Function run_local_python

catalog/code/:exec/python/backend.rs:380–430

Execute the wrapped script via the host's `python3` interpreter. Used only when DEPLOYMENT_MODE != cloud. No sandboxing, no isolation: this is intended for the developer running their own code on their own machine.

(code: &str)

/// Used only when DEPLOYMENT_MODE != cloud. No sandboxing, no isolation: this
/// is intended for the developer running their own code on their own machine.
async fn run_local_python(code: &str) -> Result<ExecOutcome, String> {
    let output = Command::new("python3")
        .arg("-c")
        .arg(code)
        .output()
        .await
        .map_err(|e| format!("Failed to spawn local python3: {}", e))?;

    let stdout_full = String::from_utf8_lossy(&output.stdout).into_owned();
    let stderr = String::from_utf8_lossy(&output.stderr).into_owned();

    if !output.status.success() {
        let msg = if stderr.is_empty() {
            format!("python3 exited with status {}", output.status)
        } else {
            stderr.trim_end().to_string()
        };
        return Ok(ExecOutcome::UserError(msg));
    }

    // Wrapper always prefixes the marker with "\n" and json.dumps produces a
    // single line, so we can anchor on "\nWEFT_RESULT_JSON=" regardless of
    // whether the user's last print had a trailing newline. Using the LAST
    // marker occurrence means a user who prints the literal "WEFT_RESULT_JSON="
    // themselves cannot hijack us. Content AFTER the marker's terminating "\n"
    // (e.g. atexit / CPython shutdown prints) is preserved in the stdout port.
    const MARKER_ANCHOR: &str = "\nWEFT_RESULT_JSON=";
    let pos = stdout_full.rfind(MARKER_ANCHOR).ok_or_else(|| {
        "Local python3 finished without emitting a result marker. The wrapper may have been altered.".to_string()
    })?;
    let after = &stdout_full[pos + MARKER_ANCHOR.len()..];
    let (json_str, tail_after_marker) = match after.find('\n') {
        Some(nl) => (&after[..nl], &after[nl + 1..]),
        None => (after, ""),
    };
    let parsed: Value = serde_json::from_str(json_str)
        .map_err(|e| format!("Could not parse local result JSON: {} (raw: {})", e, json_str))?;
    let ports = parsed.as_object()
        .ok_or_else(|| format!("Local result was not a JSON object: {}", parsed))?
        .clone();

    let mut user_stdout = stdout_full[..pos].to_string();
    if !tail_after_marker.is_empty() {
        if !user_stdout.is_empty() && !user_stdout.ends_with('\n') {
            user_stdout.push('\n');
        }
        user_stdout.push_str(tail_after_marker);
    }

    Ok(ExecOutcome::Ok { ports, stdout: user_stdout, stderr })
}

/// Extracted sandbox handle. Owned by the caller; the caller is responsible
/// for calling `delete_sandbox` once it is done.