go exportdata 源码
golang exportdata 代码
文件路径：/src/cmd/compile/internal/importer/exportdata.go
// Copyright 2011 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.
// This file implements FindExportData.
package importer
import (
"bufio"
"fmt"
"io"
"strconv"
"strings"
)
func readGopackHeader(r *bufio.Reader) (name string, size int, err error) {
// See $GOROOT/include/ar.h.
hdr := make([]byte, 16+12+6+6+8+10+2)
_, err = io.ReadFull(r, hdr)
if err != nil {
return
}
// leave for debugging
if false {
fmt.Printf("header: %s", hdr)
}
s := strings.TrimSpace(string(hdr[16+12+6+6+8:][:10]))
size, err = strconv.Atoi(s)
if err != nil || hdr[len(hdr)-2] != '`' || hdr[len(hdr)-1] != '\n' {
err = fmt.Errorf("invalid archive header")
return
}
name = strings.TrimSpace(string(hdr[:16]))
return
}
// FindExportData positions the reader r at the beginning of the
// export data section of an underlying GC-created object/archive
// file by reading from it. The reader must be positioned at the
// start of the file before calling this function. The hdr result
// is the string before the export data, either "$$" or "$$B".
//
// If size is non-negative, it's the number of bytes of export data
// still available to read from r.
func FindExportData(r *bufio.Reader) (hdr string, size int, err error) {
// Read first line to make sure this is an object file.
line, err := r.ReadSlice('\n')
if err != nil {
err = fmt.Errorf("can't find export data (%v)", err)
return
}
if string(line) == "!<arch>\n" {
// Archive file. Scan to __.PKGDEF.
var name string
if name, size, err = readGopackHeader(r); err != nil {
return
}
// First entry should be __.PKGDEF.
if name != "__.PKGDEF" {
err = fmt.Errorf("go archive is missing __.PKGDEF")
return
}
// Read first line of __.PKGDEF data, so that line
// is once again the first line of the input.
if line, err = r.ReadSlice('\n'); err != nil {
err = fmt.Errorf("can't find export data (%v)", err)
return
}
}
// Now at __.PKGDEF in archive or still at beginning of file.
// Either way, line should begin with "go object ".
if !strings.HasPrefix(string(line), "go object ") {
err = fmt.Errorf("not a Go object file")
return
}
size -= len(line)
// Skip over object header to export data.
// Begins after first line starting with $$.
for line[0] != '$' {
if line, err = r.ReadSlice('\n'); err != nil {
err = fmt.Errorf("can't find export data (%v)", err)
return
}
size -= len(line)
}
hdr = string(line)
return
}
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