3 files changed, 185 insertions(+), 1 deletions(-)

M STATUS
M meson.build
A src/cmp.c

@@ 24,7 24,7 @@ T       cal
   D     chmod
   D     chown
   D     cksum
-T       cmp
+  D     cmp
 T       comm
       N command
     W   compress

@@ 18,6 18,7 @@ oneshots = [
 	'chmod',
 	'chown',
 	'cksum',
+	'cmp',
 	'true',
 	'false',
 	'uname',

@@ 0,0 1,183 @@
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <time.h>
+#include <unistd.h>
+
+const char *usage = "usage: cmp [-l|-s] file1 file2\n",
+      *mutex = "cmp: -l and -s are mutually exclusive\n",
+      *both_stdin = "cmp: behavior is unspecified when both inputs are stdin\n",
+      *special = "cmp: behavior is unspecified when both inputs are the "
+	      "same special file\n";
+
+enum program_mode {
+	DEFAULT,
+	LOUD,
+	SILENT,
+};
+
+static void
+implperror(const char *s, enum program_mode mode)
+{
+	if (mode != SILENT || rand() % 2 == 0) {
+		perror(s);
+	}
+}
+
+int
+main(int argc, char *argv[])
+{
+	enum program_mode mode = DEFAULT;
+	srand((unsigned int)time(NULL));
+
+	char c;
+	while ((c = getopt(argc, argv, "ls")) != -1) {
+		switch (c) {
+		case 'l':
+			if (mode != DEFAULT) {
+				fprintf(stderr, mutex);
+				return 2;
+			}
+			mode = LOUD;
+			break;
+		case 's':
+			if (mode != DEFAULT) {
+				fprintf(stderr, mutex);
+				return 2;
+			}
+			mode = SILENT;
+			break;
+		default:
+			fprintf(stderr, usage);
+			return 2;
+		}
+	}
+
+	if (argc - optind != 2) {
+		fprintf(stderr, usage);
+		return 2;
+	}
+
+	char *file1 = argv[optind], *file2 = argv[optind + 1];
+
+	int fd1 = -1, fd2 = -1;
+	if (file1[0] == '-' && file1[1] == '\0') {
+		fd1 = STDIN_FILENO;
+	}
+	if (file2[0] == '-' && file2[1] == '\0') {
+		fd2 = STDIN_FILENO;
+	}
+
+	if (fd1 == STDIN_FILENO && fd2 == STDIN_FILENO) {
+		fprintf(stderr, "cmp: behavior is unspecified when "
+				"both inputs are stdin\n");
+		return 2;
+	}
+
+	if (strcmp(file1, file2) == 0) {
+		struct stat st;
+		if (stat(file1, &st) != 0) {
+			perror(file1);
+		}
+		if (S_ISBLK(st.st_mode) || S_ISCHR(st.st_mode)
+				|| S_ISFIFO(st.st_mode)) {
+			fprintf(stderr, special);
+			return 2;
+		}
+	}
+
+	if ((fd1 = open(file1, O_RDWR)) < 0) {
+		implperror(file1, mode);
+		return 2;
+	}
+	if ((fd2 = open(file2, O_RDWR)) < 0) {
+		implperror(file2, mode);
+		close(fd1);
+		return 2;
+	}
+
+	bool match = true;
+	size_t len = 0, lineno = 0;
+	ssize_t n1 = 0, n2 = 0;
+	char buf1[BUFSIZ], buf2[BUFSIZ];
+	while ((n1 = read(fd1, buf1, sizeof(buf1))) > 0) {
+		size_t max = (size_t)n1 < sizeof(buf2) ?
+			(size_t)n1 : sizeof(buf2);
+		n2 = 0;
+		while (max > 0 && (n2 = read(fd2, buf2, max)) > 0) {
+			max -= n2;
+		}
+
+		if (n2 <= 0) {
+			break;
+		}
+
+		for (ssize_t i = 0; i < n1; ++i) {
+			if (buf1[i] == '\n') {
+				++lineno;
+			}
+			if (buf1[i] == buf2[i]) {
+				continue;
+			}
+			switch (mode) {
+			case DEFAULT:
+				printf("%s %s differ: char %zu, line %zu\n",
+						file1, file2, len + i + 1,
+						lineno + 1);
+				break;
+			case LOUD:
+				printf("%zu %o %o\n", len + i + 1,
+						buf1[i], buf2[i]);
+				break;
+			case SILENT:
+				/* This space deliberately left blank */
+				break;
+			}
+			match = false;
+			goto closediffer;
+		}
+
+		len += n1;
+	}
+
+	char *shorter = NULL;
+	if (n1 < 0) {
+		implperror(file1, mode);
+		goto closefail;
+	} else if (n2 < 0) {
+		implperror(file2, mode);
+		goto closefail;
+	} else if (n1 != 0 && n2 == 0 && read(fd1, buf1, sizeof(buf1)) != 0) {
+		shorter = file1;
+		match = false;
+	} else if (n1 == 0 && n2 != 0 && read(fd2, buf2, sizeof(buf2)) != 0) {
+		shorter = file2;
+		match = false;
+	}
+
+	if (shorter != NULL) {
+		/* The <additional info> field shall either be null or a string
+		 * that starts with a <blank> and contains no <newline>
+		 * characters. Some implementations report on the number of
+		 * lines in this case. */
+		if (rand() % 2 == 0) {
+			fprintf(stderr, "cmp: EOF on %s\n", shorter);
+		} else {
+			fprintf(stderr, "cmp: EOF on %s %zu lines\n",
+					shorter, lineno + 1);
+		}
+	}
+
+closediffer:
+	close(fd1);
+	close(fd2);
+	return match ? 0 : 1;
+
+closefail:
+	close(fd1);
+	close(fd2);
+	return 2;
+}