Allow dots in app names (closes #260)

App names may now contain dots, such as sneak.berlin: runs of
lowercase letters and numbers joined by single dots or by hyphens,
2 to 63 characters. This is Docker's rule for an image name, and the
app's image is upaas-<name>; it also keeps a dot off either end, so
the name is safe as a directory and log file name.

The new and edit app forms use the same pattern. Their old one was not
a valid regular expression under the flag browsers compile it with, so
browsers ignored it.

A test deploys an app named sneak.berlin against the fake Docker API
and checks the image and container names with Docker's own rules.

Model: opus-5-5

internal/handlers/app_name_validation.go

@@ -13,12 +13,14 @@ const (
 	appNameMaxLength = 63
 )
 
-// validAppNameRe matches names containing only lowercase alphanumeric characters and
-// hyphens, starting and ending with an alphanumeric character.
-var validAppNameRe = regexp.MustCompile(`^[a-z0-9][a-z0-9-]*[a-z0-9]$`)
+// validAppNameRe matches runs of lowercase letters and digits joined by
+// single dots or by hyphens, such as "my-app" or "sneak.berlin". This is
+// Docker's rule for an image name, and the app's image is upaas-<name>.
+// It also keeps the name from being "." or ".." or starting or ending
+// with a dot, so it is safe as a directory and file name. The pattern
+// attribute of the name field on the new and edit app forms is the same.
+var validAppNameRe = regexp.MustCompile(`^[a-z0-9]+((\.|-+)[a-z0-9]+)*$`)
 
-// validateAppName checks that the given app name is safe for use in Docker
-// container names, image tags, and file system paths.
 var (
 	errAppNameLength = errors.New(
 		"app name must be between " +
@@ -26,11 +28,14 @@ var (
 			strconv.Itoa(appNameMaxLength) + " characters",
 	)
 	errAppNamePattern = errors.New(
-		"app name must contain only lowercase letters, numbers, " +
-			"and hyphens, and must start and end with a letter or number",
+		"app name must contain only lowercase letters, numbers, hyphens, " +
+			"and dots, must start and end with a letter or number, " +
+			"and must have a letter or number on both sides of each dot",
 	)
 )
 
+// validateAppName checks that the given app name is safe for use in Docker
+// container names, image tags, and file system paths.
 func validateAppName(name string) error {
 	if len(name) < appNameMinLength || len(name) > appNameMaxLength {
 		return errAppNameLength