Support creating directories

Previously Varvara did not have a way to create new directories.
This change adds that capability without adding or modifying any
device ports.

The changes are:

 (1) When a filename ends in the directory separator, writing
     any value to File/write will create a directory. Unlike
     with regular files, the value is ignored.

 (2) When writing any path (regular files or directories) if
     there are missing parent directories Varvara will attempt
     to create them first. This behavior is similar to mkdir -p.

The directory separator is / on most platforms, and \ on Windows.
On POSIX platforms the directories will be created with permission
0755 (modified by the user's umask value).

This change has been tested and works in both uxnemu and uxncli.

src/devices/file.c

@@ -9,17 +9,20 @@
 #include <unistd.h>
 
 #ifdef _WIN32
+#include <direct.h>
 #include <libiberty/libiberty.h>
 #define realpath(s, dummy) lrealpath(s)
 #define DIR_SEP_CHAR '\\'
 #define DIR_SEP_STR "\\"
 #define pathcmp(path1, path2, length) strncasecmp(path1, path2, length) /* strncasecmp provided by libiberty */
 #define notdriveroot(file_name) (file_name[0] != DIR_SEP_CHAR && ((strlen(file_name) > 2 && file_name[1] != ':') || strlen(file_name) <= 2))
+#define mkdir(file_name) (_mkdir(file_name) == 0)
 #else
 #define DIR_SEP_CHAR '/'
 #define DIR_SEP_STR "/"
 #define pathcmp(path1, path2, length) strncmp(path1, path2, length)
 #define notdriveroot(file_name) (file_name[0] != DIR_SEP_CHAR)
+#define mkdir(file_name) (mkdir(file_name, 0755) == 0)
 #endif
 
 #ifndef PATH_MAX
@@ -48,7 +51,9 @@ typedef struct {
 	enum { IDLE,
 		FILE_READ,
 		FILE_WRITE,
-		DIR_READ } state;
+		DIR_READ,
+		DIR_WRITE
+	} state;
 	int outside_sandbox;
 } UxnFile;
 
@@ -207,20 +212,58 @@ file_read(UxnFile *c, void *dest, int len)
 	return 0;
 }
 
+static int
+is_dir_path(char *p)
+{
+	char c;
+	int saw_slash = 0;
+	while (c = *p++)
+		saw_slash = c == DIR_SEP_CHAR;
+	return saw_slash;
+}
+
+int
+dir_exists(char *p)
+{
+	struct stat st;
+	return stat(p, &st) == 0 && S_ISDIR(st.st_mode);
+}
+
+int
+ensure_parent_dirs(char *p)
+{
+	int ok = 1;
+	char c, *s = p;
+	for(; ok && (c = *p); p++) {
+		if (c == DIR_SEP_CHAR) {
+			*p = '\0';
+			ok = dir_exists(s) || mkdir(s);
+			*p = c;
+		}
+	}
+	return ok;
+}
+
 static Uint16
 file_write(UxnFile *c, void *src, Uint16 len, Uint8 flags)
 {
 	Uint16 ret = 0;
 	if(c->outside_sandbox) return 0;
-	if(c->state != FILE_WRITE) {
+	ensure_parent_dirs(c->current_filename);
+	if(c->state != FILE_WRITE && c->state != DIR_WRITE) {
 		reset(c);
-		if((c->f = fopen(c->current_filename, (flags & 0x01) ? "ab" : "wb")) != NULL)
+		if (is_dir_path(c->current_filename))
+			c->state = DIR_WRITE;
+		else if((c->f = fopen(c->current_filename, (flags & 0x01) ? "ab" : "wb")) != NULL)
 			c->state = FILE_WRITE;
 	}
 	if(c->state == FILE_WRITE) {
 		if((ret = fwrite(src, 1, len, c->f)) > 0 && fflush(c->f) != 0)
 			ret = 0;
 	}
+	if (c->state == DIR_WRITE) {
+		ret = dir_exists(c->current_filename);
+	}
 	return ret;
 }