Report serde parse errors to stderr

[garious]

The executables (solana-mint, solana-genesis, solana-testnode, solana-client-demo) all panic if serde fails to parse the JSON on stdin. Instead, report the parser errors on stderr and exit cleanly.

[rlkelly]

I'm going to take a stab at this, I'll try to have a PR ready for Monday

[garious]

Thanks. Bonus points for an error message when you try to pipe a nonexistent file into stdin. In the C world, the function you'd use is called isatty(). I trip on that regularly when I mistakenly run the client demo from the src directory the mint.json is up in the top-level directory.

[garious]

@rleungx, did you test-drive that "bonus points" case? Easy to imagine that was implicitly handled by your patch. If not, I'll create a separate issue for that.

[rleungx]

Hi, @garious. I'm not sure about how isatty() works here. I've changed some code as below.

    let mint: Mint = if stdin_isatty() {
        serde_json::from_reader(stdin()).unwrap_or_else(|e| {
            eprintln!("failed to parse json: {}", e);
            exit(1);
        })
    } else {
        eprintln!("file may not exist");
        exit(1);
    };

Is this correct?

[garious]

"Look before you leap". Are you able to detect no file was passed to stdin before invoking from_reader?

[rleungx]

My bad. I've edited the comment. How it looks now？

[garious]

How about something like the following? That way if isatty isn't available on some platform (Windows?), we can compile it out without any additional restructuring.

    if !stdin_isatty() {
        eprintln!("file may not exist");
        exit(1);
    };
    let mint: Mint = serde_json::from_reader(stdin()).unwrap_or_else(|e| {
        eprintln!("failed to parse json: {}", e);
        exit(1);
    });

[rleungx]

I just found that we should use stdin_isatty() inside unwrap_or_else as I did before. Because it will always exit if we put stdin_isatty() before from_reader , right?

[garious]

There's 4 cases:

• No "cat mint.json |"
• mint.json isn't in the current directory
• mint.json has corrupt data
• mint.json is good

I'm just looking for it to exit early if we can detect either of the first two.

[rleungx]

Thanks for your explanation! Actually, what I mean is that stdin_isatty will all return true, except the first one. Any idea about how to make it work?

[garious]

That's perfect. So the thing that should change from my last code sample is just the error message. It should read something like, "nothing found on stdin, expected a JSON file".

For the second case, check if the stream is empty and report an error that says something like, "empty file on stdin, expected a JSON file".

And then the last two are good as-is.