bug report

README.md

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+# Bug Report for XTerm
+
+## Summary
+
+With 1002 and 1016 mode enabled, XTerm may produce invalid CSI sequence.
+
+## Prerequisites
+
+* XTerm version: 365
+* XTerm configuration: default
+* Operating System: GNU/Linux
+
+## Steps to Reproduce
+
+1. Compile [test.c](test.c) with `gcc -o test-xterm test.c`.
+2. In XTerm, run `script -I input.esc`.
+3. Run `./test-xterm`.
+4. Move mouse pointer into the terminal window.
+5. Press down mouse button (do not release yet).
+6. Move mouse pointer across the top or left border of the terminal window.
+7. Release mouse button.
+8. Press Ctrl+D to quit the test program.
+9. Execute `exit` to quit the `script` session.
+10. Run `teseq -L input.esc | less`.
+
+## Analyze the Input Log
+
+In Teseq's output, you may see something like this:
+
+```
+: Esc [ < 32 ; 9 ; 492 M
+: Esc [ < 32 ; 5 ; 492 M
+: Esc [ < 32 ; 1 ; 492 M
+: Esc [
+|<32;-3;492M|
+: Esc [
+|<32;-5;492M|
+: Esc [
+|<32;-7;492M|
+```
+
+After the mouse pointer moves across the window border, XTerm prints the negative coordinates in the CSI sequence.
+
+However, the hyphen character "-" is not a valid CSI parameter byte, according to ECMA-48.
+
+## Bugfix
+
+The bug is caused by the following code in button.c:
+
+```C
+// ...
+    if (screen->extend_coords == SET_PIXEL_POSITION_MOUSE) {
+    row = event->y - OriginY(screen);
+    col = event->x - OriginX(screen);
+    } else {
+    /* Compute character position of mouse pointer */
+    row = (event->y - screen->border) / FontHeight(screen);
+    col = (event->x - OriginX(screen)) / FontWidth(screen);
+
+    /* Limit to screen dimensions */
+    if (row < 0)
+        row = 0;
+    else if (row > screen->max_row)
+        row = screen->max_row;
+
+    if (col < 0)
+        col = 0;
+    else if (col > screen->max_col)
+        col = screen->max_col;
+// ...
+```
+
+When 1016 mode is enabled, XTerm does not limit the coordinates to the screen dimensions, so that negative values may be produced.
+
+Apply the patch [button.c.patch](button.c.patch) to button.c to fix the bug.

button.c.patch

@@ -0,0 +1,13 @@
+--- button.c	2021-02-04 09:00:26.000000000 +0800
++++ button.patched.c	2021-02-07 21:31:45.960978282 +0800
+@@ -5258,6 +5258,10 @@
+     if (screen->extend_coords == SET_PIXEL_POSITION_MOUSE) {
+ 	row = event->y - OriginY(screen);
+ 	col = event->x - OriginX(screen);
++	if (row < 0)
++	    row = 0;
++	if (col < 0)
++	    col = 0;
+     } else {
+ 	/* Compute character position of mouse pointer */
+ 	row = (event->y - screen->border) / FontHeight(screen);

test.c

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+#include <stdio.h>
+#include <termios.h>
+#include <unistd.h>
+
+int main()
+{
+    struct termios old_termios, new_termios;
+    int ch, fd_in = STDIN_FILENO;
+    tcgetattr(fd_in, &old_termios);
+    new_termios = old_termios;
+    new_termios.c_lflag &= ~(ICANON | ECHO);
+    tcsetattr(fd_in, TCSANOW, &new_termios);
+    setvbuf(stdout, NULL, _IONBF, 0);
+    printf("\033[?1002h");
+    printf("\033[?1016h");
+    while (EOF != (ch = getchar())) {
+        if (ch == 0x04) {
+            break;
+        }
+    }
+    printf("\033[?1016l");
+    printf("\033[?1002l");
+    tcsetattr(fd_in, TCSANOW, &old_termios);
+    return 0;
+}