Return an error instead of a panic for an unclosed quoted-KV.

fbconn/config.go

@@ -603,6 +603,9 @@ func parseKeywordValueSettings(s string) (map[string]string, error) {
 				}
 				if s[end] == '\\' {
 					end++
+					if end == len(s) {
+						return nil, errors.New("unterminated quoted string in connection info string")
+					}
 				}
 			}
 			if end == len(s) {

fbconn/config_test.go

@@ -772,3 +772,31 @@ func TestParseConfigEnv(t *testing.T) {
 		})
 	}
 }
+
+// A backslash as the last byte of an unterminated quoted value must be
+// rejected as an unterminated string, not panic with a slice bounds error.
+// The quoted-string loop advances past a backslash without bounds-checking
+// the resulting index, so `='\` (and `0='\`, reached via the fbxpool path)
+// previously panicked with "slice bounds out of range [:2] with length 1".
+func TestParseConfigKVQuotedTrailingBackslashDoesNotPanic(t *testing.T) {
+	tests := []struct {
+		name       string
+		connString string
+	}{
+		{name: "bare quoted trailing backslash", connString: `='\`},
+		{name: "quoted trailing backslash with key", connString: `0='\`},
+		{name: "quoted trailing backslash after value", connString: `host='a\`},
+		{name: "quoted trailing backslash after escaped pair", connString: `host='a\\b\`},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var err error
+			assert.NotPanics(t, func() {
+				_, err = fbconn.ParseConfig(tt.connString)
+			})
+			require.Error(t, err)
+			assert.Contains(t, err.Error(), "unterminated quoted string in connection info string")
+		})
+	}
+}