pkg/urlutil: deprecate, and move to builder/remotecontext/urlutil

pkg/urlutil (despite its poorly chosen name) is not really intended as a generic
utility to handle URLs, and should only be used by the builder to handle (remote)
build contexts.

- IsURL() only does a very rudimentary check for http(s):// prefixes, without any
  other validation, but due to its name may give incorrect expectations.
- IsGitURL() is written specifically with docker build remote git contexts in
  mind, and has handling for backward-compatibility, where strings that are
  not URLs, but start with "github.com/" are accepted.

Because of the above, this patch:

- moves the package inside builder/remotecontext, close to where it's intended
  to be used (ideally this would be part of build/remotecontext itself, but this
  package imports many other dependencies, which would introduce those as extra
  dependencies in the CLI).
- deprecates pkg/urlutil, but adds aliases as there are some external consumers.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/image/build/internal/urlutil/urlutil.go

@@ -0,0 +1,46 @@
+// Package urlutil provides helper function to check urls kind.
+// It supports http and git urls.
+package urlutil // import "github.com/docker/docker/builder/remotecontext/urlutil"
+
+import (
+	"regexp"
+	"strings"
+)
+
+var (
+	validPrefixes = map[string][]string{
+		"url": {"http://", "https://"},
+
+		// The github.com/ prefix is a special case used to treat context-paths
+		// starting with `github.com` as a git URL if the given path does not
+		// exist locally. The "github.com/" prefix is kept for backward compatibility,
+		// and is a legacy feature.
+		//
+		// Going forward, no additional prefixes should be added, and users should
+		// be encouraged to use explicit URLs (https://github.com/user/repo.git) instead.
+		"git": {"git://", "github.com/", "git@"},
+	}
+	urlPathWithFragmentSuffix = regexp.MustCompile(".git(?:#.+)?$")
+)
+
+// IsURL returns true if the provided str is an HTTP(S) URL.
+func IsURL(str string) bool {
+	return checkURL(str, "url")
+}
+
+// IsGitURL returns true if the provided str is a git repository URL.
+func IsGitURL(str string) bool {
+	if IsURL(str) && urlPathWithFragmentSuffix.MatchString(str) {
+		return true
+	}
+	return checkURL(str, "git")
+}
+
+func checkURL(str, kind string) bool {
+	for _, prefix := range validPrefixes[kind] {
+		if strings.HasPrefix(str, prefix) {
+			return true
+		}
+	}
+	return false
+}

cli/command/image/build/internal/urlutil/urlutil_test.go

@@ -0,0 +1,41 @@
+package urlutil // import "github.com/docker/docker/builder/remotecontext/urlutil"
+
+import "testing"
+
+var (
+	gitUrls = []string{
+		"git://github.com/docker/docker",
+		"git@github.com:docker/docker.git",
+		"git@bitbucket.org:atlassianlabs/atlassian-docker.git",
+		"https://github.com/docker/docker.git",
+		"http://github.com/docker/docker.git",
+		"http://github.com/docker/docker.git#branch",
+		"http://github.com/docker/docker.git#:dir",
+	}
+	incompleteGitUrls = []string{
+		"github.com/docker/docker",
+	}
+	invalidGitUrls = []string{
+		"http://github.com/docker/docker.git:#branch",
+	}
+)
+
+func TestIsGIT(t *testing.T) {
+	for _, url := range gitUrls {
+		if !IsGitURL(url) {
+			t.Fatalf("%q should be detected as valid Git url", url)
+		}
+	}
+
+	for _, url := range incompleteGitUrls {
+		if !IsGitURL(url) {
+			t.Fatalf("%q should be detected as valid Git url", url)
+		}
+	}
+
+	for _, url := range invalidGitUrls {
+		if IsGitURL(url) {
+			t.Fatalf("%q should not be detected as valid Git prefix", url)
+		}
+	}
+}