MAJOR: spoe: Add support of pipelined and asynchronous exchanges with agents

Now, HAProxy and agents can announce the support for "pipelining" and/or "async"
capabilities during the HELLO handshake. For now, HAProxy always announces the
support of both. In addition, in its HELLO frames. HAproxy adds the "engine-id"
key. It is a uniq string that identify a SPOE engine.

The "pipelining" capability is the ability for a peer to decouple NOTIFY and ACK
frames. This is a symmectical capability. To be used, it must be supported by
HAproxy and agents. Unlike HTTP pipelining, the ACK frames can be send in any
order, but always on the same TCP connection used for the corresponding NOTIFY
frame.

The "async" capability is similar to the pipelining, but here any TCP connection
established between HAProxy and the agent can be used to send ACK frames. if an
agent accepts connections from multiple HAProxy, it can use the "engine-id"
value to group TCP connections.

doc/SPOE.txt

@@ -505,8 +505,23 @@ equal to 256 bytes.
 
 Here are the list of official capabilities that HAProxy and agents can support:
 
-  * fragmentation: This is the abaility for a peer to support fragmented
-                   payload in received frames.
+  * fragmentation: This is the ability for a peer to support fragmented
+                   payload in received frames. This is an asymmectical
+                   capability, it only concerns the peer that announces
+                   it. This is the responsibility to the other peer to use it
+                   or not.
+
+  * pipelining: This is the ability for a peer to decouple NOTIFY and ACK
+                frames. This is a symmectical capability. To be used, it must
+                be supported by HAproxy and agents. Unlike HTTP pipelining, the
+                ACK frames can be send in any order, but always on the same TCP
+                connection used for the corresponding NOTIFY frame.
+
+  * async: This ability is similar to the pipelining, but here any TCP
+           connection established between HAProxy and the agent can be used to
+           send ACK frames. if an agent accepts connections from multiple
+           HAProxy, it can use the "engine-id" value to group TCP
+           connections. See details about HAPROXY-HELLO frame.
 
 Unsupported or unknown capabilities are silently ignored, when possible.
 
@@ -653,6 +668,10 @@ Following optional items can be added in the KV-LIST:
     If this item is set to TRUE, then the HAPROXY-HELLO frame is sent during a
     SPOE health check. When set to FALSE, this item can be ignored.
 
+  * "engine-id"    <STRING>
+
+    This is a uniq string that identify a SPOE engine.
+
 To finish the HELLO handshake, the agent must return an AGENT-HELLO frame with
 its supported SPOP version, the lower value between its maximum size allowed
 for a frame and the HAProxy one and capabilities it supports. If an error
@@ -834,7 +853,7 @@ Here is the list of supported actions:
     SESSION     : <1>
     TRANSACTION : <2>
     REQUEST     : <3>
-    RESERVED    : <4>
+    RESPONSE    : <4>
 
   * unset-var    unset the value for an existing variable. 2 arguments must be
                  attached to this action: the variable scope (proc, sess, txn,
@@ -851,7 +870,7 @@ Here is the list of supported actions:
     SESSION     : <1>
     TRANSACTION : <2>
     REQUEST     : <3>
-    RESERVED    : <4>
+    RESPONSE    : <4>
 
 
 NOTE: Name of the variables will be automatically prefixed by HAProxy to avoid

include/types/applet.h

@@ -85,10 +85,11 @@ struct appctx {
 		} hlua_apphttp;                 /* used by the Lua HTTP services */
 		struct {
 			struct task *task;
-			void        *ctx;
 			void        *agent;
 			unsigned int version;
 			unsigned int max_frame_size;
+			unsigned int flags;
+			struct list  waiting_queue;
 			struct list  list;
 		} spoe;                         /* used by SPOE filter */
 		struct {