FIXUP! cancel current line on CTRL-C.

CTRL-C now cancels the current line instead of exiting, similar to
how getty works.

This is a suggestion of @benemorius.

sys/shell/shell.c

@@ -227,22 +227,23 @@ static int readline(char *buf, size_t size)
         }
 
         int c = getchar();
-        if (c < 0 || c == '\x03' || c == '\x04') {
+        if (c < 0 || c == '\x04') {
             return EOF;
         }
 
         /* We allow Unix linebreaks (\n), DOS linebreaks (\r\n), and Mac linebreaks (\r). */
         /* QEMU transmits only a single '\r' == 13 on hitting enter ("-serial stdio"). */
         /* DOS newlines are handled like hitting enter twice, but empty lines are ignored. */
-        if (c == '\r' || c == '\n') {
+        /* Ctrl-C cancels the current line. */
+        if (c == '\r' || c == '\n' || c == '\x03') {
             *line_buf_ptr = '\0';
 #ifndef SHELL_NO_ECHO
             _putchar('\r');
             _putchar('\n');
 #endif
 
             /* return 1 if line is empty, 0 otherwise */
-            return line_buf_ptr == buf;
+            return c == '\x03' || line_buf_ptr == buf;
         }
         /* QEMU uses 0x7f (DEL) as backspace, while 0x08 (BS) is for most terminals */
         else if (c == 0x08 || c == 0x7f) {

tests/shell/tests/01-run.py

@@ -32,10 +32,14 @@
 # literal ETX instead of SIGINT.
 # When using a board (with miniterm.py) it is not a problem.
 
+DLE = '\x16'
+
 if os.environ['BOARD'] == 'native':
-    CONTROL_C = '\x16\x03'
+    CONTROL_C = DLE+'\x03'
+    CONTROL_D = DLE+'\x04'
 else:
     CONTROL_C = '\x03'
+    CONTROL_D = '\x04'
 
 CMDS = (
     ('start_test', ('[TEST_START]')),
@@ -49,9 +53,10 @@
     ('echo a string', ('\"echo\"\"a\"\"string\"')),
     ('ps', EXPECTED_PS),
     ('reboot', ('test_shell.')),
-    (CONTROL_C, ('shell exited (1)')),
+    (CONTROL_D, ('shell exited (1)')),
     ('echo', ('"echo"')),
-    ('\x04', ('shell exited (2)'))
+    ('garbage1234'+CONTROL_C, ('>')), # test cancelling a line
+    ('help', EXPECTED_HELP),
 )