InnoSetup's equivalent of "overwrite destination if it hasn't changed since the last install"?

Question

After scouring the web, the closest thing I can find to "overwrite all the files that the user didn't change" for InnoSetup is this link here:

InnoSetup: don't uninstall changed files

However, it's incomplete and I'm no Pascal expert. I don't see how it saves the tStringList (and it didn't when I tested it).

My application installs a lot of XML files from a dozen sources into the public user's documents folder. (And, yes, my sources use the ** subpath operator.) The user may change some of the files. The application may change some of them. I don't want to undo any user work, but when I upgrade I do want to replace any XML files that the user hasn't touched. How can I do this with InnoSetup? (And similarly, it seems that when I uninstall I should remove all files that the user/app didn't change.)

I just would not do it that way. When designing an install program, always keep in mind the option of changing the app to make installation cleaner. — David Heffernan
I just came across this link: innosetup.uservoice.com/forums/… — Brannon
Yes, our newer version of the software does away with this silliness. Unfortunately, I still have three years of supporting the current version. — Brannon
Currently, I can think just about the comparetimestamp flag (but you would have to rely on the target system clock and you would have to use a date time deep in the past). However, from [Code] section might be possible to store a list of those installed files with their hashes and in upgrade setup compare this file hash list with new file hashes before they would be overwritten. — TLama

Miral Miral · Accepted Answer · 2013-10-31T08:53:02

There probably isn't really any good way of distinguishing user edits from application edits, unless you know exactly what sort of changes the application might make and that users would not make similar changes, and if you're willing and able to write [Code] to detect the difference by reading the file contents.

You can, however, make it replace specific versions of older files, provided that you still have copies of these files yourself. One example of how you might do so (this is just written on the spot; I haven't tested it):

[Files]
Source: SomeFile.xml; ...; Check: IsOverwritable('123456FEDCBA,ABD48291')

[Code]
function IsOverwritable(HashText: String): Boolean;
var
  Filename, Hash: String;
  Hashes: TStringList;
begin
  Filename := ExpandConstant(CurrentFileName);
  if not FileExists(Filename) then begin
    Result := True;
  end else begin
    Hash := GetMD5OfFile(Filename);
    Hashes := TStringList.Create();
    Hashes.CommaText := HashText;
    Result := Hashes.IndexOf(Hash) >= 0;
    Hashes.Free();
  end;
end;

After adding this, you should just need to replace the parameter used in the Check call with the comma-separated list of MD5 values (gathered eg. using md5sum) of all the possible versions of the file that were distributed by previous versions of the application that you wish to overwrite with your replacement version.

If the file does not exist, it will be installed. If it does exist, and its hash value matches one of the ones specified, it will be overwritten. Otherwise it will be left alone.

Note that there is a small chance that a file will be mistakenly overwritten due to having the same MD5 hash despite having different contents, as hashing can have collisions. However the chances of this happening by accident are slim and you can usually get away with ignoring it. (Another option is to use the SHA-1 hash instead of the MD5 hash; as this is longer there is a smaller chance of collision.)

InnoSetup's equivalent of "overwrite destination if it hasn't changed since the last install"?

1 Answers