Sort webseed request heap deterministically

diff --git a/webseed-requesting.go b/webseed-requesting.go
index 22d30160b858a3e0422e5b2c98f2f94ed557e834..abb297addb7f6138887c028e10d74be8d2d9274f 100644 (file)
--- a/webseed-requesting.go
+++ b/webseed-requesting.go
@@ -1,6 +1,7 @@
 package torrent
 
 import (
+       "bytes"
        "cmp"
        "context"
        "fmt"
@@ -72,6 +73,7 @@ func (cl *Client) updateWebseedRequests() {
                }
                aprioriMap[uniqueKey.aprioriWebseedRequestKey] = aprioriMapValue{uniqueKey.startRequest, value}
        }
+       // TODO: This should not be keyed on startRequest but only on sliceIndex.
        existingRequests := maps.Collect(cl.iterCurrentWebseedRequests())
        // We don't need the value but maybe cloning is just faster anyway?
        unusedExistingRequests := maps.Clone(existingRequests)
@@ -117,7 +119,7 @@ func (cl *Client) updateWebseedRequests() {
                &heapSlice,
                func(l heapElem, r heapElem) bool {
                        // Not stable ordering but being sticky to existing webseeds should be enough.
-                       return cmp.Or(
+                       ret := cmp.Or(
                                // Prefer highest priority
                                -cmp.Compare(l.priority, r.priority),
                                // Then existing requests
@@ -129,7 +131,16 @@ func (cl *Client) updateWebseedRequests() {
                                // No need to prefer longer files anymore now that we're using slices?
                                //// Longer files first.
                                //-cmp.Compare(l.longestFile().Unwrap(), r.longestFile().Unwrap()),
-                       ) < 0
+                               // Easier to debug than infohashes...
+                               cmp.Compare(l.t.info.Name, r.t.info.Name),
+                               bytes.Compare(l.t.canonicalShortInfohash()[:], r.t.canonicalShortInfohash()[:]),
+                               // It's possible for 2 heap elements to have the same slice index from the same
+                               // torrent, but they'll differ in existingWebseedRequest and be sorted before this.
+                               // Doing earlier chunks first means more compact files for partial file hashing.
+                               cmp.Compare(l.sliceIndex, r.sliceIndex),
+                       )
+                       panicif.Zero(ret)
+                       return ret < 0
                },
        )