Add JS implementation of ImgFile

Builds on the abstraction introduced in d4c9db7
to allow the Emscripten/JS port to implement disk image operations using
the workerApi.disks.* functions.

Updates mihaip/infinite-mac#219

utils/imgfile_js.cpp

@@ -0,0 +1,75 @@
+/*
+DingusPPC - The Experimental PowerPC Macintosh emulator
+Copyright (C) 2018-23 divingkatae and maximum
+                      (theweirdo)     spatium
+
+(Contact divingkatae#1017 or powermax#2286 on Discord for more info)
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+#include <utils/imgfile.h>
+
+#include <emscripten.h>
+
+class ImgFile::Impl {
+public:
+    int disk_id;
+};
+
+ImgFile::ImgFile(): impl(std::make_unique<Impl>())
+{
+
+}
+
+ImgFile::~ImgFile() = default;
+
+bool ImgFile::open(const std::string &img_path)
+{
+    int disk_id = EM_ASM_INT({
+        return workerApi.disks.open(UTF8ToString($0));
+    }, img_path.c_str());
+    if (disk_id == -1) {
+        return false;
+    }
+
+    impl->disk_id = disk_id;
+    return true;
+}
+
+void ImgFile::close()
+{
+    EM_ASM_({ workerApi.disks.close($0); }, impl->disk_id);
+}
+
+size_t ImgFile::size() const
+{
+    return EM_ASM_INT({ return workerApi.disks.size($0); }, impl->disk_id);
+}
+
+size_t ImgFile::read(void* buf, off_t offset, size_t length) const
+{
+    int read_size = EM_ASM_INT({
+        return workerApi.disks.read($0, $1, $2, $3);
+    }, impl->disk_id, buf, int(offset), int(length));
+    return read_size;
+}
+
+size_t ImgFile::write(const void* buf, off_t offset, size_t length)
+{
+    int write_size = EM_ASM_INT({
+        return workerApi.disks.write($0, $1, $2, $3);
+    }, impl->disk_id, buf, int(offset), int(length));
+    return write_size;
+}