Add Server-Sent-Event support

Server-Sent-Event is a standard describing how servers can initiate
data transmission towards clients once an initial client connection has
been established. Unlike websockets (which are bidirectional),
Server-Sent-Events(SSE) are unidirectional and commonly used to send
message updates or continuous data streams to a browser client.

This is base patch for adding Server-Sent-Events routing support to
bmcweb. Redfish EventService SSE style subscription uses SSE route for
sending the Events/MetricReports to client which establishes the
connection.

Tested this patch with along with EventService SSE support patches and
verified the functionalty on browser.

Tested:
 - Tested using follow-up patches on top which adds
   support for Redfish EventService SSE style subscription
   and observed events are getting sent periodically.
 - Created SSE subscription from the browser by visiting
   https://<BMC IP>/redfish/v1/EventService/SSE

Change-Id: I36956565cbba30c2007852c9471f477f6d1736e9
Signed-off-by: AppaRao Puli <apparao.puli@linux.intel.com>
Signed-off-by: P Dheeraj Srujan Kumar <p.dheeraj.srujan.kumar@intel.com>
Signed-off-by: V-Sanjana <sanjana.v@intel.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/http/http_response.hpp b/http/http_response.hpp
index 1a4ef16d4e..06b693915f 100644
--- a/http/http_response.hpp
+++ b/http/http_response.hpp
@@ -16,10 +16,18 @@ namespace crow
 template <typename Adaptor, typename Handler>
 class Connection;
 
+namespace sse_socket
+{
+template <typename Adaptor>
+class ConnectionImpl;
+} // namespace sse_socket
+
 struct Response
 {
     template <typename Adaptor, typename Handler>
     friend class crow::Connection;
+    template <typename Adaptor>
+    friend class crow::sse_socket::ConnectionImpl;
     using response_type =
         boost::beast::http::response<boost::beast::http::string_body>;