From 6b90e0e1da2d82f571fd6166b6275c8e66c4a69e Mon Sep 17 00:00:00 2001
From: DTB <trinity@trinity.moe>
Date: Wed, 17 Apr 2024 14:21:11 -0600
Subject: [PATCH] peek(1): handle ^C elegantly

---
 peek/peek.c | 107 ++++++++++++++++++++++++++++++++++------------------
 1 file changed, 71 insertions(+), 36 deletions(-)

diff --git a/peek/peek.c b/peek/peek.c
index 78f4725..d6915c6 100644
--- a/peek/peek.c
+++ b/peek/peek.c
@@ -1,6 +1,7 @@
+#include <signal.h> /* sigaction(2), struct sigaction, SIGINT */
 #include <stdio.h> /* fprintf(3), getc(3), perror(3), putc(3), stderr, stdin,
                     * stdout, EOF, NULL */
-#include <stdlib.h> /* size_t */
+#include <stdlib.h> /* exit(3), size_t, EXIT_FAILURE */
 #include <string.h> /* strerror(3) */
 #if !defined EX_OK || !defined EX_OSERR || !defined EX_USAGE
 #	include <sysexits.h>
@@ -12,16 +13,31 @@
 static int oserr(char *s){ perror(s); return EX_OSERR; }
 
 static char *program_name = "peek";
+
 static int usage(char *s){
 	fprintf(stderr, "Usage: %s (-1enot) (-p [program [arguments...]])\n",
 		s == NULL ? program_name : s);
 	return EX_USAGE;
 }
 
+/* Restores terminal echo; otherwise when a user ^Cs the terminal would
+ * continue to not display typed text. If sig isn't zero, this will terminate
+ * the program. */
+void restore_echo(int sig){
+	static struct termios t;
+
+	tcgetattr(STDIN_FILENO, &t);
+	t.c_lflag |= ECHO;
+	tcsetattr(STDIN_FILENO, TCSAFLUSH, &t);
+
+	if(sig != 0)
+		exit(EXIT_FAILURE);
+	else
+		return;
+}
+
 int main(int argc, char *argv[]){
-	int c;
 	int eof;
-	size_t i;
 	char include_eof;
 	FILE *outputs[] = {
 		NULL /* stdout */,
@@ -29,31 +45,34 @@ int main(int argc, char *argv[]){
 		NULL /* -p */
 	};
 	int p[2] = {0, 0};
-	struct termios t;
 
 	if(argc < 1)
 		usage(argv[0]);
 
 	eof = EOF;
 	include_eof = 0;
-	while((c = getopt(argc, argv, "1enopt")) != -1)
-		switch(c){
-		case '1':	eof = '\n';          break;
-		case 'n':	include_eof = 1;     break;
-		case 'o':	outputs[0] = stdout; break;
-		case 'e':	outputs[1] = stderr; break;
-		case 'p':
-			if(pipe(p) != 0 || (outputs[2] = fdopen(p[1], "ab")) == NULL)
-				return oserr(argv[0]);
-			break;
-		case 't':
-			if(isatty(STDIN_FILENO) != 1){
-				fprintf(stderr, "%s: Must be run in a terminal"
-					" (option -t specified)\n", argv[0]);
-				return EX_USAGE;
+	{ /* options parsing */
+		int c;
+
+		while((c = getopt(argc, argv, "1enopt")) != -1)
+			switch(c){
+			case '1':	eof = '\n';          break;
+			case 'n':	include_eof = 1;     break;
+			case 'o':	outputs[0] = stdout; break;
+			case 'e':	outputs[1] = stderr; break;
+			case 'p':
+				if(pipe(p) != 0 || (outputs[2] = fdopen(p[1], "ab")) == NULL)
+					return oserr(argv[0]);
+				break;
+			case 't':
+				if(isatty(STDIN_FILENO) != 1){
+					fprintf(stderr, "%s: Must be run in a terminal"
+						" (option -t specified)\n", argv[0]);
+					return EX_USAGE;
+				}
+			default:	return usage(argv[0]);
 			}
-		default:	return usage(argv[0]);
-		}
+	}
 
 	/* If -p is used there must be additional arguments. getopt(3) wouldn't
 	 * work for this because optarg would have to be one string to give to
@@ -75,23 +94,39 @@ int main(int argc, char *argv[]){
 				return oserr(argv[0]);
 		}
 
-	/* terminal echo */
-	tcgetattr(STDIN_FILENO, &t);
-	t.c_lflag ^= ECHO;
-	tcsetattr(STDIN_FILENO, TCSAFLUSH, &t);
+	{ /* install signal handler for ^C to avoid terminal phooeyness */
+		struct sigaction act = { 0 };
 
-	do{	if((c = getc(stdin)) != eof || include_eof)
-			for(i = 0; i < (sizeof outputs)/(sizeof *outputs); ++i)
-				if(outputs[i] != NULL && putc(c, outputs[i]) == EOF){
-					if(outputs[i] != stdout && outputs[i] != stderr)
-						fclose(outputs[i]);
-					outputs[i] = NULL;
-				}
-	}while(c != eof);
+		act.sa_handler = restore_echo;
+		/* This error isn't terminating because the worst that happens is some
+		 * terminal phooeyness if things go awry. */
+		if(sigaction(SIGINT, &act, NULL) != 0)
+			perror(argv[0]);
+	}
+	
+	{ /* banish terminal echo */
+		struct termios t;
 
-	tcgetattr(STDIN_FILENO, &t);
-	t.c_lflag |= ECHO;
-	tcsetattr(STDIN_FILENO, TCSAFLUSH, &t);
+		tcgetattr(STDIN_FILENO, &t);
+		t.c_lflag ^= ECHO;
+		tcsetattr(STDIN_FILENO, TCSAFLUSH, &t);
+	}
+
+	{ /* actual input loop */
+		int c;
+		size_t i;
+
+		do{	if((c = getc(stdin)) != eof || include_eof)
+				for(i = 0; i < (sizeof outputs)/(sizeof *outputs); ++i)
+					if(outputs[i] != NULL && putc(c, outputs[i]) == EOF){
+						if(outputs[i] != stdout && outputs[i] != stderr)
+							fclose(outputs[i]);
+						outputs[i] = NULL;
+					}
+		}while(c != eof);
+	}
+
+	restore_echo(0);
 
 	return EX_OK;
 }