From a727f4d8b155a2489ab24eb7c366aef8a814c8e2 Mon Sep 17 00:00:00 2001
From: Kleissner <peter@kleissner.investments>
Date: Sat, 13 Nov 2021 14:41:14 +0100
Subject: [PATCH] Define and document the flow window size for transfer.
 Document webapi timeout parameters.

---
 Transfer UDT.go | 7 +++++++
 webapi/API.go   | 4 +++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/Transfer UDT.go b/Transfer UDT.go
index 107b8ea..a942566 100644
--- a/Transfer UDT.go	
+++ b/Transfer UDT.go	
@@ -27,6 +27,11 @@ import (
 // transferSequenceTimeout is the timeout for a follow-up message to appear, otherwise the transfer will be terminated.
 var transferSequenceTimeout = time.Minute * 10
 
+// maxFlowWinSize is the maximum number of unacknowledged packets to permit. A higher number means using more memory, but reduces potential overhead since it does not stop so quickly for missing packets.
+// Each unacknowledged packet may store protocol.TransferMaxEmbedSize (currently 1121 bytes) payload data in memory. A too high number may impact the speed of real-time streaming in case of lost packets.
+// The actual used number will be negotiated through the UDT handshake and must be a minimum of 32.
+const maxFlowWinSize = 64
+
 // startFileTransferUDT starts a file transfer from the local warehouse to the remote peer.
 // It creates a virtual UDT client to transfer data to a remote peer. Counterintuitively, this will be the "file server" peer.
 func (peer *PeerInfo) startFileTransferUDT(hash []byte, fileSize uint64, offset, limit uint64, sequenceNumber uint32) (err error) {
@@ -46,6 +51,7 @@ func (peer *PeerInfo) startFileTransferUDT(hash []byte, fileSize uint64, offset,
 
 	udtConfig := udt.DefaultConfig()
 	udtConfig.MaxPacketSize = protocol.TransferMaxEmbedSize
+	udtConfig.MaxFlowWinSize = maxFlowWinSize
 
 	// start UDT sender
 	// Set streaming to true, otherwise udtSocket.Read returns the error "Message truncated" in case the reader has a smaller buffer.
@@ -85,6 +91,7 @@ func (peer *PeerInfo) FileTransferRequestUDT(hash []byte, offset, limit uint64)
 
 	udtConfig := udt.DefaultConfig()
 	udtConfig.MaxPacketSize = protocol.TransferMaxEmbedSize
+	udtConfig.MaxFlowWinSize = maxFlowWinSize
 
 	// start UDT receiver
 	udtListener := udt.ListenUDT(udtConfig, virtualConn, virtualConn.incomingData, virtualConn.outgoingData, virtualConn.terminationSignal)
diff --git a/webapi/API.go b/webapi/API.go
index 61d6b9d..b4ad608 100644
--- a/webapi/API.go
+++ b/webapi/API.go
@@ -31,7 +31,8 @@ var WSUpgrader = websocket.Upgrader{
 	},
 }
 
-// Start starts the API. ListenAddresses is a list of IP:Ports
+// Start starts the API. ListenAddresses is a list of IP:Ports.
+// The certificate file and key are only used if SSL is enabled. The read and write timeout may be 0 for no timeout.
 func Start(ListenAddresses []string, UseSSL bool, CertificateFile, CertificateKey string, TimeoutRead, TimeoutWrite time.Duration) {
 	if len(ListenAddresses) == 0 {
 		return
@@ -77,6 +78,7 @@ func Start(ListenAddresses []string, UseSSL bool, CertificateFile, CertificateKe
 }
 
 // startWebServer starts a web-server with given parameters and logs the status. If may block forever and only returns if there is an error.
+// The certificate file and key are only used if SSL is enabled. The read and write timeout may be 0 for no timeout.
 func startWebServer(WebListen string, UseSSL bool, CertificateFile, CertificateKey string, Handler http.Handler, Info string, ReadTimeout, WriteTimeout time.Duration) {
 	tlsConfig := &tls.Config{MinVersion: tls.VersionTLS12} // for security reasons disable TLS 1.0/1.1