Does some existing parser actually implement that skipping feature?
There would not be any need for a end-tag. Let's assume that there
would be two different tags
2 - Length_Delimited, which could contain a packed list of bytes
(string, memory block) or other types where the parser needs to know
what is packed inside (no tags)
6 - Group or Element_Delimited - which would be like Length_Delimited
but have the number of elements that follow that belong to this field
So for an example message where the first field is a group
(1,6),3 - field numbered 1 of the message, type 6 = Group and 3
elements that follow belong to this group
(1,2),5,"Hello" -field number 1 of the embedded message would be a
string
(3,1),120 - field nr 3 of the embedded message, varint of value 120
(4,1),0 - field nr 4 of the embedded message, varint of value 0
(2,2),5,"World" - field nr 2 of the message
this would be the encoding of the following TheMessage
message Embedded {
required string greeting = 1;
optional int32 useless = 2;
required int32 good = 3;
required int32 evil = 4;
}
message TheMessage {
required Embedded e = 1;
required string target = 2;
}
So in this case there would not be need for an end tag. When
constructing the message it should be relatively easy to count the
number of embedded elements instead of knowing how much space they
occupy. This would enable streaming/serializing the elements
recursively out one by one.
On Jun 23, 9:07 pm, Kenton Varda <ken...@google.com> wrote:
> The advantage of writing the length is that a parser can skip the entire
> sub-message easily without having to parse its contents. Otherwise, we
> would probably use the "group" encoding for sub-messages, where a special
> end tag marks the end of the message.
>
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