folly/folly/gen/String.h

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * 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.
 */

#pragma once
#define FOLLY_GEN_STRING_H_

#include <folly/Range.h>
#include <folly/gen/Base.h>
#include <folly/io/IOBuf.h>

namespace folly {
namespace gen {

namespace detail {
class StringResplitter;

template <class Delimiter>
class SplitStringSource;

template <class Delimiter, class Output>
class Unsplit;

template <class Delimiter, class OutputBuffer>
class UnsplitBuffer;

template <class TargetContainer, class Delimiter, class... Targets>
class SplitTo;

} // namespace detail

/**
 * Split the output from a generator into StringPiece "lines" delimited by
 * the given delimiter.  Delimters are NOT included in the output.
 *
 * resplit() behaves as if the input strings were concatenated into one long
 * string and then split.
 *
 * Equivalently, you can use StreamSplitter outside of a folly::gen setting.
 */
// make this a template so we don't require StringResplitter to be complete
// until use
template <class S = detail::StringResplitter>
S resplit(char delimiter, bool keepDelimiter = false) { … }

template <class S = detail::SplitStringSource<char>>
S split(const StringPiece source, char delimiter) { … }

template <class S = detail::SplitStringSource<StringPiece>>
S split(StringPiece source, StringPiece delimiter) { … }

/**
 * EOL terms ("\r", "\n", or "\r\n").
 */
class MixedNewlines { … };

/**
 * Split by EOL ("\r", "\n", or "\r\n").
 * @see split().
 */
template <class S = detail::SplitStringSource<MixedNewlines>>
S lines(StringPiece source) { … }

/*
 * Joins a sequence of tokens into a string, with the chosen delimiter.
 *
 * E.G.
 *   fbstring result = split("a,b,c", ",") | unsplit(",");
 *   assert(result == "a,b,c");
 *
 *   std::string result = split("a,b,c", ",") | unsplit<std::string>(" ");
 *   assert(result == "a b c");
 */

// NOTE: The template arguments are reversed to allow the user to cleanly
// specify the output type while still inferring the type of the delimiter.
template <
    class Output = folly::fbstring,
    class Delimiter,
    class Unsplit = detail::Unsplit<Delimiter, Output>>
Unsplit unsplit(const Delimiter& delimiter) { … }

template <
    class Output = folly::fbstring,
    class Unsplit = detail::Unsplit<fbstring, Output>>
Unsplit unsplit(const char* delimiter) { … }

/*
 * Joins a sequence of tokens into a string, appending them to the output
 * buffer.  If the output buffer is empty, an initial delimiter will not be
 * inserted at the start.
 *
 * E.G.
 *   std::string buffer;
 *   split("a,b,c", ",") | unsplit(",", &buffer);
 *   assert(buffer == "a,b,c");
 *
 *   std::string anotherBuffer("initial");
 *   split("a,b,c", ",") | unsplit(",", &anotherbuffer);
 *   assert(anotherBuffer == "initial,a,b,c");
 */
template <
    class Delimiter,
    class OutputBuffer,
    class UnsplitBuffer = detail::UnsplitBuffer<Delimiter, OutputBuffer>>
UnsplitBuffer unsplit(Delimiter delimiter, OutputBuffer* outputBuffer) { … }

template <
    class OutputBuffer,
    class UnsplitBuffer = detail::UnsplitBuffer<fbstring, OutputBuffer>>
UnsplitBuffer unsplit(const char* delimiter, OutputBuffer* outputBuffer) { … }

template <class... Targets>
detail::Map<detail::SplitTo<std::tuple<Targets...>, char, Targets...>>
eachToTuple(char delim) { … }

template <class... Targets>
detail::Map<detail::SplitTo<std::tuple<Targets...>, fbstring, Targets...>>
eachToTuple(StringPiece delim) { … }

template <class First, class Second>
detail::Map<detail::SplitTo<std::pair<First, Second>, char, First, Second>>
eachToPair(char delim) { … }

template <class First, class Second>
detail::Map<detail::SplitTo<std::pair<First, Second>, fbstring, First, Second>>
eachToPair(StringPiece delim) { … }

/**
 * Outputs exactly the same bytes as the input stream, in different chunks.
 * A chunk boundary occurs after each delimiter, or, if maxLength is
 * non-zero, after maxLength bytes, whichever comes first.  Your callback
 * can return false to stop consuming the stream at any time.
 *
 * The splitter buffers the last incomplete chunk, so you must call flush()
 * to consume the piece of the stream after the final delimiter.  This piece
 * may be empty.  After a flush(), the splitter can be re-used for a new
 * stream.
 *
 * operator() and flush() return false iff your callback returns false. The
 * internal buffer is not flushed, so reusing such a splitter will have
 * indeterminate results.  Same goes if your callback throws.  Feel free to
 * fix these corner cases if needed.
 *
 * Tips:
 *  - Create via streamSplitter() to take advantage of template deduction.
 *  - If your callback needs an end-of-stream signal, test for "no
 *    trailing delimiter **and** shorter than maxLength".
 *  - You can fine-tune the initial capacity of the internal IOBuf.
 */
template <class Callback>
class StreamSplitter { … };

template <class Callback> // Helper to enable template deduction
StreamSplitter<Callback> streamSplitter(
    char delimiter, Callback&& pieceCb, uint64_t capacity = 0) { … }

} // namespace gen
} // namespace folly

#include <folly/gen/String-inl.h>