| // Licensed to the Apache Software Foundation (ASF) under one or more |
| // contributor license agreements. See the NOTICE file distributed with |
| // this work for additional information regarding copyright ownership. |
| // The ASF licenses this file to You under the Apache License, Version 2.0 |
| // (the "License"); you may not use this file except in compliance with |
| // the License. You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| package beam |
| |
| import ( |
| "io" |
| "reflect" |
| |
| "github.com/apache/beam/sdks/go/pkg/beam/core/graph/coder" |
| "github.com/apache/beam/sdks/go/pkg/beam/core/runtime/graphx/schema" |
| ) |
| |
| // RegisterSchemaProvider allows pipeline authors to provide special handling |
| // to convert types to schema representations, when those types are used as |
| // fields in types being encoded as schema rows. |
| // |
| // At present, the only supported provider interface is SchemaProvider, |
| // though this may change in the future. |
| // |
| // Providers only need to support a limited set of types for conversion, |
| // specifically a single struct type or a pointer to struct type, |
| // or an interface type, which they are registered with. |
| // |
| // Providers have three tasks with respect to a given supported logical type: |
| // |
| // * Producing schema representative types for their logical types. |
| // * Producing schema encoders for values of that type, writing beam |
| // schema encoded bytes for a value, matching the schema representative type. |
| // * Producing schema decoders for values of that type, reading beam |
| // schema encoded bytes, and producing a value of that type. |
| // |
| // Representative Schema types must be structs with only exported fields. |
| // |
| // A provider should be thread safe, but it's not required that a produced |
| // encoder or decoder is thread safe, since a separate encoder or decoder |
| // will be used for simultaneously executed bundles. |
| // |
| // If the supported type is an interface, that interface must have a non-empty |
| // method set. That is, it cannot be the empty interface. |
| // |
| // RegisterSchemaProvider must be called before beam.Init(), and conventionally |
| // is called in a package init() function. |
| func RegisterSchemaProvider(rt reflect.Type, provider interface{}) { |
| p := provider.(SchemaProvider) |
| schema.RegisterLogicalTypeProvider(rt, p.FromLogicalType) |
| coder.RegisterSchemaProviders(rt, p.BuildEncoder, p.BuildDecoder) |
| } |
| |
| // SchemaProvider specializes schema handling for complex types, including conversion to a |
| // valid schema base type, |
| // |
| // In particular, they are intended to handle schema for interface types. |
| // |
| // Sepearated out the acting type from the provider implementation is good. |
| type SchemaProvider interface { |
| FromLogicalType(reflect.Type) (reflect.Type, error) |
| BuildEncoder(rt reflect.Type) (func(interface{}, io.Writer) error, error) |
| BuildDecoder(rt reflect.Type) (func(io.Reader) (interface{}, error), error) |
| } |