Fix nil pointer dereference on initialization

[ophum]

Signed-off-by: ophum [email protected]

Please excuse my poor English.

Summary

line 116 in cmd/cmd.go
will happen invalid memory address or nil pointer dereference when err is not nil.
because client is nil

unuse returned client. use empty pack.Client.

Output

Before

After

Documentation

• Should this change be documented?
  • Yes, see #___
  • No

Related

Resolves #___

[jromero]

Hi @ophum, I'm curious as to how you came about this error. In Go, it's common practice to not use the non-error return values when error is not nil. In other words, this is expected.

Let me know if I'm missing something.

References:

• Error handling and go

[ophum]

@jromero thank you for your reply.

Will happen error when following command is execute.

$ DOCKER_HOST=192.168.10.1:2375 pack build imageName
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0xb2ef61]

goroutine 1 [running]:
github.com/buildpacks/pack/cmd.initClient(0x7f4384b63250, 0xc00029aaf0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
        github.com/buildpacks/pack@/cmd/cmd.go:116 +0xd1
github.com/buildpacks/pack/cmd.NewPackCommand(0xe308e0, 0xc00029aaf0, 0xe123c0, 0xc000285e00, 0x0)
        github.com/buildpacks/pack@/cmd/cmd.go:31 +0x1b0
main.main()
        github.com/buildpacks/pack@/cmd/pack/main.go:19 +0x9a

192.168.10.1:2375 is docker daemon.
Because DOCKER_HOST must be assign in format of tcp://192.168.10.1:2375.

Error of pack.NewClient() is errors.Wrap(err, "creating docker client") line 146 in pack/client.go at this time.
So that error is returned on line 116 in pack/cmd/cmd.go .
But *client is returned on line 116 in pack/cmd/cmd.go.
Will happen invalid memory address or nil pointer dereference at this time, because client is nil when err is not nil.

So I changed return *client, err to return pack.Client{}, err.

$ DOCKER_HOST=192.168.10.1:2375 pack build imageName
ERROR: creating docker client: unable to parse docker host `192.168.10.1:2375`

[jromero]

Ah! I see now! Thank you for taking the time to dig in and explain it to me. 🙏