Support cancellation of tasks with FetchHTTPClient

Examples/WASMClient/main.swift

@@ -22,7 +22,6 @@ import JavaScriptKit
 typealias DefaultExecutorFactory = JavaScriptEventLoop
 JavaScriptEventLoop.installGlobalExecutor()
 
-let client = FetchHTTPClient()
 let status = Status()
 
 // Ask the user for the URL string.
@@ -52,9 +51,10 @@ if method == .post || method == .put {
     }
 }
 
-status.set("⏳ Making \(method) request to \(url)")
+func makeRequest(url: URL, method: HTTPRequest.Method, body: HTTPClientRequestBody<FetchHTTPClient.RequestBodyWriter>?) async throws {
+    let client = FetchHTTPClient()
+    status.set("⏳ Making \(method) request to \(url)")
 
-do {
     try await client.perform(
         request: .init(
             method: method,
@@ -117,6 +117,21 @@ do {
             div("<binary>")
         }
     }
+}
+
+let requestTask = Task {
+    try await makeRequest(url: url, method: method, body: body)
+}
+
+let sleepTask = Task {
+    status.set("💤 Waiting for 10 seconds")
+    try await Task.sleep(for: .seconds(10))
+    status.set("🚫 Cancelling task")
+    requestTask.cancel()
+}
+
+do {
+    try await requestTask.value
 } catch {
     status.set("❌ Fetch failed: \(error)")
 }

Sources/FetchHTTPClient/FetchHTTPClient.swift

@@ -83,8 +83,21 @@ public final class FetchHTTPClient: HTTPAPIs.HTTPClient {
         }
 
         // Perform the request
-        let requestInit = RequestInit(body: jsBody, method: request.method.rawValue, headers: requestHeaders)
-        let response = try await fetch(url.absoluteString, requestInit)
+        let abortController = try AbortController()
+        let signal = try abortController.signal
+        let requestInit = RequestInit(body: jsBody, method: request.method.rawValue, headers: requestHeaders, signal: signal)
+
+        // No matter what, we should abort the request at the end of this function
+        defer {
+            try? abortController.abort()
+        }
+
+        let response = try await withTaskCancellationHandler {
+            return try await fetch(url.absoluteString, requestInit)
+        } onCancel: {
+            try? abortController.abort()
+        }
+
         let responseStatus = try response.status
         let responseStatusText = try response.statusText
         let stream = try response.body
@@ -163,8 +176,16 @@ public final class FetchHTTPClient: HTTPAPIs.HTTPClient {
             if buffer.isEmpty {
                 // Read more data in from JS
                 let chunk: Chunk
+
+                // TODO: Find a way to make this safe.
+                nonisolated(unsafe) let reader = reader
+
                 do {
-                    chunk = try await reader.read()
+                    chunk = try await withTaskCancellationHandler {
+                        try await reader.read()
+                    } onCancel: {
+                        try? reader.releaseLock()
+                    }
                 } catch {
                     throw .first(error)
                 }

Sources/FetchHTTPClient/JSImports.swift

@@ -16,6 +16,13 @@ import JavaScriptKit
 /// # Javascript Imports
 /// This file defines the Javascript classes and functions imported into Swift.
 
+// https://developer.mozilla.org/en-US/docs/Web/API/AbortController
+@JSClass(from: .global) struct AbortController: @unchecked Sendable {
+    @JSGetter var signal: JSObject?
+    @JSFunction init() throws(JSException)
+    @JSFunction func abort() throws(JSException)
+}
+
 // https://developer.mozilla.org/en-US/docs/Web/API/Headers
 @JSClass(from: .global) struct Headers {
     @JSFunction init() throws(JSException)
@@ -58,11 +65,13 @@ import JavaScriptKit
     let body: JSObject?
     let method: String?
     let headers: Headers?
+    let signal: JSObject?
 
-    init(body: JSObject?, method: String?, headers: Headers?) {
+    init(body: JSObject?, method: String?, headers: Headers?, signal: JSObject?) {
         self.body = body
         self.method = method
         self.headers = headers
+        self.signal = signal
     }
 }
 
@@ -76,6 +85,7 @@ import JavaScriptKit
 // TODO: Find a way to remove the @unchecked. This object has to be moved through the different Swift reader types.
 @JSClass(from: .global) struct ReadableStreamDefaultReader: @unchecked Sendable {
     @JSFunction func read() async throws(JSException) -> Chunk
+    @JSFunction func releaseLock() throws(JSException)
 }
 
 // https://developer.mozilla.org/en-US/docs/Web/API/ReadableStream