url validity check

app/src/main/java/com/github/libretube/dialogs/CustomInstanceDialog.kt

@@ -14,6 +14,7 @@ import androidx.preference.PreferenceManager
 import com.github.libretube.R
 import com.google.android.material.dialog.MaterialAlertDialogBuilder
 import com.google.android.material.textfield.TextInputEditText
+import java.net.URL
 
 class CustomInstanceDialog : DialogFragment() {
     val TAG = "CustomInstanceDialog"
@@ -35,7 +36,41 @@ class CustomInstanceDialog : DialogFragment() {
             addInstanceButton.setOnClickListener {
                 val instanceName = instanceNameEditText.text.toString()
                 val instanceApiUrl = instanceApiUrlEditText.text.toString()
+
                 if (instanceName != "" && instanceApiUrl != "") {
+                    try {
+                        // check whether the URL is valid, otherwise catch
+                        val u = URL(instanceApiUrl).toURI()
+                        saveCustomInstance(instanceName, instanceApiUrl)
+                        activity?.recreate()
+                        dismiss()
+                    } catch (e: Exception) {
+                        // invalid URL
+                        Toast.makeText(context, getString(R.string.invalid_url), Toast.LENGTH_SHORT).show()
+                    }
+                } else {
+                    // at least one empty input
+                    Toast.makeText(
+                        context, context?.getString(R.string.empty_instance), Toast.LENGTH_SHORT
+                    ).show()
+                }
+            }
+
+            val typedValue = TypedValue()
+            this.requireActivity().theme.resolveAttribute(R.attr.colorPrimaryDark, typedValue, true)
+            val hexColor = String.format("#%06X", (0xFFFFFF and typedValue.data))
+            val appName = HtmlCompat.fromHtml(
+                "Libre<span  style='color:$hexColor';>Tube</span>",
+                HtmlCompat.FROM_HTML_MODE_COMPACT
+            )
+            view.findViewById<TextView>(R.id.title).text = appName
+
+            builder.setView(view)
+            builder.create()
+        } ?: throw IllegalStateException("Activity cannot be null")
+    }
+
+    private fun saveCustomInstance(instanceName: String, instanceApiUrl: String) {
         val sharedPreferences = PreferenceManager
             .getDefaultSharedPreferences(requireContext())
 
@@ -65,26 +100,5 @@ class CustomInstanceDialog : DialogFragment() {
             .putStringSet("custom_instances_name", HashSet(customInstancesNames))
             .putStringSet("custom_instances_url", HashSet(customInstancesUrls))
             .apply()
-                    activity?.recreate()
-                    dismiss()
-                } else {
-                    Toast.makeText(
-                        context, context?.getString(R.string.empty_instance), Toast.LENGTH_SHORT
-                    ).show()
-                }
-            }
-
-            val typedValue = TypedValue()
-            this.requireActivity().theme.resolveAttribute(R.attr.colorPrimaryDark, typedValue, true)
-            val hexColor = String.format("#%06X", (0xFFFFFF and typedValue.data))
-            val appName = HtmlCompat.fromHtml(
-                "Libre<span  style='color:$hexColor';>Tube</span>",
-                HtmlCompat.FROM_HTML_MODE_COMPACT
-            )
-            view.findViewById<TextView>(R.id.title).text = appName
-
-            builder.setView(view)
-            builder.create()
-        } ?: throw IllegalStateException("Activity cannot be null")
     }
 }

app/src/main/res/values/strings.xml

@@ -168,4 +168,5 @@
     <string name="addInstance">Add Instance</string>
     <string name="empty_instance">You have to fill in the name and the API url.</string>
     <string name="clear_customInstances">Clear custom instances</string>
+    <string name="invalid_url">Please enter a valid url</string>
 </resources>