Base web seed pipeline length on piece length

Before this, the web seed pipeline length was based on the block size,
just like it is for wire connections, which are block-based.

This meant that we were massively over-estimating the number of http
requests to make to the web seed servers.

Now we use the piece length, since each web seed request is a piece
length in size.

lib/torrent.js

@@ -932,9 +932,9 @@ Torrent.prototype._updateWire = function (wire) {
   if (wire.peerChoking) return
   if (!wire.downloaded) return validateWire()
 
-  var minOutstandingRequests = getPipelineLength(wire, PIPELINE_MIN_DURATION)
+  var minOutstandingRequests = getBlockPipelineLength(wire, PIPELINE_MIN_DURATION)
   if (wire.requests.length >= minOutstandingRequests) return
-  var maxOutstandingRequests = getPipelineLength(wire, PIPELINE_MAX_DURATION)
+  var maxOutstandingRequests = getBlockPipelineLength(wire, PIPELINE_MAX_DURATION)
 
   trySelectWire(false) || trySelectWire(true)
 
@@ -1187,7 +1187,7 @@ Torrent.prototype._hotswap = function (wire, index) {
     var req = minWire.requests[i]
     if (req.piece !== index) continue
 
-    self.pieces[index].cancel((req.offset / Piece.BLOCK_SIZE) | 0)
+    self.pieces[index].cancel((req.offset / Piece.BLOCK_LENGTH) | 0)
   }
 
   self.emit('hotswap', minWire, wire, index)
@@ -1204,12 +1204,13 @@ Torrent.prototype._request = function (wire, index, hotswap) {
 
   if (self.bitfield.get(index)) return false
 
-  var maxOutstandingRequests = getPipelineLength(wire, PIPELINE_MAX_DURATION)
-  if (isWebSeed) {
-    // A webseed will handle it's real max requests
-    if (maxOutstandingRequests > 2) maxOutstandingRequests -= 2
-    if (self.maxWebConns) maxOutstandingRequests = Math.min(maxOutstandingRequests, self.maxWebConns)
-  }
+  var maxOutstandingRequests = isWebSeed
+    ? Math.min(
+        getPiecePipelineLength(wire, PIPELINE_MAX_DURATION, self.pieceLength),
+        self.maxWebConns
+      )
+    : getBlockPipelineLength(wire, PIPELINE_MAX_DURATION)
+
   if (numRequests >= maxOutstandingRequests) return false
   // var endGame = (wire.requests.length === 0 && self.store.numMissing < 30)
 
@@ -1383,8 +1384,12 @@ Torrent.prototype._debug = function () {
   debug.apply(null, args)
 }
 
-function getPipelineLength (wire, duration) {
-  return Math.ceil(2 + duration * wire.downloadSpeed() / Piece.BLOCK_LENGTH)
+function getBlockPipelineLength (wire, duration) {
+  return 2 + Math.ceil(duration * wire.downloadSpeed() / Piece.BLOCK_LENGTH)
+}
+
+function getPiecePipelineLength (wire, duration, pieceLength) {
+  return 1 + Math.ceil(duration * wire.downloadSpeed() / pieceLength)
 }
 
 /**