Add ByteBufBodyHandler

Allows a response from HttpClient to be efficiently read into a ByteBuf.

Signed-off-by: Graham <gpe@openrs2.org>

buffer/src/main/kotlin/org/openrs2/buffer/ByteBufBodyHandler.kt

@@ -0,0 +1,47 @@
+package org.openrs2.buffer
+
+import io.netty.buffer.ByteBuf
+import io.netty.buffer.ByteBufAllocator
+import io.netty.buffer.Unpooled
+import java.net.http.HttpResponse
+import java.nio.ByteBuffer
+import java.util.concurrent.CompletableFuture
+import java.util.concurrent.CompletionStage
+import java.util.concurrent.Flow
+import javax.inject.Inject
+import javax.inject.Singleton
+
+@Singleton
+public class ByteBufBodyHandler @Inject constructor(
+    private val alloc: ByteBufAllocator = ByteBufAllocator.DEFAULT
+) : HttpResponse.BodyHandler<ByteBuf> {
+    override fun apply(responseInfo: HttpResponse.ResponseInfo): HttpResponse.BodySubscriber<ByteBuf> {
+        return object : HttpResponse.BodySubscriber<ByteBuf> {
+            private val buf = alloc.compositeBuffer()
+            private val future = CompletableFuture<ByteBuf>()
+
+            override fun onSubscribe(subscription: Flow.Subscription) {
+                subscription.request(Long.MAX_VALUE)
+            }
+
+            override fun onNext(item: MutableList<ByteBuffer>) {
+                for (b in item) {
+                    buf.addComponent(Unpooled.wrappedBuffer(b))
+                }
+            }
+
+            override fun onError(throwable: Throwable) {
+                future.completeExceptionally(throwable)
+                buf.release()
+            }
+
+            override fun onComplete() {
+                future.complete(buf)
+            }
+
+            override fun getBody(): CompletionStage<ByteBuf> {
+                return future
+            }
+        }
+    }
+}