Implement Oar file reading logic in archive file system

src/main.zig

@@ -27,7 +27,7 @@ fn run(app: *sys.AppContext, graphics: *sys.GraphicsContext) anyerror!void {
     defer _ = gpa.deinit();
 
     {
-        const file_access = try (try app.data().joinedPath(&.{"ona.lua"})).open(.readonly);
+        var file_access = try (try app.data().joinedPath(&.{"ona.lua"})).open(.readonly);
 
         defer file_access.close();
 

src/oar.zig

@@ -9,36 +9,34 @@ const sys = @import("./sys.zig");
 pub const Entry = extern struct {
     signature: [3]u8 = signature_magic,
     revision: u8,
-    name_length: u8 = 0,
     name_buffer: [255]u8 = std.mem.zeroes([255]u8),
+    name_length: u8 = 0,
     file_size: u64,
-    padding: [244]u8 = std.mem.zeroes([244]u8),
+    file_offset: u64,
+    padding: [232]u8 = std.mem.zeroes([232]u8),
 
-    ///
-    /// Returns `true` if `entry` correctly identifies itself as a valid Oar entry, otherwise
-    /// `false`.
-    ///
-    pub fn isValid(entry: Entry) bool {
-        return std.mem.eql(u8, &entry.signature, signature_magic[0 ..]);
+    comptime {
+        const entry_size = @sizeOf(Entry);
+
+        if (entry_size != 512)
+            @compileError("Entry is " ++ std.fmt.comptimePrint("{d}", .{entry_size}) ++ " bytes");
     }
 
     ///
-    /// Attempts to read an [Entry] from `file_access` at its current cursor position.
     ///
-    /// Returns the read [Entry] value or `null` if the end of file is reached before completing the
-    /// read.
     ///
-    pub fn read(file_access: *sys.FileAccess) sys.FileAccess.Error!?Entry {
-        var entry = std.mem.zeroes(Entry);
-        const origin = try file_access.queryCursor();
+    pub const FindError = sys.FileAccess.Error || error {
+        EntryNotFound,
+    };
 
-        if ((try file_access.read(std.mem.asBytes(&entry))) != @sizeOf(Entry)) {
-            try file_access.seek(origin);
+    ///
+    ///
+    ///
+    pub fn find(file_access: sys.FileAccess, entry_name: []const u8) FindError!Entry {
+        _ = file_access;
+        _ = entry_name;
 
-            return null;
-        }
-
-        return entry;
+        return error.EntryNotFound;
     }
 
     ///

src/sys.zig

@@ -128,19 +128,19 @@ pub const AppContext = opaque {
         }
 
         ///
-        /// Initializes a new [Implemenation] with `data_archive_path` as the read-only data archive
-        /// to read from and `user_path_prefix` as the native writable user data directory.
+        /// Initializes a new [Implemenation] with `data_archive_file_access` as the data archive to
+        /// read from and `user_path_prefix` as the native writable user data directory.
         ///
         /// Returns the created [Implementation] value on success or [InitError] on failure.
         ///
-        fn init(data_archive_path: []const u8,
+        fn init(data_archive_file_access: FileAccess,
             user_path_prefix: []const u8) InitError!Implementation {
 
             return Implementation{
                 .message_semaphore = ext.SDL_CreateSemaphore(0) orelse return error.OutOfSemaphores,
                 .message_mutex = ext.SDL_CreateMutex() orelse return error.OutOfMutexes,
-                .data_file_system = .{.archive = data_archive_path},
-                .user_file_system = .{.native = user_path_prefix},
+                .data_file_system = .{.archive = .{.file_access = data_archive_file_access}},
+                .user_file_system = .{.native = .{.path_prefix = user_path_prefix}},
                 .message_thread = null,
             };
         }
@@ -204,7 +204,7 @@ pub const AppContext = opaque {
     ///
     /// Returns a reference to the currently loaded data file-system.
     ///
-    pub fn data(app_context: *AppContext) *const FileSystem {
+    pub fn data(app_context: *AppContext) *FileSystem {
         return &Implementation.cast(app_context).data_file_system;
     }
 
@@ -245,7 +245,7 @@ pub const AppContext = opaque {
     ///
     /// Returns a reference to the currently loaded user file-system.
     ///
-    pub fn user(app_context: *AppContext) *const FileSystem {
+    pub fn user(app_context: *AppContext) *FileSystem {
         return &Implementation.cast(app_context).user_file_system;
     }
 };
@@ -253,7 +253,22 @@ pub const AppContext = opaque {
 ///
 /// File-system agnostic abstraction for manipulating a file.
 ///
-pub const FileAccess = opaque {
+pub const FileAccess = struct {
+    context: *anyopaque,
+    implementation: *const Implementation,
+
+    ///
+    /// Provides a set of implementation-specific behaviors to a [FileAccess] instance.
+    ///
+    pub const Implementation = struct {
+        close: fn (*anyopaque) void,
+        queryCursor: fn (*anyopaque) Error!u64,
+        queryLength: fn (*anyopaque) Error!u64,
+        read: fn (*anyopaque, []u8) Error!usize,
+        seek: fn (*anyopaque, u64) Error!void,
+        seekToEnd: fn (*anyopaque) Error!void,
+    };
+
     ///
     /// [Error.FileInaccessible] is a generic catch-all for a [FileAccess] reference no longer
     /// pointing to a file or the file becomming invalid for whatever reason.
@@ -262,13 +277,6 @@ pub const FileAccess = opaque {
         FileInaccessible,
     };
 
-    ///
-    /// Returns `file_access` casted to a [ext.SDL_RWops].
-    ///
-    fn asRwOps(file_access: *FileAccess) *ext.SDL_RWops {
-        return @ptrCast(*ext.SDL_RWops, @alignCast(@alignOf(ext.SDL_RWops), file_access));
-    }
-
     ///
     /// Close the file referenced by `file_access` on the main thread, invalidating the reference to
     /// it and releasing any associated resources.
@@ -277,8 +285,7 @@ pub const FileAccess = opaque {
     /// wasted effort.
     ///
     pub fn close(file_access: *FileAccess) void {
-        if (ext.SDL_RWclose(file_access.asRwOps()) != 0)
-            ext.SDL_LogWarn(ext.SDL_LOG_CATEGORY_APPLICATION, "Closed an invalid file reference");
+        return file_access.implementation.close(file_access.context);
     }
 
     ///
@@ -288,13 +295,7 @@ pub const FileAccess = opaque {
     /// [Error] on failure.
     ///
     pub fn queryCursor(file_access: *FileAccess) Error!u64 {
-        ext.SDL_ClearError();
-
-        const sought = ext.SDL_RWtell(file_access.asRwOps());
-
-        if (sought < 0) return error.FileInaccessible;
-
-        return @intCast(u64, sought);
+        return file_access.implementation.queryCursor(file_access.context);
     }
 
     ///
@@ -304,13 +305,7 @@ pub const FileAccess = opaque {
     /// failed to be queried.
     ///
     pub fn queryLength(file_access: *FileAccess) Error!u64 {
-        ext.SDL_ClearError();
-
-        const sought = ext.SDL_RWsize(file_access.asRwOps());
-
-        if (sought < 0) return error.FileInaccessible;
-
-        return @intCast(u64, sought);
+        return file_access.implementation.queryLength(file_access.context);
     }
 
     ///
@@ -319,14 +314,7 @@ pub const FileAccess = opaque {
     /// Returns the number of bytes that were available to be read, otherwise an [Error] on failure.
     ///
     pub fn read(file_access: *FileAccess, buffer: []u8) Error!usize {
-        ext.SDL_ClearError();
-
-        const buffer_read =
-            ext.SDL_RWread(file_access.asRwOps(), buffer.ptr, @sizeOf(u8), buffer.len);
-
-        if ((buffer_read == 0) and (ext.SDL_GetError() != null)) return error.FileInaccessible;
-
-        return buffer_read;
+        return file_access.implementation.read(file_access.context, buffer);
     }
 
     ///
@@ -335,19 +323,7 @@ pub const FileAccess = opaque {
     /// Returns [Error] on failure.
     ///
     pub fn seek(file_access: *FileAccess, cursor: u64) Error!void {
-        var to_seek = cursor;
-
-        while (to_seek != 0) {
-            const sought = @intCast(i64, std.math.min(to_seek, std.math.maxInt(i64)));
-
-            ext.SDL_ClearError();
-
-            if (ext.SDL_RWseek(file_access.asRwOps(), sought, ext.RW_SEEK_CUR) < 0)
-                return error.FileInaccessible;
-
-            // Cannot be less than zero because it is derived from `read`.
-            to_seek -= @intCast(u64, sought);
-        }
+        return file_access.implementation.seek(file_access.context, cursor);
     }
 
     ///
@@ -357,10 +333,7 @@ pub const FileAccess = opaque {
     /// Returns [Error] on failure.
     ///
     pub fn seekToEnd(file_access: *FileAccess) Error!void {
-        ext.SDL_ClearError();
-
-        if (ext.SDL_RWseek(file_access.asRwOps(), 0, ext.RW_SEEK_END) < 0)
-            return error.FileInaccessible;
+        return file_access.implementation.seekToEnd(file_access.context);
     }
 };
 
@@ -369,14 +342,33 @@ pub const FileAccess = opaque {
 /// available to the application in a sandboxed environment.
 ///
 pub const FileSystem = union(enum) {
-    native: []const u8,
-    archive: []const u8,
+    native: struct {
+        path_prefix: []const u8,
+    },
+
+    archive: struct {
+        file_access: FileAccess,
+
+        entry_table: [max_open_entries]ArchiveEntry =
+            std.mem.zeroes([max_open_entries]ArchiveEntry),
+
+        const max_open_entries = 16;
+    },
+
+    ///
+    /// Handles the state of an opened archive entry.
+    ///
+    const ArchiveEntry = struct {
+        using: ?*FileAccess,
+        header: oar.Entry,
+        cursor: u64,
+    };
 
     ///
     /// Platform-agnostic mechanism for referencing files and directories on a [FileSystem].
     ///
     pub const Path = struct {
-        file_system: *const FileSystem,
+        file_system: *FileSystem,
         length: u8,
         buffer: [max]u8,
 
@@ -390,9 +382,13 @@ pub const FileSystem = union(enum) {
         /// should be tried or, if no mode other is suitable, that the resource is effectively
         /// unavailable.
         ///
+        /// If the number of known [FileAccess] handles has been exhausted, [OpenError.OutOfFiles]
+        /// is used to communicate this.
+        ///
         pub const OpenError = error {
             FileNotFound,
             ModeUnsupported,
+            OutOfFiles,
         };
 
         ///
@@ -442,59 +438,205 @@ pub const FileSystem = union(enum) {
         /// Returns a [FileAccess] reference that provides access to the file referenced by `path`
         /// or a [OpenError] if it failed.
         ///
-        pub fn open(path: Path, mode: OpenMode) OpenError!*FileAccess {
+        pub fn open(path: Path, mode: OpenMode) OpenError!FileAccess {
             switch (path.file_system.*) {
-                .archive => |archive| {
-                    if (archive.len == 0) return error.FileNotFound;
-
+                .archive => |*archive| {
                     if (mode != .readonly) return error.ModeUnsupported;
 
-                    var path_buffer = std.mem.zeroes([4096]u8);
+                    for (archive.entry_table) |_, index| {
+                        if (archive.entry_table[index].using == null) {
+                            archive.entry_table[index] = .{
+                                .header = oar.Entry.find(archive.file_access, path.
+                                    buffer[0 .. path.length]) catch return error.FileNotFound,
 
-                    if (archive.len >= path_buffer.len) return error.FileNotFound;
+                                .using = &archive.file_access,
+                                .cursor = 0,
+                            };
 
-                    std.mem.copy(u8, path_buffer[0 ..], archive);
+                            const Implementation = struct {
+                                fn archiveEntryCast(context: *anyopaque) *ArchiveEntry {
+                                    return @ptrCast(*ArchiveEntry, @alignCast(
+                                        @alignOf(ArchiveEntry), context));
+                                }
 
-                    const file_access = @ptrCast(*FileAccess, ext.SDL_RWFromFile(
-                        &path_buffer, "rb") orelse return error.FileNotFound);
+                                fn close(context: *anyopaque) void {
+                                    archiveEntryCast(context).using = null;
+                                }
 
-                    while (oar.Entry.read(file_access) catch return error.FileNotFound) |entry| {
-                        if (!entry.isValid()) break;
+                                fn queryCursor(context: *anyopaque) FileAccess.Error!u64 {
+                                    const archive_entry = archiveEntryCast(context);
 
-                        if (std.mem.eql(u8, entry.name_buffer[0 .. entry.name_length],
-                            path.buffer[0 .. path.length])) return file_access;
+                                    if (archive_entry.using == null) return error.FileInaccessible;
 
-                        file_access.seek(entry.file_size) catch break;
+                                    return archive_entry.cursor;
+                                }
+
+                                fn queryLength(context: *anyopaque) FileAccess.Error!u64 {
+                                    const archive_entry = archiveEntryCast(context);
+
+                                    if (archive_entry.using == null) return error.FileInaccessible;
+
+                                    return archive_entry.header.file_size;
+                                }
+
+                                fn read(context: *anyopaque, buffer: []u8) FileAccess.Error!usize {
+                                    const archive_entry = archiveEntryCast(context);
+
+                                    const file_access = archive_entry.using orelse
+                                        return error.FileInaccessible;
+
+                                    if (archive_entry.cursor >= archive_entry.header.file_size)
+                                        return error.FileInaccessible;
+
+                                    try file_access.seek(archive_entry.header.file_offset);
+
+                                    return file_access.read(buffer[0 .. std.math.min(
+                                        buffer.len, archive_entry.header.file_size)]);
+                                }
+
+                                fn seek(context: *anyopaque, cursor: usize) FileAccess.Error!void {
+                                    const archive_entry = archiveEntryCast(context);
+
+                                    if (archive_entry.using == null) return error.FileInaccessible;
+
+                                    archive_entry.cursor = cursor;
+                                }
+
+                                fn seekToEnd(context: *anyopaque) FileAccess.Error!void {
+                                    const archive_entry = archiveEntryCast(context);
+
+                                    if (archive_entry.using == null) return error.FileInaccessible;
+
+                                    archive_entry.cursor = archive_entry.header.file_size;
+                                }
+                            };
+
+                            return FileAccess{
+                                .context = &archive.entry_table[index],
+
+                                .implementation = &.{
+                                    .close = Implementation.close,
+                                    .queryCursor = Implementation.queryCursor,
+                                    .queryLength = Implementation.queryLength,
+                                    .read = Implementation.read,
+                                    .seek = Implementation.seek,
+                                    .seekToEnd = Implementation.seekToEnd,
+                                },
+                            };
+                        }
                     }
 
-                    return error.FileNotFound;
+                    return error.OutOfFiles;
                 },
 
                 .native => |native| {
-                    if (native.len == 0) return error.FileNotFound;
+                    if (native.path_prefix.len == 0) return error.FileNotFound;
 
                     var path_buffer = std.mem.zeroes([4096]u8);
                     const seperator = '/';
-                    const seperator_length = @boolToInt(native[native.len - 1] != seperator);
 
-                    if ((native.len + seperator_length + path.length) >= path_buffer.len)
-                        return error.FileNotFound;
+                    const seperator_length = @boolToInt(native.path_prefix[
+                        native.path_prefix.len - 1] != seperator);
 
-                    std.mem.copy(u8, path_buffer[0 ..], native);
+                    if ((native.path_prefix.len + seperator_length + path.length) >=
+                        path_buffer.len) return error.FileNotFound;
+
+                    std.mem.copy(u8, path_buffer[0 ..], native.path_prefix);
 
                     if (seperator_length != 0)
-                        path_buffer[native.len] = seperator;
+                        path_buffer[native.path_prefix.len] = seperator;
 
-                    std.mem.copy(u8, path_buffer[native.len .. path_buffer.len],
-                        path.buffer[0 .. path.length]);
+                    std.mem.copy(u8, path_buffer[native.path_prefix.len ..
+                        path_buffer.len], path.buffer[0 .. path.length]);
 
                     ext.SDL_ClearError();
 
-                    return @ptrCast(*FileAccess, ext.SDL_RWFromFile(&path_buffer, switch (mode) {
-                        .readonly => "rb",
-                        .overwrite => "wb",
-                        .append => "ab",
-                    }) orelse return error.FileNotFound);
+                    const Implementation = struct {
+                        fn rwOpsCast(context: *anyopaque) *ext.SDL_RWops {
+                            return @ptrCast(*ext.SDL_RWops, @alignCast(
+                                @alignOf(ext.SDL_RWops), context));
+                        }
+
+                        fn close(context: *anyopaque) void {
+                            ext.SDL_ClearError();
+
+                            if (ext.SDL_RWclose(rwOpsCast(context)) != 0)
+                                ext.SDL_LogWarn(ext.SDL_LOG_CATEGORY_APPLICATION, ext.SDL_GetError());
+                        }
+
+                        fn queryCursor(context: *anyopaque) FileAccess.Error!u64 {
+                            ext.SDL_ClearError();
+
+                            const sought = ext.SDL_RWtell(rwOpsCast(context));
+
+                            if (sought < 0) return error.FileInaccessible;
+
+                            return @intCast(u64, sought);
+                        }
+
+                        fn queryLength(context: *anyopaque) FileAccess.Error!u64 {
+                            ext.SDL_ClearError();
+
+                            const sought = ext.SDL_RWsize(rwOpsCast(context));
+
+                            if (sought < 0) return error.FileInaccessible;
+
+                            return @intCast(u64, sought);
+                        }
+
+                        fn read(context: *anyopaque, buffer: []u8) FileAccess.Error!usize {
+                            ext.SDL_ClearError();
+
+                            const buffer_read = ext.SDL_RWread(rwOpsCast(
+                                context), buffer.ptr, @sizeOf(u8), buffer.len);
+
+                            if ((buffer_read == 0) and (ext.SDL_GetError() != null))
+                                return error.FileInaccessible;
+
+                            return buffer_read;
+                        }
+
+                        fn seek(context: *anyopaque, cursor: usize) FileAccess.Error!void {
+                            var to_seek = cursor;
+
+                            while (to_seek != 0) {
+                                const math = std.math;
+                                const sought = @intCast(i64, math.min(to_seek, math.maxInt(i64)));
+
+                                ext.SDL_ClearError();
+
+                                if (ext.SDL_RWseek(rwOpsCast(context), sought, ext.RW_SEEK_CUR) < 0)
+                                    return error.FileInaccessible;
+
+                                // Cannot be less than zero because it is derived from `read`.
+                                to_seek -= @intCast(u64, sought);
+                            }
+                        }
+
+                        fn seekToEnd(context: *anyopaque) FileAccess.Error!void {
+                            ext.SDL_ClearError();
+
+                            if (ext.SDL_RWseek(rwOpsCast(context), 0, ext.RW_SEEK_END) < 0)
+                                return error.FileInaccessible;
+                        }
+                    };
+
+                    return FileAccess{
+                        .context = ext.SDL_RWFromFile(&path_buffer, switch (mode) {
+                            .readonly => "rb",
+                            .overwrite => "wb",
+                            .append => "ab",
+                        }) orelse return error.FileNotFound,
+
+                        .implementation = &.{
+                            .close = Implementation.close,
+                            .queryCursor = Implementation.queryCursor,
+                            .queryLength = Implementation.queryLength,
+                            .read = Implementation.read,
+                            .seek = Implementation.seek,
+                            .seekToEnd = Implementation.seekToEnd,
+                        },
+                    };
                 },
             }
         }
@@ -515,9 +657,7 @@ pub const FileSystem = union(enum) {
     /// A [Path] value is returned containing the fully qualified path from the file-system root or
     /// a [PathError] if it could not be created.
     ///
-    pub fn joinedPath(file_system: *const FileSystem,
-        sequences: []const []const u8) PathError!Path {
-
+    pub fn joinedPath(file_system: *FileSystem, sequences: []const []const u8) PathError!Path {
         var path = Path{
             .file_system = file_system,
             .buffer = std.mem.zeroes([Path.max]u8),
@@ -644,8 +784,7 @@ pub const RunError = error {
 };
 
 ///
-/// Runs a graphical application referenced by `run` with `error` as its error set and `allocator`
-/// as the underlying memory allocation strategy for its graphical runtime.
+/// Runs a graphical application referenced by `run` with `error` as its error set.
 ///
 /// Should an error from `run` occur, an `Error` is returned, otherwise a [RunError] is returned if
 /// the underlying runtime fails and is logged.
@@ -694,8 +833,15 @@ pub fn runGraphics(comptime Error: anytype,
 
     defer ext.SDL_free(user_path_prefix);
 
-    var app_context = AppContext.Implementation.init("./data.oar", user_path_prefix
-        [0 .. std.mem.len(user_path_prefix)]) catch |err| {
+    var cwd_file_system = FileSystem{.native =.{.path_prefix = "./"}};
+
+    var data_archive_file_access = try (try cwd_file_system.
+        joinedPath(&.{"./data.oar"})).open(.readonly);
+
+    defer data_archive_file_access.close();
+
+    var app_context = AppContext.Implementation.init(data_archive_file_access,
+        user_path_prefix[0 .. std.mem.len(user_path_prefix)]) catch |err| {
 
         ext.SDL_LogCritical(ext.SDL_LOG_CATEGORY_APPLICATION, switch (err) {
             error.OutOfMemory => "Failed to allocate necessary memory",