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62 lines
3.6 KiB
Go
62 lines
3.6 KiB
Go
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// Package bsoncodec provides a system for encoding values to BSON representations and decoding
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// values from BSON representations. This package considers both binary BSON and ExtendedJSON as
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// BSON representations. The types in this package enable a flexible system for handling this
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// encoding and decoding.
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//
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// The codec system is composed of two parts:
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//
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// 1) ValueEncoders and ValueDecoders that handle encoding and decoding Go values to and from BSON
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// representations.
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//
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// 2) A Registry that holds these ValueEncoders and ValueDecoders and provides methods for
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// retrieving them.
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//
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// ValueEncoders and ValueDecoders
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//
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// The ValueEncoder interface is implemented by types that can encode a provided Go type to BSON.
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// The value to encode is provided as a reflect.Value and a bsonrw.ValueWriter is used within the
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// EncodeValue method to actually create the BSON representation. For convenience, ValueEncoderFunc
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// is provided to allow use of a function with the correct signature as a ValueEncoder. An
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// EncodeContext instance is provided to allow implementations to lookup further ValueEncoders and
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// to provide configuration information.
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//
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// The ValueDecoder interface is the inverse of the ValueEncoder. Implementations should ensure that
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// the value they receive is settable. Similar to ValueEncoderFunc, ValueDecoderFunc is provided to
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// allow the use of a function with the correct signature as a ValueDecoder. A DecodeContext
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// instance is provided and serves similar functionality to the EncodeContext.
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//
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// Registry and RegistryBuilder
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//
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// A Registry is an immutable store for ValueEncoders, ValueDecoders, and a type map. For looking up
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// ValueEncoders and Decoders the Registry first attempts to find a ValueEncoder or ValueDecoder for
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// the type provided; if one cannot be found it then checks to see if a registered ValueEncoder or
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// ValueDecoder exists for an interface the type implements. Finally, the reflect.Kind of the type
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// is used to lookup a default ValueEncoder or ValueDecoder for that kind. If no ValueEncoder or
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// ValueDecoder can be found, an error is returned.
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//
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// The Registry also holds a type map. This allows users to retrieve the Go type that should be used
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// when decoding a BSON value into an empty interface. This is primarily only used for the empty
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// interface ValueDecoder.
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//
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// A RegistryBuilder is used to construct a Registry. The Register methods are used to associate
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// either a reflect.Type or a reflect.Kind with a ValueEncoder or ValueDecoder. A RegistryBuilder
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// returned from NewRegistryBuilder contains no registered ValueEncoders nor ValueDecoders and
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// contains an empty type map.
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//
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// The RegisterTypeMapEntry method handles associating a BSON type with a Go type. For example, if
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// you want to decode BSON int64 and int32 values into Go int instances, you would do the following:
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//
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// var regbuilder *RegistryBuilder = ... intType := reflect.TypeOf(int(0))
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// regbuilder.RegisterTypeMapEntry(bsontype.Int64, intType).RegisterTypeMapEntry(bsontype.Int32,
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// intType)
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//
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// DefaultValueEncoders and DefaultValueDecoders
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//
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// The DefaultValueEncoders and DefaultValueDecoders types provide a full set of ValueEncoders and
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// ValueDecoders for handling a wide range of Go types, including all of the types within the
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// primitive package. To make registering these codecs easier, a helper method on each type is
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// provided. For the DefaultValueEncoders type the method is called RegisterDefaultEncoders and for
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// the DefaultValueDecoders type the method is called RegisterDefaultDecoders, this method also
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// handles registering type map entries for each BSON type.
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package bsoncodec
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