Repeated Fields Encoding
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Timothy Parez
Feb 1, 2011, 6:01:21 AM2/1/11
to Protocol Buffers
Hello,
Considering the following proto file:
message FileDescriptor
{
required string Filename = 1;
optional int64 Size = 2 [default = 0];
}
message FileList
{
repeated FileDescriptor Files = 1;
}
If you create something like this:
(and I'm duplicating the data because it made it easier to spot in a
hex editor)
files.Files.Add(new FileDescriptor() { Filename = "AAAAAAA", Size =
100 });
files.Files.Add(new FileDescriptor() { Filename = "AAAAAAA", Size =
100 });
files.Files.Add(new FileDescriptor() { Filename = "AAAAAAA", Size =
100 });
files.Files.Add(new FileDescriptor() { Filename = "AAAAAAA", Size =
100 });
and then serialize it using the Protobuf.Serializer I expected it to
generate something like
Tag for the FileList -> Id 1, WireType 2 => 0x0A
Length of the payload (all the bytes for all the files that follow)
But instead I found everything is simply repeated.
0A 0B 0A 07 41 41 41 41 41 41 41 10 64
0A 0B 0A 07 41 41 41 41 41 41 41 10 64
0A 0B 0A 07 41 41 41 41 41 41 41 10 64
0A 0B 0A 07 41 41 41 41 41 41 41 10 64
I'm wondering, is this an implementation detail (and allowed by the
protobol buffer specifications)
or a requirement of the google protocol buffer specifications ?
It does seem to add quite a bit of overhead, imagine the FileList has
other properties,
they would be repeated for every instance of FileDescriptor ?
Or am I missing something ?
Considering the following proto file:
message FileDescriptor
{
required string Filename = 1;
optional int64 Size = 2 [default = 0];
}
message FileList
{
repeated FileDescriptor Files = 1;
}
If you create something like this:
(and I'm duplicating the data because it made it easier to spot in a
hex editor)
files.Files.Add(new FileDescriptor() { Filename = "AAAAAAA", Size =
100 });
files.Files.Add(new FileDescriptor() { Filename = "AAAAAAA", Size =
100 });
files.Files.Add(new FileDescriptor() { Filename = "AAAAAAA", Size =
100 });
files.Files.Add(new FileDescriptor() { Filename = "AAAAAAA", Size =
100 });
and then serialize it using the Protobuf.Serializer I expected it to
generate something like
Tag for the FileList -> Id 1, WireType 2 => 0x0A
Length of the payload (all the bytes for all the files that follow)
But instead I found everything is simply repeated.
0A 0B 0A 07 41 41 41 41 41 41 41 10 64
0A 0B 0A 07 41 41 41 41 41 41 41 10 64
0A 0B 0A 07 41 41 41 41 41 41 41 10 64
0A 0B 0A 07 41 41 41 41 41 41 41 10 64
I'm wondering, is this an implementation detail (and allowed by the
protobol buffer specifications)
or a requirement of the google protocol buffer specifications ?
It does seem to add quite a bit of overhead, imagine the FileList has
other properties,
they would be repeated for every instance of FileDescriptor ?
Or am I missing something ?
Marc Gravell
Feb 1, 2011, 12:57:29 PM2/1/11
to Timothy Parez, Protocol Buffers
I think this also came to me directly and I answered earlier, but this is the expected layout of "repeated" data, where each item in a list is mapped separately in the data stream.
Marc
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