Fix snapshot download since parameter to use closed/inclusive semantics

CHANGELOG.md

@@ -13,6 +13,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 - Added `make_cose_verifier_from_pem_cert()` and `make_cose_verifier_from_der_cert()` that accept certificates in a known format. The existing `make_cose_verifier_cert()` is renamed to `make_cose_verifier_any_cert()` (#7768).
 
+### Changed
+
+- The `since` query parameter on the `GET /node/snapshot` endpoint now uses closed (inclusive) semantics, consistent with the `since` parameter on `GET /node/ledger_chunk`. A request with `?since=N` will now return snapshots with index greater than or equal to `N`, rather than strictly greater than `N` (#7742).
+
 ## [7.0.0-dev13]
 
 [7.0.0-dev13]: https://github.com/microsoft/CCF/releases/tag/ccf-7.0.0-dev13

src/node/node_state.h

@@ -3134,9 +3134,7 @@ namespace ccf
                   snapshot_evidence.version);
                 backup_snapshot_fetch_task =
                   std::make_shared<BackupSnapshotFetch>(
-                    config.snapshots,
-                    snapshot_evidence.version - 1 /* YIKES */,
-                    this);
+                    config.snapshots, snapshot_evidence.version, this);
                 ccf::tasks::add_task(backup_snapshot_fetch_task);
               }
             }

src/snapshots/filenames.h

@@ -187,7 +187,7 @@ namespace snapshots
         }
 
         const auto idx = get_snapshot_idx_from_file_name(file_name.string());
-        if (minimum_idx.has_value() && idx <= minimum_idx.value())
+        if (minimum_idx.has_value() && idx < minimum_idx.value())
         {
           LOG_DEBUG_FMT(
             "Ignoring snapshot file {} below minimum idx {}",

tests/e2e_operations.py

@@ -305,13 +305,17 @@ def do_request(http_verb, *args, **kwargs):
             assert location == f"{loc}{path}"
             LOG.warning(r.headers)
 
+            # since uses closed/inclusive semantics: since=N returns snapshots
+            # with index >= N. So since=snapshot_index returns the snapshot
+            # (inclusive boundary), while since=snapshot_index+1 does not
+            # (strictly past the available snapshot index).
             for since, expected in (
                 (0, location),
                 (1, location),
                 (snapshot_index // 2, location),
                 (snapshot_index - 1, location),
-                (snapshot_index, None),
-                (snapshot_index + 1, None),
+                (snapshot_index, location),  # inclusive: exact index is returned
+                (snapshot_index + 1, None),  # strictly past: nothing returned
             ):
                 for method in ("GET", "HEAD"):
                     r = do_request(