Telephony Issue: Apn config mmsc should start with http but is 啊.

Test: Visual Test
Fix: 313630772
Change-Id: I46dfabde31f0df7b4b0fd473aff24f9707987114

res/values/strings.xml

@@ -3267,6 +3267,8 @@
     <string name="error_mnc_not23">MNC field must be 2 or 3 digits.</string>
     <!-- APN error dialog messages: -->
     <string name="error_adding_apn_type">Carrier does not allow adding APNs of type %s.</string>
+    <!-- APN error messages: -->
+    <string name="error_mmsc_valid">MMSC field must be valid.</string>
     <!-- The message of dialog indicated restoring default APN settings in progress -->
     <string name="restore_default_apn">Restoring default APN settings.</string>
     <!-- APNs screen menu option to reset default APN settings -->

src/com/android/settings/network/apn/ApnEditPageProvider.kt

@@ -150,6 +150,7 @@ fun ApnPage(apnDataInit: ApnData, apnDataCur: MutableState<ApnData>, uriInit: Ur
             SettingsOutlinedTextField(
                 value = apnData.mmsc,
                 label = stringResource(R.string.apn_mmsc),
+                errorMessage = validateMMSC(apnData.mmsc, context),
                 enabled = apnData.mmscEnabled
             ) { apnData = apnData.copy(mmsc = it) }
             SettingsOutlinedTextField(

src/com/android/settings/network/apn/ApnStatus.kt

@@ -239,7 +239,12 @@ fun validateAndSaveApnData(
     if (apnData.customizedConfig.readOnlyApn) {
         return true
     }
-    val errorMsg = validateApnData(apnData, context)
+    var errorMsg = validateApnData(apnData, context)
+    if (errorMsg != null) {
+        //TODO: showError(this)
+        return false
+    }
+    errorMsg = validateMMSC(apnData.mmsc, context)
     if (errorMsg != null) {
         //TODO: showError(this)
         return false
@@ -529,4 +534,9 @@ private fun getEditableApnType(apnData: ApnData): String {
 fun deleteApn(uri: Uri, context: Context) {
     val contentResolver = context.contentResolver
     contentResolver.delete(uri, null, null)
+}
+
+fun validateMMSC(mmsc: String, context: Context): String? {
+    return if (mmsc.matches(Regex("^https?:\\/\\/.+"))) null
+            else context.resources.getString(R.string.error_mmsc_valid)
 }