Add production hardening: monitoring, backups, caching, and high-traffic resilience

- Recovery middleware (no more crash-on-panic), request metrics/monitoring
  store + admin API, in-memory TTL caching for read-heavy option/question/
  category lookups, gzip + rate-limiting middleware, sanitized chat message
  encoding, and pg_dump-based database backups with an admin API.
- Fix N+1 queries in the discover feed, candidate detail, and match list
  endpoints by batching selection/photo/user/last-message lookups into
  single queries instead of one-per-item loops.
- Tune DB connection pooling and add HTTP server timeouts + graceful
  shutdown so the API degrades gracefully instead of falling over under load.
- Fix a null (vs empty array) JSON response for candidates/matches without
  photos or interests, which crashed the web app's swipe card.

internal/utils/age_test.go

@@ -0,0 +1,26 @@
+package utils
+
+import (
+	"testing"
+	"time"
+)
+
+func TestCalcAge_NilBirthDate(t *testing.T) {
+	if age := CalcAge(nil); age != 0 {
+		t.Fatalf("expected 0 for nil birth date, got %d", age)
+	}
+}
+
+func TestCalcAge_BirthdayAlreadyPassedThisYear(t *testing.T) {
+	birth := time.Now().AddDate(-25, -1, 0) // ۲۵ سال و ۱ ماه پیش -> تولد امسال رد شده
+	if age := CalcAge(&birth); age != 25 {
+		t.Fatalf("expected age 25, got %d", age)
+	}
+}
+
+func TestCalcAge_BirthdayNotYetThisYear(t *testing.T) {
+	birth := time.Now().AddDate(-25, 1, 0) // تولد ۱ ماه دیگه‌ست -> هنوز ۲۴ سالشه
+	if age := CalcAge(&birth); age != 24 {
+		t.Fatalf("expected age 24, got %d", age)
+	}
+}

internal/utils/geo_test.go

@@ -0,0 +1,18 @@
+package utils
+
+import "testing"
+
+func TestHaversineKM_SamePoint(t *testing.T) {
+	d := HaversineKM(35.6892, 51.3890, 35.6892, 51.3890)
+	if d > 0.001 {
+		t.Fatalf("expected ~0km for identical points, got %v", d)
+	}
+}
+
+func TestHaversineKM_TehranToIsfahan(t *testing.T) {
+	// فاصله‌ی تهران تا اصفهان تقریباً ۳۴۰ کیلومتره (خط مستقیم)
+	d := HaversineKM(35.6892, 51.3890, 32.6546, 51.6680)
+	if d < 300 || d > 380 {
+		t.Fatalf("expected ~340km between Tehran and Isfahan, got %v", d)
+	}
+}

internal/utils/sanitize.go

@@ -0,0 +1,47 @@
+package utils
+
+import (
+	"errors"
+	"strings"
+	"unicode/utf8"
+)
+
+var (
+	ErrInvalidMessageEncoding = errors.New("متن پیام معتبر نیست (کدگذاری اشتباه)")
+	ErrMessageEmpty           = errors.New("متن پیام نمی‌تواند خالی باشد")
+	ErrMessageTooLong         = errors.New("متن پیام بیش از حد مجاز طولانی است")
+)
+
+const MaxMessageLength = 2000
+
+// SanitizeMessageText متن یک پیام چت رو قبل از ذخیره‌سازی پاک‌سازی/اعتبارسنجی می‌کنه:
+//   - رد کردن رشته‌هایی که UTF-8 معتبر نیستن (بایت خراب/دستکاری‌شده)
+//   - حذف کاراکترهای کنترلی (به‌جز \n و \t) که می‌تونن نمایش یا لاگ‌ها رو خراب کنن
+//   - trim فاصله‌های اضافه و محدود کردن طول
+func SanitizeMessageText(raw string) (string, error) {
+	if !utf8.ValidString(raw) {
+		return "", ErrInvalidMessageEncoding
+	}
+
+	var b strings.Builder
+	b.Grow(len(raw))
+	for _, r := range raw {
+		if r == '\n' || r == '\t' {
+			b.WriteRune(r)
+			continue
+		}
+		if r < 0x20 || r == 0x7F {
+			continue
+		}
+		b.WriteRune(r)
+	}
+
+	text := strings.TrimSpace(b.String())
+	if text == "" {
+		return "", ErrMessageEmpty
+	}
+	if utf8.RuneCountInString(text) > MaxMessageLength {
+		return "", ErrMessageTooLong
+	}
+	return text, nil
+}

internal/utils/sanitize_test.go

@@ -0,0 +1,71 @@
+package utils
+
+import (
+	"errors"
+	"strings"
+	"testing"
+)
+
+func TestSanitizeMessageText_TrimsWhitespace(t *testing.T) {
+	got, err := SanitizeMessageText("  سلام دوست من  ")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != "سلام دوست من" {
+		t.Fatalf("expected trimmed text, got %q", got)
+	}
+}
+
+func TestSanitizeMessageText_EmptyAfterTrim(t *testing.T) {
+	_, err := SanitizeMessageText("     ")
+	if !errors.Is(err, ErrMessageEmpty) {
+		t.Fatalf("expected ErrMessageEmpty, got %v", err)
+	}
+}
+
+func TestSanitizeMessageText_StripsControlChars(t *testing.T) {
+	got, err := SanitizeMessageText("سلام\x00\x07دنیا")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != "سلامدنیا" {
+		t.Fatalf("expected control chars stripped, got %q", got)
+	}
+}
+
+func TestSanitizeMessageText_KeepsNewlinesAndTabs(t *testing.T) {
+	got, err := SanitizeMessageText("خط اول\nخط دوم\tبا تب")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != "خط اول\nخط دوم\tبا تب" {
+		t.Fatalf("expected newline/tab preserved, got %q", got)
+	}
+}
+
+func TestSanitizeMessageText_InvalidUTF8(t *testing.T) {
+	invalid := string([]byte{0xff, 0xfe, 0xfd})
+	_, err := SanitizeMessageText(invalid)
+	if !errors.Is(err, ErrInvalidMessageEncoding) {
+		t.Fatalf("expected ErrInvalidMessageEncoding, got %v", err)
+	}
+}
+
+func TestSanitizeMessageText_TooLong(t *testing.T) {
+	long := strings.Repeat("a", MaxMessageLength+1)
+	_, err := SanitizeMessageText(long)
+	if !errors.Is(err, ErrMessageTooLong) {
+		t.Fatalf("expected ErrMessageTooLong, got %v", err)
+	}
+}
+
+func TestSanitizeMessageText_ExactlyMaxLength(t *testing.T) {
+	exact := strings.Repeat("a", MaxMessageLength)
+	got, err := SanitizeMessageText(exact)
+	if err != nil {
+		t.Fatalf("unexpected error at exact max length: %v", err)
+	}
+	if len(got) != MaxMessageLength {
+		t.Fatalf("expected length %d, got %d", MaxMessageLength, len(got))
+	}
+}