{

/// <summary>

/// The PostgreSQL type handled by this type handler.

/// </summary>

internal PostgresType PostgresType { get; }

/// <summary>

/// Constructs a <see cref="NpgsqlTypeHandler"/>.

/// </summary>

protected NpgsqlTypeHandler(PostgresType postgresType) => PostgresType = postgresType;

#region Read

/// <summary>

/// Reads a value of type <typeparamref name="TAny"/> with the given length from the provided buffer,

/// using either sync or async I/O.

/// </summary>

/// <param name="buf">The buffer from which to read.</param>

/// <param name="len">The byte length of the value. The buffer might not contain the full length, requiring I/O to be performed.</param>

/// <param name="async">If I/O is required to read the full length of the value, whether it should be performed synchronously or asynchronously.</param>

/// <param name="fieldDescription">Additional PostgreSQL information about the type, such as the length in varchar(30).</param>

/// <returns>The fully-read value.</returns>

protected internal abstract ValueTask<TAny> Read<TAny>(NpgsqlReadBuffer buf, int len, bool async, FieldDescription? fieldDescription = null);

/// <summary>

/// Reads a value of type <typeparamref name="TAny"/> with the given length from the provided buffer,

/// with the assumption that it is entirely present in the provided memory buffer and no I/O will be

/// required. This can save the overhead of async functions and improves performance.

/// </summary>

/// <param name="buf">The buffer from which to read.</param>

/// <param name="len">The byte length of the value. The buffer might not contain the full length, requiring I/O to be performed.</param>

/// <param name="fieldDescription">Additional PostgreSQL information about the type, such as the length in varchar(30).</param>

/// <returns>The fully-read value.</returns>

internal abstract TAny Read<TAny>(NpgsqlReadBuffer buf, int len, FieldDescription? fieldDescription = null);

/// <summary>

/// Reads a column as the type handler's default read type, assuming that it is already entirely

/// in memory (i.e. no I/O is necessary). Called by <see cref="NpgsqlDataReader"/> in non-sequential mode, which

/// buffers entire rows in memory.

/// </summary>

internal abstract object ReadAsObject(NpgsqlReadBuffer buf, int len, FieldDescription? fieldDescription = null);

/// <summary>

/// Reads a column as the type handler's default read type. If it is not already entirely in

/// memory, sync or async I/O will be performed as specified by <paramref name="async"/>.

/// </summary>

internal abstract ValueTask<object> ReadAsObject(NpgsqlReadBuffer buf, int len, bool async, FieldDescription? fieldDescription = null);

/// <summary>

/// Reads a column as the type handler's provider-specific type, assuming that it is already entirely

/// in memory (i.e. no I/O is necessary). Called by <see cref="NpgsqlDataReader"/> in non-sequential mode, which

/// buffers entire rows in memory.

/// </summary>

internal virtual object ReadPsvAsObject(NpgsqlReadBuffer buf, int len, FieldDescription? fieldDescription = null)

=> ReadAsObject(buf, len, fieldDescription);

/// <summary>

/// Reads a column as the type handler's provider-specific type. If it is not already entirely in

/// memory, sync or async I/O will be performed as specified by <paramref name="async"/>.

/// </summary>

internal virtual ValueTask<object> ReadPsvAsObject(NpgsqlReadBuffer buf, int len, bool async, FieldDescription? fieldDescription = null)

=> ReadAsObject(buf, len, async, fieldDescription);

/// <summary>

/// Reads a value from the buffer, assuming our read position is at the value's preceding length.

/// If the length is -1 (null), this method will return the default value.

/// </summary>

internal async ValueTask<TAny> ReadWithLength<TAny>(NpgsqlReadBuffer buf, bool async, FieldDescription? fieldDescription = null)

{

await buf.Ensure(4, async);

var len = buf.ReadInt32();

return len == -1

? default!

: NullableHandler<TAny>.Exists

? await NullableHandler<TAny>.ReadAsync(this, buf, len, async, fieldDescription)

: await Read<TAny>(buf, len, async, fieldDescription);

}

#endregion

#region Write

/// <summary>

/// Called to validate and get the length of a value of a generic <see cref="NpgsqlParameter{T}"/>.

/// </summary>

protected internal abstract int ValidateAndGetLength<TAny>(TAny value, ref NpgsqlLengthCache? lengthCache, NpgsqlParameter? parameter);

/// <summary>

/// Called to write the value of a generic <see cref="NpgsqlParameter{T}"/>.

/// </summary>

internal abstract Task WriteWithLengthInternal<TAny>([AllowNull] TAny value, NpgsqlWriteBuffer buf, NpgsqlLengthCache? lengthCache, NpgsqlParameter? parameter, bool async);

/// <summary>

/// Responsible for validating that a value represents a value of the correct and which can be

/// written for PostgreSQL - if the value cannot be written for any reason, an exception shold be thrown.

/// Also returns the byte length needed to write the value.

/// </summary>

/// <param name="value">The value to be written to PostgreSQL</param>

/// <param name="lengthCache">

/// If the byte length calculation is costly (e.g. for UTF-8 strings), its result can be stored in the

/// length cache to be reused in the writing process, preventing recalculation.

/// </param>

/// <param name="parameter">

/// The <see cref="NpgsqlParameter"/> instance where this value resides. Can be used to access additional

/// information relevant to the write process (e.g. <see cref="NpgsqlParameter.Size"/>).

/// </param>

/// <returns>The number of bytes required to write the value.</returns>

protected internal abstract int ValidateObjectAndGetLength(object value, ref NpgsqlLengthCache? lengthCache, NpgsqlParameter? parameter);

/// <summary>

/// Writes a value to the provided buffer, using either sync or async I/O.

/// </summary>

/// <param name="value">The value to write.</param>

/// <param name="buf">The buffer to which to write.</param>

/// <param name="lengthCache"></param>

/// <param name="parameter">

/// The <see cref="NpgsqlParameter"/> instance where this value resides. Can be used to access additional

/// information relevant to the write process (e.g. <see cref="NpgsqlParameter.Size"/>).

/// </param>

/// <param name="async">If I/O is required to read the full length of the value, whether it should be performed synchronously or asynchronously.</param>

protected internal abstract Task WriteObjectWithLength(object value, NpgsqlWriteBuffer buf, NpgsqlLengthCache? lengthCache, NpgsqlParameter? parameter, bool async);

#endregion Write

#region Misc

internal abstract Type GetFieldType(FieldDescription? fieldDescription = null);

internal abstract Type GetProviderSpecificFieldType(FieldDescription? fieldDescription = null);

internal virtual bool PreferTextWrite => false;

/// <summary>

/// Creates a type handler for arrays of this handler's type.

/// </summary>

public abstract ArrayHandler CreateArrayHandler(PostgresArrayType arrayBackendType);

/// <summary>

/// Creates a type handler for ranges of this handler's type.

/// </summary>

public abstract RangeHandler CreateRangeHandler(PostgresRangeType rangeBackendType);

/// <summary>

/// Used to create an exception when the provided type can be converted and written, but an

/// instance of <see cref="NpgsqlParameter"/> is required for caching of the converted value

/// (in <see cref="NpgsqlParameter.ConvertedValue"/>.

/// </summary>

protected Exception CreateConversionButNoParamException(Type clrType)

=> new InvalidCastException($"Can't convert .NET type '{clrType}' to PostgreSQL '{PgDisplayName}' within an array");

internal string PgDisplayName => PostgresType.DisplayName;

#endregion Misc

#region Code generation for non-generic writing

internal delegate Task NonGenericWriteWithLength(NpgsqlTypeHandler handler, object value, NpgsqlWriteBuffer buf, NpgsqlLengthCache? lengthCache, NpgsqlParameter? parameter, bool async);

internal static NonGenericWriteWithLength GenerateNonGenericWriteMethod(Type handlerType, Type interfaceType)

{

var interfaces = handlerType.GetInterfaces().Where(i =>

i.GetTypeInfo().IsGenericType &&

i.GetGenericTypeDefinition() == interfaceType

).Reverse().ToList();

Expression? ifElseExpression = null;

// NpgsqlTypeHandler handler, object value, NpgsqlWriteBuffer buf, NpgsqlLengthCache lengthCache, NpgsqlParameter parameter, bool async

var handlerParam = Expression.Parameter(typeof(NpgsqlTypeHandler), "handler");

var valueParam = Expression.Parameter(typeof(object), "value");

var bufParam = Expression.Parameter(typeof(NpgsqlWriteBuffer), "buf");

var lengthCacheParam = Expression.Parameter(typeof(NpgsqlLengthCache), "lengthCache");

var parameterParam = Expression.Parameter(typeof(NpgsqlParameter), "parameter");

var asyncParam = Expression.Parameter(typeof(bool), "async");

var resultVariable = Expression.Variable(typeof(Task), "result");

foreach (var i in interfaces)

{

var handledType = i.GenericTypeArguments[0];

ifElseExpression = Expression.IfThenElse(

// Test whether the type of the value given to the delegate corresponds

// to our current interface's handled type (i.e. the T in INpgsqlTypeHandler<T>)

Expression.TypeEqual(valueParam, handledType),

// If it corresponds, call the handler's Write method with the appropriate generic parameter

Expression.Assign(

resultVariable,

Expression.Call(

handlerParam,

// Call the generic WriteWithLengthInternal<T2> with our handled type

nameof(WriteWithLengthInternal),

new[] { handledType },

// Cast the value from object down to the interface's T

Expression.Convert(valueParam, handledType),

bufParam,

lengthCacheParam,

parameterParam,

asyncParam

)

),

// If this is the first interface we're looking at, the else clause throws.

// Note that this should never happen since we passed ValidateAndGetLength.

// Otherwise we stick the previous interface's IfThenElse in our else clause

ifElseExpression ?? Expression.Throw(Expression.New(typeof(InvalidCastException)))

);

}

return Expression.Lambda<NonGenericWriteWithLength>(

Expression.Block(

new[] { resultVariable },

ifElseExpression, resultVariable

),

handlerParam, valueParam, bufParam, lengthCacheParam, parameterParam, asyncParam

).Compile();

}

#endregion Code generation for non-generic writing