1// Copyright 2011 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// This file is a copy of $GOROOT/src/go/internal/gcimporter/exportdata.go.
6
7// This file implements FindExportData.
8
9package gcimporter
10
11import (
12	"bufio"
13	"fmt"
14	"io"
15	"strconv"
16	"strings"
17)
18
19func readGopackHeader(r *bufio.Reader) (name string, size int, err error) {
20	// See $GOROOT/include/ar.h.
21	hdr := make([]byte, 16+12+6+6+8+10+2)
22	_, err = io.ReadFull(r, hdr)
23	if err != nil {
24		return
25	}
26	// leave for debugging
27	if false {
28		fmt.Printf("header: %s", hdr)
29	}
30	s := strings.TrimSpace(string(hdr[16+12+6+6+8:][:10]))
31	size, err = strconv.Atoi(s)
32	if err != nil || hdr[len(hdr)-2] != '`' || hdr[len(hdr)-1] != '\n' {
33		err = fmt.Errorf("invalid archive header")
34		return
35	}
36	name = strings.TrimSpace(string(hdr[:16]))
37	return
38}
39
40// FindExportData positions the reader r at the beginning of the
41// export data section of an underlying GC-created object/archive
42// file by reading from it. The reader must be positioned at the
43// start of the file before calling this function. The hdr result
44// is the string before the export data, either "$$" or "$$B".
45//
46func FindExportData(r *bufio.Reader) (hdr string, err error) {
47	// Read first line to make sure this is an object file.
48	line, err := r.ReadSlice('\n')
49	if err != nil {
50		err = fmt.Errorf("can't find export data (%v)", err)
51		return
52	}
53
54	if string(line) == "!<arch>\n" {
55		// Archive file. Scan to __.PKGDEF.
56		var name string
57		if name, _, err = readGopackHeader(r); err != nil {
58			return
59		}
60
61		// First entry should be __.PKGDEF.
62		if name != "__.PKGDEF" {
63			err = fmt.Errorf("go archive is missing __.PKGDEF")
64			return
65		}
66
67		// Read first line of __.PKGDEF data, so that line
68		// is once again the first line of the input.
69		if line, err = r.ReadSlice('\n'); err != nil {
70			err = fmt.Errorf("can't find export data (%v)", err)
71			return
72		}
73	}
74
75	// Now at __.PKGDEF in archive or still at beginning of file.
76	// Either way, line should begin with "go object ".
77	if !strings.HasPrefix(string(line), "go object ") {
78		err = fmt.Errorf("not a Go object file")
79		return
80	}
81
82	// Skip over object header to export data.
83	// Begins after first line starting with $$.
84	for line[0] != '$' {
85		if line, err = r.ReadSlice('\n'); err != nil {
86			err = fmt.Errorf("can't find export data (%v)", err)
87			return
88		}
89	}
90	hdr = string(line)
91
92	return
93}
94