From 102705470366b871109d2c3bf182c151ab71eb01 Mon Sep 17 00:00:00 2001
From: Simon Rettberg
Date: Tue, 17 Oct 2017 12:08:55 +0200
Subject: [*] Support hop-counting in request header, protocol version 3

We steal 8 bits from the request offset to count hops when requests
get relayed by proxies. This still leaves plenty of bits for the
offset (56 bits, supporting images of up to 72 petabytes).
This is used to detect proxy cycles. The algorithm is not perfect
but should prevent endless relays of the same request.
This is backwards compatible to old clients and servers, as the server
only ever sets the hopcount in relayed requests if the upstream server
is using protocol version 3 or newer, and clients are automatically
upwards compatible as there is practically no image larger than 74PB,
so the newly introduced hop count field is always 0 even in requests
from old clients.
---
 src/config.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

(limited to 'src/config.h')

diff --git a/src/config.h b/src/config.h
index 9f8ee10..50336af 100644
--- a/src/config.h
+++ b/src/config.h
@@ -32,7 +32,8 @@
 // Protocol version should be increased whenever new features/messages are added,
 // so either the client or server can run in compatibility mode, or they can
 // cancel the connection right away if the protocol has changed too much
-#define PROTOCOL_VERSION 2
+#define PROTOCOL_VERSION 3
+// 2017-10-16: Update to v3: Change header to support request hop-counting
 
 #define NUMBER_SERVERS 8 // Number of alt servers per image/device
 
-- 
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