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// 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 gcimporter
import (
"bufio"
"errors"
"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 = errors.New("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.
//
func FindExportData(r *bufio.Reader) (err error) {
// Read first line to make sure this is an object file.
line, err := r.ReadSlice('\n')
if err != nil {
return
}
if string(line) == "!<arch>\n" {
// Archive file. Scan to __.PKGDEF.
var name string
var size int
if name, size, err = readGopackHeader(r); err != nil {
return
}
// Optional leading __.GOSYMDEF or __.SYMDEF.
// Read and discard.
if name == "__.SYMDEF" || name == "__.GOSYMDEF" {
const block = 4096
tmp := make([]byte, block)
for size > 0 {
n := size
if n > block {
n = block
}
if _, err = io.ReadFull(r, tmp[:n]); err != nil {
return
}
size -= n
}
if name, size, err = readGopackHeader(r); err != nil {
return
}
}
// First real entry should be __.PKGDEF.
if name != "__.PKGDEF" {
err = errors.New("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 {
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 = errors.New("not a go object file")
return
}
// Skip over object header to export data.
// Begins after first line with $$.
for line[0] != '$' {
if line, err = r.ReadSlice('\n'); err != nil {
return
}
}
return
}
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