cipd: Add -tag option to 'create' and 'pkg-register' subcomands.

go/src/infra/tools/cipd/common.go

Index: go/src/infra/tools/cipd/common.go
diff --git a/go/src/infra/tools/cipd/common.go b/go/src/infra/tools/cipd/common.go
index 3bcc9da209552737dc63e307f5fe07c2c64f27a4..e4c2859eb2f84ce73d9bbc8f6d6a23ab3e01a9b2 100644
--- a/go/src/infra/tools/cipd/common.go
+++ b/go/src/infra/tools/cipd/common.go
@@ -10,6 +10,7 @@ import (
 	"io"
 	"io/ioutil"
 	"regexp"
+	"strings"
 
 	"infra/libs/build"
 )
@@ -20,10 +21,13 @@ const packageServiceDir = ".cipdpkg"
 // Name of the directory inside an installation root reserved for cipd stuff.
 const siteServiceDir = ".cipd"
 
-// packageNameRe is a Regular expression for a package name: <word>/<word/<word>
+// packageNameRe is a regular expression for a package name: <word>/<word/<word>
 // Package names must be lower case.
 var packageNameRe = regexp.MustCompile(`^([a-z0-9_\-]+/)*[a-z0-9_\-]+$`)
 
+// instanceTagKeyRe is a regular expression for a tag key.
+var instanceTagKeyRe = regexp.MustCompile(`^[a-z0-9_\-]+$`)
+
 // Name of the manifest file inside the package.
 const manifestName = packageServiceDir + "/manifest.json"
 
@@ -58,6 +62,21 @@ func ValidateInstanceID(s string) error {
 	return nil
 }
 
+// ValidateInstanceTag returns error if a string doesn't look like a valid tag.
+func ValidateInstanceTag(t string) error {
+	chunks := strings.SplitN(t, ":", 2)
+	if len(chunks) != 2 {
+		return fmt.Errorf("The string %q doesn't look like a tag (a key:value pair)", t)
+	}
+	if len(t) > 400 {
+		return fmt.Errorf("The tag is too long: %q", t)
+	}
+	if !instanceTagKeyRe.MatchString(chunks[0]) {
+		return fmt.Errorf("Invalid tag key in %q. Should be a lowercase word.", t)
+	}
+	return nil
+}
+
 // DefaultServiceURL returns URL to a backend to use by default.
 func DefaultServiceURL() string {
 	if build.ReleaseBuild {