Potential buffer over-read (yielding exception) in Npgsql code when reading arrays with ArrayNullabilityMode.PerInstance about dapper

[John-Paul-R]

Upon doing a bit more digging into the Npgsql source, I believe this is indeed a bug in their PolymorphicArrayConverter<T> implementation. The other converters I've seen specify the number of bytes that must be read-ahead in a CanConvert that looks something like this (this example is for Guids):

public override bool CanConvert(DataFormat format, out BufferRequirements bufferRequirements)
{
    bufferRequirements = BufferRequirements.CreateFixedSize(16 * sizeof(byte));
    return format is DataFormat.Binary;
}

PolymorphicArrayConverter<T> does not override CanConvert, despite unconditionally reading at least 8 bytes any time it is used.

Opening an issue in Npgsql.

[John-Paul-R]

closing as suspected Npgsql issue.