90 lines
2.7 KiB
C
90 lines
2.7 KiB
C
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/*
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* Copyright (c) Meta Platforms, Inc. and affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*/
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#pragma once
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#include <functional>
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#include <memory>
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#include <ostream>
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#include <streambuf>
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#include <string>
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namespace facebook {
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namespace hermes {
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namespace inspector {
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namespace detail {
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/// Subclass of \c std::ostream where flushing is implemented through a
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/// callback. Writes are collected in a buffer. When filled, the buffer's
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/// contents are emptied out and sent to a callback.
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struct CallbackOStream : public std::ostream {
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/// Signature of callback called to flush buffer contents. Accepts the buffer
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/// as a string. Returns a boolean indicating whether flushing succeeded.
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/// Callback failure will be translated to stream failure. If the callback
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/// throws an exception it will be swallowed and translated into stream
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/// failure.
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using Fn = std::function<bool(std::string)>;
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/// Construct a new stream.
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///
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/// \p sz The size of the buffer -- how large it can get before it must be
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/// flushed. Must be non-zero.
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/// \p cb The callback function.
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CallbackOStream(size_t sz, Fn cb);
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/// This class is neither movable nor copyable.
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CallbackOStream(CallbackOStream &&that) = delete;
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CallbackOStream &operator=(CallbackOStream &&that) = delete;
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CallbackOStream(const CallbackOStream &that) = delete;
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CallbackOStream &operator=(const CallbackOStream &that) = delete;
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private:
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/// \c std::streambuf sub-class backed by a std::string buffer and
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/// implementing overflow by calling a callback.
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struct StreamBuf : public std::streambuf {
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/// Construct a new streambuf. Parameters are the same as those of
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/// \c CallbackOStream .
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StreamBuf(size_t sz, Fn cb);
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/// Destruction will flush any remaining buffer contents.
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~StreamBuf();
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/// StreamBufs are not copyable, to avoid the flush callback receiving
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/// the contents of multiple streams.
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StreamBuf(const StreamBuf &) = delete;
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StreamBuf &operator=(const StreamBuf &) = delete;
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protected:
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/// std::streambuf overrides
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int_type overflow(int_type ch) override;
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int sync() override;
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private:
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/// The size of the backing buffer. Fixed for an instance of the streambuf.
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size_t sz_;
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/// The backing buffer that writes will go to until full.
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std::unique_ptr<char[]> buf_;
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/// The function called when buf_ has been filled.
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Fn cb_;
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/// Clears the backing buffer.
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void reset();
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/// Clears the backing buffer and returns it contents in a string.
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std::string take();
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};
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StreamBuf sbuf_;
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};
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} // namespace detail
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} // namespace inspector
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} // namespace hermes
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} // namespace facebook
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