From 9a1171a0efcd9226c1df7976048e26ce6eef3d72 Mon Sep 17 00:00:00 2001
From: vyzo <vyzo@hackzen.org>
Date: Mon, 25 May 2020 10:39:29 +0300
Subject: [PATCH] fix outbound constraint satisfaction in oversubscription
 pruning

---
 gossipsub.go | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/gossipsub.go b/gossipsub.go
index c4bebc00..7f5694dc 100644
--- a/gossipsub.go
+++ b/gossipsub.go
@@ -1302,15 +1302,33 @@ func (gs *GossipSubRouter) heartbeat() {
 
 			// if it's less than D_out, bubble up some outbound peers from the random selection
 			if outbound < gs.Dout {
+				rotate := func(i int) {
+					// rotate the plst to the right and put the ith peer in the front
+					p := plst[i]
+					for j := i; j > 0; j-- {
+						plst[j] = plst[j-1]
+					}
+					plst[0] = p
+				}
+
+				// first bubble up all outbound peers already in the selection to the front
+				if outbound > 0 {
+					ihave := outbound
+					for i := 1; i < gs.D && ihave > 0; i++ {
+						p := plst[i]
+						if gs.outbound[p] {
+							rotate(i)
+							ihave--
+						}
+					}
+				}
+
+				// now bubble up enough outbound peers outside the selection to the front
 				ineed := gs.Dout - outbound
 				for i := gs.D; i < len(plst) && ineed > 0; i++ {
 					p := plst[i]
 					if gs.outbound[p] {
-						// rotate the plst to the right and put the outbound peer in the front
-						for j := i; j > 0; j-- {
-							plst[j] = plst[j-1]
-						}
-						plst[0] = p
+						rotate(i)
 						ineed--
 					}
 				}