fix: try finding a socket, otherwise fail, respect user choice

[catthehacker]

Fixes #1658

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ EDITORCONFIG	editorconfig-checker	2		0	0.03s
✅ REPOSITORY	gitleaks	yes		no	2.44s
✅ REPOSITORY	git_diff	yes		no	0.0s
✅ REPOSITORY	secretlint	yes		no	1.31s

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[codecov]

Codecov Report

Merging #1745 (24298dd) into master (4989f44) will increase coverage by 1.06%.
The diff coverage is 66.12%.

@@            Coverage Diff             @@
##           master    #1745      +/-   ##
==========================================
+ Coverage   61.22%   62.28%   +1.06%     
==========================================
  Files          46       48       +2     
  Lines        7141     7576     +435     
==========================================
+ Hits         4372     4719     +347     
- Misses       2462     2527      +65     
- Partials      307      330      +23     

Impacted Files	Coverage Δ
pkg/common/outbound_ip.go	0.00% <0.00%> (ø)
pkg/container/docker_cli.go	82.23% <ø> (ø)
pkg/container/docker_logger.go	52.08% <ø> (ø)
pkg/container/docker_pull.go	33.33% <ø> (ø)
pkg/container/docker_run.go	13.58% <0.00%> (-0.01%)	⬇️
pkg/container/docker_volume.go	0.00% <ø> (ø)
pkg/container/file_collector.go	37.30% <0.00%> (ø)
pkg/container/host_environment.go	0.00% <0.00%> (ø)
...ontainer/linux_container_environment_extensions.go	23.07% <0.00%> (-1.25%)	⬇️
pkg/exprparser/functions.go	66.32% <0.00%> (-1.04%)	⬇️
... and 22 more

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[wolfogre]

How about:

Suggested change

	// returns socket path or false if not found any
	func socketLocation() (string, bool) {
	if dockerHost, exists := os.LookupEnv("DOCKER_HOST"); exists {
	return dockerHost, true
	}
	for _, p := range commonSocketPaths {
	if _, err := os.Lstat(os.ExpandEnv(p)); err == nil {
	if strings.HasPrefix(p, `\\.\`) {
	return "npipe://" + os.ExpandEnv(p), true
	}
	return "unix://" + os.ExpandEnv(p), true
	}
	}
	return "", false
	}
	// socketLocation returns socket path or false if not found any
	func socketLocation() (string, bool) {
	if dockerHost, exists := os.LookupEnv("DOCKER_HOST"); exists {
	return dockerHost, true
	}
	for _, p := range commonSocketPaths {
	p = os.ExpandEnv(p)
	// `os.Stat` to find a working file, not `os.Lstate`, or the mode could be `ModeSymlink`
	if info, err := os.Stat(p); err == nil {
	switch info.Mode().Type() {
	case os.ModeSocket:
	return "unix://" + p, true
	case os.ModeNamedPipe:
	return "npipe://" + p, true
	default:
	return p, true
	}
	}
	}
	return "", false
	}

[ChristopherHX]

I prefer the suggestions of wolfogre, but that's no reason for me to not approve your PR.

Windows works, however I was unshure that npipe://\\.\pipe\docker_engine is accepted by docker due to mixed \ and /.

[LenaWil]

@jpdrsn claims ~/.rd/docker.sock is also one of the possible locations.