cfg: improve validation of app and task names

Fail if an app or task name contains leading or trailing whitespaces or
non-printable characters.
Names containing these characters are error-prone and unnecessary.
Because app and task names are also used in multiple other commands as
arguments, these characters make the CLI harder to use.

internal/command/release_create.go

@@ -7,10 +7,10 @@ import (
 	"io"
 	"os"
 	"strings"
-	"unicode"
 
 	"github.com/simplesurance/baur/v3/internal/command/term"
 	"github.com/simplesurance/baur/v3/internal/log"
+	"github.com/simplesurance/baur/v3/internal/validation"
 	"github.com/simplesurance/baur/v3/pkg/baur"
 	"github.com/simplesurance/baur/v3/pkg/storage"
 
@@ -98,24 +98,12 @@ func newReleaseCreateCmd() *releaseCreateCmd {
 	return &cmd
 }
 
-func mustValidateReleaseName(releaseName string) {
-	for pos, r := range releaseName {
-		if (pos == 0 || pos == len(releaseName)-1) && unicode.IsSpace(r) {
-			fatalf("release name must not contain leading or trailing whitespaces, got: %q\n",
-				releaseName)
-		}
-
-		if !unicode.IsPrint(r) {
-			fatalf("release name contains non-printable character: %q\n", r)
-		}
-	}
-}
-
 func (c *releaseCreateCmd) run(cmd *cobra.Command, args []string) {
 	ctx := cmd.Context()
 	releaseName := args[0]
 
-	mustValidateReleaseName(releaseName)
+	err := validation.StrID(releaseName)
+	exitOnErrf(err, "invalid release name: %q", releaseName)
 
 	stdout.Printf("creating release: %s\n", term.Highlight(releaseName))
 

internal/validation/validation.go

@@ -0,0 +1,23 @@
+package validation
+
+import (
+	"errors"
+	"fmt"
+	"unicode"
+)
+
+// StrID ensures that id does not contain leading or trailing white spaces
+// ([unicode.IsSpace] and only printable characters ([unicode.IsPrint].
+func StrID(id string) error {
+	for pos, r := range id {
+		if (pos == 0 || pos == len(id)-1) && unicode.IsSpace(r) {
+			return errors.New("contains leading or trailing white spaces")
+		}
+
+		if !unicode.IsPrint(r) {
+			return fmt.Errorf("contains non-printable character: %x", r)
+		}
+	}
+
+	return nil
+}

pkg/cfg/validation.go

@@ -4,6 +4,8 @@ import (
 	"errors"
 	"fmt"
 	"strings"
+
+	"github.com/simplesurance/baur/v3/internal/validation"
 )
 
 var forbiddenNameRunes = [...]rune{
@@ -23,5 +25,5 @@ func validateTaskOrAppName(name string) error {
 		}
 	}
 
-	return nil
+	return validation.StrID(name)
 }