build: split buildflags package

Planned to be imported by nerdctl in future.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

util/buildflags/ssh.go

@@ -0,0 +1,38 @@
+package buildflags
+
+import (
+	"strings"
+
+	"github.com/moby/buildkit/session"
+	"github.com/moby/buildkit/session/sshforward/sshprovider"
+	"github.com/moby/buildkit/util/gitutil"
+)
+
+func ParseSSHSpecs(sl []string) (session.Attachable, error) {
+	configs := make([]sshprovider.AgentConfig, 0, len(sl))
+	for _, v := range sl {
+		c, err := parseSSH(v)
+		if err != nil {
+			return nil, err
+		}
+		configs = append(configs, *c)
+	}
+	return sshprovider.NewSSHAgentProvider(configs)
+}
+
+func parseSSH(value string) (*sshprovider.AgentConfig, error) {
+	parts := strings.SplitN(value, "=", 2)
+	cfg := sshprovider.AgentConfig{
+		ID: parts[0],
+	}
+	if len(parts) > 1 {
+		cfg.Paths = strings.Split(parts[1], ",")
+	}
+	return &cfg, nil
+}
+
+// IsGitSSH returns true if the given repo URL is accessed over ssh
+func IsGitSSH(url string) bool {
+	_, gitProtocol := gitutil.ParseProtocol(url)
+	return gitProtocol == gitutil.SSHProtocol
+}