1 files changed, 215 insertions, 0 deletions
diff --git a/src/internal/coverage/encodemeta/encode.go b/src/internal/coverage/encodemeta/encode.go
new file mode 100644
index 0000000..d211c7c
--- /dev/null
+++ b/src/internal/coverage/encodemeta/encode.go
@@ -0,0 +1,215 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package encodemeta
+
+// This package contains APIs and helpers for encoding the meta-data
+// "blob" for a single Go package, created when coverage
+// instrumentation is turned on.
+
+import (
+	"bytes"
+	"crypto/md5"
+	"encoding/binary"
+	"fmt"
+	"hash"
+	"internal/coverage"
+	"internal/coverage/stringtab"
+	"internal/coverage/uleb128"
+	"io"
+	"os"
+)
+
+type CoverageMetaDataBuilder struct {
+	stab    stringtab.Writer
+	funcs   []funcDesc
+	tmp     []byte // temp work slice
+	h       hash.Hash
+	pkgpath uint32
+	pkgname uint32
+	modpath uint32
+	debug   bool
+	werr    error
+}
+
+func NewCoverageMetaDataBuilder(pkgpath string, pkgname string, modulepath string) (*CoverageMetaDataBuilder, error) {
+	if pkgpath == "" {
+		return nil, fmt.Errorf("invalid empty package path")
+	}
+	x := &CoverageMetaDataBuilder{
+		tmp: make([]byte, 0, 256),
+		h:   md5.New(),
+	}
+	x.stab.InitWriter()
+	x.stab.Lookup("")
+	x.pkgpath = x.stab.Lookup(pkgpath)
+	x.pkgname = x.stab.Lookup(pkgname)
+	x.modpath = x.stab.Lookup(modulepath)
+	io.WriteString(x.h, pkgpath)
+	io.WriteString(x.h, pkgname)
+	io.WriteString(x.h, modulepath)
+	return x, nil
+}
+
+func h32(x uint32, h hash.Hash, tmp []byte) {
+	tmp = tmp[:0]
+	tmp = append(tmp, []byte{0, 0, 0, 0}...)
+	binary.LittleEndian.PutUint32(tmp, x)
+	h.Write(tmp)
+}
+
+type funcDesc struct {
+	encoded []byte
+}
+
+// AddFunc registers a new function with the meta data builder.
+func (b *CoverageMetaDataBuilder) AddFunc(f coverage.FuncDesc) uint {
+	hashFuncDesc(b.h, &f, b.tmp)
+	fd := funcDesc{}
+	b.tmp = b.tmp[:0]
+	b.tmp = uleb128.AppendUleb128(b.tmp, uint(len(f.Units)))
+	b.tmp = uleb128.AppendUleb128(b.tmp, uint(b.stab.Lookup(f.Funcname)))
+	b.tmp = uleb128.AppendUleb128(b.tmp, uint(b.stab.Lookup(f.Srcfile)))
+	for _, u := range f.Units {
+		b.tmp = uleb128.AppendUleb128(b.tmp, uint(u.StLine))
+		b.tmp = uleb128.AppendUleb128(b.tmp, uint(u.StCol))
+		b.tmp = uleb128.AppendUleb128(b.tmp, uint(u.EnLine))
+		b.tmp = uleb128.AppendUleb128(b.tmp, uint(u.EnCol))
+		b.tmp = uleb128.AppendUleb128(b.tmp, uint(u.NxStmts))
+	}
+	lit := uint(0)
+	if f.Lit {
+		lit = 1
+	}
+	b.tmp = uleb128.AppendUleb128(b.tmp, lit)
+	fd.encoded = bytes.Clone(b.tmp)
+	rv := uint(len(b.funcs))
+	b.funcs = append(b.funcs, fd)
+	return rv
+}
+
+func (b *CoverageMetaDataBuilder) emitFuncOffsets(w io.WriteSeeker, off int64) int64 {
+	nFuncs := len(b.funcs)
+	var foff int64 = coverage.CovMetaHeaderSize + int64(b.stab.Size()) + int64(nFuncs)*4
+	for idx := 0; idx < nFuncs; idx++ {
+		b.wrUint32(w, uint32(foff))
+		foff += int64(len(b.funcs[idx].encoded))
+	}
+	return off + (int64(len(b.funcs)) * 4)
+}
+
+func (b *CoverageMetaDataBuilder) emitFunc(w io.WriteSeeker, off int64, f funcDesc) (int64, error) {
+	ew := len(f.encoded)
+	if nw, err := w.Write(f.encoded); err != nil {
+		return 0, err
+	} else if ew != nw {
+		return 0, fmt.Errorf("short write emitting coverage meta-data")
+	}
+	return off + int64(ew), nil
+}
+
+func (b *CoverageMetaDataBuilder) reportWriteError(err error) {
+	if b.werr != nil {
+		b.werr = err
+	}
+}
+
+func (b *CoverageMetaDataBuilder) wrUint32(w io.WriteSeeker, v uint32) {
+	b.tmp = b.tmp[:0]
+	b.tmp = append(b.tmp, []byte{0, 0, 0, 0}...)
+	binary.LittleEndian.PutUint32(b.tmp, v)
+	if nw, err := w.Write(b.tmp); err != nil {
+		b.reportWriteError(err)
+	} else if nw != 4 {
+		b.reportWriteError(fmt.Errorf("short write"))
+	}
+}
+
+// Emit writes the meta-data accumulated so far in this builder to 'w'.
+// Returns a hash of the meta-data payload and an error.
+func (b *CoverageMetaDataBuilder) Emit(w io.WriteSeeker) ([16]byte, error) {
+	// Emit header.  Length will initially be zero, we'll
+	// back-patch it later.
+	var digest [16]byte
+	copy(digest[:], b.h.Sum(nil))
+	mh := coverage.MetaSymbolHeader{
+		// hash and length initially zero, will be back-patched
+		PkgPath:    uint32(b.pkgpath),
+		PkgName:    uint32(b.pkgname),
+		ModulePath: uint32(b.modpath),
+		NumFiles:   uint32(b.stab.Nentries()),
+		NumFuncs:   uint32(len(b.funcs)),
+		MetaHash:   digest,
+	}
+	if b.debug {
+		fmt.Fprintf(os.Stderr, "=-= writing header: %+v\n", mh)
+	}
+	if err := binary.Write(w, binary.LittleEndian, mh); err != nil {
+		return digest, fmt.Errorf("error writing meta-file header: %v", err)
+	}
+	off := int64(coverage.CovMetaHeaderSize)
+
+	// Write function offsets section
+	off = b.emitFuncOffsets(w, off)
+
+	// Check for any errors up to this point.
+	if b.werr != nil {
+		return digest, b.werr
+	}
+
+	// Write string table.
+	if err := b.stab.Write(w); err != nil {
+		return digest, err
+	}
+	off += int64(b.stab.Size())
+
+	// Write functions
+	for _, f := range b.funcs {
+		var err error
+		off, err = b.emitFunc(w, off, f)
+		if err != nil {
+			return digest, err
+		}
+	}
+
+	// Back-patch the length.
+	totalLength := uint32(off)
+	if _, err := w.Seek(0, io.SeekStart); err != nil {
+		return digest, err
+	}
+	b.wrUint32(w, totalLength)
+	if b.werr != nil {
+		return digest, b.werr
+	}
+	return digest, nil
+}
+
+// HashFuncDesc computes an md5 sum of a coverage.FuncDesc and returns
+// a digest for it.
+func HashFuncDesc(f *coverage.FuncDesc) [16]byte {
+	h := md5.New()
+	tmp := make([]byte, 0, 32)
+	hashFuncDesc(h, f, tmp)
+	var r [16]byte
+	copy(r[:], h.Sum(nil))
+	return r
+}
+
+// hashFuncDesc incorporates a given function 'f' into the hash 'h'.
+func hashFuncDesc(h hash.Hash, f *coverage.FuncDesc, tmp []byte) {
+	io.WriteString(h, f.Funcname)
+	io.WriteString(h, f.Srcfile)
+	for _, u := range f.Units {
+		h32(u.StLine, h, tmp)
+		h32(u.StCol, h, tmp)
+		h32(u.EnLine, h, tmp)
+		h32(u.EnCol, h, tmp)
+		h32(u.NxStmts, h, tmp)
+	}
+	lit := uint32(0)
+	if f.Lit {
+		lit = 1
+	}
+	h32(lit, h, tmp)
+}