fix(sentinel): handle empty address (#3577)

* improvements

* linter fixes

* prevention on unnecessary allocations in case of bad configuration

* Test/Benchmark, old code with safety harness preventing panic

---------

Co-authored-by: manish <manish.sharma@manifestit.io>
Co-authored-by: Nedyalko Dyakov <1547186+ndyakov@users.noreply.github.com>

export_test.go

@@ -106,3 +106,7 @@ func (c *ModuleLoadexConfig) ToArgs() []interface{} {
 func ShouldRetry(err error, retryTimeout bool) bool {
 	return shouldRetry(err, retryTimeout)
 }
+
+func JoinErrors(errs []error) string {
+	return joinErrors(errs)
+}

sentinel.go

@@ -843,6 +843,11 @@ func (c *sentinelFailover) MasterAddr(ctx context.Context) (string, error) {
 		}
 	}
 
+	// short circuit if no sentinels configured
+	if len(c.sentinelAddrs) == 0 {
+		return "", errors.New("redis: no sentinels configured")
+	}
+
 	var (
 		masterAddr string
 		wg         sync.WaitGroup
@@ -890,10 +895,12 @@ func (c *sentinelFailover) MasterAddr(ctx context.Context) (string, error) {
 }
 
 func joinErrors(errs []error) string {
+	if len(errs) == 0 {
+		return ""
+	}
 	if len(errs) == 1 {
 		return errs[0].Error()
 	}
-
 	b := []byte(errs[0].Error())
 	for _, err := range errs[1:] {
 		b = append(b, '\n')

sentinel_test.go

@@ -682,3 +682,99 @@ func compareSlices(t *testing.T, a, b []string, name string) {
 		}
 	}
 }
+
+type joinErrorsTest struct {
+	name     string
+	errs     []error
+	expected string
+}
+
+func TestJoinErrors(t *testing.T) {
+	tests := []joinErrorsTest{
+		{
+			name:     "empty slice",
+			errs:     []error{},
+			expected: "",
+		},
+		{
+			name:     "single error",
+			errs:     []error{errors.New("first error")},
+			expected: "first error",
+		},
+		{
+			name:     "two errors",
+			errs:     []error{errors.New("first error"), errors.New("second error")},
+			expected: "first error\nsecond error",
+		},
+		{
+			name: "multiple errors",
+			errs: []error{
+				errors.New("first error"),
+				errors.New("second error"),
+				errors.New("third error"),
+			},
+			expected: "first error\nsecond error\nthird error",
+		},
+		{
+			name:     "nil slice",
+			errs:     nil,
+			expected: "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := redis.JoinErrors(tt.errs)
+			if result != tt.expected {
+				t.Errorf("joinErrors() = %q, want %q", result, tt.expected)
+			}
+		})
+	}
+}
+
+func BenchmarkJoinErrors(b *testing.B) {
+	benchmarks := []joinErrorsTest{
+		{
+			name:     "empty slice",
+			errs:     []error{},
+			expected: "",
+		},
+		{
+			name:     "single error",
+			errs:     []error{errors.New("first error")},
+			expected: "first error",
+		},
+		{
+			name:     "two errors",
+			errs:     []error{errors.New("first error"), errors.New("second error")},
+			expected: "first error\nsecond error",
+		},
+		{
+			name: "multiple errors",
+			errs: []error{
+				errors.New("first error"),
+				errors.New("second error"),
+				errors.New("third error"),
+			},
+			expected: "first error\nsecond error\nthird error",
+		},
+		{
+			name:     "nil slice",
+			errs:     nil,
+			expected: "",
+		},
+	}
+	for _, bm := range benchmarks {
+		b.Run(bm.name, func(b *testing.B) {
+			b.ResetTimer()
+			b.RunParallel(func(pb *testing.PB) {
+				for pb.Next() {
+					result := redis.JoinErrors(bm.errs)
+					if result != bm.expected {
+						b.Errorf("joinErrors() = %q, want %q", result, bm.expected)
+					}
+				}
+			})
+		})
+	}
+}