string.go

Documentation: debug/pe

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