1 files changed, 53 insertions, 0 deletions
diff --git a/Firestore/core/src/firebase/firestore/util/string_util.cc b/Firestore/core/src/firebase/firestore/util/string_util.cc
new file mode 100644
index 0000000..b7f1ed9
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/util/string_util.cc
@@ -0,0 +1,53 @@
+/*
+ * Copyright 2017 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Firestore/core/src/firebase/firestore/util/string_util.h"
+
+namespace firebase {
+namespace firestore {
+namespace util {
+
+std::string PrefixSuccessor(absl::string_view prefix) {
+  // We can increment the last character in the string and be done
+  // unless that character is 255 (0xff), in which case we have to erase the
+  // last character and increment the previous character, unless that
+  // is 255, etc. If the string is empty or consists entirely of
+  // 255's, we just return the empty string.
+  std::string limit(prefix);
+  while (!limit.empty()) {
+    size_t index = limit.length() - 1;
+    if (limit[index] == '\xff') {  // char literal avoids signed/unsigned.
+      limit.erase(index);
+    } else {
+      limit[index]++;
+      break;
+    }
+  }
+  return limit;
+}
+
+std::string ImmediateSuccessor(absl::string_view s) {
+  // Return the input string, with an additional NUL byte appended.
+  std::string out;
+  out.reserve(s.size() + 1);
+  out.append(s.data(), s.size());
+  out.push_back('\0');
+  return out;
+}
+
+}  // namespace util
+}  // namespace firestore
+}  // namespace firebase