build(wasm): embed HTML files in the builder

The `prefix` path had stopped working following the latest Zig update,
which means an alternative had to be found that doesn't depend on
`@src().file` (which now only returns paths relative to the module
root). For now, the best solution I've found is to embed the files in
the WebServerStep.

build_capy.zig

@@ -91,7 +91,6 @@ const WebServerStep = struct {
 
     fn handler(self: *WebServerStep, build: *std.Build, res: *Server) !void {
         const allocator = build.allocator;
-        const prefix = (comptime std.fs.path.dirname(@src().file) orelse "./") ++ std.fs.path.sep_str;
 
         var req = try res.receiveHead();
         var arena = std.heap.ArenaAllocator.init(allocator);
@@ -100,10 +99,17 @@ const WebServerStep = struct {
 
         const path = req.head.target;
         var file_path: []const u8 = "";
+        var file_content: ?[]const u8 = null;
         var content_type: []const u8 = "text/html";
         if (std.mem.eql(u8, path, "/")) {
-            file_path = try std.fs.path.join(req_allocator, &.{ prefix, "src/backends/wasm/index.html" });
+            file_content = @embedFile("src/backends/wasm/index.html");
             content_type = "text/html";
+        } else if (std.mem.eql(u8, path, "/capy.js")) {
+            file_content = @embedFile("src/backends/wasm/capy.js");
+            content_type = "application/javascript";
+        } else if (std.mem.eql(u8, path, "/capy-worker.js")) {
+            file_content = @embedFile("src/backends/wasm/capy-worker.js");
+            content_type = "application/javascript";
         } else if (std.mem.eql(u8, path, "/zig-app.wasm")) {
             file_path = self.exe.getEmittedBin().getPath2(build, &self.step);
             content_type = "application/wasm";
@@ -113,28 +119,34 @@ const WebServerStep = struct {
                 content_type = "application/javascript";
             }
         } else {
-            file_path = try std.fs.path.join(req_allocator, &.{ prefix, "src/backends/wasm", path });
+            // else try the HTML files supplied by the application (in the 'html' project relative
+            // to the project root)
+            file_path = try std.fs.path.join(req_allocator, &.{ "html", path });
             content_type = "application/javascript";
         }
 
         if (self.options.wasm_debug_requests) {
             std.log.debug("{s} -> {s}", .{ path, file_path });
         }
-        const file: ?std.fs.File = std.fs.cwd().openFile(file_path, .{ .mode = .read_only }) catch |err| blk: {
-            switch (err) {
-                error.FileNotFound => break :blk null,
-                else => return err,
-            }
-        };
 
         var status: std.http.Status = .ok;
         const content = blk: {
-            if (file) |f| {
-                defer f.close();
-                break :blk try f.readToEndAlloc(req_allocator, std.math.maxInt(usize));
+            if (file_content) |presupplied_content| {
+                break :blk presupplied_content;
             } else {
-                status = .not_found;
-                break :blk "404 Not Found";
+                const file: ?std.fs.File = std.fs.cwd().openFile(file_path, .{ .mode = .read_only }) catch |err| blk2: {
+                    switch (err) {
+                        error.FileNotFound => break :blk2 null,
+                        else => return err,
+                    }
+                };
+                if (file) |f| {
+                    defer f.close();
+                    break :blk try f.readToEndAlloc(req_allocator, std.math.maxInt(usize));
+                } else {
+                    status = .not_found;
+                    break :blk "404 Not Found";
+                }
             }
         };