Read installation path from JSON file in Inno Setup - inno-setup

Question

I want to create a script for Inno Setup where the install path would be taken from a file in defined directory - no registry. I suppose it would require writing specific code for it, where would be defined some variable which will contain the value after reading the file. The path and name of the file is always the same for any user so the only value that changes is the install path.
Complete structure, where InstallLocation is the variable:
{
"FormatVersion": 0,
"bIsIncompleteInstall": false,
"AppVersionString": "1.0.1",
...
"InstallLocation": "h:\\Program Files\\Epic Games\\Limbo",
...
}
Any ideas for ideal code that would do this?
Thank you

Answer 1

Implement a scripted constant to provide the value to DefaultDirName directive.
You can use JsonParser library to parse the JSON config file.
[Setup]
DefaultDirName={code:GetInstallLocation}
[Code]
#include "JsonParser.pas"
// Here go the other functions the below code needs.
// See the comments at the end of the post.
const
CP_UTF8 = 65001;
var
InstallLocation: string;
<event('InitializeSetup')>
function InitializeSetupParseConfig(): Boolean;
var
Json: string;
ConfigPath: string;
JsonParser: TJsonParser;
JsonRoot: TJsonObject;
S: TJsonString;
begin
Result := True;
ConfigPath := 'C:\path\to\config.json';
Log(Format('Reading "%s"', [ConfigPath]));
if not LoadStringFromFileInCP(ConfigPath, Json, CP_UTF8) then
begin
MsgBox(Format('Error reading "%s"', [ConfigPath]), mbError, MB_OK);
Result := False;
end
else
if not ParseJsonAndLogErrors(JsonParser, Json) then
begin
MsgBox(Format('Error parsing "%s"', [ConfigPath]), mbError, MB_OK);
Result := False;
end
else
begin
JsonRoot := GetJsonRoot(JsonParser.Output);
if not FindJsonString(JsonParser.Output, JsonRoot, 'InstallLocation', S) then
begin
MsgBox(Format('Cannot find InstallLocation in "%s"', [ConfigPath]),
mbError, MB_OK);
Result := False;
end
else
begin
InstallLocation := S;
Log(Format('Found InstallLocation = "%s"', [InstallLocation]));
end;
ClearJsonParser(JsonParser);
end;
end;
function GetInstallLocation(Param: string): string;
begin
Result := InstallLocation;
end;
The code uses functions from:
How to parse a JSON string in Inno Setup? (ParseJsonAndLogErrors, ClearJsonParser, GetJsonRoot, FindJsonValue and FindJsonString);
Inno Setup - Convert array of string to Unicode and back to ANSI (MultiByteToWideChar and LoadStringFromFileInCP).