SERVER-55904: Consolidate getFirstOplogEntry and getLeastRecentOp helpers

2 files changed, 11 insertions, 17 deletions

diff --git a/jstests/replsets/rslib.js b/jstests/replsets/rslib.js
index 84c7d8db92a..76820184355 100644
--- a/jstests/replsets/rslib.js
+++ b/jstests/replsets/rslib.js
@@ -3,7 +3,6 @@ var wait;
 var occasionally;
 var reconnect;
 var getLatestOp;
-var getLeastRecentOp;
 var waitForAllMembers;
 var reconfig;
 var awaitOpTime;
@@ -155,16 +154,6 @@ getLatestOp = function(server) {
     return null;
 };
 
-getLeastRecentOp = function({server, readConcern}) {
-    server.getDB("admin").getMongo().setSlaveOk();
-    const oplog = server.getDB("local").oplog.rs;
-    const cursor = oplog.find().sort({$natural: 1}).limit(1).readConcern(readConcern);
-    if (cursor.hasNext()) {
-        return cursor.next();
-    }
-    return null;
-};
-
 waitForAllMembers = function(master, timeout) {
     var failCount = 0;
 
@@ -601,16 +590,22 @@ getLastOpTime = function(conn) {
 /**
  * Returns the oldest oplog entry.
  */
-getFirstOplogEntry = function(conn) {
-    let firstEntry;
+getFirstOplogEntry = function(server, opts = {}) {
+    server.getDB("admin").getMongo().setSecondaryOk();
+
+    let firstEntryQuery = server.getDB('local').oplog.rs.find().sort({$natural: 1}).limit(1);
+    if (opts.readConcern) {
+        firstEntryQuery = firstEntryQuery.readConcern(opts.readConcern);
+    }
+
     // The query plan may yield between the cursor establishment and iterating to retrieve the first
     // result. During this yield it's possible for the oplog to "roll over" or shrink. This is rare,
     // but if these both happen the cursor will be unable to resume after yielding and return a
     // "CappedPositionLost" error. This can be safely retried.
+    let firstEntry;
     assert.soon(() => {
         try {
-            firstEntry =
-                conn.getDB('local').oplog.rs.find().sort({$natural: 1}).limit(1).toArray()[0];
+            firstEntry = firstEntryQuery.toArray()[0];
             return true;
         } catch (e) {
             if (e.code == ErrorCodes.CappedPositionLost) {
diff --git a/jstests/sharding/resume_change_stream.js b/jstests/sharding/resume_change_stream.js
index 34afc9c0208..2da931c0fa6 100644
--- a/jstests/sharding/resume_change_stream.js
+++ b/jstests/sharding/resume_change_stream.js
@@ -109,8 +109,7 @@ function testResume(mongosColl, collToWatch) {
         // everything in the oplog is newer than what used to be the newest entry.
         return bsonWoCompare(
                    mostRecentOplogEntry.ts,
-                   getLeastRecentOp({server: shardWithResumeToken, readConcern: "majority"}).ts) <
-            0;
+                   getFirstOplogEntry(shardWithResumeToken, {readConcern: "majority"}).ts) < 0;
     }
 
     while (!oplogIsRolledOver()) {