class Message

Append raw bytes for a field, using the supplied |ranges| to

copy from |num_ranges| individual buffers.

The ctor is deliberately a no-op to avoid forwarding args from all

subclasses. The real initialization is performed by Reset().

Nested messages are allocated via placement new by MessageArena and

implictly destroyed when the RootMessage's arena goes away. This is

fine as long as all the fields are PODs, which is checked by the

static_assert()s in the Reset() method.

Proto types: sint64, sint32.

Proto types: bool, enum (small).

Faster version of AppendVarInt for tiny numbers.

Proto types: fixed64, sfixed64, fixed32, sfixed32, double, float.

Clears up the state, allowing the message to be reused as a fresh one

with the specified encoding.

Finalizes all open children, then seals this message:

- Length-delimited: writes the encoded size into the reserved length field,

if present. For short messages within the current chunk, compaction can

reduce the field from proto_utils::kMessageLengthFieldSize bytes to one.

- kProtoGroup: writes nothing. The parent writes the closing byte.

Returns the encoded size of this message's fields, including nested

messages. It excludes this message's own tag, length field and closing

byte.

Finalize is idempotent and can be called several times w/o side effects.

Returns the encoding each new child inherits.

Convenience wrapper for the default length-delimited encoding.

See the TODO on RootMessage::Reset().

Optional. If is_valid() == true, the corresponding memory region (its

length == proto_utils::kMessageLengthFieldSize) is backfilled with the size

of this message. This is the mechanism used by messages to backfill their

corresponding size field in the parent message. In most cases this is only

used for nested messages and the ScatteredStreamWriter::Delegate (e.g.

TraceWriterImpl), takes case of the outer message.

In kProtoGroup mode, this pointer must always be null.

Proto types: uint64, uint32, int64, int32, bool, enum.

Begins a nested message. The returned object is owned by the MessageArena

of the root message. The nested message ends either when Finalize() is

called or when any other Append* method is called in the parent class.

The template argument T is supposed to be a stub class auto generated from

a .proto, hence a subclass of Message.

Gives read-only access to the underlying stream_writer. This is used only

by few internals to query the state of the underlying buffer. It is almost

always a bad idea to poke at the stream_writer() internals.

Appends some raw bytes to the message. The use-case for this is preserving

unknown fields in the decode -> re-encode path of xxx.gen.cc classes

generated by the cppgen_plugin.cc.

The caller needs to guarantee that the appended data is properly

proto-encoded and each field has a proto preamble.

In kProtoGroup mode:

- |data| must not contain protobuf group fields. This mode reserves wire

types 3 and 4 for nested message boundaries.

- A nested message must contain only proto fields. For a raw string or

bytes payload, use AppendBytes() on the parent.

Encoding for nested messages. The root selects it in Reset(). Each child

inherits its parent's encoding.

Keep in sync with PerfettoPbMsgEncoding in perfetto/public/pb_msg.h.