From e1e8a34ba8c6f2a6399b0b610d176a46c32376c0 Mon Sep 17 00:00:00 2001
From: Karthik Abram <karthik.abram@appian.com>
Date: Fri, 7 Jul 2023 15:31:41 -0400
Subject: [PATCH] Introduce a postWrite hook.

If you are sending large amounts of data (multiple megabytes) and you don't want to allocate that large a byte slice, one option is to send the data and have a mechanism to Wake() the connection up after the write is done. This will require a postWrite(conn) hook that also provides a reference to the connection for which data was just written. This way the application can maintain state in the context and in the postWrite hook, call Wake() and send the next batch of data when the Data() hook gets called.
---
 evio.go      | 2 ++
 evio_std.go  | 9 +++++++++
 evio_unix.go | 6 ++++++
 3 files changed, 17 insertions(+)

diff --git a/evio.go b/evio.go
index 8e31287..f5548a9 100644
--- a/evio.go
+++ b/evio.go
@@ -115,6 +115,8 @@ type Events struct {
 	Detached func(c Conn, rwc io.ReadWriteCloser) (action Action)
 	// PreWrite fires just before any data is written to any client socket.
 	PreWrite func()
+	// PostWrite fires just after any data is written to any client socket.
+	PostWrite func(c Conn)
 	// Data fires when a connection sends the server data.
 	// The in parameter is the incoming data.
 	// Use the out return value to write data to the connection.
diff --git a/evio_std.go b/evio_std.go
index 4eb3e27..ba01691 100644
--- a/evio_std.go
+++ b/evio_std.go
@@ -384,6 +384,9 @@ func stdloopRead(s *stdserver, l *stdloop, c *stdconn, in []byte) error {
 				s.events.PreWrite()
 			}
 			c.conn.Write(out)
+			if s.events.PostWrite != nil {
+				s.events.PostWrite(c)
+			}
 		}
 		switch action {
 		case Shutdown:
@@ -405,6 +408,9 @@ func stdloopReadUDP(s *stdserver, l *stdloop, c *stdudpconn) error {
 				s.events.PreWrite()
 			}
 			s.lns[c.addrIndex].pconn.WriteTo(out, c.remoteAddr)
+			if s.events.PostWrite != nil {
+				s.events.PostWrite(c)
+			}
 		}
 		switch action {
 		case Shutdown:
@@ -439,6 +445,9 @@ func stdloopAccept(s *stdserver, l *stdloop, c *stdconn) error {
 				s.events.PreWrite()
 			}
 			c.conn.Write(out)
+			if s.events.PostWrite != nil {
+				s.events.PostWrite(c)
+			}
 		}
 		if opts.TCPKeepAlive > 0 {
 			if c, ok := c.conn.(*net.TCPConn); ok {
diff --git a/evio_unix.go b/evio_unix.go
index 6efbca1..30c87c4 100644
--- a/evio_unix.go
+++ b/evio_unix.go
@@ -333,6 +333,9 @@ func loopUDPRead(s *server, l *loop, lnidx, fd int) error {
 				s.events.PreWrite()
 			}
 			syscall.Sendto(fd, out, 0, sa)
+			if s.events.PostWrite != nil {
+				s.events.PostWrite(c)
+			}
 		}
 		switch action {
 		case Shutdown:
@@ -391,6 +394,9 @@ func loopWrite(s *server, l *loop, c *conn) error {
 	if len(c.out) == 0 && c.action == None {
 		l.poll.ModRead(c.fd)
 	}
+	if len(c.out) == 0 && s.events.PostWrite != nil {
+		s.events.PostWrite(c)
+	}
 	return nil
 }