Allow enabling gitlab-shell "discover"-feature

This adds the possibility to enable features for GitLab shell.

The first feature being recognized is "Discover": It's the command
that is executed when running `ssh git@gitlab.example.com` and is
called without a command.

The gitlab key id or username is already parsed from the command line
arguments.

Currently we only support communicating with GitLab-rails using unix
sockets. So features will not be enabled if the GitLab-url is using a
different protocol. The url for this read from the config yaml.

Pending ruby-specs have been added for the gitlab-shell command.

Refactor to have separate command packages

1 files changed, 82 insertions, 0 deletions

diff --git a/go/internal/command/commandargs/command_args.go b/go/internal/command/commandargs/command_args.go
new file mode 100644
index 0000000..7bc13b6
--- /dev/null
+++ b/go/internal/command/commandargs/command_args.go
@@ -0,0 +1,82 @@
+package commandargs
+
+import (
+	"errors"
+	"os"
+	"regexp"
+)
+
+type CommandType string
+
+const (
+	Discover CommandType = "discover"
+)
+
+var (
+	whoKeyRegex      = regexp.MustCompile(`\bkey-(?P<keyid>\d+)\b`)
+	whoUsernameRegex = regexp.MustCompile(`\busername-(?P<username>\S+)\b`)
+)
+
+type CommandArgs struct {
+	GitlabUsername string
+	GitlabKeyId    string
+	SshCommand     string
+	CommandType    CommandType
+}
+
+func Parse(arguments []string) (*CommandArgs, error) {
+	if sshConnection := os.Getenv("SSH_CONNECTION"); sshConnection == "" {
+		return nil, errors.New("Only ssh allowed")
+	}
+
+	info := &CommandArgs{}
+
+	info.parseWho(arguments)
+	info.parseCommand(os.Getenv("SSH_ORIGINAL_COMMAND"))
+
+	return info, nil
+}
+
+func (info *CommandArgs) parseWho(arguments []string) {
+	for _, argument := range arguments {
+		if keyId := tryParseKeyId(argument); keyId != "" {
+			info.GitlabKeyId = keyId
+			break
+		}
+
+		if username := tryParseUsername(argument); username != "" {
+			info.GitlabUsername = username
+			break
+		}
+	}
+}
+
+func tryParseKeyId(argument string) string {
+	matchInfo := whoKeyRegex.FindStringSubmatch(argument)
+	if len(matchInfo) == 2 {
+		// The first element is the full matched string
+		// The second element is the named `keyid`
+		return matchInfo[1]
+	}
+
+	return ""
+}
+
+func tryParseUsername(argument string) string {
+	matchInfo := whoUsernameRegex.FindStringSubmatch(argument)
+	if len(matchInfo) == 2 {
+		// The first element is the full matched string
+		// The second element is the named `username`
+		return matchInfo[1]
+	}
+
+	return ""
+}
+
+func (c *CommandArgs) parseCommand(commandString string) {
+	c.SshCommand = commandString
+
+	if commandString == "" {
+		c.CommandType = Discover
+	}
+}