fix flush operation on OutputStream sub-classes

avaje-jex/src/main/java/io/avaje/jex/compression/CompressedOutputStream.java

@@ -63,6 +63,15 @@ public void write(int byteVal) throws IOException {
     (compressedStream != null ? compressedStream : originStream).write(byteVal);
   }
 
+  @Override
+  public void flush() throws IOException {
+    if (compressedStream != null) {
+      compressedStream.flush();
+    } else {
+      originStream.flush();
+    }
+  }
+
   @Override
   public void close() throws IOException {
     if (compressedStream != null) {

avaje-jex/src/main/java/io/avaje/jex/core/BufferedOutStream.java

@@ -66,6 +66,14 @@ private void useJdkOutput() throws IOException {
     }
   }
 
+  @Override
+  public void flush() throws IOException {
+    if (!jdkOutput) {
+      useJdkOutput();
+    }
+    out.flush();
+  }
+
   @Override
   public void close() throws IOException {
     if (jdkOutput) {

avaje-jex/src/test/java/io/avaje/jex/compression/CompressionTest.java

@@ -3,6 +3,8 @@
 import static org.assertj.core.api.Assertions.assertThat;
 
 import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
 import java.net.http.HttpResponse;
 import java.util.zip.GZIPInputStream;
 
@@ -22,18 +24,21 @@ static TestPair init() {
 
     final Jex app =
         Jex.create()
-            .routing(
-                r ->
-                    r.get(
-                            "/compress",
-                            ctx ->
-                                ctx.contentType(ContentType.APPLICATION_JSON)
-                                    .write(CompressionTest.class.getResourceAsStream("/64KB.json")))
-                        .get(
-                            "/sus",
-                            ctx ->
-                                ctx.write(
-                                    CompressionTest.class.getResourceAsStream("/public/sus.txt"))));
+            .get(
+                "/compress",
+                ctx ->
+                    ctx.contentType(ContentType.APPLICATION_JSON)
+                        .write(CompressionTest.class.getResourceAsStream("/64KB.json")))
+            .get(
+                "/flush",
+                ctx -> {
+                  transferStream(
+                      CompressionTest.class.getResourceAsStream("/64KB.json"),
+                      ctx.contentType(ContentType.APPLICATION_JSON).outputStream());
+                })
+            .get(
+                "/sus",
+                ctx -> ctx.write(CompressionTest.class.getResourceAsStream("/public/sus.txt")));
 
     return TestPair.create(app);
   }
@@ -62,6 +67,25 @@ void testCompression() throws IOException {
     assertThat(decompressed).isEqualTo(expected);
   }
 
+  @Test
+  void testCompressionFlush() throws IOException {
+    var res =
+        pair.request()
+            .header(Constants.ACCEPT_ENCODING, "deflate, gzip;q=1.0, *;q=0.5")
+            .path("flush")
+            .GET()
+            .asInputStream();
+    assertThat(res.statusCode()).isEqualTo(200);
+    assertThat(res.headers().firstValue(Constants.CONTENT_ENCODING)).contains("gzip");
+
+    var expected = CompressionTest.class.getResourceAsStream("/64KB.json").readAllBytes();
+
+    final var gzipInputStream = new GZIPInputStream(res.body());
+    var decompressed = gzipInputStream.readAllBytes();
+    gzipInputStream.close();
+    assertThat(decompressed).isEqualTo(expected);
+  }
+
   @Test
   void testNoCompression() {
     HttpResponse<String> res =
@@ -88,4 +112,26 @@ void testCompressionRange() throws IOException {
     gzipInputStream.close();
     assertThat(decompressed).isEqualTo(expected);
   }
+
+  /**
+   * Reads data from the input stream in chunks of 1024 bytes and writes it immediately to the
+   * output stream.
+   *
+   * @param in The InputStream to read data from.
+   * @param out The OutputStream to write data to.
+   * @throws IOException If an I/O error occurs during read or write operations.
+   */
+  public static void transferStream(InputStream in, OutputStream out) throws IOException {
+    // Define the buffer size as 1024 bytes (1KB)
+    final int BUFFER_SIZE = 2048;
+    byte[] buffer = new byte[BUFFER_SIZE];
+
+    int bytesRead;
+    while ((bytesRead = in.read(buffer)) != -1) {
+
+      out.write(buffer, 0, bytesRead);
+      out.flush();
+    }
+    out.close();
+  }
 }