SERVER-21863 Prevent map-reduce from inserting >16MB documents.

1 files changed, 54 insertions, 0 deletions

diff --git a/jstests/core/mr_bigobject_replace.js b/jstests/core/mr_bigobject_replace.js
new file mode 100644
index 00000000000..dbed4664e7a
--- /dev/null
+++ b/jstests/core/mr_bigobject_replace.js
@@ -0,0 +1,54 @@
+/**
+ * Test that the server returns an error response for map-reduce operations that attempt to insert a
+ * document larger than 16MB as a result of the reduce() or finalize() functions and using the
+ * "replace" action for the out collection.
+ */
+(function() {
+    function mapper() {
+        // Emit multiple values to ensure that the reducer gets called.
+        emit(this._id, 1);
+        emit(this._id, 1);
+    }
+
+    function createBigDocument() {
+        // Returns a document of the form { _id: ObjectId(...), value: '...' } with the specified
+        // 'targetSize' in bytes.
+        function makeDocWithSize(targetSize) {
+            var doc = {_id: new ObjectId(), value: ''};
+
+            var size = Object.bsonsize(doc);
+            assert.gte(targetSize, size);
+
+            // Set 'value' as a string with enough characters to make the whole document 'size'
+            // bytes long.
+            doc.value = new Array(targetSize - size + 1).join('x');
+            assert.eq(targetSize, Object.bsonsize(doc));
+
+            return doc;
+        }
+
+        var maxDocSize = 16 * 1024 * 1024;
+        return makeDocWithSize(maxDocSize + 1).value;
+    }
+
+    function runTest(testOptions) {
+        db.input.drop();
+        db.mr_bigobject_replace.drop();
+
+        // Insert a document so the mapper gets run.
+        assert.writeOK(db.input.insert({}));
+
+        var res = db.runCommand(Object.extend({
+            mapReduce: "input",
+            map: mapper,
+            out: {replace: "mr_bigobject_replace"},
+        }, testOptions));
+
+        assert.commandFailed(res, "creating a document larger than 16MB didn't fail");
+        assert.lte(0, res.errmsg.indexOf("object to insert too large"),
+                   "map-reduce command failed for a reason other than inserting a large document");
+    }
+
+    runTest({reduce: createBigDocument});
+    runTest({reduce: function() { return 1; }, finalize: createBigDocument});
+})();