npgsql 8 regression: System.ArgumentException: Name is too long and would be truncated

[cjlotz]

Steps to reproduce

• Upgrade to Npgsql 8.0
• Code starts failing with System.ArgumentException: Name is too long and would be truncated to: ... exceptions

The issue

The length calculation in the DataTypeName ctor is incorrect.

System.ArgumentException: Name is too long and would be truncated to: ampc.asset_monitoring_point_trigger_expression_parameter_cache_ite
   at Npgsql.Internal.Postgres.DataTypeName..ctor(String fullyQualifiedDataTypeName, Boolean validated)
   at Npgsql.Internal.Postgres.DataTypeName..ctor(String fullyQualifiedDataTypeName)
   at Npgsql.Internal.Postgres.DataTypeName.FromDisplayName(String displayName, String schema)
   at Npgsql.PostgresTypes.PostgresType..ctor(String ns, String name, UInt32 oid)
   at Npgsql.PostgresTypes.PostgresCompositeType..ctor(String ns, String name, UInt32 oid)
   at Npgsql.PostgresDatabaseInfo.LoadBackendTypes(NpgsqlConnector conn, NpgsqlTimeout timeout, Boolean async)
   at Npgsql.PostgresDatabaseInfo.LoadPostgresInfo(NpgsqlConnector conn, NpgsqlTimeout timeout, Boolean async)
   at Npgsql.PostgresDatabaseInfoFactory.Load(NpgsqlConnector conn, NpgsqlTimeout timeout, Boolean async)
   at Npgsql.Internal.NpgsqlDatabaseInfo.Load(NpgsqlConnector conn, NpgsqlTimeout timeout, Boolean async)
   at Npgsql.NpgsqlDataSource.Bootstrap(NpgsqlConnector connector, NpgsqlTimeout timeout, Boolean forceReload, Boolean async, CancellationToken cancellationToken)
   at Npgsql.Internal.NpgsqlConnector.Open(NpgsqlTimeout timeout, Boolean async, CancellationToken cancellationToken)
   at Npgsql.UnpooledDataSource.Get(NpgsqlConnection conn, NpgsqlTimeout timeout, Boolean async, CancellationToken cancellationToken)
   at Npgsql.NpgsqlConnection.<Open>g__OpenAsync|42_0(Boolean async, CancellationToken cancellationToken)
   at Pragma.OnKey.Data.SqlConnection.Open() in C:\Dev\git\onkey-plus-server\src\Pragma.OnKey.Infrastructure\Data\SqlConnection.cs:line 205
   at Pragma.OnKey.Migrations.MigrationContext.InitialiseMigration(IMigrationDao dao, IMigrationRegistry migrationRegistry) in C:\Dev\git\onkey-plus-server\src\Pragma.OnKey.Infrastructure\Migrations\MigrationContext.cs:line 536
   at Pragma.OnKey.Migrations.MigrationContext.InitialiseMigration(IMigrationDao dao, IMigrationRegistry migrationRegistry) in C:\Dev\git\onkey-plus-server\src\Pragma.OnKey.Infrastructure\Migrations\MigrationContext.cs:line 545
   at Pragma.OnKey.Migrations.MigrationContext.RunMigration(IMigrationDao dao, IMigrationRegistry migrationRegistry, CancellationToken cancellationToken) in C:\Dev\git\onkey-plus-server\src\Pragma.OnKey.Infrastructure\Migrations\Migrati

From investigation it seems the length is currently calculated incorrectly in the ctor here

Shouldn't it rather be be var typeNameLength = fullyQualifiedDataTypeName.Length - (schemaEndIndex + 1);

Can be verified with the following snippet:

	// create 63 characters max PG length type
	var name = "asset_monitoring_point_trigger_expression_parameter_cache_item";
	var fullyQualifiedDataTypeName= $"ampc.{name}";
	var schemaEndIndex = fullyQualifiedDataTypeName.IndexOf('.');

	var buggyTypeNameLength = fullyQualifiedDataTypeName.Length - schemaEndIndex + 1;
	var fixedTypeNameLength = fullyQualifiedDataTypeName.Length - (schemaEndIndex + 1);
	var actualLength = name.Length;
	
	Debug.Assert(actualLength == fixedTypeNameLength, "Bug not fixed");		
	Debug.Assert(actualLength == buggyTypeNameLength, "Bug illustrated");	

Further technical details

Npgsql version: 8.0.0
PostgreSQL version:
Operating system: Windows