fixed http client write buffer failed.

vertx-core/src/main/java/io/vertx/core/http/impl/HttpClientRequestImpl.java

@@ -482,18 +482,31 @@ public Future<Void> write(String chunk, String enc) {
     return write(BufferInternal.buffer(chunk, enc).getByteBuf(), false);
   }
 
-  private boolean requiresContentLength() {
+  private boolean requiresContentLength(boolean writeHead) {
+    if (writeHead) {
+      return !chunked && (headers == null || !headers.contains(CONTENT_LENGTH)) && !isConnect;
+    }
+    if (version() == HttpVersion.HTTP_2) {
+      return false;
+    }
     return !chunked && (headers == null || !headers.contains(CONTENT_LENGTH)) && !isConnect;
   }
 
   private Future<Void> write(ByteBuf buff, boolean end) {
     if (end) {
-      if (buff != null && requiresContentLength()) {
-        headers().set(CONTENT_LENGTH, HttpUtils.positiveLongToString(buff.readableBytes()));
+      if (buff != null && requiresContentLength(true)) {
+        boolean headWritten;
+        synchronized (this) {
+          headWritten = this.headWritten;
+        }
+        if (!headWritten) {
+          headers().set(CONTENT_LENGTH, HttpUtils.positiveLongToString(buff.readableBytes()));
+        }
       }
-    } else if (requiresContentLength()) {
-      throw new IllegalStateException("You must set the Content-Length header to be the total size of the message "
+    } else if (requiresContentLength(false)) {
+      IllegalStateException e = new IllegalStateException("You must set the Content-Length header to be the total size of the message "
         + "body BEFORE sending any data if you are not using HTTP chunked encoding.");
+      return Future.failedFuture(e);
     }
     return doWrite(buff, end, false);
   }

vertx-core/src/test/java/io/vertx/tests/http/Http2ClientTest.java

@@ -2330,4 +2330,52 @@ public void testClearTestDirectServerCloseBeforeSettingsRead() {
     }));
     await();
   }
+
+  @Test
+  public void testWriteChunked() throws Exception {
+    String p1 = "12345";
+    String p2 = "56789";
+    server.requestHandler(req -> {
+      Buffer buffer = Buffer.buffer();
+      AtomicInteger handleChunkCount = new AtomicInteger();
+      req.handler(buff -> {
+        buffer.appendBuffer(buff);
+        handleChunkCount.incrementAndGet();
+      });
+      req.endHandler(v -> {
+        assertEquals(handleChunkCount.get(), 2);
+        assertEquals(buffer.toString(), p1 + p2);
+
+        HttpServerResponse response = req.response();
+        response.setStatusCode(200);
+        response
+          .write(p2)
+          .flatMap(v0 -> response.end(p1));
+      });
+    });
+    startServer();
+
+    client.request(requestOptions).onComplete(onSuccess(req -> {
+      req.write(p1)
+        .flatMap(v -> req.end(p2));
+
+      AtomicInteger handleChunkCount = new AtomicInteger();
+      Buffer buffer = Buffer.buffer();
+      req.response().onComplete(onSuccess(response -> {
+        response.handler(buf -> {
+          buffer.appendBuffer(buf);
+          handleChunkCount.incrementAndGet();
+        });
+
+        response.endHandler(v -> {
+          assertEquals(handleChunkCount.get(), 2);
+          assertEquals(buffer.toString(), p2 + p1);
+          complete();
+        });
+      }));
+    }));
+
+    await();
+  }
+
 }