Stop CHOICE from waiting for input when EOF is reachedkc/choice-break-1

Flagged by SanekGamer007 in
 https://github.com/joncampbell123/dosbox-x/issues/3613 and
documented and fixed by Jookia in
https://github.com/joncampbell123/dosbox-x/pull/3648, as follows:

Running 'REM | CHOICE' or 'CHOICE < NUL' will freeze CHOICE
as it doesn't check for the end of file (EOF) condition.

FreeDOS and MS-DOS documentation specify the following behaviour:
- 0 is returned on abort (in this case Ctrl-C or break is pressed)
- 255 is returned on error (in this case no more input)

---

This commit was adapted from the EOF check authored by Jookia
in https://github.com/joncampbell123/dosbox-x/pull/3648.

This commit also improves the reporting for the EOF and
abort conditions.

Thanks, SanekGamer007 and Jookia!

Reported-by: SanekGamer007 <SanekGamer007@users.noreply.github.com>
Co-Authored-by: Jookia <contact@jookia.org>

2 files changed, 14 insertions, 5 deletions

diff --git a/src/shell/shell.cpp b/src/shell/shell.cpp
index d5d3042fd..c6ee9eb20 100644
--- a/src/shell/shell.cpp
+++ b/src/shell/shell.cpp
@@ -1408,7 +1408,8 @@ void SHELL_Init() {
 	        "Examples:\n"
 	        "  [color=green]choice[reset] /t:[color=white]y[reset],[color=magenta]2[reset] [color=cyan]Continue?[reset]\n"
 	        "  [color=green]choice[reset] /c:[color=white]abc[reset] /s [color=cyan]Type the letter a, b, or c[reset]\n");
-	MSG_Add("SHELL_CMD_CHOICE_ABORTED", "\nChoice aborted.\n");
+	MSG_Add("SHELL_CMD_CHOICE_EOF", "\n[color=red]Choice failed[reset]: the input stream ended without a valid choice.\n");
+	MSG_Add("SHELL_CMD_CHOICE_ABORTED", "\n[color=yellow]Choice aborted.[reset]\n");
 	MSG_Add("SHELL_CMD_PATH_HELP",
 	        "Displays or sets a search path for executable files.\n");
 	MSG_Add("SHELL_CMD_PATH_HELP_LONG",
diff --git a/src/shell/shell_cmds.cpp b/src/shell/shell_cmds.cpp
index 03b6b7277..f369b23c5 100644
--- a/src/shell/shell_cmds.cpp
+++ b/src/shell/shell_cmds.cpp
@@ -2067,9 +2067,16 @@ void DOS_Shell::CMD_CHOICE(char * args){
 	// Begin waiting for input, but maybe break on some conditions
 	constexpr char ctrl_c = 3;
 	char choice = '\0';
+	uint16_t bytes_read = 1;
 	while (!contains(choices, choice)) {
-		uint16_t n = 1;
-		DOS_ReadFile(STDIN, reinterpret_cast<uint8_t *>(&choice), &n);
+		DOS_ReadFile(STDIN, reinterpret_cast<uint8_t *>(&choice), &bytes_read);
+		if (!bytes_read) {
+			WriteOut_NoParsing(MSG_Get("SHELL_CMD_CHOICE_EOF"));
+			dos.return_code = 255;
+			LOG_ERR("CHOICE: Failed, returing errorlevel %u",
+			        dos.return_code);
+			return;
+		}
 		if (always_capitalize)
 			choice = static_cast<char>(toupper(choice));
 		if (using_auto_type)
@@ -2091,8 +2098,9 @@ void DOS_Shell::CMD_CHOICE(char * args){
 	} else {
 		WriteOut_NoParsing(MSG_Get("SHELL_CMD_CHOICE_ABORTED"));
 		dos.return_code = 0;
-		LOG_MSG("CHOICE: Aborted, returning %u (from %d choices)",
-		        dos.return_code, num_choices);
+		LOG_WARNING("CHOICE: Aborted, returning errorlevel %u (from %d choices)",
+		            dos.return_code,
+		            num_choices);
 	}
 }