add impl for file fetch

src/main.zig

@@ -21,7 +21,7 @@ pub fn main() anyerror!void {
         comptime http.router.router(&[_]http.router.Route{
             http.router.get("/", index),
             http.router.post("/api/upload", uploadFile),
-            http.router.post("/:filename", fetchFile),
+            http.router.get("/i/:filename", fetchFile),
         }),
     );
 }
@@ -67,6 +67,21 @@ fn uploadFile(response: *http.Response, request: http.Request) !void {
 
 fn fetchFile(response: *http.Response, request: http.Request, filename: []const u8) !void {
     std.log.info("got name: {s}", .{filename});
+    var image_path_buffer: [512]u8 = undefined;
+
     const images_dir = try std.fs.cwd().openDir(images_dir_path, .{});
-    try response.writer().writeAll("Hello Zig! fetch");
+    const image_path = try std.fmt.bufPrint(
+        &image_path_buffer,
+        "{s}/{s}",
+        .{ images_dir_path, filename },
+    );
+
+    // TODO return 404 on error
+    const image_file = try std.fs.cwd().openFile(image_path, .{ .read = false });
+    while (true) {
+        var file_write_buffer: [1024]u8 = undefined;
+        const bytes_read = try image_file.read(&file_write_buffer);
+        if (bytes_read == 0) return;
+        try response.writer().writeAll(&file_write_buffer);
+    }
 }