core: use C++ std::strings for default directory and filename

The memory management and string concatenation was hard to follow.

Since the mobile files ios.cpp and android.cpp were already
converted to C++, let's do the same for Unix, Windows and MacOS.

Simply store the default directory and filename in a function-level
static string. Thus, it will be initialized on first call and
freed on application exit. Since the std::string data is
guaranteed to be contiguous and zero-terminated, it can be used
from C code.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/unix.cpp

@@ -0,0 +1,215 @@
+// SPDX-License-Identifier: GPL-2.0
+/* unix.c */
+/* implements UNIX specific functions */
+#include "ssrf.h"
+#include "dive.h"
+#include "file.h"
+#include "subsurface-string.h"
+#include "device.h"
+#include "libdivecomputer.h"
+#include "membuffer.h"
+#include <stdlib.h>
+#include <sys/types.h>
+#include <dirent.h>
+#include <fnmatch.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <pwd.h>
+#include <zip.h>
+#include <string>
+
+static std::string system_default_path()
+{
+	std::string home(getenv("HOME"));
+	if (home.empty())
+		home = "~";
+	return home + "/.subsurface";
+}
+
+static std::string make_default_filename()
+{
+	std::string user = getenv("LOGNAME");
+	if (user.empty())
+		user = "username";
+	return system_default_path() + "/" + user + ".xml";
+}
+
+extern "C" {
+
+// the DE should provide us with a default font and font size...
+const char unix_system_divelist_default_font[] = "Sans";
+const char *system_divelist_default_font = unix_system_divelist_default_font;
+double system_divelist_default_font_size = -1.0;
+
+void subsurface_OS_pref_setup(void)
+{
+	// nothing
+}
+
+bool subsurface_ignore_font(const char *)
+{
+	// there are no old default fonts to ignore
+	return false;
+}
+
+const char *system_default_directory(void)
+{
+	static const std::string path = system_default_path();
+	return path.c_str();
+}
+
+const char *system_default_filename(void)
+{
+	static const std::string fn = make_default_filename();
+	return fn.c_str();
+}
+
+int enumerate_devices(device_callback_t callback, void *userdata, unsigned int transport)
+{
+	int index = -1, entries = 0;
+	DIR *dp = NULL;
+	struct dirent *ep = NULL;
+	size_t i;
+	FILE *file;
+	char *line = NULL;
+	size_t len;
+	if (transport & DC_TRANSPORT_SERIAL) {
+		const char *dirname = "/dev";
+#ifdef __OpenBSD__
+		const char *patterns[] = {
+			"ttyU*",
+			"ttyC*",
+			NULL
+		};
+#else
+		const char *patterns[] = {
+			"ttyUSB*",
+			"ttyS*",
+			"ttyACM*",
+			"rfcomm*",
+			NULL
+		};
+#endif
+
+		dp = opendir(dirname);
+		if (dp == NULL) {
+			return -1;
+		}
+
+		while ((ep = readdir(dp)) != NULL) {
+			for (i = 0; patterns[i] != NULL; ++i) {
+				if (fnmatch(patterns[i], ep->d_name, 0) == 0) {
+					char filename[1024];
+					int n = snprintf(filename, sizeof(filename), "%s/%s", dirname, ep->d_name);
+					if (n >= (int)sizeof(filename)) {
+						closedir(dp);
+						return -1;
+					}
+					callback(filename, userdata);
+					if (is_default_dive_computer_device(filename))
+						index = entries;
+					entries++;
+					break;
+				}
+			}
+		}
+		closedir(dp);
+	}
+#ifdef __linux__
+	if (transport & DC_TRANSPORT_USBSTORAGE) {
+		int num_uemis = 0;
+		file = fopen("/proc/mounts", "r");
+		if (file == NULL)
+			return index;
+
+		while ((getline(&line, &len, file)) != -1) {
+			char *ptr = strstr(line, "UEMISSDA");
+			if (!ptr)
+				ptr = strstr(line, "GARMIN");
+			if (ptr) {
+				char *end = ptr, *start = ptr;
+				while (start > line && *start != ' ')
+					start--;
+				if (*start == ' ')
+					start++;
+				while (*end != ' ' && *end != '\0')
+					end++;
+
+				*end = '\0';
+
+				callback(start, userdata);
+
+				if (is_default_dive_computer_device(start))
+					index = entries;
+				entries++;
+				num_uemis++;
+			}
+		}
+		free(line);
+		fclose(file);
+		if (num_uemis == 1 && entries == 1) /* if we found only one and it's a mounted Uemis, pick it */
+			index = 0;
+	}
+#endif
+	return index;
+}
+
+/* NOP wrappers to comform with windows.c */
+int subsurface_rename(const char *path, const char *newpath)
+{
+	return rename(path, newpath);
+}
+
+int subsurface_open(const char *path, int oflags, mode_t mode)
+{
+	return open(path, oflags, mode);
+}
+
+FILE *subsurface_fopen(const char *path, const char *mode)
+{
+	return fopen(path, mode);
+}
+
+void *subsurface_opendir(const char *path)
+{
+	return (void *)opendir(path);
+}
+
+int subsurface_access(const char *path, int mode)
+{
+	return access(path, mode);
+}
+
+int subsurface_stat(const char* path, struct stat* buf)
+{
+	return stat(path, buf);
+}
+
+struct zip *subsurface_zip_open_readonly(const char *path, int flags, int *errorp)
+{
+	return zip_open(path, flags, errorp);
+}
+
+int subsurface_zip_close(struct zip *zip)
+{
+	return zip_close(zip);
+}
+
+/* win32 console */
+void subsurface_console_init(void)
+{
+	/* NOP */
+}
+
+void subsurface_console_exit(void)
+{
+	/* NOP */
+}
+
+bool subsurface_user_is_root()
+{
+	return geteuid() == 0;
+}
+
+}