🩺 HealthCheck (GoMT4)

Goal: perform a fast terminal health check right after connect — using the same calls and patterns that exist in this repo.

Real code refs:

• Account: examples/mt4/MT4Account.go (AccountSummary, Quote, retry/backoff helpers)
• Service demo: examples/mt4/MT4_service.go (summary/quote examples)
• Config: examples/config/config.json

---

✅ What we consider "healthy"

• MT4 terminal is running and connected to broker.
• AccountSummary returns within a short timeout (≈3s).
• Optionally: a Quote(symbol) succeeds for your DefaultSymbol from config.json.

---

⏱️ Quick summary-based check (3s timeout + retry on transport)

func HealthCheck(ctx context.Context, a *MT4Account) error {
    // Short deadline: we want a quick yes/no
    hctx, cancel := context.WithTimeout(ctx, 3*time.Second)
    defer cancel()

    // Retry only transient transport errors (codes.Unavailable)
    return a.callWithRetry(hctx, func(c context.Context) error {
        _, err := a.AccountSummary(c)
        return err
    })
}

Why this works: AccountSummary is lightweight and exercises the session; your callWithRetry already implements exponential backoff + jitter and respects context.

---

💱 Optional: include a quote probe for DefaultSymbol

func HealthCheckWithQuote(ctx context.Context, a *MT4Account, symbol string) error {
    if err := HealthCheck(ctx, a); err != nil { return err }

    qctx, cancel := context.WithTimeout(ctx, 2*time.Second)
    defer cancel()

    return a.callWithRetry(qctx, func(c context.Context) error {
        _, err := a.Quote(c, symbol)
        return err
    })
}

Use the DefaultSymbol from examples/config/config.json, making sure the symbol is visible in Market Watch (suffixes like EURUSD.m are broker‑specific).

---

🧪 Interpreting results

• OK: both calls return under the deadlines.
• Timeout (context deadline exceeded): terminal is not ready or network stalls — wait a bit and retry; consider higher backoffMax.
• Business error: bubble it up (do not retry): fix login/server/symbol.

---

🧭 Where the knobs live (no magic numbers)

Backoff/jitter/retry limits are centralized in examples/mt4/MT4Account.go:

const (
    backoffBase = 300 * time.Millisecond
    backoffMax  = 5 * time.Second
    jitterRange = 200 * time.Millisecond
    maxRetries  = 10
)

Tune them for your environment (home Wi‑Fi vs VPS/LAN). Timeouts in the health‑check are per‑call and independent from backoff caps.

---

🧰 Usage example (service layer)

⚠️ Note: Your base project does not include a method named EnsureHealthy. This section is shown only as a convenience wrapper idea — a way to combine the health‑check calls (AccountSummary + Quote) into one place. You may add such a method if you want a single entry point to verify that MT4 is ready.

Why useful?

• Before running strategies or bots, you can call EnsureHealthy to quickly confirm the terminal is connected and symbols are available.
• It saves copy‑pasting the same two checks (AccountSummary + Quote) everywhere.
• If something is wrong (wrong server, hidden symbol, no connection) you fail fast with a clear error.

Example implementation:

func (s *MT4Service) EnsureHealthy(ctx context.Context) error {
    // 1) Summary probe
    if err := HealthCheck(ctx, s.account); err != nil {
        return fmt.Errorf("health summary failed: %w", err)")
    }

    // 2) Quote probe for default symbol
    sym := s.cfg.DefaultSymbol
    if sym != "" {
        if err := HealthCheckWithQuote(ctx, s.account, sym); err != nil {
            return fmt.Errorf("health quote failed for %s: %w", sym, err)
        }
    }

    log.Println("✅ MT4 is healthy and ready")
    return nil
}

---

⚠️ Pitfalls

• Hidden symbol / suffix mismatch → EURUSD vs EURUSD.m; fix config or show all symbols in MT4.
• No cancel → always defer cancel() after WithTimeout to avoid leaks.
• Retrying business errors → don’t; adjust credentials/server/symbol.

---

📎 See also

• UnaryRetries.md — per‑call retry wrapper used above.
• AccountSummary.md — details on fields and risk checks.
• GetQuote.md — one‑shot quote used in the probe.