Runtime environment variable changes ignored on Windows

[pitrou]

Confirm by changing [ ] to [x] below to ensure that it's a bug:

• [x] I've gone though Developer Guide and API reference
• [x] I've searched for previous similar issues and didn't find any solution

Describe the bug It seems that, under Windows, runtime changes (inside the running process) to environment variables (such as AWS_DEFAULT_REGION, AWS_EC2_METADATA_DISABLED, etc.) are ignored.

I suspect the reason is that the SDK uses the CRT's _dupenv_s function in its implementation of Aws::Environment::GetEnv. The CRT uses its own copy of the environment that is made at process startup. Any further changes to environment variables are not seen.

The fix is to use the Windows API GetEnvironmentVariable.

You can see a similar issue here: https://github.com/AcademySoftwareFoundation/OpenColorIO/issues/756

SDK version number 1.8.54.

Platform/OS/Hardware/Device Windows.

[KaibaLopez]

Hi @pitrou , ok so I've been trying to test this and for me it works, but it is kind of confusing how it actually happens so here let me show you how I tested it and so if I missed out something let me know.

#include <windows.h>
#include <aws/core/Aws.h>
#include <aws/core/platform/Environment.h>
#include <aws/s3/S3Client.h>

#include <iostream>
#include <fstream>
#include <string>
#include <stdlib.h>
Aws::SDKOptions options;
//test with the windows api getenviroment
const char * getEnv(Aws::String varName){
    const DWORD buffSize = 65535;
    static char buffer[buffSize];
    if (GetEnvironmentVariableA(varName.c_str(), buffer, buffSize))
    {
        return buffer;
    }
    else
    {
        return 0;
    }
}
//set enviroment variable pragmatically
int setenv(const char *name, const char *value, int overwrite)
{
    int errcode = 0;
    if(!overwrite) {
        size_t envsize = 0;
        errcode = getenv_s(&envsize, NULL, 0, name);
        if(errcode || envsize) return errcode;
    }
    return _putenv_s(name, value);
}
int main()
{
    //get enviroment variable before any changes.
    std::cout << getEnv("AWS_DEFAULT_REGION") <<std::endl;

    options.loggingOptions.logLevel = Aws::Utils::Logging::LogLevel::Trace;

    Aws::InitAPI(options);
    {
        //overwrite env variables
        setenv("AWS_DEFAULT_REGION","fake-region-1",1);
        setenv("AWS_EC2_METADATA_DISABLED","false",1);
        Aws::Client::ClientConfiguration clientConfig;
        std::cout<<clientConfig.region << std::endl; // here it prints the changed enviroment variable
        std::cout << getEnv("AWS_DEFAULT_REGION") <<std::endl; // same result with the windows api call
    }
    Aws::ShutdownAPI(options);
}

Did I misunderstand something? I see no difference with the windows api or the sdk's getenviroment.

[pitrou]

Your setenv function is using _putenv_s, so it modifies the CRT's copy of the environment. In our use case, we're using the Windows API SetEnvironmentVariable.

Here is another similar issue reported to another project: https://github.com/ocaml/ocaml/pull/1479

And here is a relevant excerpt (though not very clear) from the Microsoft docs: https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/getenv-wgetenv?view=vs-2019

getenv and _putenv use the copy of the environment pointed to by the global variable _environ to access the environment. getenv operates only on the data structures accessible to the run-time library and not on the environment "segment" created for the process by the operating system.

[jmklix]

@pitrou are you still seeing this bug with environment variables?

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