From 5fdda3fa837f3138973d754f05aec7f541f806ce Mon Sep 17 00:00:00 2001 From: zxu Date: Thu, 25 Jan 2018 13:03:07 -0500 Subject: normalize string_util (#708) * refactoring string_util * port string_util to iOS --- .../src/firebase/firestore/util/CMakeLists.txt | 2 + .../src/firebase/firestore/util/string_util.cc | 53 ++++++++++++++++ .../core/src/firebase/firestore/util/string_util.h | 72 ++++++++++++++++++++++ 3 files changed, 127 insertions(+) create mode 100644 Firestore/core/src/firebase/firestore/util/string_util.cc create mode 100644 Firestore/core/src/firebase/firestore/util/string_util.h (limited to 'Firestore/core/src/firebase/firestore/util') diff --git a/Firestore/core/src/firebase/firestore/util/CMakeLists.txt b/Firestore/core/src/firebase/firestore/util/CMakeLists.txt index 09db164..51621a0 100644 --- a/Firestore/core/src/firebase/firestore/util/CMakeLists.txt +++ b/Firestore/core/src/firebase/firestore/util/CMakeLists.txt @@ -113,6 +113,8 @@ cc_library( firebase_assert.h log.h secure_random.h + string_util.cc + string_util.h DEPENDS ${UTIL_DEPENDS} firebase_firestore_util_base 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 diff --git a/Firestore/core/src/firebase/firestore/util/string_util.h b/Firestore/core/src/firebase/firestore/util/string_util.h new file mode 100644 index 0000000..3de177d --- /dev/null +++ b/Firestore/core/src/firebase/firestore/util/string_util.h @@ -0,0 +1,72 @@ +/* + * 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. + */ + +// Useful string functions and so forth. This is a grab-bag file. +// +// These functions work fine for UTF-8 strings as long as you can +// consider them to be just byte strings. For example, due to the +// design of UTF-8 you do not need to worry about accidental matches, +// as long as all your inputs are valid UTF-8 (use \uHHHH, not \xHH or \oOOO). + +#ifndef FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_STRING_UTIL_H_ +#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_STRING_UTIL_H_ + +#include + +#include "absl/strings/string_view.h" + +namespace firebase { +namespace firestore { +namespace util { + +/* + * Returns the smallest lexicographically larger string of equal or smaller + * length. Returns an empty string if there is no such successor (if the input + * is empty or consists entirely of 0xff bytes). + * Useful for calculating the smallest lexicographically larger string + * that will not be prefixed by the input string. + * + * Examples: + * "a" -> "b", "aaa" -> "aab", "aa\xff" -> "ab", "\xff" -> "", "" -> "" + */ +std::string PrefixSuccessor(absl::string_view prefix); + +/* + * Returns the immediate lexicographically-following string. This is useful to + * turn an inclusive range into something that can be used with Bigtable's + * SetLimitRow(): + * + * // Inclusive range [min_element, max_element]. + * string min_element = ...; + * string max_element = ...; + * + * // Equivalent range [range_start, range_end). + * string range_start = min_element; + * string range_end = ImmediateSuccessor(max_element); + * + * WARNING: Returns the input string with a '\0' appended; if you call c_str() + * on the result, it will compare equal to s. + * + * WARNING: Transforms "" -> "\0"; this doesn't account for Bigtable's special + * treatment of "" as infinity. + */ +std::string ImmediateSuccessor(absl::string_view s); + +} // namespace util +} // namespace firestore +} // namespace firebase + +#endif // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_STRING_UTIL_H_ -- cgit v1.2.3