fix missing sync check in download range (#721)

* fix missing sync check in download range

* set bound on request tries

* do while cause needs to runs once

Author: mafintosh

lib/replicator.js

@@ -1325,6 +1325,8 @@ class Peer {
   }
 
   _requestRange (r) {
+    if (this.syncsProcessing > 0) return false
+
     const { length, fork } = this.core.state
 
     if (r.blocks) {
@@ -1343,31 +1345,39 @@ class Peer {
       return false
     }
 
-    const end = Math.min(this.core.state.length, Math.min(r.end === -1 ? this.remoteLength : r.end, this.remoteLength))
+    // if we can upgrade the remote, or the remote is ahead, then all the remotes blocks are valid
+    // otherwise truncate to the last length the remote has acked for us
+    const maxLocalLength = this.canUpgrade || this.remoteLength >= this.core.state.length
+      ? this.core.state.length
+      : fork === this.lastUpgradableFork ? Math.min(this.lastUpgradableLength, this.core.state.length) : 0
+
+    const end = Math.min(maxLocalLength, Math.min(r.end === -1 ? this.remoteLength : r.end, this.remoteLength))
     if (end <= r.start || fork !== this.remoteFork) return false
 
     const len = end - r.start
     const off = r.start + (r.linear ? 0 : Math.floor(Math.random() * len))
 
     let i = off
+    // should be way less than this, but this is worst case upper bound for the skiplist
+    let tries = this.inflight
 
-    while (true) {
+    do {
       i = this._findNext(i)
       if (i === -1 || i >= end) break
 
       if (this._requestRangeBlock(i, length)) return true
       i++
-    }
+    } while (tries-- > 0)
 
     i = r.start
 
-    while (true) {
+    do {
       i = this._findNext(i)
       if (i === -1 || i >= off) break
 
       if (this._requestRangeBlock(i, length)) return true
       i++
-    }
+    } while (tries-- > 0)
 
     this._maybeWant(r.start, len)
     return false