/// <summary>
/// Builds a deserializer for the Confluent wire format.
/// </summary>
/// <typeparam name="T">
/// The type to be deserialized.
/// </typeparam>
/// <param name="id">
/// A schema ID that all payloads must be serialized with. If a received schema ID does not
/// match this ID, <see cref="InvalidEncodingException" /> will be thrown.
/// </param>
/// <param name="json">
/// The schema to build the Avro deserializer from.
/// </param>
/// <param name="tombstoneBehavior">
/// The behavior of the deserializer on tombstone records.
/// </param>
/// <returns>
/// A <see cref="IDeserializer{T}" /> based on <paramref name="json" />.
/// </returns>
protected virtual IDeserializer <T> Build <T>(
int id,
string json,
TombstoneBehavior tombstoneBehavior)
{
var schema = SchemaReader.Read(json);
if (tombstoneBehavior != TombstoneBehavior.None)
{
if (default(T) != null)
{
throw new UnsupportedTypeException(typeof(T), $"{typeof(T)} cannot represent tombstone values.");
}
var hasNull = schema is NullSchema ||
(schema is UnionSchema union && union.Schemas.Any(s => s is NullSchema));
if (tombstoneBehavior == TombstoneBehavior.Strict && hasNull)
{
throw new UnsupportedSchemaException(schema, "Tombstone deserialization is not supported for schemas that can represent null values.");
}
}
var inner = DeserializerBuilder.BuildDelegateExpression <T>(schema);
var span = Expression.Parameter(typeof(ReadOnlySpan <byte>));
var readerConstructor = inner.Parameters[0].Type
.GetConstructor(new[] { span.Type });
if (schema is BytesSchema)
{
inner = new WireFormatBytesDeserializerRewriter(span)
.VisitAndConvert(inner, GetType().Name);
}
return(new DelegateDeserializer <T>(
Expression
.Lambda <DelegateDeserializer <T> .Implementation>(
Expression.Invoke(
inner,
Expression.New(readerConstructor, span)),
new[] { span })
.Compile(),
id,
tombstoneBehavior));
}
