command exec: Adding support for streamProtocolV4

[jraby]

I've had a use case to exec some commands in pods and return the exit code of the remote program transparently to the parent process.

At the moment doing so involves fishing out the exit code by parsing the string returned via the error channel of the websocket when the remote command exit.

While looking at how kubectl handles this, I found that the api does in fact support reporting the exit code directly via the error channel of the websocket since this commit:
kubernetes/kubernetes@e792d41

This requires support for the v4 stream protocol by the client (server defaults to v3).

I'm not sure what would be the best way to add support for this.
In my test, simply adding this header to the upgrade request makes it Just Work, but I'm not sure if this would be an appropriate fix:

diff --git a/kubernetes/client/ws_client.py b/kubernetes/client/ws_client.py
index b0a60e5..edcaa08 100644
--- a/kubernetes/client/ws_client.py
+++ b/kubernetes/client/ws_client.py
@@ -46,6 +46,8 @@ class WSClient:
         if headers and 'authorization' in headers:
             header.append("authorization: %s" % headers['authorization'])
 
+        header.append('Sec-WebSocket-Protocol: v4.channel.k8s.io')
+
         if url.startswith('wss://') and configuration.verify_ssl:
             ssl_opts = {
                 'cert_reqs': ssl.CERT_REQUIRED,

With this patch, instead of getting a plain string down the error channel, we get this:

    "metadata": {},
    "status": "Failure",
    "message": "command terminated with non-zero exit code: Error executing in Docker Container: 4",
    "reason": "NonZeroExitCode",
    "details": {
        "causes": [
            {
                "reason": "ExitCode",
                "message": "4"
            }
        ]
    }
}

originally we'd get this:

command terminated with non-zero exit code: Error executing in Docker Container: 4

What would be a good way forward for this? Should the client default to v4? Or should it provide a handle to set whatever protocol version string we might wish to send?

Thanks.

[dims]

@jraby since that commit you referenced has been in kubernetes since v1.4.0-alpha.3, we should just default to v4. However it's @mbohlool 's call :)

[mbohlool]

I don't see any problem with making v4 default. I would make it a configuration though so people can change it. Also a general headers configuration would be useful (that is better to be added upstream to swagger-codegen).