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136 lines
8.2 KiB
136 lines
8.2 KiB
// Copyright (C) MongoDB, Inc. 2017-present.
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may
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// not use this file except in compliance with the License. You may obtain
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// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
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// Package bson is a library for reading, writing, and manipulating BSON. BSON is a binary serialization format used to
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// store documents and make remote procedure calls in MongoDB. The BSON specification is located at https://bsonspec.org.
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// The BSON library handles marshalling and unmarshalling of values through a configurable codec system. For a description
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// of the codec system and examples of registering custom codecs, see the bsoncodec package.
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//
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// Raw BSON
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//
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// The Raw family of types is used to validate and retrieve elements from a slice of bytes. This
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// type is most useful when you want do lookups on BSON bytes without unmarshaling it into another
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// type.
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//
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// Example:
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// var raw bson.Raw = ... // bytes from somewhere
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// err := raw.Validate()
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// if err != nil { return err }
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// val := raw.Lookup("foo")
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// i32, ok := val.Int32OK()
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// // do something with i32...
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//
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// Native Go Types
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//
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// The D and M types defined in this package can be used to build representations of BSON using native Go types. D is a
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// slice and M is a map. For more information about the use cases for these types, see the documentation on the type
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// definitions.
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//
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// Example:
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// bson.D{{"foo", "bar"}, {"hello", "world"}, {"pi", 3.14159}}
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// bson.M{"foo": "bar", "hello": "world", "pi": 3.14159}
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//
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// When decoding BSON to a D or M, the following type mappings apply when unmarshalling:
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//
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// 1. BSON int32 unmarshals to an int32.
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// 2. BSON int64 unmarshals to an int64.
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// 3. BSON double unmarshals to a float64.
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// 4. BSON string unmarshals to a string.
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// 5. BSON boolean unmarshals to a bool.
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// 6. BSON embedded document unmarshals to the parent type (i.e. D for a D, M for an M).
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// 7. BSON array unmarshals to a bson.A.
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// 8. BSON ObjectId unmarshals to a primitive.ObjectID.
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// 9. BSON datetime unmarshals to a primitive.DateTime.
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// 10. BSON binary unmarshals to a primitive.Binary.
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// 11. BSON regular expression unmarshals to a primitive.Regex.
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// 12. BSON JavaScript unmarshals to a primitive.JavaScript.
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// 13. BSON code with scope unmarshals to a primitive.CodeWithScope.
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// 14. BSON timestamp unmarshals to an primitive.Timestamp.
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// 15. BSON 128-bit decimal unmarshals to an primitive.Decimal128.
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// 16. BSON min key unmarshals to an primitive.MinKey.
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// 17. BSON max key unmarshals to an primitive.MaxKey.
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// 18. BSON undefined unmarshals to a primitive.Undefined.
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// 19. BSON null unmarshals to nil.
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// 20. BSON DBPointer unmarshals to a primitive.DBPointer.
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// 21. BSON symbol unmarshals to a primitive.Symbol.
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//
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// The above mappings also apply when marshalling a D or M to BSON. Some other useful marshalling mappings are:
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//
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// 1. time.Time marshals to a BSON datetime.
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// 2. int8, int16, and int32 marshal to a BSON int32.
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// 3. int marshals to a BSON int32 if the value is between math.MinInt32 and math.MaxInt32, inclusive, and a BSON int64
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// otherwise.
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// 4. int64 marshals to BSON int64.
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// 5. uint8 and uint16 marshal to a BSON int32.
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// 6. uint, uint32, and uint64 marshal to a BSON int32 if the value is between math.MinInt32 and math.MaxInt32,
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// inclusive, and BSON int64 otherwise.
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// 7. BSON null and undefined values will unmarshal into the zero value of a field (e.g. unmarshalling a BSON null or
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// undefined value into a string will yield the empty string.).
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//
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// Structs
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//
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// Structs can be marshalled/unmarshalled to/from BSON or Extended JSON. When transforming structs to/from BSON or Extended
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// JSON, the following rules apply:
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//
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// 1. Only exported fields in structs will be marshalled or unmarshalled.
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//
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// 2. When marshalling a struct, each field will be lowercased to generate the key for the corresponding BSON element.
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// For example, a struct field named "Foo" will generate key "foo". This can be overriden via a struct tag (e.g.
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// `bson:"fooField"` to generate key "fooField" instead).
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//
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// 3. An embedded struct field is marshalled as a subdocument. The key will be the lowercased name of the field's type.
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//
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// 4. A pointer field is marshalled as the underlying type if the pointer is non-nil. If the pointer is nil, it is
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// marshalled as a BSON null value.
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//
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// 5. When unmarshalling, a field of type interface{} will follow the D/M type mappings listed above. BSON documents
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// unmarshalled into an interface{} field will be unmarshalled as a D.
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//
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// The encoding of each struct field can be customized by the "bson" struct tag.
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//
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// This tag behavior is configurable, and different struct tag behavior can be configured by initializing a new
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// bsoncodec.StructCodec with the desired tag parser and registering that StructCodec onto the Registry. By default, JSON tags
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// are not honored, but that can be enabled by creating a StructCodec with JSONFallbackStructTagParser, like below:
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//
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// Example:
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// structcodec, _ := bsoncodec.NewStructCodec(bsoncodec.JSONFallbackStructTagParser)
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//
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// The bson tag gives the name of the field, possibly followed by a comma-separated list of options.
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// The name may be empty in order to specify options without overriding the default field name. The following options can be used
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// to configure behavior:
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//
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// 1. omitempty: If the omitempty struct tag is specified on a field, the field will not be marshalled if it is set to
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// the zero value. Fields with language primitive types such as integers, booleans, and strings are considered empty if
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// their value is equal to the zero value for the type (i.e. 0 for integers, false for booleans, and "" for strings).
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// Slices, maps, and arrays are considered empty if they are of length zero. Interfaces and pointers are considered
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// empty if their value is nil. By default, structs are only considered empty if the struct type implements the
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// bsoncodec.Zeroer interface and the IsZero method returns true. Struct fields whose types do not implement Zeroer are
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// never considered empty and will be marshalled as embedded documents.
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// NOTE: It is recommended that this tag be used for all slice and map fields.
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//
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// 2. minsize: If the minsize struct tag is specified on a field of type int64, uint, uint32, or uint64 and the value of
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// the field can fit in a signed int32, the field will be serialized as a BSON int32 rather than a BSON int64. For other
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// types, this tag is ignored.
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//
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// 3. truncate: If the truncate struct tag is specified on a field with a non-float numeric type, BSON doubles unmarshalled
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// into that field will be trucated at the decimal point. For example, if 3.14 is unmarshalled into a field of type int,
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// it will be unmarshalled as 3. If this tag is not specified, the decoder will throw an error if the value cannot be
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// decoded without losing precision. For float64 or non-numeric types, this tag is ignored.
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//
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// 4. inline: If the inline struct tag is specified for a struct or map field, the field will be "flattened" when
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// marshalling and "un-flattened" when unmarshalling. This means that all of the fields in that struct/map will be
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// pulled up one level and will become top-level fields rather than being fields in a nested document. For example, if a
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// map field named "Map" with value map[string]interface{}{"foo": "bar"} is inlined, the resulting document will be
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// {"foo": "bar"} instead of {"map": {"foo": "bar"}}. There can only be one inlined map field in a struct. If there are
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// duplicated fields in the resulting document when an inlined struct is marshalled, the inlined field will be overwritten.
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// If there are duplicated fields in the resulting document when an inlined map is marshalled, an error will be returned.
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// This tag can be used with fields that are pointers to structs. If an inlined pointer field is nil, it will not be
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// marshalled. For fields that are not maps or structs, this tag is ignored.
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//
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// Marshalling and Unmarshalling
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//
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// Manually marshalling and unmarshalling can be done with the Marshal and Unmarshal family of functions.
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package bson
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