There's no distinction between
message Foo {
int32 foo = 1;
}
and
message Bar {
int32 bar = 1;
}
It's all encoded as tags and values, the type and field names aren't
on the wire. Unknown tags are ignored (or put into a "unknown tag"
list). The framing is entirely up to you. One non-horrible thing to do
is to create e.g. a
message Header {
string type = 1;
int32 length = 2;
}
Then write a len(header) varint, header, payload. Then you can decode
them sequentially and get the right data on the other end. (The
horrible thing to do is to create a "container" message which has the
the payload data in a "bytes" field, since you end up
double-encoding/decoding the data.)
-ilia
On Mon, Apr 30, 2018 at 3:49 PM, Andrew Bouchard <[email protected]> wrote:
> I'm using the MOOS communications framework, which allows me to send
> messages between modules in a binary, string, or numerical format using a
> centralized database. In order to minimize the number of new interfaces that
> I need to create, I'd like to send multiple messages over the same
> interface, then differentiate between them on the other end. The method I
> struck on to do this was to use ParseFromString to see whether the received
> message parsed successfully as a given type. Here's a simple example:
>
> void CModule::ProcessMessages( CMOOSMsg &msg )
> {
> // Declare message types
> MyMessages::TypeA type_a;
> MyMessages::TypeB type_b;
>
> // Parse a message of type A
> if( type_a.ParseFromString( msg.GetString() ) )
> {
> printf( "Received a message of type A\n" );
> }
> // Parse a message of type B
> else if( type_b.ParseFromString( msg.GetString() ) )
> {
> printf( "Received a message of type B\n" );
> }
> else
> {
> printf( "ERROR: Unrecognized message type" );
> }
> }
>
> I think that I have misunderstood how ParseFromString works, because instead
> of the first call returning FALSE when msg is a serialized message of type
> B, it attempts to shoehorn the fields from type B into type A; as you might
> guess, this is causing all sorts of problems.
>
> I've been looking into the MessageLite class and its ParseFromCodedStream
> method. I think that it may do what I want, but I'm hesitant to go down the
> rabbit hole of learning a new tool if I can talk to someone else and learn
> if this is really what I want first. Does anyone here have any advice?
> Thanks very much!
>
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