[client] Fix HttpClient support for reading empty stream

The HttpClient uses the BodyHandlers.ofLines() but was not filtering out empty lines.
These empty lines can fail the assigned body handler (e.g. json parsing error).

The fix is to filter out empty lines when reading the stream.

Author: rob-bygrave

http-client/src/main/java/io/avaje/http/client/DHttpClientRequest.java

@@ -585,7 +585,7 @@ private <T> Stream<T> stream(BodyReader<T> bodyReader) {
     final HttpResponse<Stream<String>> res = handler(HttpResponse.BodyHandlers.ofLines());
     this.httpResponse = res;
     checkResponse(res);
-    return res.body().map(bodyReader::readBody);
+    return res.body().filter(line -> !line.isEmpty()).map(bodyReader::readBody);
   }
 
   @Override

http-client/src/test/java/io/avaje/http/client/HelloControllerTest.java

@@ -271,6 +271,18 @@ void get_stream_as() {
     assertThat(first.name).isEqualTo("one");
   }
 
+  @Test
+  void get_stream_as_when_empty() {
+    final HttpResponse<Stream<SimpleData>> res = clientContext.request()
+      .path("hello").path("streamEmpty")
+      .GET()
+      .asStream(SimpleData.class);
+
+    assertThat(res.statusCode()).isEqualTo(200);
+    final List<SimpleData> data = res.body().collect(Collectors.toList());
+    assertThat(data).isEmpty();
+  }
+
   @Test
   void get_stream_NotFoundException() {
     clientContext.metrics(true);

http-client/src/test/java/org/example/webserver/HelloController$Route.java

@@ -52,6 +52,11 @@ private void routes(JavalinDefaultRouting cfg) {
       controller.stream(ctx);
     });
 
+    cfg.get("/hello/streamEmpty", ctx -> {
+      ctx.status(200);
+      controller.streamEmpty(ctx);
+    });
+
     cfg.get("/hello/{id}/{date}", ctx -> {
       ctx.status(200);
       final int id = asInt(ctx.pathParam("id"));

http-client/src/test/java/org/example/webserver/HelloController.java

@@ -63,6 +63,13 @@ void stream(Context context) {
     context.result(content);
   }
 
+  @Get("streamEmpty")
+  void streamEmpty(Context context) {
+    // simulate x-json-stream response with empty stream
+    context.header("content-type", "application/x-json-stream");
+    context.result("\n");
+  }
+
   /**
    * Return the Hello DTO.
    *