Goencodingjson

Goencodingjson, commonly referred to as encoding/json, is a package in the Go standard library that implements encoding and decoding of JSON data. It provides facilities to marshal Go values into JSON and to unmarshal JSON data into Go values, supporting a range of data structures and types.

Key features include a streaming API with Decoder and Encoder for handling large or incremental JSON data, as well as convenience functions like Marshal, Unmarshal, and MarshalIndent for producing human-readable JSON. The package also offers json.RawMessage to defer decoding of embedded JSON, and support for custom marshaling via the Marshaler and Unmarshaler interfaces. Struct field tags under the json key customize encoding, allowing options such as specifying key names, omitting empty fields with omitempty, ignoring fields with -, and encoding numbers as strings with ,string.

Data mapping and types: JSON objects map to Go maps or structs, arrays to slices, and primitive values to corresponding Go types. When decoding into interface{}, JSON objects become map[string]interface{} and arrays become []interface{}. Time values are encoded as RFC3339 strings by default. Decoder has options such as UseNumber to preserve numbers as json.Number and DisallowUnknownFields to reject unknown keys.

Limitations and considerations: JSON object key order is not guaranteed due to map semantics. The package relies on reflection, which can affect performance for large or deeply nested structures. It does not support JSON with comments, and numeric precision requires careful handling if exact values are needed.

History and usage: encoding/json has been a core part of Go since early releases, forming the backbone for JSON handling in many Go applications and APIs. It is widely used for web services, configuration, and data interchange within the Go ecosystem.