string.mx raw

   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  
   5  package pe
   6  
   7  import (
   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.
  17  func cstring(b []byte) []byte {
  18  	i := bytes.IndexByte(b, 0)
  19  	if i == -1 {
  20  		i = len(b)
  21  	}
  22  	return []byte(b[:i])
  23  }
  24  
  25  // StringTable is a COFF string table.
  26  type StringTable []byte
  27  
  28  func 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.
  59  func (st StringTable) String(start uint32) ([]byte, 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