Add custom short code support to web UI

Allow users to optionally specify their own short code when
shortening a URL, instead of always generating a random one.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

handler.go

@@ -5,6 +5,7 @@ import (
 	"database/sql"
 	"embed"
 	"net/http"
+	"regexp"
 	"strings"
 
 	"git.wntrmute.dev/mc/mcdsl/auth"
@@ -82,6 +83,14 @@ func (srv *server) postURL(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	customShort := strings.TrimSpace(r.FormValue("custom"))
+	if customShort != "" {
+		if !regexp.MustCompile(`^[a-zA-Z0-9]+$`).MatchString(customShort) {
+			http.Error(w, "custom short code must be letters and numbers only", http.StatusBadRequest)
+			return
+		}
+	}
+
 	url, err = links.CleanString(url, stripQuery)
 	if err != nil {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
@@ -89,7 +98,7 @@ func (srv *server) postURL(w http.ResponseWriter, r *http.Request) {
 	}
 
 	ctx := context.Background()
-	short, err := links.StoreURL(ctx, srv.db, url)
+	short, err := links.StoreURL(ctx, srv.db, url, customShort)
 	if err != nil {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return

links/url.go

@@ -134,14 +134,16 @@ func Lookup(ctx context.Context, db *sql.DB, s string) (string, error) {
 	return short, nil
 }
 
-func StoreURL(ctx context.Context, db *sql.DB, s string) (string, error) {
-	short, err := Lookup(ctx, db, s)
-	if err == nil {
-		return short, nil
-	}
+func StoreURL(ctx context.Context, db *sql.DB, s string, customShort string) (string, error) {
+	if customShort == "" {
+		short, err := Lookup(ctx, db, s)
+		if err == nil {
+			return short, nil
+		}
 
-	if err != sql.ErrNoRows {
-		return "", err
+		if err != sql.ErrNoRows {
+			return "", err
+		}
 	}
 
 	u, err := FromString(s)
@@ -149,6 +151,10 @@ func StoreURL(ctx context.Context, db *sql.DB, s string) (string, error) {
 		return "", err
 	}
 
+	if customShort != "" {
+		u.Short = customShort
+	}
+
 	err = u.Store(ctx, db)
 	if err != nil {
 		return "", err

templates/index.html

@@ -13,6 +13,10 @@
             <label for="value">URL</label>
             <input type="text" id="value" name="value" placeholder="https://..." required>
         </div>
+        <div class="form-group">
+            <label for="custom">Custom short code (optional)</label>
+            <input type="text" id="custom" name="custom" placeholder="e.g. mylink" pattern="[a-zA-Z0-9]+" title="Letters and numbers only">
+        </div>
         <div class="form-group">
             <label>
                 <input type="checkbox" name="strip"> Strip query string