JamesNK/Newtonsoft.Json · error · ArgumentException

The number of elements in the source JObject is greater than

Error message

The number of elements in the source JObject is greater than the available space from arrayIndex to the end of the destination array.

What it means

CopyItemsTo throws ArgumentException when the source container's Count exceeds the available space from arrayIndex to the end of the destination array (Count > array.Length - arrayIndex). The destination must be large enough to hold every child token.

Source

Thrown at Src/Newtonsoft.Json/Linq/JContainer.cs:605

        }

        internal virtual void CopyItemsTo(Array array, int arrayIndex)
        {
            if (array == null)
            {
                throw new ArgumentNullException(nameof(array));
            }
            if (arrayIndex < 0)
            {
                throw new ArgumentOutOfRangeException(nameof(arrayIndex), "arrayIndex is less than 0.");
            }
            if (arrayIndex >= array.Length && arrayIndex != 0)
            {
                throw new ArgumentException("arrayIndex is equal to or greater than the length of array.");
            }
            if (Count > array.Length - arrayIndex)
            {
                throw new ArgumentException("The number of elements in the source JObject is greater than the available space from arrayIndex to the end of the destination array.");
            }

            int index = 0;
            foreach (JToken token in ChildrenTokens)
            {
                array.SetValue(token, arrayIndex + index);
                index++;
            }
        }

        internal static bool IsTokenUnchanged(JToken currentValue, JToken? newValue)
        {
            if (currentValue is JValue v1)
            {
                if (newValue == null)
                {
                    // null will get turned into a JValue of type null
                    return v1.Type == JTokenType.Null;

View on GitHub (pinned to 4f73e74372)

Solutions

Allocate destination as new JToken[container.Count] and copy at index 0.
When using an offset, size as new JToken[arrayIndex + container.Count].
Check Count and array.Length - arrayIndex before calling CopyTo.

Example fix

// before
var dest = new JToken[2];
arr.CopyTo(dest, 0);
// after
var dest = new JToken[arr.Count];
arr.CopyTo(dest, 0);

Defensive patterns

Strategy: validation

Validate before calling

if (container.Count > dest.Length - arrayIndex) {
    Array.Resize(ref dest, arrayIndex + container.Count);
}
container.CopyTo(dest, arrayIndex);

Try / catch

try { container.CopyTo(dest, arrayIndex); }
catch (ArgumentException ex) when (ex.Message.Contains("available space")) {
    Array.Resize(ref dest, arrayIndex + container.Count);
    container.CopyTo(dest, arrayIndex);
}

Prevention

Allocate dest as new JToken[container.Count] and copy at 0 when possible.
When using an offset, size as arrayIndex + container.Count.
Check Count against dest.Length - arrayIndex before CopyTo.

When it happens

Trigger: Copying a 5-element JArray into a 3-element array; an arrayIndex that leaves too little room.

Common situations: Undersized destination array; offset that shrinks available space below Count.

Related errors

AI-assisted analysis of JamesNK/Newtonsoft.Json@4f73e74372 (2026-08-07). Data as JSON: /api/errors/2c91e111bc082cb0. Report an issue: GitHub.