Fix HtmlAsyncRenderer never flushing when the chunk size has been exceeded

Author: mesram

Sources/Elementary/Rendering/HtmlAsyncRenderer.swift

@@ -15,7 +15,7 @@ struct AsyncHTMLRenderer<Writer: HTMLStreamWriter>: _AsyncHTMLRendering {
     mutating func appendToken(_ token: consuming _HTMLRenderToken) async throws {
         // let value = token.renderedValue.utf8
         buffer.appendToken(token)
-        if buffer.count >= buffer.capacity {
+        if buffer.count >= self.chunkSize {
             try await flush()
             buffer.replaceSubrange(0...buffer.count - 1, with: [])
         }

Tests/ElementaryTests/AsyncRenderingTests.swift

@@ -70,6 +70,24 @@ final class AsyncRenderingTests: XCTestCase {
             "<p>late response foo</p><p>late response bar</p>"
         )
     }
+    
+    func testBufferFlushesWhenChunkSizeExceeded() async throws {
+        let writer = TestBufferWriter()
+        try await div { "This is some content" }
+            .render(into: writer, chunkSize: 1)
+        
+        XCTAssertEqual("<div>This is some content</div>", String(decoding: writer.result, as: UTF8.self), file: #filePath, line: #line)
+        XCTAssertGreaterThan(writer.writeCount, 1)
+    }
+    
+    func testBufferFlushesExactlyOnceOnSmallInput() async throws {
+        let writer = TestBufferWriter()
+        try await div { "This is some content" }
+            .render(into: writer, chunkSize: 1024)
+        
+        XCTAssertEqual("<div>This is some content</div>", String(decoding: writer.result, as: UTF8.self), file: #filePath, line: #line)
+        XCTAssertEqual(writer.writeCount, 1)
+    }
 }
 
 private struct AwaitedP: HTML {

Tests/ElementaryTests/Utilities.swift

@@ -15,3 +15,13 @@ func HTMLAssertEqualAsyncOnly(_ html: some HTML, _ expected: String, file: Stati
 func HTMLFormattedAssertEqual(_ html: some HTML, _ expected: String, file: StaticString = #filePath, line: UInt = #line) {
     XCTAssertEqual(expected, html.renderFormatted(), file: file, line: line)
 }
+
+final class TestBufferWriter: HTMLStreamWriter {
+    var result: [UInt8] = []
+    var writeCount: Int = 0
+
+    func write(_ bytes: ArraySlice<UInt8>) async throws {
+        writeCount += 1
+        result.append(contentsOf: bytes)
+    }
+}