stSize)
    51  	}
    52  
    53  	// Compute total size
    54  	tlen := preambleLength
    55  	for i := 0; i < len(blobs); i++ {
    56  		tlen += uint64(len(blobs[i]))
    57  	}
    58  
    59  	// Emit header
    60  	mh := coverage.MetaFileHeader{
    61  		Magic:        coverage.CovMetaMagic,
    62  		Version:      coverage.MetaFileVersion,
    63  		TotalLength:  tlen,
    64  		Entries:      uint64(len(blobs)),
    65  		MetaFileHash: finalHash,
    66  		StrTabOffset: uint32(stOffset),
    67  		StrTabLength: stSize,
    68  		CMode:        mode,
    69  		CGranularity: granularity,
    70  	}
    71  	var err error
    72  	if err = binary.Write(m.w, binary.LittleEndian, mh); err != nil {
    73  		return fmt.Errorf("error writing %s: %v", m.mfname, err)
    74  	}
    75  
    76  	if m.debug {
    77  		fmt.Fprintf(os.Stderr, "=+= len(blobs) is %d\n", mh.Entries)
    78  	}
    79  
    80  	// Emit package offsets section followed by package lengths section.
    81  	off := preambleLength
    82  	off2 := mhsz
    83  	buf := make([]byte, 8)
    84  	for _, blob := range blobs {
    85  		binary.LittleEndian.PutUint64(buf, off)
    86  		if _, err = m.w.Write(buf); err != nil {
    87  			return fmt.Errorf("error writing %s: %v", m.mfname, err)
    88  		}
    89  		if m.debug {
    90  			fmt.Fprintf(os.Stderr, "=+= pkg offset %d 0x%x\n", off, off)
    91  		}
    92  		off += uint64(len(blob))
    93  		off2 += 8
    94  	}
    95  	for _, blob := range blobs {
    96  		bl := uint64(len(blob))
    97  		binary.LittleEndian.PutUint64(buf, bl)
    98  		if _, err = m.w.Write(buf); err != nil {
    99  			return fmt.Errorf("error writing %s: %v", m.mfname, err)
   100  		}
   101  		if m.debug {
   102  			fmt.Fprintf(os.Stderr, "=+= pkg len %d 0x%x\n", bl, bl)
   103  		}
   104  		off2 += 8
   105  	}
   106  
   107  	// Emit string table
   108  	if err = m.stab.Write(m.w); err != nil {
   109  		return err
   110  	}
   111  
   112  	// Now emit blobs themselves.
   113  	for k, blob := range blobs {
   114  		if m.debug {
   115  			fmt.Fprintf(os.Stderr, "=+= writing blob %d len %d at off=%d hash %s\n", k, len(blob), off2, fmt.Sprintf("%x", md5.Sum(blob)))
   116  		}
   117  		if _, err = m.w.Write(blob); err != nil {
   118  			return fmt.Errorf("error writing %s: %v", m.mfname, err)
   119  		}
   120  		if m.debug {
   121  			fmt.Fprintf(os.Stderr, "=+= wrote package payload of %d bytes\n",
   122  				len(blob))
   123  		}
   124  		off2 += uint64(len(blob))
   125  	}
   126  
   127  	// Flush writer, and we're done.
   128  	if err = m.w.Flush(); err != nil {
   129  		return fmt.Errorf("error writing %s: %v", m.mfname, err)
   130  	}
   131  	return nil
   132  }
   133
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