perf: Change return type of custom protocol handler from Vec<u8> to Cow<'static, [u8]>, closes #796 (#797)

* perf: Change return type of custom protocol handler from `Vec<u8>` to `Cow<'static, [u8]>`

to allow returning static resources without heap allocation

* chore(examples): Fix some comments

following the review https://github.com/tauri-apps/wry/pull/797#pullrequestreview-1210580935

* fix(android): Change return type of response to `Cow`

.changes/change_custom_protocol_handler_response_to_cow.md

@@ -0,0 +1,5 @@
+---
+"wry": "minor"
+---
+
+Change return type of [custom protocol handlers](https://docs.rs/wry/latest/wry/webview/struct.WebViewBuilder.html#method.with_custom_protocol) from `Result<Response<Vec<u8>>>` to `Result<Response<Cow<'static, [u8]>>>`. This allows the handlers to return static resources without heap allocations. This is effective when you embed some large files like bundled JavaScript source as `&'static [u8]` using [`include_bytes!`](https://doc.rust-lang.org/std/macro.include_bytes.html).

examples/custom_protocol.rs

@@ -2,6 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0
 // SPDX-License-Identifier: MIT
 
+const PAGE1_HTML: &[u8] = include_bytes!("custom_protocol_page1.html");
+
 fn main() -> wry::Result<()> {
   use std::{
     fs::{canonicalize, read},
@@ -27,21 +29,19 @@ fn main() -> wry::Result<()> {
   let _webview = WebViewBuilder::new(window)
     .unwrap()
     .with_custom_protocol("wry".into(), move |request| {
-      let path = &request.uri().path();
+      let path = request.uri().path();
       // Read the file content from file path
-      let content = read(canonicalize(PathBuf::from("examples").join(
-        if path == &"/" {
-          "custom_protocol_page1.html"
-        } else {
-          // remove leading slash
-          &path[1..]
-        },
-      ))?)?;
+      let content = if path == "/" {
+        PAGE1_HTML.into()
+      } else {
+        // `1..` for removing leading slash
+        read(canonicalize(PathBuf::from("examples").join(&path[1..]))?)?.into()
+      };
 
       // Return asset contents and mime types based on file extentions
       // If you don't want to do this manually, there are some crates for you.
       // Such as `infer` and `mime_guess`.
-      let mimetype = if path.ends_with(".html") || path == &"/" {
+      let mimetype = if path.ends_with(".html") || path == "/" {
         "text/html"
       } else if path.ends_with(".js") {
         "text/javascript"

examples/form.rs

@@ -36,7 +36,7 @@ fn main() -> wry::Result<()> {
 
       Response::builder()
         .header(CONTENT_TYPE, "text/html")
-        .body(read(canonicalize(&path)?)?)
+        .body(read(canonicalize(&path)?)?.into())
         .map_err(Into::into)
     })
     // tell the webview to load the custom protocol

examples/menu.rs

@@ -2,6 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0
 // SPDX-License-Identifier: MIT
 
+const PAGE1_HTML: &[u8] = include_bytes!("custom_protocol_page1.html");
+
 fn main() -> wry::Result<()> {
   use std::{
     fs::{canonicalize, read},
@@ -53,21 +55,19 @@ fn main() -> wry::Result<()> {
   let _webview = WebViewBuilder::new(window)
     .unwrap()
     .with_custom_protocol("wry".into(), move |request| {
-      let path = &request.uri().path();
+      let path = request.uri().path();
       // Read the file content from file path
-      let content = read(canonicalize(PathBuf::from("examples").join(
-        if path == &"/" {
-          "custom_protocol_page1.html"
-        } else {
-          // remove leading slash
-          &path[1..]
-        },
-      ))?)?;
+      let content = if path == "/" {
+        PAGE1_HTML.into()
+      } else {
+        // `1..` for removing leading slash
+        read(canonicalize(PathBuf::from("examples").join(&path[1..]))?)?.into()
+      };
 
       // Return asset contents and mime types based on file extentions
       // If you don't want to do this manually, there are some crates for you.
       // Such as `infer` and `mime_guess`.
-      let (data, meta) = if path.ends_with(".html") || path == &"/" {
+      let (data, meta) = if path.ends_with(".html") || path == "/" {
         (content, "text/html")
       } else if path.ends_with(".js") {
         (content, "text/javascript")

examples/stream_range.rs

@@ -57,7 +57,7 @@ fn main() -> wry::Result<()> {
       let path = &request.uri().path()[1..];
 
       // Read the file content from file path
-      let mut content = File::open(canonicalize(&path)?)?;
+      let mut content = File::open(canonicalize(path)?)?;
 
       // Return asset contents and mime types based on file extentions
       // If you don't want to do this manually, there are some crates for you.
@@ -125,7 +125,7 @@ fn main() -> wry::Result<()> {
       response
         .header(CONTENT_TYPE, mimetype)
         .status(status_code)
-        .body(buf)
+        .body(buf.into())
         .map_err(Into::into)
     })
     // tell the webview to load the custom protocol

src/webview/android/mod.rs

@@ -13,7 +13,7 @@ use http::{
 use kuchiki::NodeRef;
 use once_cell::sync::OnceCell;
 use sha2::{Digest, Sha256};
-use std::rc::Rc;
+use std::{borrow::Cow, rc::Rc};
 use tao::platform::android::ndk_glue::{
   jni::{
     errors::Error as JniError,
@@ -66,9 +66,11 @@ impl UnsafeIpc {
 unsafe impl Send for UnsafeIpc {}
 unsafe impl Sync for UnsafeIpc {}
 
-pub struct UnsafeRequestHandler(Box<dyn Fn(Request<Vec<u8>>) -> Option<Response<Vec<u8>>>>);
+pub struct UnsafeRequestHandler(
+  Box<dyn Fn(Request<Vec<u8>>) -> Option<Response<Cow<'static, [u8]>>>>,
+);
 impl UnsafeRequestHandler {
-  pub fn new(f: Box<dyn Fn(Request<Vec<u8>>) -> Option<Response<Vec<u8>>>>) -> Self {
+  pub fn new(f: Box<dyn Fn(Request<Vec<u8>>) -> Option<Response<Cow<'static, [u8]>>>>) -> Self {
     Self(f)
   }
 }
@@ -182,7 +184,7 @@ impl InnerWebView {
             {
               if !initialization_scripts.is_empty() {
                 let mut document =
-                  kuchiki::parse_html().one(String::from_utf8_lossy(&response.body()).into_owned());
+                  kuchiki::parse_html().one(String::from_utf8_lossy(response.body()).into_owned());
                 let csp = response.headers_mut().get_mut(CONTENT_SECURITY_POLICY);
                 let mut hashes = Vec::new();
                 with_html_head(&mut document, |head| {
@@ -208,7 +210,7 @@ impl InnerWebView {
                   *csp = HeaderValue::from_str(&csp_string).unwrap();
                 }
 
-                *response.body_mut() = document.to_string().as_bytes().to_vec();
+                *response.body_mut() = document.to_string().into_bytes().into();
               }
             }
             return Some(response);

src/webview/mod.rs

@@ -48,6 +48,7 @@ use webview2_com::Microsoft::Web::WebView2::Win32::ICoreWebView2Controller;
 #[cfg(target_os = "windows")]
 use windows::{Win32::Foundation::HWND, Win32::UI::WindowsAndMessaging::DestroyWindow};
 
+use std::borrow::Cow;
 use std::{path::PathBuf, rc::Rc};
 
 pub use url::Url;
@@ -137,7 +138,7 @@ pub struct WebViewAttributes {
   /// [bug]: https://bugs.webkit.org/show_bug.cgi?id=229034
   pub custom_protocols: Vec<(
     String,
-    Box<dyn Fn(&Request<Vec<u8>>) -> Result<Response<Vec<u8>>>>,
+    Box<dyn Fn(&Request<Vec<u8>>) -> Result<Response<Cow<'static, [u8]>>>>,
   )>,
   /// Set the IPC handler to receive the message from Javascript on webview to host Rust code.
   /// The message sent from webview should call `window.ipc.postMessage("insert_message_here");`.
@@ -394,7 +395,7 @@ impl<'a> WebViewBuilder<'a> {
   #[cfg(feature = "protocol")]
   pub fn with_custom_protocol<F>(mut self, name: String, handler: F) -> Self
   where
-    F: Fn(&Request<Vec<u8>>) -> Result<Response<Vec<u8>>> + 'static,
+    F: Fn(&Request<Vec<u8>>) -> Result<Response<Cow<'static, [u8]>>> + 'static,
   {
     self
       .webview

src/webview/webkitgtk/web_context.rs

@@ -8,6 +8,7 @@ use crate::{webview::web_context::WebContextData, Error};
 use glib::FileError;
 use http::{header::CONTENT_TYPE, Request, Response};
 use std::{
+  borrow::Cow,
   cell::RefCell,
   collections::{HashSet, VecDeque},
   path::PathBuf,
@@ -110,7 +111,7 @@ pub trait WebContextExt {
   /// relying on the platform's implementation to properly handle duplicated scheme handlers.
   fn register_uri_scheme<F>(&mut self, name: &str, handler: F) -> crate::Result<()>
   where
-    F: Fn(&Request<Vec<u8>>) -> crate::Result<Response<Vec<u8>>> + 'static;
+    F: Fn(&Request<Vec<u8>>) -> crate::Result<Response<Cow<'static, [u8]>>> + 'static;
 
   /// Register a custom protocol to the web context, only if it is not a duplicate scheme.
   ///
@@ -118,7 +119,7 @@ pub trait WebContextExt {
   /// function will return `Err(Error::DuplicateCustomProtocol)`.
   fn try_register_uri_scheme<F>(&mut self, name: &str, handler: F) -> crate::Result<()>
   where
-    F: Fn(&Request<Vec<u8>>) -> crate::Result<Response<Vec<u8>>> + 'static;
+    F: Fn(&Request<Vec<u8>>) -> crate::Result<Response<Cow<'static, [u8]>>> + 'static;
 
   /// Add a [`WebView`] to the queue waiting to be opened.
   ///
@@ -155,7 +156,7 @@ impl WebContextExt for super::WebContext {
 
   fn register_uri_scheme<F>(&mut self, name: &str, handler: F) -> crate::Result<()>
   where
-    F: Fn(&Request<Vec<u8>>) -> crate::Result<Response<Vec<u8>>> + 'static,
+    F: Fn(&Request<Vec<u8>>) -> crate::Result<Response<Cow<'static, [u8]>>> + 'static,
   {
     actually_register_uri_scheme(self, name, handler)?;
     if self.os.registered_protocols.insert(name.to_string()) {
@@ -167,7 +168,7 @@ impl WebContextExt for super::WebContext {
 
   fn try_register_uri_scheme<F>(&mut self, name: &str, handler: F) -> crate::Result<()>
   where
-    F: Fn(&Request<Vec<u8>>) -> crate::Result<Response<Vec<u8>>> + 'static,
+    F: Fn(&Request<Vec<u8>>) -> crate::Result<Response<Cow<'static, [u8]>>> + 'static,
   {
     if self.os.registered_protocols.insert(name.to_string()) {
       actually_register_uri_scheme(self, name, handler)
@@ -275,7 +276,7 @@ fn actually_register_uri_scheme<F>(
   handler: F,
 ) -> crate::Result<()>
 where
-  F: Fn(&Request<Vec<u8>>) -> crate::Result<Response<Vec<u8>>> + 'static,
+  F: Fn(&Request<Vec<u8>>) -> crate::Result<Response<Cow<'static, [u8]>>> + 'static,
 {
   use webkit2gtk::traits::*;
   let context = &context.os.context;

src/webview/wkwebview/mod.rs

@@ -18,6 +18,7 @@ use cocoa::{
 };
 
 use std::{
+  borrow::Cow,
   ffi::{c_void, CStr},
   os::raw::c_char,
   ptr::{null, null_mut},
@@ -77,7 +78,7 @@ pub(crate) struct InnerWebView {
   #[cfg(target_os = "macos")]
   file_drop_ptr: *mut (Box<dyn Fn(&Window, FileDropEvent) -> bool>, Rc<Window>),
   download_delegate: id,
-  protocol_ptrs: Vec<*mut Box<dyn Fn(&Request<Vec<u8>>) -> Result<Response<Vec<u8>>>>>,
+  protocol_ptrs: Vec<*mut Box<dyn Fn(&Request<Vec<u8>>) -> Result<Response<Cow<'static, [u8]>>>>>,
 }
 
 impl InnerWebView {

src/webview/wkwebview/web_context.rs

@@ -6,10 +6,11 @@ use crate::Result;
 
 use crate::webview::web_context::WebContextData;
 use http::{Request, Response};
+use std::borrow::Cow;
 
 #[derive(Debug)]
 pub struct WebContextImpl {
-  protocols: Vec<*mut Box<dyn Fn(&Request<Vec<u8>>) -> Result<Response<Vec<u8>>>>>,
+  protocols: Vec<*mut Box<dyn Fn(&Request<Vec<u8>>) -> Result<Response<Cow<'static, [u8]>>>>>,
 }
 
 impl WebContextImpl {
@@ -23,7 +24,7 @@ impl WebContextImpl {
 
   pub fn registered_protocols(
     &mut self,
-    handler: *mut Box<dyn Fn(&Request<Vec<u8>>) -> Result<Response<Vec<u8>>>>,
+    handler: *mut Box<dyn Fn(&Request<Vec<u8>>) -> Result<Response<Cow<'static, [u8]>>>>,
   ) {
     self.protocols.push(handler);
   }