perf(macOS): avoid copying large protocol bodies

Author: Tunglies

.changes/macos-protocol-body-nocopy.md

@@ -0,0 +1,5 @@
+---
+"wry": patch
+---
+
+On macOS, avoid an extra copy for owned custom protocol response bodies of 128KB or larger by transferring the body buffer into `NSData`.

Cargo.lock

@@ -138,6 +138,7 @@ objc2-core-foundation = { version = "0.3.0", default-features = false, features
 ] }
 objc2-foundation = { version = "0.3.0", default-features = false, features = [
   "std",
+  "block2",
   "objc2-core-foundation",
   "NSURLRequest",
   "NSURL",

Cargo.toml

@@ -26,6 +26,8 @@ use objc2_web_kit::{WKURLSchemeHandler, WKURLSchemeTask};
 
 use crate::{wkwebview::WEBVIEW_STATE, RequestAsyncResponder, WryWebView};
 
+const NO_COPY_DATA_THRESHOLD: usize = 128 * 1024;
+
 pub fn create(name: &str) -> &AnyClass {
   unsafe {
     // Include the address of WEBVIEW_STATE in the class name so that each dylib in the process
@@ -215,6 +217,7 @@ extern "C" fn start_task(
                 check_task_is_valid(&webview, task_key, task_uuid.clone())?;
 
                 let content = sent_response.body();
+                let content_len = content.len();
                 // default: application/octet-stream, but should be provided by the client
                 let wanted_mime = sent_response.headers().get(CONTENT_TYPE);
                 // default to 200
@@ -231,7 +234,7 @@ extern "C" fn start_task(
                 }
                 headers.insert(
                   &*NSString::from_str(CONTENT_LENGTH.as_str()),
-                  &*NSString::from_str(&content.len().to_string()),
+                  &*NSString::from_str(&content_len.to_string()),
                 );
 
                 // add headers
@@ -264,15 +267,24 @@ extern "C" fn start_task(
                 }))
                 .map_err(|_e| crate::Error::CustomProtocolTaskInvalid)?;
 
-                // Send data
-                let data = NSData::alloc();
-                // MIGRATE NOTE: we copied the content to the NSData because content will be freed
-                // when out of scope but NSData will also free the content when it's done and cause doube free.
-                let data = NSData::initWithBytes_length(
-                  data,
-                  content.as_ptr() as *mut c_void,
-                  content.len(),
-                );
+                let data = if content_len < NO_COPY_DATA_THRESHOLD {
+                  let data = NSData::alloc();
+                  // Keep small responses on the original copy path; no-copy deallocation costs more.
+                  NSData::initWithBytes_length(data, content.as_ptr() as *mut c_void, content.len())
+                } else {
+                  match sent_response.into_body() {
+                    Cow::Owned(content) => NSData::from_vec(content),
+                    Cow::Borrowed(content) => {
+                      let data = NSData::alloc();
+                      // Copy borrowed responses because NSData cannot take ownership.
+                      NSData::initWithBytes_length(
+                        data,
+                        content.as_ptr() as *mut c_void,
+                        content.len(),
+                      )
+                    }
+                  }
+                };
 
                 // Check validity again
                 check_webview_id_valid(webview_id)?;