Writing binary file in Inno Setup - inno-setup

Question

How does one write to a binary file in Inno Setup script? It's a configuration file I want to edit in the PrepareToInstall step. The problem is that I'm looking at the support functions:
TStream = class(TObject)
function Read(Buffer: String; Count: Longint): Longint;
function Write(Buffer: String; Count: Longint): Longint;
function Seek(Offset: Longint; Origin: Word): Longint;
procedure ReadBuffer(Buffer: String; Count: Longint);
procedure WriteBuffer(Buffer: String; Count: Longint);
function CopyFrom(Source: TStream; Count: Longint): Longint;
property Position: Longint; read write;
property Size: Longint; read write;
end;
And it seems even the most basic write function writes strings. Should I just do it in a batch script?

Answer 1

Consider the string in the TStream interface as a buffer of chars/bytes.
It's bit more complicated with Unicode version of Inno Setup, where the string is an array of 2-byte chars (comparing to legacy Ansi version, as there one byte equals one char – Though as of Inno Setup 6, Unicode is actually the only version available anyway).
See also Read bytes from file at desired position with Inno Setup.
To convert a hex string to the actual binary data, you can use the CryptStringToBinary Windows API function.
The following code works both in Ansi and Unicode version of Inno Setup.
#ifndef Unicode
const CharSize = 1;
#define AW "A"
#else
const CharSize = 2;
#define AW "W"
#endif
function CryptStringToBinary(
sz: string; cch: LongWord; flags: LongWord; binary: string; var size: LongWord;
skip: LongWord; flagsused: LongWord): Integer;
external 'CryptStringToBinary{#AW}#crypt32.dll stdcall';
const
CRYPT_STRING_HEX = $04;
procedure WriteHexToFile(Hex: string; FileName: string);
var
Stream: TFileStream;
Buffer: string;
Size: LongWord;
begin
Stream := TFileStream.Create(FileName, fmCreate);
try
SetLength(Buffer, (Length(Hex) div 2*CharSize) + CharSize - 1);
Size := Length(Hex) div 2;
if (CryptStringToBinary(
Hex, Length(Hex), CRYPT_STRING_HEX, Buffer, Size, 0, 0) = 0) or
(Size <> Length(Hex) div 2) then
begin
RaiseException('Error decoding hex string');
end;
Stream.WriteBuffer(Buffer, Size);
finally
Stream.Free;
end;
end;
Use it like:
procedure WriteHexToFileTest;
var
Hex: string;
begin
Hex :=
'000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f' +
'202122232425262728292a2b2c2d2e2f303132333435363738393a3b3c3d3e3f' +
'404142434445464748494a4b4c4d4e4f505152535455565758595a5b5c5d5e5f' +
'606162636465666768696a6b6c6d6e6f707172737475767778797a7b7c7d7e7f' +
'808182838485868788898a8b8c8d8e8f909192939495969798999a9b9c9d9e9f' +
'a0a1a2a3a4a5a6a7a8a9aaabacadaeafb0b1b2b3b4b5b6b7b8b9babbbcbdbebf' +
'c0c1c2c3c4c5c6c7c8c9cacbcccdcecfd0d1d2d3d4d5d6d7d8d9dadbdcdddedf' +
'e0e1e2e3e4e5e6e7e8e9eaebecedeeeff0f1f2f3f4f5f6f7f8f9fafbfcfdfeff';
WriteHexToFile(Hex, 'my_binary_file.dat');
end;