Fix infinite loop on IsValidBase

csharp/src/HgResume.Api/HgRunner.cs

@@ -182,7 +182,14 @@ private List<string> GetRevisionsInternal(int offset, int quantity, string? bran
             var (tip, _) = ProcessRunner.RunSync(RepoPath, "hg", "tip", "--template", "{rev}:{branches}\n");
             if (tip.Count == 1 && tip[0].StartsWith("-1"))
             {
-                // e.g. '-1:default' -> '0:default' to signal the empty repo
+                // Empty repo (hg init, zero changesets). At offset 0 we emit '0:<branch>' (from
+                // '-1:<branch>') as the sentinel callers expect; past offset 0 there is nothing more,
+                // so return empty. Returning the sentinel for every offset would make paginating
+                // callers (e.g. IsValidBase) loop forever, since they never see an empty page.
+                if (offset > 0)
+                {
+                    return new List<string>();
+                }
                 tip[0] = Regex.Replace(tip[0], "^-1", "0");
                 return tip;
             }
@@ -205,7 +212,7 @@ public bool IsValidBase(IReadOnlyList<string> hashes)
             var revisions = GetRevisions(i, q);
             if (revisions.Count == 0)
             {
-                return false;
+                return false; // paged past the last revision without matching every hash
             }
             foreach (var hashAndBranch in revisions)
             {
@@ -217,8 +224,16 @@ public bool IsValidBase(IReadOnlyList<string> hashes)
                     if (foundHash >= hashes.Count) break;
                 }
             }
+            // A page shorter than the requested quantity means hg returned everything it had, so this
+            // was the last page. Stop rather than advancing the offset again: this guarantees the loop
+            // terminates even if GetRevisions ever returns a fixed non-empty page regardless of offset
+            // (the empty-repo '0:' sentinel bug, or any similar future quirk).
+            if (revisions.Count < q)
+            {
+                break;
+            }
             i += q;
         }
-        return true;
+        return foundHash >= hashes.Count;
     }
 }

csharp/test/HgResume.HttpTests/PullFacts.cs

@@ -159,6 +159,54 @@ public void PullBundleChunk_EmptyRepositoryReturnsNoChanges()
         Assert.Equal("NOCHANGE", r.Status);
     }
 
+    [Fact]
+    public async Task PullBundleChunk_EmptyRepoWithNonZeroBaseHash_FailsWithoutHanging()
+    {
+        // Regression: IsValidBase looped forever on an empty (hg init, zero-changeset) repo whenever the
+        // requested baseHash was anything other than "0". GetRevisions returns ["0:"] for the empty repo
+        // regardless of offset, so the hash is never found and IsValidBase keeps advancing the offset and
+        // re-querying forever, hanging the request. Contrast with PullBundleChunk_EmptyRepositoryReturnsNoChanges,
+        // which passes baseHash "0" and short-circuits before the loop.
+        _fx.SeedRepo("emptyHgRepo.zip");
+        string tx = nameof(PullBundleChunk_EmptyRepoWithNonZeroBaseHash_FailsWithoutHanging);
+        Api.FinishPullBundle(tx);
+
+        // Run on a background task with a timeout so the bug surfaces as a fast, clear failure rather than
+        // hanging until the HTTP client's 120s timeout (or forever, once the fix removes that safety net).
+        var call = Task.Run(() => Api.PullBundleChunk("emptyHgRepo", new[] { "fakehash" }, 0, 50, tx));
+        var finished = await Task.WhenAny(call, Task.Delay(TimeSpan.FromSeconds(30)));
+        Assert.True(finished == call,
+            "PullBundleChunk against an empty repo with a non-zero baseHash did not return within 30s — " +
+            "IsValidBase is looping forever.");
+
+        // An unknown baseHash is invalid, so the API should reject it the same way it does on a non-empty repo.
+        var r = await call;
+        Assert.Equal("FAIL", r.Status);
+    }
+
+    [Fact]
+    public async Task PullBundleChunk_NonEmptyRepoMissingHashAcrossPages_FailsWithoutHanging()
+    {
+        // manyRevsHgRepo has 205 revisions, more than IsValidBase's page size (q = 200). A baseHash that
+        // does not exist forces the pagination loop past the first full page (offset 0 -> 200) and onto a
+        // short final page, exercising the offset-advancement + short-page-break branch that the
+        // single-page PullBundleChunk_InvalidHash_FailCode test never reaches. It must terminate with FAIL
+        // rather than paging forever.
+        _fx.SeedRepo("manyRevsHgRepo.zip");
+        string tx = nameof(PullBundleChunk_NonEmptyRepoMissingHashAcrossPages_FailsWithoutHanging);
+        Api.FinishPullBundle(tx);
+
+        // Guard with a timeout so a non-terminating loop surfaces as a fast, clear failure.
+        var call = Task.Run(() => Api.PullBundleChunk("manyRevsHgRepo", new[] { "ffffffffffff" }, 0, 50, tx));
+        var finished = await Task.WhenAny(call, Task.Delay(TimeSpan.FromSeconds(30)));
+        Assert.True(finished == call,
+            "PullBundleChunk against a >200-revision repo with a missing baseHash did not return within 30s — " +
+            "IsValidBase pagination is not terminating.");
+
+        var r = await call;
+        Assert.Equal("FAIL", r.Status);
+    }
+
     [Fact]
     public void PullBundleChunk_LongMakeBundle_InProgressCode()
     {