shared: add file_create_dated() helper

For easy creation of unique new files. I'm looking at you,
screenshooter.

This code is based on timeline.c weston_timeline_do_open().

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Tested-by: Nobuhiko Tanibata <NOBUHIKO_TANIBATA@xddp.denso.co.jp>
Reviewed-by: Daniel Stone <daniels@collabora.com>

Makefile.am

@@ -884,6 +884,8 @@ libshared_la_SOURCES =				\
 	shared/config-parser.c			\
 	shared/option-parser.c			\
 	shared/config-parser.h			\
+	shared/file-util.c			\
+	shared/file-util.h			\
 	shared/os-compatibility.c		\
 	shared/os-compatibility.h
 

shared/file-util.c

@@ -0,0 +1,118 @@
+/*
+ * Copyright © 2015 Collabora, Ltd.
+ *
+ * Permission to use, copy, modify, distribute, and sell this software and
+ * its documentation for any purpose is hereby granted without fee, provided
+ * that the above copyright notice appear in all copies and that both that
+ * copyright notice and this permission notice appear in supporting
+ * documentation, and that the name of the copyright holders not be used in
+ * advertising or publicity pertaining to distribution of the software
+ * without specific, written prior permission.  The copyright holders make
+ * no representations about the suitability of this software for any
+ * purpose.  It is provided "as is" without express or implied warranty.
+ *
+ * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS
+ * SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS, IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER
+ * RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF
+ * CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "config.h"
+
+#include <stdio.h>
+#include <errno.h>
+#include <time.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "file-util.h"
+
+static int
+current_time_str(char *str, size_t len, const char *fmt)
+{
+	time_t t;
+	struct tm *t_local;
+	int ret;
+
+	t = time(NULL);
+	t_local = localtime(&t);
+	if (!t_local) {
+		errno = ETIME;
+		return -1;
+	}
+
+	ret = strftime(str, len, fmt, t_local);
+	if (ret == 0) {
+		errno = ETIME;
+		return -1;
+	}
+
+	return ret;
+}
+
+static int
+create_file_excl(const char *fname)
+{
+	return open(fname, O_RDWR | O_CLOEXEC | O_CREAT | O_EXCL, 00666);
+}
+
+/** Create a unique file with date and time in the name
+ *
+ * \param path_prefix Path and file name prefix.
+ * \param suffix File name suffix.
+ * \param name_out[out] Buffer for the resulting file name.
+ * \param name_len Number of bytes usable in name_out.
+ * \return stdio FILE pointer, or NULL on failure.
+ *
+ * Create and open a new file with the name concatenated from
+ * path_prefix, date and time, and suffix. If a file with this name
+ * already exists, an counter number is added to the end of the
+ * date and time sub-string. The counter is increased until a free file
+ * name is found.
+ *
+ * Once creating the file succeeds, the name of the file is in name_out.
+ * On failure, the contents of name_out are undefined and errno is set.
+ */
+FILE *
+file_create_dated(const char *path_prefix, const char *suffix,
+		  char *name_out, size_t name_len)
+{
+	char timestr[128];
+	int ret;
+	int fd;
+	int cnt = 0;
+
+	if (current_time_str(timestr, sizeof(timestr), "%F_%H-%M-%S") < 0)
+		return NULL;
+
+	ret = snprintf(name_out, name_len, "%s%s%s",
+		       path_prefix, timestr, suffix);
+	if (ret < 0 || (size_t)ret >= name_len) {
+		errno = ENOBUFS;
+		return NULL;
+	}
+
+	fd = create_file_excl(name_out);
+
+	while (fd == -1 && errno == EEXIST) {
+		cnt++;
+
+		ret = snprintf(name_out, name_len, "%s%s-%d%s",
+			       path_prefix, timestr, cnt, suffix);
+		if (ret < 0 || (size_t)ret >= name_len) {
+			errno = ENOBUFS;
+			return NULL;
+		}
+
+		fd = create_file_excl(name_out);
+	}
+
+	if (fd == -1)
+		return NULL;
+
+	return fdopen(fd, "w");
+}

shared/file-util.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright © 2015 Collabora, Ltd.
+ *
+ * Permission to use, copy, modify, distribute, and sell this software and
+ * its documentation for any purpose is hereby granted without fee, provided
+ * that the above copyright notice appear in all copies and that both that
+ * copyright notice and this permission notice appear in supporting
+ * documentation, and that the name of the copyright holders not be used in
+ * advertising or publicity pertaining to distribution of the software
+ * without specific, written prior permission.  The copyright holders make
+ * no representations about the suitability of this software for any
+ * purpose.  It is provided "as is" without express or implied warranty.
+ *
+ * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS
+ * SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS, IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER
+ * RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF
+ * CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifndef WESTON_FILE_UTIL_H
+#define WESTON_FILE_UTIL_H
+
+#ifdef  __cplusplus
+extern "C" {
+#endif
+
+#include <stdio.h>
+
+FILE *
+file_create_dated(const char *path_prefix, const char *suffix,
+		  char *name_out, size_t name_len);
+
+#ifdef  __cplusplus
+}
+#endif
+
+#endif /* WESTON_FILE_UTIL_H */