fix error in XADD arg-count calculation

fix #2940

Author: mgravell

src/StackExchange.Redis/RedisDatabase.cs

@@ -4598,13 +4598,12 @@ private Message GetStreamAddMessage(RedisKey key, RedisValue entryId, long? maxL
                 throw new ArgumentOutOfRangeException(nameof(maxLength), "maxLength must be greater than 0.");
             }
 
-            var includeMaxLen = maxLength.HasValue ? 2 : 0;
-            var includeApproxLen = maxLength.HasValue && useApproximateMaxLength ? 1 : 0;
-
             var totalLength = (streamPairs.Length * 2) // Room for the name/value pairs
-                                + 1 // The stream entry ID
-                                + includeMaxLen // 2 or 0 (MAXLEN keyword & the count)
-                                + includeApproxLen;        // 1 or 0
+                + 1 // The stream entry ID
+                + (maxLength.HasValue ? 2 : 0) // MAXLEN N
+                + (maxLength.HasValue && useApproximateMaxLength ? 1 : 0) // ~
+                + (mode == StreamTrimMode.KeepReferences ? 0 : 1) // relevant trim-mode keyword
+                + (limit.HasValue ? 2 : 0); // LIMIT N
 
             var values = new RedisValue[totalLength];
 

tests/StackExchange.Redis.Tests/StreamTests.cs

@@ -2155,6 +2155,28 @@ public async Task AddWithApproxCount(StreamTrimMode mode)
         db.StreamAdd(key, "field", "value", maxLength: 10, useApproximateMaxLength: true, trimMode: mode, flags: CommandFlags.None);
     }
 
+    [Theory]
+    [InlineData(StreamTrimMode.KeepReferences, 1)]
+    [InlineData(StreamTrimMode.DeleteReferences, 1)]
+    [InlineData(StreamTrimMode.Acknowledged, 1)]
+    [InlineData(StreamTrimMode.KeepReferences, 2)]
+    [InlineData(StreamTrimMode.DeleteReferences, 2)]
+    [InlineData(StreamTrimMode.Acknowledged, 2)]
+    public async Task AddWithMultipleApproxCount(StreamTrimMode mode, int count)
+    {
+        await using var conn = Create(require: ForMode(mode));
+
+        var db = conn.GetDatabase();
+        var key = Me() + ":" + mode;
+
+        var pairs = new NameValueEntry[count];
+        for (var i = 0; i < count; i++)
+        {
+            pairs[i] = new NameValueEntry($"field{i}", $"value{i}");
+        }
+        db.StreamAdd(key, maxLength: 10, useApproximateMaxLength: true, trimMode: mode, flags: CommandFlags.None, streamPairs: pairs);
+    }
+
     [Fact]
     public async Task StreamReadGroupWithNoAckShowsNoPendingMessages()
     {