don't allow f-k-r to run if stdin/stdout not a tty

Another developer noticed that redirecting stdin of `fish_key_reader`
results in weird behavior.  Which is not at all surprising. So add checks
to ensure stdin and stdout are attached to a tty.

Add some rudimentary unit tests for this program.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/fish_key_reader.cpp b/src/fish_key_reader.cpp
index 0051ebb4..72d550c2 100644
--- a/src/fish_key_reader.cpp
+++ b/src/fish_key_reader.cpp
@@ -281,6 +281,11 @@ int main(int argc, char **argv) {
         return 1;
     }
 
+    if (!isatty(STDIN_FILENO) || !isatty(STDOUT_FILENO)) {
+        fprintf(stderr, "Stdin and stdout must be attached to a tty, redirection not allowed.\n");
+        return 1;
+    }
+
     setup_and_process_keys(continuous_mode);
     return 0;
 }