message_lite.h

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// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
//
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// modification, are permitted provided that the following conditions are
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//
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// notice, this list of conditions and the following disclaimer.
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// in the documentation and/or other materials provided with the
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//
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// Authors: wink@google.com (Wink Saville),
//          kenton@google.com (Kenton Varda)
//  Based on original Protocol Buffers design by
//  Sanjay Ghemawat, Jeff Dean, and others.
//
// Defines MessageLite, the abstract interface implemented by all (lite
// and non-lite) protocol message objects.

#ifndef GOOGLE_PROTOBUF_MESSAGE_LITE_H__
#define GOOGLE_PROTOBUF_MESSAGE_LITE_H__

#include <google/protobuf/stubs/common.h>


namespace google {
namespace protobuf {
  class Arena;
namespace io {
  class CodedInputStream;
  class CodedOutputStream;
  class ZeroCopyInputStream;
  class ZeroCopyOutputStream;
}

// Interface to light weight protocol messages.
//
// This interface is implemented by all protocol message objects.  Non-lite
// messages additionally implement the Message interface, which is a
// subclass of MessageLite.  Use MessageLite instead when you only need
// the subset of features which it supports -- namely, nothing that uses
// descriptors or reflection.  You can instruct the protocol compiler
// to generate classes which implement only MessageLite, not the full
// Message interface, by adding the following line to the .proto file:
//
//   option optimize_for = LITE_RUNTIME;
//
// This is particularly useful on resource-constrained systems where
// the full protocol buffers runtime library is too big.
//
// Note that on non-constrained systems (e.g. servers) when you need
// to link in lots of protocol definitions, a better way to reduce
// total code footprint is to use optimize_for = CODE_SIZE.  This
// will make the generated code smaller while still supporting all the
// same features (at the expense of speed).  optimize_for = LITE_RUNTIME
// is best when you only have a small number of message types linked
// into your binary, in which case the size of the protocol buffers
// runtime itself is the biggest problem.
class LIBPROTOBUF_EXPORT MessageLite {
 public:
  inline MessageLite() {}
  virtual ~MessageLite();

  // Basic Operations ------------------------------------------------

  // Get the name of this message type, e.g. "foo.bar.BazProto".
  virtual string GetTypeName() const = 0;

  // Construct a new instance of the same type.  Ownership is passed to the
  // caller.
  virtual MessageLite* New() const = 0;

  // Construct a new instance on the arena. Ownership is passed to the caller
  // if arena is a NULL. Default implementation for backwards compatibility.
  virtual MessageLite* New(::google::protobuf::Arena* arena) const;

  // Get the arena, if any, associated with this message. Virtual method
  // required for generic operations but most arena-related operations should
  // use the GetArenaNoVirtual() generated-code method. Default implementation
  // to reduce code size by avoiding the need for per-type implementations when
  // types do not implement arena support.
  virtual ::google::protobuf::Arena* GetArena() const { return NULL; }

  // Get a pointer that may be equal to this message's arena, or may not be. If
  // the value returned by this method is equal to some arena pointer, then this
  // message is on that arena; however, if this message is on some arena, this
  // method may or may not return that arena's pointer. As a tradeoff, this
  // method may be more efficient than GetArena(). The intent is to allow
  // underlying representations that use e.g. tagged pointers to sometimes store
  // the arena pointer directly, and sometimes in a more indirect way, and allow
  // a fastpath comparison against the arena pointer when it's easy to obtain.
  virtual void* GetMaybeArenaPointer() const { return GetArena(); }

  // Clear all fields of the message and set them to their default values.
  // Clear() avoids freeing memory, assuming that any memory allocated
  // to hold parts of the message will be needed again to hold the next
  // message.  If you actually want to free the memory used by a Message,
  // you must delete it.
  virtual void Clear() = 0;

  // Quickly check if all required fields have values set.
  virtual bool IsInitialized() const = 0;

  // This is not implemented for Lite messages -- it just returns "(cannot
  // determine missing fields for lite message)".  However, it is implemented
  // for full messages.  See message.h.
  virtual string InitializationErrorString() const;

  // If |other| is the exact same class as this, calls MergeFrom().  Otherwise,
  // results are undefined (probably crash).
  virtual void CheckTypeAndMergeFrom(const MessageLite& other) = 0;

  // Parsing ---------------------------------------------------------
  // Methods for parsing in protocol buffer format.  Most of these are
  // just simple wrappers around MergeFromCodedStream().  Clear() will be called
  // before merging the input.

  // Fill the message with a protocol buffer parsed from the given input stream.
  // Returns false on a read error or if the input is in the wrong format.  A
  // successful return does not indicate the entire input is consumed, ensure
  // you call ConsumedEntireMessage() to check that if applicable.
  bool ParseFromCodedStream(io::CodedInputStream* input);
  // Like ParseFromCodedStream(), but accepts messages that are missing
  // required fields.
  bool ParsePartialFromCodedStream(io::CodedInputStream* input);
  // Read a protocol buffer from the given zero-copy input stream.  If
  // successful, the entire input will be consumed.
  bool ParseFromZeroCopyStream(io::ZeroCopyInputStream* input);
  // Like ParseFromZeroCopyStream(), but accepts messages that are missing
  // required fields.
  bool ParsePartialFromZeroCopyStream(io::ZeroCopyInputStream* input);
  // Read a protocol buffer from the given zero-copy input stream, expecting
  // the message to be exactly "size" bytes long.  If successful, exactly
  // this many bytes will have been consumed from the input.
  bool ParseFromBoundedZeroCopyStream(io::ZeroCopyInputStream* input, int size);
  // Like ParseFromBoundedZeroCopyStream(), but accepts messages that are
  // missing required fields.
  bool ParsePartialFromBoundedZeroCopyStream(io::ZeroCopyInputStream* input,
                                             int size);
  // Parses a protocol buffer contained in a string. Returns true on success.
  // This function takes a string in the (non-human-readable) binary wire
  // format, matching the encoding output by MessageLite::SerializeToString().
  // If you'd like to convert a human-readable string into a protocol buffer
  // object, see google::protobuf::TextFormat::ParseFromString().
  bool ParseFromString(const string& data);
  // Like ParseFromString(), but accepts messages that are missing
  // required fields.
  bool ParsePartialFromString(const string& data);
  // Parse a protocol buffer contained in an array of bytes.
  bool ParseFromArray(const void* data, int size);
  // Like ParseFromArray(), but accepts messages that are missing
  // required fields.
  bool ParsePartialFromArray(const void* data, int size);


  // Reads a protocol buffer from the stream and merges it into this
  // Message.  Singular fields read from the input overwrite what is
  // already in the Message and repeated fields are appended to those
  // already present.
  //
  // It is the responsibility of the caller to call input->LastTagWas()
  // (for groups) or input->ConsumedEntireMessage() (for non-groups) after
  // this returns to verify that the message's end was delimited correctly.
  //
  // ParsefromCodedStream() is implemented as Clear() followed by
  // MergeFromCodedStream().
  bool MergeFromCodedStream(io::CodedInputStream* input);

  // Like MergeFromCodedStream(), but succeeds even if required fields are
  // missing in the input.
  //
  // MergeFromCodedStream() is just implemented as MergePartialFromCodedStream()
  // followed by IsInitialized().
  virtual bool MergePartialFromCodedStream(io::CodedInputStream* input) = 0;


  // Serialization ---------------------------------------------------
  // Methods for serializing in protocol buffer format.  Most of these
  // are just simple wrappers around ByteSize() and SerializeWithCachedSizes().

  // Write a protocol buffer of this message to the given output.  Returns
  // false on a write error.  If the message is missing required fields,
  // this may GOOGLE_CHECK-fail.
  bool SerializeToCodedStream(io::CodedOutputStream* output) const;
  // Like SerializeToCodedStream(), but allows missing required fields.
  bool SerializePartialToCodedStream(io::CodedOutputStream* output) const;
  // Write the message to the given zero-copy output stream.  All required
  // fields must be set.
  bool SerializeToZeroCopyStream(io::ZeroCopyOutputStream* output) const;
  // Like SerializeToZeroCopyStream(), but allows missing required fields.
  bool SerializePartialToZeroCopyStream(io::ZeroCopyOutputStream* output) const;
  // Serialize the message and store it in the given string.  All required
  // fields must be set.
  bool SerializeToString(string* output) const;
  // Like SerializeToString(), but allows missing required fields.
  bool SerializePartialToString(string* output) const;
  // Serialize the message and store it in the given byte array.  All required
  // fields must be set.
  bool SerializeToArray(void* data, int size) const;
  // Like SerializeToArray(), but allows missing required fields.
  bool SerializePartialToArray(void* data, int size) const;

  // Make a string encoding the message. Is equivalent to calling
  // SerializeToString() on a string and using that.  Returns the empty
  // string if SerializeToString() would have returned an error.
  // Note: If you intend to generate many such strings, you may
  // reduce heap fragmentation by instead re-using the same string
  // object with calls to SerializeToString().
  string SerializeAsString() const;
  // Like SerializeAsString(), but allows missing required fields.
  string SerializePartialAsString() const;

  // Like SerializeToString(), but appends to the data to the string's existing
  // contents.  All required fields must be set.
  bool AppendToString(string* output) const;
  // Like AppendToString(), but allows missing required fields.
  bool AppendPartialToString(string* output) const;

  // Computes the serialized size of the message.  This recursively calls
  // ByteSize() on all embedded messages.  If a subclass does not override
  // this, it MUST override SetCachedSize().
  //
  // ByteSize() is generally linear in the number of fields defined for the
  // proto.
  virtual int ByteSize() const = 0;

  // Serializes the message without recomputing the size.  The message must
  // not have changed since the last call to ByteSize(); if it has, the results
  // are undefined.
  virtual void SerializeWithCachedSizes(
      io::CodedOutputStream* output) const = 0;

  // Like SerializeWithCachedSizes, but writes directly to *target, returning
  // a pointer to the byte immediately after the last byte written.  "target"
  // must point at a byte array of at least ByteSize() bytes.
  virtual uint8* SerializeWithCachedSizesToArray(uint8* target) const;

  // Returns the result of the last call to ByteSize().  An embedded message's
  // size is needed both to serialize it (because embedded messages are
  // length-delimited) and to compute the outer message's size.  Caching
  // the size avoids computing it multiple times.
  //
  // ByteSize() does not automatically use the cached size when available
  // because this would require invalidating it every time the message was
  // modified, which would be too hard and expensive.  (E.g. if a deeply-nested
  // sub-message is changed, all of its parents' cached sizes would need to be
  // invalidated, which is too much work for an otherwise inlined setter
  // method.)
  virtual int GetCachedSize() const = 0;

 private:
  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MessageLite);
};

}  // namespace protobuf

}  // namespace google
#endif  // GOOGLE_PROTOBUF_MESSAGE_LITE_H__