HOME envvar should not be required for credentials path expansion

[bbstilson]

Python (via boto3) uses os.path.expanduser (I believe here) while Rust uses the HOME envvar (here). Not all environments have the HOME envvar (e.g., Bazel runtimes). Ideally the behaviors between Python and Rust AWS libraries would be as similar as possible.

[aajtodd]

Thanks for the issue. Can you provide details on what is failing and where? What are you trying to do?

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Python expanduser is documented as:

On Unix, an initial ~ is replaced by the environment variable HOME if it is set; otherwise the current user’s home directory is looked up in the password directory through the built-in module pwd. An initial ~user is looked up directly in the password directory.

On Windows, USERPROFILE will be used if set, otherwise a combination of HOMEPATH and HOMEDRIVE will be used. An initial ~user is handled by checking that the last directory component of the current user’s home directory matches USERNAME, and replacing it if so.

If the expansion fails or if the path does not begin with a tilde, the path is returned unchanged.

It seems the missing functionality you're looking for is the lookup of the current user in the password directory for unix which is indeed not implemented right now.

[bbstilson]

I ran into this issue when I was trying to run a Rust binary from a Python subprocess within a Bazel runtime (I hate my sanity). The Rust binary couldn't connect to AWS due to credentials being unloadable (confirmed via debug logging on the aws_config library (RUST_LOG=info,aws_config=debug) and by failing to do something simple like head an object or list buckets). In Python, however, Boto3 worked fine from the same Bazel runtime. I was able to work around this issue by inheriting the HOME envvar in my bazel target (env_inherit = ["HOME"]). This lead me on the hunt to figure out how these different libraries resolve the ~/.aws/credentials path.

[joshtriplett]

I believe that calling std::env::home_dir (in Rust 1.85 and newer) will do exactly what you want.