Talking across versions

[osrf-migration]

Original report (archived issue) by Louise Poubel (Bitbucket: chapulina, GitHub: chapulina).

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Description

It's possible to install 2 ign-transport versions side-by-side, but they don't seem to be able to talk to each other. Not sure if that's expected.

Steps to Reproduce

1. Install ign-transport6 and ign-transport7

2. Clone branch multi-version (e3cc098), where I created a little example that has 2 publishers and 2 subscribers

3. Compile the example:

    cd multi-version
    mkdir build
    cd build
    cmake ..
    make
   

4. On one terminal, start subscriber6:

    cd build
    ./subscriber6
   

5. On another terminal, start subscriber7:

    cd build
    ./subscriber7
   

6. On another terminal, start publisher6:

    cd build
    ./publisher6
   

   Only subscriber6 will receive the message

7. Now try publisher7, and only subscriber7 will receive the message.

Expected behavior:

Both subscribers receive messages from both publishers.

Actual behavior:

Only pub/sub with matching versions can see each other.

Reproduces how often:

100%

Versions

Tested with 6/7

Additional Information

Again, I'm not sure if this is expected. If it is, we can close this issue, but be more strict with our transport / msgs versions on all Ignition libraries.

[osrf-migration]

Original comment by Carlos Agüero (Bitbucket: caguero, GitHub: caguero).

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Yes, it's possible if the wire protocol changes. In particular it happened from 6 to 7, so this is expected.

[osrf-migration]

Original comment by Louise Poubel (Bitbucket: chapulina, GitHub: chapulina).

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After talking offline, some conclusions:

1. We should try to prevent users from mixing versions, by preventing compilation linking to both 6 and 7 and / or printing runtime errors if both versions are in use
2. There are changes that can be made to the discovery protocol to make future changes backwards compatible