From 51096225bd70ebb62e9c816b9358441e46aa2faf Mon Sep 17 00:00:00 2001
From: Charles Kerr <charles@transmissionbt.com>
Date: Wed, 8 Aug 2007 06:01:52 +0000
Subject: [PATCH] (trunk) rewrite peerCheck code based on comments from mtolman
 in http://transmission.m0k.org/forum/viewtopic.php?t=2106

---
 libtransmission/peerutils.h | 121 ++++++++++++++----------------------
 1 file changed, 47 insertions(+), 74 deletions(-)

diff --git a/libtransmission/peerutils.h b/libtransmission/peerutils.h
index 90014c502..099b55a70 100644
--- a/libtransmission/peerutils.h
+++ b/libtransmission/peerutils.h
@@ -34,81 +34,54 @@ static int peerCmp( tr_peer_t * peer1, tr_peer_t * peer2 )
     return memcmp( peer1->id, peer2->id, 20 );
 }
 
-static int checkPeer( tr_peer_t * peer )
+static int
+checkPeer( tr_peer_t * peer )
 {
-	tr_torrent_t * tor = peer->tor;
-    
-	uint64_t now;
-	int      idleTime, peersWanted, percentOfRange;
-	int      ret;
-	
-	now = tr_date();
-	idleTime = now - peer->date;
-	
-	/* assume any peer over with an idleTime lower than 
-		8 seconds has not timed out */
-	if ( idleTime > MIN_CON_TIMEOUT )
-	{
-		peersWanted = ( TR_MAX_PEER_COUNT * PERCENT_PEER_WANTED ) / 100;
-		if ( tor->peerCount > peersWanted )
-		{
-			/* strict requirements for connecting timeout */
-			if ( peer->status < PEER_STATUS_CONNECTED )
-			{
-				peer_dbg( "connection timeout, idled %i seconds", 
-						  ( idleTime / 1000 ) );
-				return TR_ERROR;
-			}
-			
-			/* strict requirements for idle uploading timeout */
-			if ( peer->inRequestCount && idleTime > MIN_UPLOAD_IDLE )
-			{
-				peer_dbg( "idle uploader timeout, idled %i seconds", 
-						  ( idleTime / 1000 ) );
-				return TR_ERROR;
-			}
-			
-			/* strict requirements for keep-alive timeout */
-			if ( idleTime > MIN_KEEP_ALIVE )
-			{
-				peer_dbg( "peer timeout, idled %i seconds", 
-						  ( idleTime / 1000 ) );
-				return TR_ERROR;
-			}
-		} 
-		/* if we are tight for peers, relax the enforcement of timeouts */
-		else 
-		{
-			percentOfRange = tor->peerCount / (TR_MAX_PEER_COUNT - peersWanted);
-			
-			/* relax requirements for connecting timeout */
-			if ( peer->status < PEER_STATUS_CONNECTED && idleTime > MIN_CON_TIMEOUT + 
-				 ( MAX_CON_TIMEOUT - MIN_CON_TIMEOUT ) * percentOfRange )
-			{
-				peer_dbg( "connection timeout, idled %i seconds", 
-						  ( idleTime / 1000 ) );
-				return TR_ERROR;
-			} 
-					
-			/* relax requirements for idle uploading timeout */
-			if ( peer->inRequestCount && idleTime >  MIN_UPLOAD_IDLE + 
-				 ( MAX_UPLOAD_IDLE - MIN_UPLOAD_IDLE ) * percentOfRange )
-			{
-				peer_dbg( "idle uploader timeout, idled %i seconds", 
-						  ( idleTime / 1000 ) );
-				return TR_ERROR;
-			}
-					
-			/* relax requirements for keep-alive timeout */
-			if ( idleTime >  MIN_KEEP_ALIVE + 
-				 ( MAX_KEEP_ALIVE - MIN_KEEP_ALIVE ) * percentOfRange )
-			{
-				peer_dbg( "peer timeout, idled %i seconds", 
-						  ( idleTime / 1000 ) );
-				return TR_ERROR;
-			}
-		}
-	}
+    int ret;
+    tr_torrent_t * tor = peer->tor;
+    const uint64_t now = tr_date( );
+    const uint64_t idleTime = now - peer->date;
+    uint64_t lo, hi, minimum;
+    int relaxStrictnessIfFewerThanN;
+    double strictness;
+
+    /* when deciding whether or not to keep a peer, judge its responsiveness
+       on a sliding scale that's based on how many other peers are available */
+    relaxStrictnessIfFewerThanN = (int)(((TR_MAX_PEER_COUNT * PERCENT_PEER_WANTED) / 100.0) + 0.5);
+
+    /* if we have >= relaxIfFewerThan, strictness is 100%.
+       if we have zero connections, strictness is 0% */
+    if( tor->peerCount >= relaxStrictnessIfFewerThanN )
+        strictness = 1.0;
+    else
+        strictness = tor->peerCount / (double)relaxStrictnessIfFewerThanN;
+
+    /* test: has it been too long since we were properly connected to them? */
+    lo = MIN_CON_TIMEOUT;
+    hi = MAX_CON_TIMEOUT;
+    minimum = lo + ((hi-lo) * strictness);
+    if( peer->status < PEER_STATUS_CONNECTED && idleTime > minimum ) {
+        peer_dbg( "connection timeout, idled %i seconds", (int)(idleTime/1000) );
+        return TR_ERROR;
+    }
+
+    /* test: have we been waiting on a request for too long? */
+    lo = MIN_UPLOAD_IDLE; 
+    hi = MAX_UPLOAD_IDLE;
+    minimum = lo + ((hi-lo) * strictness);
+    if( peer->inRequestCount && idleTime > minimum ) {
+        peer_dbg( "idle uploader timeout, idled %d seconds", (int)(idleTime/1000));
+        return TR_ERROR;
+    }
+
+    /* test: has it been too long since the peer gave us any response at all? */
+    lo = MIN_KEEP_ALIVE;
+    hi = MAX_KEEP_ALIVE;
+    minimum = lo + ((hi-lo) * strictness);
+    if( idleTime > minimum ) {
+        peer_dbg( "peer timeout, idled %d seconds", (int)(idleTime/1000) );
+        return TR_ERROR;
+    }
 
     if( PEER_STATUS_CONNECTED == peer->status )
     {