Don Newton | 379ae25 | 2019-04-01 12:17:06 -0400 | [diff] [blame^] | 1 | // Package bsoncodec provides a system for encoding values to BSON representations and decoding |
| 2 | // values from BSON representations. This package considers both binary BSON and ExtendedJSON as |
| 3 | // BSON representations. The types in this package enable a flexible system for handling this |
| 4 | // encoding and decoding. |
| 5 | // |
| 6 | // The codec system is composed of two parts: |
| 7 | // |
| 8 | // 1) ValueEncoders and ValueDecoders that handle encoding and decoding Go values to and from BSON |
| 9 | // representations. |
| 10 | // |
| 11 | // 2) A Registry that holds these ValueEncoders and ValueDecoders and provides methods for |
| 12 | // retrieving them. |
| 13 | // |
| 14 | // ValueEncoders and ValueDecoders |
| 15 | // |
| 16 | // The ValueEncoder interface is implemented by types that can encode a provided Go type to BSON. |
| 17 | // The value to encode is provided as a reflect.Value and a bsonrw.ValueWriter is used within the |
| 18 | // EncodeValue method to actually create the BSON representation. For convenience, ValueEncoderFunc |
| 19 | // is provided to allow use of a function with the correct signature as a ValueEncoder. An |
| 20 | // EncodeContext instance is provided to allow implementations to lookup further ValueEncoders and |
| 21 | // to provide configuration information. |
| 22 | // |
| 23 | // The ValueDecoder interface is the inverse of the ValueEncoder. Implementations should ensure that |
| 24 | // the value they receive is settable. Similar to ValueEncoderFunc, ValueDecoderFunc is provided to |
| 25 | // allow the use of a function with the correct signature as a ValueDecoder. A DecodeContext |
| 26 | // instance is provided and serves similar functionality to the EncodeContext. |
| 27 | // |
| 28 | // Registry and RegistryBuilder |
| 29 | // |
| 30 | // A Registry is an immutable store for ValueEncoders, ValueDecoders, and a type map. For looking up |
| 31 | // ValueEncoders and Decoders the Registry first attempts to find a ValueEncoder or ValueDecoder for |
| 32 | // the type provided; if one cannot be found it then checks to see if a registered ValueEncoder or |
| 33 | // ValueDecoder exists for an interface the type implements. Finally, the reflect.Kind of the type |
| 34 | // is used to lookup a default ValueEncoder or ValueDecoder for that kind. If no ValueEncoder or |
| 35 | // ValueDecoder can be found, an error is returned. |
| 36 | // |
| 37 | // The Registry also holds a type map. This allows users to retrieve the Go type that should be used |
| 38 | // when decoding a BSON value into an empty interface. This is primarily only used for the empty |
| 39 | // interface ValueDecoder. |
| 40 | // |
| 41 | // A RegistryBuilder is used to construct a Registry. The Register methods are used to associate |
| 42 | // either a reflect.Type or a reflect.Kind with a ValueEncoder or ValueDecoder. A RegistryBuilder |
| 43 | // returned from NewRegistryBuilder contains no registered ValueEncoders nor ValueDecoders and |
| 44 | // contains an empty type map. |
| 45 | // |
| 46 | // The RegisterTypeMapEntry method handles associating a BSON type with a Go type. For example, if |
| 47 | // you want to decode BSON int64 and int32 values into Go int instances, you would do the following: |
| 48 | // |
| 49 | // var regbuilder *RegistryBuilder = ... intType := reflect.TypeOf(int(0)) |
| 50 | // regbuilder.RegisterTypeMapEntry(bsontype.Int64, intType).RegisterTypeMapEntry(bsontype.Int32, |
| 51 | // intType) |
| 52 | // |
| 53 | // DefaultValueEncoders and DefaultValueDecoders |
| 54 | // |
| 55 | // The DefaultValueEncoders and DefaultValueDecoders types provide a full set of ValueEncoders and |
| 56 | // ValueDecoders for handling a wide range of Go types, including all of the types within the |
| 57 | // primitive package. To make registering these codecs easier, a helper method on each type is |
| 58 | // provided. For the DefaultValueEncoders type the method is called RegisterDefaultEncoders and for |
| 59 | // the DefaultValueDecoders type the method is called RegisterDefaultDecoders, this method also |
| 60 | // handles registering type map entries for each BSON type. |
| 61 | package bsoncodec |