| commit | a81b1d1c47ed47e0d86e583c40b2e75861f67435 | [log] [tgz] |
|---|---|---|
| author | Jeff Mitchell <jeffrey.mitchell@gmail.com> | Mon Aug 08 13:10:52 2016 -0400 |
| committer | Jeff Mitchell <jeffrey.mitchell@gmail.com> | Mon Aug 08 13:10:52 2016 -0400 |
| tree | cad0e8d7d1b68f6ab351924c3e6a7af6f810e13e | |
| parent | 21a35fb16463dfb7c8eee579c65d995d95e64d1e [diff] |
Handle json.Number values.
In order to prevent the JSON decoder from converting all values to
`float64`, which causes a number of problems, one must set `UseNumber` on
a JSON decoder which tells it to unmarshal as `json.Number` values.
These can then be converted to ints, floats, or used as strings.
However, although setting this value is very common, mapstructure cannot
currently decode from a `map[string]interface{}` containing a
`json.Number` to a struct with those values represented as int or float.
This adds code and test cases to correctly decode a json.Number into an
int or float as expected. It does not decode into uint, although this
could be handled, since json.Number does not natively decode into an
unsigned int.
mapstructure is a Go library for decoding generic map values to structures and vice versa, while providing helpful error handling.
This library is most useful when decoding values from some data stream (JSON, Gob, etc.) where you don't quite know the structure of the underlying data until you read a part of it. You can therefore read a map[string]interface{} and use this library to decode it into the proper underlying native Go structure.
Standard go get:
$ go get github.com/mitchellh/mapstructure
For usage and examples see the Godoc.
The Decode function has examples associated with it there.
Go offers fantastic standard libraries for decoding formats such as JSON. The standard method is to have a struct pre-created, and populate that struct from the bytes of the encoded format. This is great, but the problem is if you have configuration or an encoding that changes slightly depending on specific fields. For example, consider this JSON:
{ "type": "person", "name": "Mitchell" }
Perhaps we can't populate a specific structure without first reading the “type” field from the JSON. We could always do two passes over the decoding of the JSON (reading the “type” first, and the rest later). However, it is much simpler to just decode this into a map[string]interface{} structure, read the “type” key, then use something like this library to decode it into the proper structure.