From 70faba9fd9c8f1894e8c32f7e393f7662e7144dc Mon Sep 17 00:00:00 2001
From: Steffen Vogel <post@steffenvogel.de>
Date: Mon, 14 Jan 2019 10:08:04 +0100
Subject: [PATCH] web: only issue a single call to lws_write() per
 LWS_*_WRITABLE callback

---
 include/villas/api/sessions/http.hpp |  3 ++
 lib/api/sessions/http.cpp            | 66 ++++++++++++++++------------
 lib/api/sessions/websocket.cpp       |  4 +-
 3 files changed, 43 insertions(+), 30 deletions(-)

diff --git a/include/villas/api/sessions/http.hpp b/include/villas/api/sessions/http.hpp
index b0fcaaa4f..61d8c5761 100644
--- a/include/villas/api/sessions/http.hpp
+++ b/include/villas/api/sessions/http.hpp
@@ -39,6 +39,9 @@ namespace sessions {
 
 class Http : public Wsi {
 
+protected:
+	bool headersSent;
+
 public:
 	Http(Api *s, lws *w);
 	virtual ~Http() { };
diff --git a/lib/api/sessions/http.cpp b/lib/api/sessions/http.cpp
index 45b5935cb..2c47fd097 100644
--- a/lib/api/sessions/http.cpp
+++ b/lib/api/sessions/http.cpp
@@ -35,7 +35,8 @@ using namespace villas::node;
 using namespace villas::node::api::sessions;
 
 Http::Http(Api *a, lws *w) :
-	Wsi(a, w)
+	Wsi(a, w),
+	headersSent(false)
 {
 	int hdrlen, options = -1, version;
 	char *uri;
@@ -86,37 +87,47 @@ int Http::complete()
 int Http::write()
 {
 	int ret;
-	json_t *resp;
 
-	resp = response.queue.pop();
+	if (!headersSent) {
+		std::stringstream headers;
 
-	response.buffer.clear();
-	response.buffer.encode(resp);
+		json_t *resp = response.queue.pop();
 
-	json_decref(resp);
+		response.buffer.clear();
+		response.buffer.encode(resp);
 
-	std::stringstream headers;
+		json_decref(resp);
 
-	headers << "HTTP/1.1 200 OK\r\n"
-	        << "Content-type: application/json\r\n"
-	        << "User-agent: " USER_AGENT "\r\n"
-	        << "Connection: close\r\n"
-	        << "Content-Length: " << response.buffer.size() << "\r\n"
-	        << "Access-Control-Allow-Origin: *\r\n"
-	        << "Access-Control-Allow-Methods: GET, POST, OPTIONS\r\n"
-	        << "Access-Control-Allow-Headers: Content-Type\r\n"
-	        << "Access-Control-Max-Age: 86400\r\n"
-	        << "\r\n";
+		headers << "HTTP/1.1 200 OK\r\n"
+			<< "Content-type: application/json\r\n"
+			<< "User-agent: " USER_AGENT "\r\n"
+			<< "Connection: close\r\n"
+			<< "Content-Length: " << response.buffer.size() << "\r\n"
+			<< "Access-Control-Allow-Origin: *\r\n"
+			<< "Access-Control-Allow-Methods: GET, POST, OPTIONS\r\n"
+			<< "Access-Control-Allow-Headers: Content-Type\r\n"
+			<< "Access-Control-Max-Age: 86400\r\n"
+			<< "\r\n";
 
-	ret = lws_write(wsi, (unsigned char *) headers.str().data(), headers.str().size(), LWS_WRITE_HTTP_HEADERS);
-	if (ret < 0)
-		return -1;
+		ret = lws_write(wsi, (unsigned char *) headers.str().data(), headers.str().size(), LWS_WRITE_HTTP_HEADERS);
+		if (ret < 0)
+			return -1;
 
-	ret = lws_write(wsi, (unsigned char *) response.buffer.data(), response.buffer.size(), LWS_WRITE_HTTP);
-	if (ret < 0)
-		return -1;
+		/* No wait, until we can send the body */
+		headersSent = true;
+		lws_callback_on_writable(wsi);
 
-	return 1;
+		return 0;
+	}
+	else {
+		ret = lws_write(wsi, (unsigned char *) response.buffer.data(), response.buffer.size(), LWS_WRITE_HTTP_FINAL);
+		if (ret < 0)
+			return -1;
+
+		headersSent = false;
+
+		return 1;
+	}
 }
 
 std::string Http::getName()
@@ -175,9 +186,10 @@ int api_http_protocol_cb(struct lws *wsi, enum lws_callback_reasons reason, void
 
 		case LWS_CALLBACK_HTTP_WRITEABLE:
 			ret = s->write();
-
-			if (lws_http_transaction_completed(wsi))
-				return -1;
+			if (ret) {
+				if (lws_http_transaction_completed(wsi))
+					return -1;
+			}
 
 			return 0;
 
diff --git a/lib/api/sessions/websocket.cpp b/lib/api/sessions/websocket.cpp
index 1706518f9..9de64c763 100644
--- a/lib/api/sessions/websocket.cpp
+++ b/lib/api/sessions/websocket.cpp
@@ -85,9 +85,7 @@ int WebSocket::write()
 
 	json_decref(resp);
 
-	lws_write(wsi, (unsigned char *) response.buffer.data() + LWS_PRE, response.buffer.size() - LWS_PRE, LWS_WRITE_TEXT);
-
-	return 0;
+	return lws_write(wsi, (unsigned char *) response.buffer.data() + LWS_PRE, response.buffer.size() - LWS_PRE, LWS_WRITE_TEXT);
 }
 
 std::string WebSocket::getName()