Source file src/encoding/json/jsontext/doc.go
1 // Copyright 2023 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 //go:build goexperiment.jsonv2 6 7 // Package jsontext implements syntactic processing of JSON 8 // as specified in RFC 4627, RFC 7159, RFC 7493, RFC 8259, and RFC 8785. 9 // JSON is a simple data interchange format that can represent 10 // primitive data types such as booleans, strings, and numbers, 11 // in addition to structured data types such as objects and arrays. 12 // 13 // This package (encoding/json/jsontext) is experimental, 14 // and not subject to the Go 1 compatibility promise. 15 // It only exists when building with the GOEXPERIMENT=jsonv2 environment variable set. 16 // Most users should use [encoding/json]. 17 // 18 // The [Encoder] and [Decoder] types are used to encode or decode 19 // a stream of JSON tokens or values. 20 // 21 // # Tokens and Values 22 // 23 // A JSON token refers to the basic structural elements of JSON: 24 // 25 // - a JSON literal (i.e., null, true, or false) 26 // - a JSON string (e.g., "hello, world!") 27 // - a JSON number (e.g., 123.456) 28 // - a begin or end delimiter for a JSON object (i.e., '{' or '}') 29 // - a begin or end delimiter for a JSON array (i.e., '[' or ']') 30 // 31 // A JSON token is represented by the [Token] type in Go. Technically, 32 // there are two additional structural characters (i.e., ':' and ','), 33 // but there is no [Token] representation for them since their presence 34 // can be inferred by the structure of the JSON grammar itself. 35 // For example, there must always be an implicit colon between 36 // the name and value of a JSON object member. 37 // 38 // A JSON value refers to a complete unit of JSON data: 39 // 40 // - a JSON literal, string, or number 41 // - a JSON object (e.g., `{"name":"value"}`) 42 // - a JSON array (e.g., `[1,2,3,]`) 43 // 44 // A JSON value is represented by the [Value] type in Go and is a []byte 45 // containing the raw textual representation of the value. There is some overlap 46 // between tokens and values as both contain literals, strings, and numbers. 47 // However, only a value can represent the entirety of a JSON object or array. 48 // 49 // The [Encoder] and [Decoder] types contain methods to read or write the next 50 // [Token] or [Value] in a sequence. They maintain a state machine to validate 51 // whether the sequence of JSON tokens and/or values produces a valid JSON. 52 // [Options] may be passed to the [NewEncoder] or [NewDecoder] constructors 53 // to configure the syntactic behavior of encoding and decoding. 54 // 55 // # Terminology 56 // 57 // The terms "encode" and "decode" are used for syntactic functionality 58 // that is concerned with processing JSON based on its grammar, and 59 // the terms "marshal" and "unmarshal" are used for semantic functionality 60 // that determines the meaning of JSON values as Go values and vice-versa. 61 // This package (i.e., [jsontext]) deals with JSON at a syntactic layer, 62 // while [encoding/json/v2] deals with JSON at a semantic layer. 63 // The goal is to provide a clear distinction between functionality that 64 // is purely concerned with encoding versus that of marshaling. 65 // For example, one can directly encode a stream of JSON tokens without 66 // needing to marshal a concrete Go value representing them. 67 // Similarly, one can decode a stream of JSON tokens without 68 // needing to unmarshal them into a concrete Go value. 69 // 70 // This package uses JSON terminology when discussing JSON, which may differ 71 // from related concepts in Go or elsewhere in computing literature. 72 // 73 // - a JSON "object" refers to an unordered collection of name/value members. 74 // - a JSON "array" refers to an ordered sequence of elements. 75 // - a JSON "value" refers to either a literal (i.e., null, false, or true), 76 // string, number, object, or array. 77 // 78 // See RFC 8259 for more information. 79 // 80 // # Specifications 81 // 82 // Relevant specifications include RFC 4627, RFC 7159, RFC 7493, RFC 8259, 83 // and RFC 8785. Each RFC is generally a stricter subset of another RFC. 84 // In increasing order of strictness: 85 // 86 // - RFC 4627 and RFC 7159 do not require (but recommend) the use of UTF-8 87 // and also do not require (but recommend) that object names be unique. 88 // - RFC 8259 requires the use of UTF-8, 89 // but does not require (but recommends) that object names be unique. 90 // - RFC 7493 requires the use of UTF-8 91 // and also requires that object names be unique. 92 // - RFC 8785 defines a canonical representation. It requires the use of UTF-8 93 // and also requires that object names be unique and in a specific ordering. 94 // It specifies exactly how strings and numbers must be formatted. 95 // 96 // The primary difference between RFC 4627 and RFC 7159 is that the former 97 // restricted top-level values to only JSON objects and arrays, while 98 // RFC 7159 and subsequent RFCs permit top-level values to additionally be 99 // JSON nulls, booleans, strings, or numbers. 100 // 101 // By default, this package operates on RFC 7493, but can be configured 102 // to operate according to the other RFC specifications. 103 // RFC 7493 is a stricter subset of RFC 8259 and fully compliant with it. 104 // In particular, it makes specific choices about behavior that RFC 8259 105 // leaves as undefined in order to ensure greater interoperability. 106 package jsontext 107 108 // requireKeyedLiterals can be embedded in a struct to require keyed literals. 109 type requireKeyedLiterals struct{} 110 111 // nonComparable can be embedded in a struct to prevent comparability. 112 type nonComparable [0]func() 113