Fix main() panicking on os.Args[1] when invoked with no arguments (closes #29)

[dolph]

Closes #29.

Summary

./ussher (no arguments) used to panic with runtime error: index out of range [1] with length 1 because main() accessed os.Args[1] on its very first line — the --version short-circuit — before the args-count check ten lines further down. The intended usage: ussher <username> message was unreachable for the no-args case.

Fix

Extract validateArgs(args []string) (string, error). It enforces len(args) == 2 and returns either the single arg (the username, or --version) or a typed usage error. main() calls it as its very first statement and log.Fatals on error.

-    if os.Args[1] == "--version" {
+    arg, err := validateArgs(os.Args)
+    if err != nil {
+        log.Fatal(err)
+    }
+    if arg == "--version" {
        PrintVersion()
        return
     }
     ...
-    if len(os.Args) != 2 {
-        log.Fatal("usage: ussher <username>")
-    }
-    username := os.Args[1]
+    username := arg

The downstream len(os.Args) != 2 check is now dead code and removed. The --version short-circuit, the security gates, initLog, and isValidUser sequencing are unchanged. This extraction is also a useful seam for the broader main() refactor proposed in #13 — that issue's parseArgs would build on this validateArgs.

Tests

New ussher_test.go with TestValidateArgs covering six cases:

• bare program name (no args) → error
• empty args slice → error
• single arg as username → returns username
• single arg as --version → returns --version
• too many args (3 with username) → error
• too many args (3 with --version) → error

Coverage 42.1% → 42.7%; tests pass under -race.

End-to-end repro

$ ./ussher
2026/04/27 20:11:26 usage: ussher <username>
$ echo $?
1

(Pre-fix: stack trace + exit 2.)

Releasing-this-thought

v1.1.0 is queued in CHANGELOG.md but not yet tagged. The new Fixed bullet lives under [Unreleased] for safety — if you want this fix in v1.1.0, move the bullet into [1.1.0] before pushing the tag; otherwise it ships in 1.1.1 / 1.2.0. Either is fine.

Test plan

• ./build.sh green; coverage 42.7%.
• go test -race ./... green.
• ./ussher (no args) prints usage: ussher <username> and exits 1 (no panic).
• ./ussher --version still prints version info.
• ./ussher root (or any valid user) still proceeds normally.
• ./ussher alice extra still rejected as wrong-arg-count.
• CI shellcheck + build jobs both green on the PR.

https://claude.ai/code/session_013HnepY8MhhxrJJjE5ysW47

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