Fix crash in getShortCallsign on all-slash callsigns (ArrayIndexOutOfBoundsException)

[patrickrb]

Root cause

GeneralVariables.getShortCallsign(String) splits a compound callsign on /
and returns the longest segment:

String[] temp = callsign.split("/");
...
return temp[max_index];   // max_index defaults to 0

For an all-slash input ("/", "//", "///") Java's String.split
strips trailing empty tokens and returns a zero-length array, so
temp[0] throws ArrayIndexOutOfBoundsException. String.contains("/") is
true for these inputs, so the guarded branch is entered and the crash fires.

Impact

getShortCallsign is only ever called on the operator's own callsign, but
that value is loaded from persisted config and used on real threads:

• DatabaseOpr ReadConfig.doInBackground (startup config load, background
  thread) — getShortCallsign(myCallsign) when the stored callsign contains
  /. An uncaught exception here crashes the app on startup, and because
  the value is persisted the crash recurs on every launch.
• GeneralVariables.checkIsMyCallsign(...) calls getShortCallsign(myCallsign)
  and runs on the decode thread for matching, so a stray-slash callsign
  also crashes each decode cycle.

A single stray / typed into (or migrated into) the callsign field turns into
a hard, recurring crash rather than being tolerated.

Fix

Fall back to the original string when the split yields no usable segment,
instead of indexing temp[0]:

String[] temp = callsign.split("/");
if (temp.length == 0) {
    return callsign;
}

Behavior is unchanged for every well-formed input — plain callsigns
(W1AW), prefix/suffix compounds (DL/W1AW, W1AW/P, W1AW/QRP), and
leading-slash forms (/W1AW) all return exactly what they did before.

Testing

• New GeneralVariablesShortCallsignTest (JUnit4 + Truth, Robolectric because
  GeneralVariables carries Android LiveData statics) covers plain,
  compound, leading-slash, and the all-slash regression cases. The all-slash
  case fails with ArrayIndexOutOfBoundsException before the fix and passes
  after.
• ./gradlew :app:testDebugUnitTest — full suite green.
• ./gradlew :app:assembleDebug — APK builds.

Risk

Minimal. One localized guard on a pathological input; no protocol, DSP, or
threading behavior changes, and all normal callsign shapes are unaffected.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 23.57%. Comparing base (66575b9) to head (f2e4495).
⚠️ Report is 4 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff            @@
##                dev     #509   +/-   ##
=========================================
  Coverage     23.57%   23.57%           
  Complexity      162      162           
=========================================
  Files           168      168           
  Lines         21628    21628           
  Branches       3154     3154           
=========================================
  Hits           5098     5098           
  Misses        16337    16337           
  Partials        193      193           

Flag	Coverage Δ
android	13.26% <ø> (ø)
native	9.93% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Copilot]

Pull request overview

Fixes a startup/decode-thread crash in GeneralVariables.getShortCallsign(String) when the operator callsign is an all-slash string (e.g. "/", "//"), by guarding against Java’s String.split("/") returning a zero-length array on that input.

Changes:

• Add a temp.length == 0 guard in getShortCallsign to avoid ArrayIndexOutOfBoundsException and fall back to the original callsign.
• Add a Robolectric JUnit test covering plain, compound, leading-slash, and all-slash regression cases.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
ft8af/app/src/main/java/com/k1af/ft8af/GeneralVariables.java	Adds a defensive check for all-slash inputs before indexing the split array.
ft8af/app/src/test/java/com/k1af/ft8af/GeneralVariablesShortCallsignTest.java	Introduces regression/unit coverage for getShortCallsign, including the all-slash crash case.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.