Adición comprobación nombre de usuario ya existe en register

users/userservice/user-service.js

@@ -45,6 +45,19 @@ app.post('/adduser', async (req, res) => {
         res.status(400).json({ error: error.message }); 
     }});
 
+app.get('/checkuser/:username', async (req, res) => {
+    try{
+      const existUser = await User.findOne({ username: req.params.username });
+      if(existUser){
+        return res.json({ exists: true });
+      }else{
+        return res.json({ exists: false });
+      }
+    } catch (error) {
+        res.status(400).json({ error: error.message }); 
+    }
+});
+
 const server = app.listen(port, () => {
   console.log(`User Service listening at http://localhost:${port}`);
 });

webapp/src/components/AddUser.js

@@ -22,6 +22,13 @@ const AddUser = () => {
         setError("Passwords don't match");
         return;
       }
+
+      const response = await axios.get(`${apiEndpoint}/checkuser/${username}`);
+      if (response.data.exists) {
+        setError("Username already exists");
+        return;
+      }
+
       await axios.post(`${apiEndpoint}/adduser`, { username, password });
       setOpenSnackbar(true);
     } catch (error) {