(#128) Throw an error when bash is not installed in the target container

[mdelapenya]

What does this PR do?

It throws an error when the evaluation of the '/bin/bash' command used to
check the host/port in the target container fails because 'bash' is not
present in the system (as it happens in most Alpine-based images).

Why is it important?

It will make the checks more reliable, as the implementation will raise an
error that could be handled by client code.

Before this change, the client code waited and a timeout happened. Now a more
accurate error is raised so it's easier to handle.

Related issues

Closes #128

[mdelapenya]

reopening for travis to rebuild

[nikolayk812]

it was a bug, yes, sorry for that

[nikolayk812]

this is unnecessary, I believe. External command fix should be enough.

[mdelapenya]

Hey, sorry for the late response. I'll revert this change and resend. TBH, not sure why the travis tests fail tough.

[mdelapenya]

Mmmm, thinking about it, the internal command should be sh, because it's very likely that bash is not present in the container (i.e. Alpine-based images)

[nikolayk812]

@mdelapenya are you planning to fix this branch?

[mdelapenya]

@mdelapenya are you planning to fix this branch?

Yes, the thing is I'm not sure why the tests are failing on Travis 🤷‍♀ I'm debugging locally trying to find the issue

[mdelapenya]

After debugging this before the sh replacement (37e3ccb) and after it (8e056de) I can see that the execution of the buildInternalCheckCommand is causing the problem.

The below output comes from debugging TestContainerCreationAndWaitForListeningPortLongEnough from VSCode before replacing BASH, adding a breakpoint at host_port.go:

exitCode, err := target.Exec(ctx, []string{"/bin/bash", "-c", command})

The generated command is:

true && (
					cat /proc/net/tcp{,6} | awk '{print $2}' | grep -i :50 ||
					nc -vz -w 1 localhost 80 ||
					/bin/bash -c '</dev/tcp/localhost/80'
				)

Entering into the created container (docker exec -ti), I can execute each of those subcommands:

root@16589f2fd2e4:/# cat /proc/net/tcp{,6} | awk '{print $2}' | grep -i :50                                               
root@16589f2fd2e4:/# cat /proc/net/tcp{,6} | awk '{print $2}'              
local_address
00000000:0050
0100007F:8200
0100007F:81F4
local_address
root@16589f2fd2e4:/# cat /proc/net/tcp{,6} | awk '{print $2}' | grep -i :0050
00000000:0050 

BTW, nc is probably not installed in the target container although not executed if the previous piped commands succeed.

The weirdest thing here is that running the tests at this point, they all pass. Replacing BASH with SH, then the command exits with errorLevel 2:

Exit code 2        Misuse of shell builtins (according to Bash documentation)        Example: empty_function() {}

@nikolayk812 could you assist me here? Thanks!

[mdelapenya]

More on this. If I run the container used in tests:

docker run --name nginx --rm -d menedev/delayed-nginx:1.15.2

And execute the internal command from my local terminal:

With /bin/bash

$ docker exec nginx /bin/bash -c "true && (cat /proc/net/tcp{,6} | awk '{print $2}' | grep -i :50)"
$ docker exec nginx /bin/bash -c "true && (cat /proc/net/tcp{,6} | awk '{print $2}' | grep -i :0050)"
   0: 00000000:0050 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 6218691 1 0000000000000000 100 0 0 10 0 

With /bin/sh

$ docker exec nginx /bin/sh -c "true && (cat /proc/net/tcp{,6} | awk '{print $2}' | grep -i :50)"  
cat: /proc/net/tcp{,6}: No such file or directory
$ docker exec nginx /bin/sh -c "true && (cat /proc/net/tcp{,6} | awk '{print $2}' | grep -i :0050)"
cat: /proc/net/tcp{,6}: No such file or directory

I'm going to check how to use /bin/sh properly

[mdelapenya]

More on this: trying to escape awk quotes properly:

$ docker exec nginx /bin/bash -c 'true && (cat /proc/net/tcp6 | awk "\"{print $2}"\" | grep -i :0050)'
$ docker exec nginx /bin/sh -c 'true && (cat /proc/net/tcp{,6} | awk "\"{print $2}"\" | grep -i :0050)' 
cat: /proc/net/tcp{,6}: No such file or directory

I see differences in how the sh command sees the tcp files.

Entering the container used in tests:

root@8da5c254bfe3:/# /bin/bash -c 'true && (cat /proc/net/tcp{,6} | awk "\"{print $2}"\" | grep -i :0050)'
   0: 00000000:0050 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 6218691 1 0000000000000000 100 0 0 10 0                   
root@8da5c254bfe3:/# echo $?
0
root@8da5c254bfe3:/# /bin/sh -c 'true && (cat /proc/net/tcp{,6} | awk "\"{print $2}"\" | grep -i :0050)'
cat: /proc/net/tcp{,6}: No such file or directory
root@8da5c254bfe3:/# echo $?
1

I see slight differences in how the command behaves.

[mdelapenya]

That was the clue!! At least, WOMC! Let's 🤞 for Travis :)

[mdelapenya]

Tests fixed! @gianarb please take a look 🙏, this is already fixed

BTW, using SH instead of BASH is what the Java impl is doing (https://github.com/testcontainers/testcontainers-java/blob/23e9718a56eeac3ca2ec87c8a2525fa8e4bf76df/core/src/main/java/org/testcontainers/containers/wait/internal/InternalCommandPortListeningCheck.java#L42), so without knowing it before, it turned out we are in the same page 😄

[gianarb]

Good job!! Thanks @mdelapenya