Add UTF-8-support to strings(1), add t-flag and refactor code

Previously, the string-length was limited to BUFSIZ, which is an
obvious deficiency.
Now the buffer only needs to be as long as the user specifies the
minimal string length.
I added UTF-8-support, because that's how POSIX wants it and there
are cases where you need this. It doesn't add ELF-barf compared to
the previous implementation.
The t-flag is also pretty important for POSIX-compliance, so I added
it.
The only trouble previously was the a-flag, but given that POSIX
leaves undefined what the a-flag actually does, we set it as default
and don't care about parsing ELF-headers, which has already
turned out to be a security issue in GNU coreutils[0].

[0]: http://lcamtuf.blogspot.ro/2014/10/psa-dont-run-strings-on-untrusted-files.html

README

@@ -67,7 +67,7 @@ The following tools are implemented ('*' == finished, '#' == UTF-8 support,
    sort            no                           -m, -o, -d, -f, -i
 =* split           yes                          none
 =* sponge          non-posix                    none
-   strings         no                           -t
+#* strings         yes                          none
 =* sync            non-posix                    none
 =* tail            yes                          none
 =* tar             non-posix                    none

strings.1

@@ -1,32 +1,52 @@
-.Dd November 23, 2014
+.Dd Februrary 17, 2015
 .Dt STRINGS 1
 .Os sbase
 .Sh NAME
 .Nm strings
-.Nd print the strings of printable characters in files
+.Nd print strings of printable characters in files
 .Sh SYNOPSIS
 .Nm
 .Op Fl a
-.Op Fl n Ar len
+.Op Fl n Ar num
+.Op Fl t Ar format
 .Op Ar file ...
 .Sh DESCRIPTION
 .Nm
-prints the printable character sequences that are at least 4 characters
-long. If no
-.Ar files
-are given,
+writes sequences of at least 4 printable characters in each
+.Ar file
+to stdout.
+If no
+.Ar file
+is given,
 .Nm
 reads from stdin.
 .Sh OPTIONS
 .Bl -tag -width Ds
 .It Fl a
-Scan files in their entirety. This is the default.
-.It Fl n Ar len
-Only print sequences that are at least
-.Ar len
-characters.  The default is 4 characters.
+Scan each
+.Ar file
+entirely. This is the default.
+.It Fl n Ar num
+Print sequences of at least
+.Ar num
+characters.  The default is 4.
+.It Fl t Ar format
+Prepend each string with its byte offset, with
+.Ar format
+being one of
+.Sy d , o , x
+for decimal, octal or hexadecimal numbers.
 .El
 .Sh STANDARDS
+The
 .Nm
-mirrors the semantics of Plan9
-.Xr strings 1 .
+utility is compliant with the
+.St -p1003.1-2008
+specification.
+.Pp
+The
+.Op Fl t
+output format has been changed from "%F %s" to "%8lF: %s", with
+.Sy F
+being one of
+.Sy d , o , x .

strings.c

@@ -1,50 +1,75 @@
 /* See LICENSE file for copyright and license details. */
-#include <ctype.h>
 #include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 
+#include "utf.h"
 #include "util.h"
 
-static void
-strings(FILE *fp, const char *fname, int len)
-{
-	unsigned char buf[BUFSIZ];
-	int c, i = 0;
-	off_t offset = 0;
+static char *format = "";
 
-	do {
-		offset++;
-		if (isprint(c = getc(fp)))
-			buf[i++] = c;
-		if ((!isprint(c) && i >= len) || i == sizeof(buf) - 1) {
-			buf[i] = '\0';
-			printf("%8ld: %s\n", (long)offset - i - 1, buf);
+static void
+strings(FILE *fp, const char *fname, size_t len)
+{
+	Rune r, *rbuf;
+	size_t i, bread;
+	off_t off;
+
+	rbuf = emalloc(len * sizeof(*rbuf));
+
+	for (off = 0, i = 0; (bread = efgetrune(&r, fp, fname)); ) {
+		off += bread;
+		if (r == Runeerror)
+			continue;
+		else if (!isprintrune(r)) {
+			if (i > len)
+				putchar('\n');
 			i = 0;
+			continue;
 		}
-	} while (c != EOF);
-	if (ferror(fp))
-		eprintf("%s: read error:", fname);
+		if (i < len) {
+			rbuf[i++] = r;
+			continue;
+		} else if (i > len) {
+			efputrune(&r, stdout, "<stdout>");
+			continue;
+		}
+		printf(format, (long)off - i);
+		for (i = 0; i < len; i++) {
+			efputrune(rbuf + i, stdout, "<stdout>");
+		}
+		i++;
+	}
+	free(rbuf);
 }
 
 static void
 usage(void)
 {
-	eprintf("usage: %s [-a] [-n len] [file ...]\n", argv0);
+	eprintf("usage: %s [-a] [-n num] [-t format] [file ...]\n", argv0);
 }
 
 int
 main(int argc, char *argv[])
 {
 	FILE *fp;
+	size_t len = 4;
 	int ret = 0;
-	int len = 4;
+	char f;
 
 	ARGBEGIN {
 	case 'a':
 		break;
 	case 'n':
-		len = estrtonum(EARGF(usage()), 1, INT_MAX);
+		len = estrtonum(EARGF(usage()), 1, LLONG_MAX);
+		break;
+	case 't':
+		format = estrdup("%8l#: ");
+		f = *EARGF(usage());
+		if (f == 'd' || f == 'o' || f == 'x')
+			format[3] = f;
+		else
+			usage();
 		break;
 	default:
 		usage();