comparison win64-msvc/include/capnp/serialize.h @ 47:d93140aac40b

Current Capnp libs and headers from git

+// Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
+// Licensed under the MIT License:
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+// This file implements a simple serialization format for Cap'n Proto messages.  The format
+// is as follows:
+//
+// * 32-bit little-endian segment count (4 bytes).
+// * 32-bit little-endian size of each segment (4*(segment count) bytes).
+// * Padding so that subsequent data is 64-bit-aligned (0 or 4 bytes).  (I.e., if there are an even
+//     number of segments, there are 4 bytes of zeros here, otherwise there is no padding.)
+// * Data from each segment, in order (8*sum(segment sizes) bytes)
+//
+// This format has some important properties:
+// - It is self-delimiting, so multiple messages may be written to a stream without any external
+//   delimiter.
+// - The total size and position of each segment can be determined by reading only the first part
+//   of the message, allowing lazy and random-access reading of the segment data.
+// - A message is always at least 8 bytes.
+// - A single-segment message can be read entirely in two system calls with no buffering.
+// - A multi-segment message can be read entirely in three system calls with no buffering.
+// - The format is appropriate for mmap()ing since all data is aligned.
+
+#ifndef CAPNP_SERIALIZE_H_
+#define CAPNP_SERIALIZE_H_
+
+#if defined(__GNUC__) && !defined(CAPNP_HEADER_WARNINGS)
+#pragma GCC system_header
+#endif
+
+#include "message.h"
+#include <kj/io.h>
+
+namespace capnp {
+
+class FlatArrayMessageReader: public MessageReader {
+  // Parses a message from a flat array.  Note that it makes sense to use this together with mmap()
+  // for extremely fast parsing.
+
+public:
+  FlatArrayMessageReader(kj::ArrayPtr<const word> array, ReaderOptions options = ReaderOptions());
+  // The array must remain valid until the MessageReader is destroyed.
+
+  kj::ArrayPtr<const word> getSegment(uint id) override;
+
+  const word* getEnd() const { return end; }
+  // Get a pointer just past the end of the message as determined by reading the message header.
+  // This could actually be before the end of the input array.  This pointer is useful e.g. if
+  // you know that the input array has extra stuff appended after the message and you want to
+  // get at it.
+
+private:
+  // Optimize for single-segment case.
+  kj::ArrayPtr<const word> segment0;
+  kj::Array<kj::ArrayPtr<const word>> moreSegments;
+  const word* end;
+};
+
+kj::ArrayPtr<const word> initMessageBuilderFromFlatArrayCopy(
+    kj::ArrayPtr<const word> array, MessageBuilder& target,
+    ReaderOptions options = ReaderOptions());
+// Convenience function which reads a message using `FlatArrayMessageReader` then copies the
+// content into the target `MessageBuilder`, verifying that the message structure is valid
+// (although not necessarily that it matches the desired schema).
+//
+// Returns an ArrayPtr containing any words left over in the array after consuming the whole
+// message. This is useful when reading multiple messages that have been concatenated. See also
+// FlatArrayMessageReader::getEnd().
+//
+// (Note that it's also possible to initialize a `MessageBuilder` directly without a copy using one
+// of `MessageBuilder`'s constructors. However, this approach skips the validation step and is not
+// safe to use on untrusted input. Therefore, we do not provide a convenience method for it.)
+
+kj::Array<word> messageToFlatArray(MessageBuilder& builder);
+// Constructs a flat array containing the entire content of the given message.
+//
+// To output the message as bytes, use `.asBytes()` on the returned word array. Keep in mind that
+// `asBytes()` returns an ArrayPtr, so you have to save the Array as well to prevent it from being
+// deleted. For example:
+//
+//     kj::Array<capnp::word> words = messageToFlatArray(myMessage);
+//     kj::ArrayPtr<kj::byte> bytes = words.asBytes();
+//     write(fd, bytes.begin(), bytes.size());
+
+kj::Array<word> messageToFlatArray(kj::ArrayPtr<const kj::ArrayPtr<const word>> segments);
+// Version of messageToFlatArray that takes a raw segment array.
+
+size_t computeSerializedSizeInWords(MessageBuilder& builder);
+// Returns the size, in words, that will be needed to serialize the message, including the header.
+
+size_t computeSerializedSizeInWords(kj::ArrayPtr<const kj::ArrayPtr<const word>> segments);
+// Version of computeSerializedSizeInWords that takes a raw segment array.
+
+size_t expectedSizeInWordsFromPrefix(kj::ArrayPtr<const word> messagePrefix);
+// Given a prefix of a serialized message, try to determine the expected total size of the message,
+// in words. The returned size is based on the information known so far; it may be an underestimate
+// if the prefix doesn't contain the full segment table.
+//
+// If the returned value is greater than `messagePrefix.size()`, then the message is not yet
+// complete and the app cannot parse it yet. If the returned value is less than or equal to
+// `messagePrefix.size()`, then the returned value is the exact total size of the message; any
+// remaining bytes are part of the next message.
+//
+// This function is useful when reading messages from a stream in an asynchronous way, but when
+// using the full KJ async infrastructure would be too difficult. Each time bytes are received,
+// use this function to determine if an entire message is ready to be parsed.
+
+// =======================================================================================
+
+class InputStreamMessageReader: public MessageReader {
+  // A MessageReader that reads from an abstract kj::InputStream. See also StreamFdMessageReader
+  // for a subclass specific to file descriptors.
+
+public:
+  InputStreamMessageReader(kj::InputStream& inputStream,
+                           ReaderOptions options = ReaderOptions(),
+                           kj::ArrayPtr<word> scratchSpace = nullptr);
+  ~InputStreamMessageReader() noexcept(false);
+
+  // implements MessageReader ----------------------------------------
+  kj::ArrayPtr<const word> getSegment(uint id) override;
+
+private:
+  kj::InputStream& inputStream;
+  byte* readPos;
+
+  // Optimize for single-segment case.
+  kj::ArrayPtr<const word> segment0;
+  kj::Array<kj::ArrayPtr<const word>> moreSegments;
+
+  kj::Array<word> ownedSpace;
+  // Only if scratchSpace wasn't big enough.
+
+  kj::UnwindDetector unwindDetector;
+};
+
+void readMessageCopy(kj::InputStream& input, MessageBuilder& target,
+                     ReaderOptions options = ReaderOptions(),
+                     kj::ArrayPtr<word> scratchSpace = nullptr);
+// Convenience function which reads a message using `InputStreamMessageReader` then copies the
+// content into the target `MessageBuilder`, verifying that the message structure is valid
+// (although not necessarily that it matches the desired schema).
+//
+// (Note that it's also possible to initialize a `MessageBuilder` directly without a copy using one
+// of `MessageBuilder`'s constructors. However, this approach skips the validation step and is not
+// safe to use on untrusted input. Therefore, we do not provide a convenience method for it.)
+
+void writeMessage(kj::OutputStream& output, MessageBuilder& builder);
+// Write the message to the given output stream.
+
+void writeMessage(kj::OutputStream& output, kj::ArrayPtr<const kj::ArrayPtr<const word>> segments);
+// Write the segment array to the given output stream.
+
+// =======================================================================================
+// Specializations for reading from / writing to file descriptors.
+
+class StreamFdMessageReader: private kj::FdInputStream, public InputStreamMessageReader {
+  // A MessageReader that reads from a steam-based file descriptor.
+
+public:
+  StreamFdMessageReader(int fd, ReaderOptions options = ReaderOptions(),
+                        kj::ArrayPtr<word> scratchSpace = nullptr)
+      : FdInputStream(fd), InputStreamMessageReader(*this, options, scratchSpace) {}
+  // Read message from a file descriptor, without taking ownership of the descriptor.
+
+  StreamFdMessageReader(kj::AutoCloseFd fd, ReaderOptions options = ReaderOptions(),
+                        kj::ArrayPtr<word> scratchSpace = nullptr)
+      : FdInputStream(kj::mv(fd)), InputStreamMessageReader(*this, options, scratchSpace) {}
+  // Read a message from a file descriptor, taking ownership of the descriptor.
+
+  ~StreamFdMessageReader() noexcept(false);
+};
+
+void readMessageCopyFromFd(int fd, MessageBuilder& target,
+                           ReaderOptions options = ReaderOptions(),
+                           kj::ArrayPtr<word> scratchSpace = nullptr);
+// Convenience function which reads a message using `StreamFdMessageReader` then copies the
+// content into the target `MessageBuilder`, verifying that the message structure is valid
+// (although not necessarily that it matches the desired schema).
+//
+// (Note that it's also possible to initialize a `MessageBuilder` directly without a copy using one
+// of `MessageBuilder`'s constructors. However, this approach skips the validation step and is not
+// safe to use on untrusted input. Therefore, we do not provide a convenience method for it.)
+
+void writeMessageToFd(int fd, MessageBuilder& builder);
+// Write the message to the given file descriptor.
+//
+// This function throws an exception on any I/O error.  If your code is not exception-safe, be sure
+// you catch this exception at the call site.  If throwing an exception is not acceptable, you
+// can implement your own OutputStream with arbitrary error handling and then use writeMessage().
+
+void writeMessageToFd(int fd, kj::ArrayPtr<const kj::ArrayPtr<const word>> segments);
+// Write the segment array to the given file descriptor.
+//
+// This function throws an exception on any I/O error.  If your code is not exception-safe, be sure
+// you catch this exception at the call site.  If throwing an exception is not acceptable, you
+// can implement your own OutputStream with arbitrary error handling and then use writeMessage().
+
+// =======================================================================================
+// inline stuff
+
+inline kj::Array<word> messageToFlatArray(MessageBuilder& builder) {
+  return messageToFlatArray(builder.getSegmentsForOutput());
+}
+
+inline size_t computeSerializedSizeInWords(MessageBuilder& builder) {
+  return computeSerializedSizeInWords(builder.getSegmentsForOutput());
+}
+
+inline void writeMessage(kj::OutputStream& output, MessageBuilder& builder) {
+  writeMessage(output, builder.getSegmentsForOutput());
+}
+
+inline void writeMessageToFd(int fd, MessageBuilder& builder) {
+  writeMessageToFd(fd, builder.getSegmentsForOutput());
+}
+
+}  // namespace capnp
+
+#endif  // SERIALIZE_H_