utils-std

commit: f5d3de45fe20ecf2c1fe97587b89c83ef2a20469
parent e5d158506c7001999b47fe5b21e187f7e8b0f0e9
Author: Haelwenn (lanodan) Monnier <contact@hacktivis.me>
Date:   Fri, 20 Sep 2024 18:35:36 +0200

cmd/mktemp: add support for -u

Diffstat:
M
cmd/mktemp.1
8
++++++--
M
cmd/mktemp.c
61
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++----

2 files changed, 63 insertions(+), 6 deletions(-)
diff --git a/cmd/mktemp.1 b/cmd/mktemp.1
@@ -1,7 +1,7 @@
 .\" utils-std: Collection of commonly available Unix tools
 .\" Copyright 2017 Haelwenn (lanodan) Monnier <contact+utils@hacktivis.me>
 .\" SPDX-License-Identifier: MPL-2.0
-.Dd 2024-07-30
+.Dd 2024-09-20
 .Dt MKTEMP 1
 .Os
 .Sh NAME
@@ -9,7 +9,7 @@
 .Nd make a new randomly-named file or directory
 .Sh SYNOPSIS
 .Nm
-.Op Fl dqt
+.Op Fl dqtu
 .Op Fl p Ar tempdir
 .Op Ar template
 .Sh DESCRIPTION
@@ -46,6 +46,10 @@ Use
 or if unset,
 .Pa /tmp ,
 as an existing directory to create into.
+.It Fl u
+Unsafe mode, generate filename and print it out without creating it.
+.Pp
+Only present for compatibility with existing scripts, do not use.
 .El
 .Sh EXIT STATUS
 .Ex -std
diff --git a/cmd/mktemp.c b/cmd/mktemp.c
@@ -2,26 +2,74 @@
 // SPDX-FileCopyrightText: 2017 Haelwenn (lanodan) Monnier <contact+utils@hacktivis.me>
 // SPDX-License-Identifier: MPL-2.0
 
-#define _POSIX_C_SOURCE 200809L
+// getentropy got in POSIX.1-2024 but defining _POSIX_C_SOURCE causes too much side-effects
+#define _DEFAULT_SOURCE // getentropy
+
 #include <errno.h>
 #include <limits.h> // PATH_MAX
 #include <stdbool.h>
 #include <stdio.h>  // fprintf
 #include <stdlib.h> // getenv
 #include <string.h> // strerror
-#include <unistd.h> // getopt
+#include <unistd.h> // getopt, getentropy
 
 const char *argv0 = "mktemp";
 
+static int
+unsafe_mktemp(char *template)
+{
+	size_t l = strlen(template);
+
+	size_t len = 0;
+	size_t off = l - 1;
+	while(off > 0 && template[off] == 'X')
+		off--, len++;
+
+	if(len < 6)
+	{
+		fprintf(stderr,
+		        "%s: error: Template '%s' is invalid (need >= 6 final X, got %zd)\n",
+		        argv0,
+		        template,
+		        len);
+		return 1;
+	}
+
+	for(int retries = 100; 0 < retries; retries--)
+	{
+		unsigned long r = 0;
+		if(getentropy(&r, sizeof(r)) != 0)
+		{
+			fprintf(stderr,
+			        "%s: error: Failed to get entropy for random filename: %s\n",
+			        argv0,
+			        strerror(errno));
+			return 1;
+		}
+
+		for(int i = len; i > 0; i--, r >>= 5)
+			template[off + i] = 'A' + (r & 15) + (r & 16) * 2;
+
+		if(access(template, F_OK) != 0 && errno == ENOENT)
+		{
+			puts(template);
+			return 0;
+		}
+	}
+
+	fprintf(stderr, "%s: error: Exhausted all 100 attempts at generating a filename\n", argv0);
+	return 1;
+}
+
 int
 main(int argc, char *argv[])
 {
-	bool o_create_dir = false, o_quiet = false;
+	bool o_create_dir = false, o_quiet = false, o_unsafe = false;
 	char template[PATH_MAX] = "tmp.XXXXXXXXXX";
 	const char *tmpdir = NULL;
 
 	int c = -1;
-	while((c = getopt(argc, argv, ":dqp:t")) != -1)
+	while((c = getopt(argc, argv, ":dqp:tu")) != -1)
 	{
 		switch(c)
 		{
@@ -38,6 +86,9 @@ main(int argc, char *argv[])
 			if(tmpdir == NULL) tmpdir = getenv("TMPDIR");
 			if(tmpdir == NULL) tmpdir = "/tmp";
 			break;
+		case 'u':
+			o_unsafe = true;
+			break;
 		case '?':
 			fprintf(stderr, "%s: error: Unrecognised option: '-%c'\n", argv0, optopt);
 			return 1;
@@ -75,6 +126,8 @@ main(int argc, char *argv[])
 		printf("%s/", tmpdir);
 	}
 
+	if(o_unsafe) return unsafe_mktemp(template);
+
 	if(o_create_dir)
 	{
 		char *dir = mkdtemp(template);