[20.10] Regression: detection of experimental --stream is incorrect

[thaJeztah]

relates to #39983
relates to docker-archive/docker-ce#660 (comment)
relates to docker/cli#2809

Looks like the report we received about the daemon producing an error about the experimental --stream option no longer being supported is not fixed yet (the fix in the CLI docker/cli#2809 is not sufficient, as older CLI's will fail)

I accidentally discovered how to reproduce:

Daemon (built from v20.10.0-beta1 tag) started without --experimental:

docker run -it --rm -v /var/run/docker.sock:/var/run/docker.sock docker:18.09 sh

echo "FROM scratch" | docker build -

Sending build context to Docker daemon  2.048kB
Step 1/1 : FROM scratch
 --->
No image was generated. Is your Dockerfile empty?

Daemon:

DEBU[2020-11-06T17:10:57.689685060Z] Calling POST /v1.39/build?buildargs={}&cachefrom=[]&cgroupparent=&cpuperiod=0&cpuquota=0&cpusetcpus=&cpusetmems=&cpushares=0&dockerfile=Dockerfile&labels={}&memory=0&memswap=0&networkmode=default&pull=1&q=1&rm=1&shmsize=0&target=&ulimits=null&version=1

Daemon, started with --experimental

docker run -it --rm -v /var/run/docker.sock:/var/run/docker.sock docker:18.09 sh

echo "FROM scratch" | docker build -
Sending build context to Docker daemon  2.048kB
Error response from daemon: experimental session with v1 builder is no longer supported, use builder version v2 (BuildKit) instead

Daemon:

DEBU[2020-11-06T17:06:11.433017409Z] Calling POST /v1.39/build?buildargs={}&cachefrom=[]&cgroupparent=&cpuperiod=0&cpuquota=0&cpusetcpus=&cpusetmems=&cpushares=0&dockerfile=Dockerfile&labels={}&memory=0&memswap=0&networkmode=default&pull=1&q=1&rm=1&session=btn05f8k6kkk2110fs3djyork&shmsize=0&target=&ulimits=null&version=1
DEBU[2020-11-06T17:06:11.434237792Z] Calling POST /session
INFO[2020-11-06T17:06:11.434395940Z] parsed scheme: ""                             module=grpc
INFO[2020-11-06T17:06:11.434453021Z] scheme "" not registered, fallback to default scheme  module=grpc
INFO[2020-11-06T17:06:11.434470626Z] ccResolverWrapper: sending update to cc: {[{  <nil> 0 <nil>}] <nil> <nil>}  module=grpc
INFO[2020-11-06T17:06:11.434477816Z] ClientConn switching balancer to "pick_first"  module=grpc
DEBU[2020-11-06T17:06:11.486615969Z] FIXME: Got an API for which error does not match any expected type!!!: experimental session with v1 builder is no longer supported, use builder version v2 (BuildKit) instead

(removed stack dump)

ERRO[2020-11-06T17:06:11.486694465Z] Handler for POST /v1.39/build returned error: experimental session with v1 builder is no longer supported, use builder version v2 (BuildKit) instead
DEBU[2020-11-06T17:06:11.486818111Z] FIXME: Got an API for which error does not match any expected type!!!: experimental session with v1 builder is no longer supported, use builder version v2 (BuildKit) instead

(removed stack dump)

WARN[2020-11-06T17:06:11.489208009Z] grpc: addrConn.createTransport failed to connect to {  <nil> 0 <nil>}. Err :connection error: desc = "transport: Error while dialing only one connection allowed". Reconnecting...  module=grpc

⚠️ Notice that the CLI sends session=btn05f8k6kkk2110fs3djyork, even without it having the --stream option set, so for some reason, it looks for the daemon to be experimental, and in that case, sends a session-id

Trying with explicit --stream:

echo "FROM scratch" | docker build --stream -
failed to open Dockerfile: open Dockerfile: no such file or directory

echo "FROM scratch" | docker build --stream=true -
failed to open Dockerfile: open Dockerfile: no such file or directory

That looks like another bug, but working around that by using a Dockerfile instead of stdin;

echo "FROM scratch" > Dockerfile

docker build --stream .
Error response from daemon: experimental session with v1 builder is no longer supported, use builder version v2 (BuildKit) instead

# without --stream
Calling POST /v1.39/build?buildargs={}&cachefrom=[]&cgroupparent=&cpuperiod=0&cpuquota=0&cpusetcpus=&cpusetmems=&cpushares=0&dockerfile=Dockerfile&labels={}&memory=0&memswap=0&networkmode=default&pull=1&q=1&rm=1&session=btn05f8k6kkk2110fs3djyork&shmsize=0&target=&ulimits=null&version=1

# With --stream
Calling POST /v1.39/build?buildargs={}&cachefrom=[]&cgroupparent=&cpuperiod=0&cpuquota=0&cpusetcpus=&cpusetmems=&cpushares=0&dockerfile=Dockerfile&labels={}&memory=0&memswap=0&networkmode=default&remote=client-session&rm=1&session=361whphfmy9h8g4u5kd2zjayi&shmsize=0&target=&ulimits=null&version=1

⚠️ So, with --stream, the remote=client-session is set: perhaps set should produce an error for that parameter instead?

[thaJeztah]

(I used the 18.09 cli when reproducing, to make sure it's not a recent regression in the CLI code)