refactor: limit message input by bytes instead of character length

app/src/main/java/com/geeksville/mesh/ui/MessagesFragment.kt

@@ -4,7 +4,6 @@ import android.graphics.Color
 import android.graphics.drawable.GradientDrawable
 import android.os.Bundle
 import android.view.*
-import android.view.inputmethod.EditorInfo
 import android.widget.*
 import androidx.appcompat.app.AppCompatActivity
 import androidx.appcompat.view.ActionMode
@@ -26,7 +25,7 @@ import com.geeksville.mesh.database.entity.QuickChatAction
 import com.geeksville.mesh.databinding.AdapterMessageLayoutBinding
 import com.geeksville.mesh.databinding.MessagesFragmentBinding
 import com.geeksville.mesh.model.UIViewModel
-import com.geeksville.mesh.util.onEditorAction
+import com.geeksville.mesh.util.Utf8ByteLengthFilter
 import com.google.android.material.chip.Chip
 import com.google.android.material.dialog.MaterialAlertDialogBuilder
 import dagger.hilt.android.AndroidEntryPoint
@@ -260,10 +259,8 @@ class MessagesFragment : Fragment(), Logging {
             sendMessageInputText()
         }
 
-        binding.messageInputText.onEditorAction(EditorInfo.IME_ACTION_SEND) {
-            debug("received IME_ACTION_SEND")
-            sendMessageInputText()
-        }
+        // max payload length should be 237 bytes but anything over 235 bytes crashes the radio
+        binding.messageInputText.filters += Utf8ByteLengthFilter(234)
 
         binding.messageListView.adapter = messagesAdapter
         val layoutManager = LinearLayoutManager(requireContext())

app/src/main/java/com/geeksville/mesh/util/Utf8ByteLengthFilter.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2011 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.geeksville.mesh.util;
+
+import android.text.InputFilter;
+import android.text.Spanned;
+
+/**
+ * This filter will constrain edits so that the text length is not
+ * greater than the specified number of bytes using UTF-8 encoding.
+ */
+public class Utf8ByteLengthFilter implements InputFilter {
+    private final int mMaxBytes;
+    public Utf8ByteLengthFilter(int maxBytes) {
+        mMaxBytes = maxBytes;
+    }
+    public CharSequence filter(CharSequence source, int start, int end,
+                               Spanned dest, int dstart, int dend) {
+        int srcByteCount = 0;
+        // count UTF-8 bytes in source substring
+        for (int i = start; i < end; i++) {
+            char c = source.charAt(i);
+            srcByteCount += (c < (char) 0x0080) ? 1 : (c < (char) 0x0800 ? 2 : 3);
+        }
+        int destLen = dest.length();
+        int destByteCount = 0;
+        // count UTF-8 bytes in destination excluding replaced section
+        for (int i = 0; i < destLen; i++) {
+            if (i < dstart || i >= dend) {
+                char c = dest.charAt(i);
+                destByteCount += (c < (char) 0x0080) ? 1 : (c < (char) 0x0800 ? 2 : 3);
+            }
+        }
+        int keepBytes = mMaxBytes - destByteCount;
+        if (keepBytes <= 0) {
+            return "";
+        } else if (keepBytes >= srcByteCount) {
+            return null; // use original dest string
+        } else {
+            // find end position of largest sequence that fits in keepBytes
+            for (int i = start; i < end; i++) {
+                char c = source.charAt(i);
+                keepBytes -= (c < (char) 0x0080) ? 1 : (c < (char) 0x0800 ? 2 : 3);
+                if (keepBytes < 0) {
+                    return source.subSequence(start, i);
+                }
+            }
+            // If the entire substring fits, we should have returned null
+            // above, so this line should not be reached. If for some
+            // reason it is, return null to use the original dest string.
+            return null;
+        }
+    }
+}

app/src/main/res/layout/messages_fragment.xml

@@ -80,7 +80,6 @@
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
             android:inputType="textMultiLine|textCapSentences"
-            android:maxLength="228"
             android:text="" />
 
     </com.google.android.material.textfield.TextInputLayout>