Fixed: Parse (but ignore for now) terminal APC sequences

terminal-emulator/src/main/java/com/termux/terminal/TerminalEmulator.java

@@ -79,6 +79,10 @@ public final class TerminalEmulator {
  private static final int ESC_CSI_SINGLE_QUOTE = 18;
  /** Escape processing: CSI ! */
  private static final int ESC_CSI_EXCLAMATION = 19;
+ /** Escape processing: "ESC _" or Application Program Command (APC). */
+ private static final int ESC_APC = 20;
+ /** Escape processing: "ESC _" or Application Program Command (APC), following by an Escape. */
+ private static final int ESC_APC_ESCAPE = 21;
 
  /** The number of parameter arguments. This name comes from the ANSI standard for terminal escape codes. */
  private static final int MAX_ESCAPE_PARAMETERS = 16;
@@ -548,6 +552,15 @@ private void processByte(byte byteToProcess) {
  }
 
  public void processCodePoint(int b) {
+ // The Application Program-Control (APC) string might be arbitrary non-printable characters, so handle that early.
+ if (mEscapeState == ESC_APC) {
+ doApc(b);
+ return;
+ } else if (mEscapeState == ESC_APC_ESCAPE) {
+ doApcEscape(b);
+ return;
+ }
+
  switch (b) {
  case 0: // Null character (NUL, ^@). Do nothing.
  break;
@@ -1004,6 +1017,30 @@ private void doDeviceControl(int b) {
  }
  }
 
+ /**
+ * When in {@link #ESC_APC} (APC, Application Program Command) sequence.
+ */
+ private void doApc(int b) {
+ if (b == 27) {
+ continueSequence(ESC_APC_ESCAPE);
+ }
+ // Eat APC sequences silently for now.
+ }
+
+ /**
+ * When in {@link #ESC_APC} (APC, Application Program Command) sequence.
+ */
+ private void doApcEscape(int b) {
+ if (b == '\\') {
+ // A String Terminator (ST), ending the APC escape sequence.
+ finishSequence();
+ } else {
+ // The Escape character was not the start of a String Terminator (ST),
+ // but instead just data inside of the APC escape sequence.
+ continueSequence(ESC_APC);
+ }
+ }
+
  private int nextTabStop(int numTabs) {
  for (int i = mCursorCol + 1; i < mColumns; i++)
  if (mTabStop[i] && --numTabs == 0) return Math.min(i, mRightMargin);
@@ -1399,6 +1436,9 @@ private void doEsc(int b) {
  case '>': // DECKPNM
  setDecsetinternalBit(DECSET_BIT_APPLICATION_KEYPAD, false);
  break;
+ case '_': // APC - Application Program Command.
+ continueSequence(ESC_APC);
+ break;
  default:
  unknownSequence(b);
  break;

terminal-emulator/src/test/java/com/termux/terminal/ApcTest.java

@@ -0,0 +1,21 @@
+package com.termux.terminal;
+
+public class ApcTest extends TerminalTestCase {
+
+ public void testApcConsumed() {
+ // At time of writing this is part of what yazi sends for probing for kitty graphics protocol support:
+ // https://github.com/sxyazi/yazi/blob/0cdaff98d0b3723caff63eebf1974e7907a43a2c/yazi-adapter/src/emulator.rs#L129
+ // This should not result in anything being written to the screen: If kitty graphics protocol support
+ // is implemented it should instead result in an error code on stdin, and if not it should be consumed
+ // silently just as xterm does. See https://sw.kovidgoyal.net/kitty/graphics-protocol/.
+ withTerminalSized(2, 2)
+ .enterString("\033_Gi=31,s=1,v=1,a=q,t=d,f=24;AAAA\033\\")
+ .assertLinesAre(" ", " ");
+
+ // It is ok for the APC content to be non printable characters:
+ withTerminalSized(12, 2)
+ .enterString("hello \033_some\023\033_\\apc#end\033\\ world")
+ .assertLinesAre("hello world", " ");
+ }
+
+}