1// Copyright 2016 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
5package pe
6
7import (
8	"bytes"
9	"encoding/binary"
10	"fmt"
11	"internal/saferio"
12	"io"
13)
14
15// cstring converts ASCII byte sequence b to string.
16// It stops once it finds 0 or reaches end of b.
17func cstring(b []byte) string {
18	i := bytes.IndexByte(b, 0)
19	if i == -1 {
20		i = len(b)
21	}
22	return string(b[:i])
23}
24
25// StringTable is a COFF string table.
26type StringTable []byte
27
28func readStringTable(fh *FileHeader, r io.ReadSeeker) (StringTable, error) {
29	// COFF string table is located right after COFF symbol table.
30	if fh.PointerToSymbolTable <= 0 {
31		return nil, nil
32	}
33	offset := fh.PointerToSymbolTable + COFFSymbolSize*fh.NumberOfSymbols
34	_, err := r.Seek(int64(offset), io.SeekStart)
35	if err != nil {
36		return nil, fmt.Errorf("fail to seek to string table: %v", err)
37	}
38	var l uint32
39	err = binary.Read(r, binary.LittleEndian, &l)
40	if err != nil {
41		return nil, fmt.Errorf("fail to read string table length: %v", err)
42	}
43	// string table length includes itself
44	if l <= 4 {
45		return nil, nil
46	}
47	l -= 4
48
49	buf, err := saferio.ReadData(r, uint64(l))
50	if err != nil {
51		return nil, fmt.Errorf("fail to read string table: %v", err)
52	}
53	return StringTable(buf), nil
54}
55
56// TODO(brainman): decide if start parameter should be int instead of uint32
57
58// String extracts string from COFF string table st at offset start.
59func (st StringTable) String(start uint32) (string, error) {
60	// start includes 4 bytes of string table length
61	if start < 4 {
62		return "", fmt.Errorf("offset %d is before the start of string table", start)
63	}
64	start -= 4
65	if int(start) > len(st) {
66		return "", fmt.Errorf("offset %d is beyond the end of string table", start)
67	}
68	return cstring(st[start:]), nil
69}
70