Json marshaling

[file:///Users/mrj/Downloads/lets-go-further/html/04.01-json-decoding.html](file:///Users/mrj/Downloads/lets-go-further/html/04.01-json-decoding.html)

Just like JSON encoding, there are two approaches that you can take to decode JSON into a native Go object: using a json.Decoder type or using the json.Unmarshal() function.

Both approaches have their pros and cons, but for the purpose of decoding JSON from a HTTP request body, using json.Decoder is generally the best choice. It’s more efficient than json.Unmarshal(), requires less code, and offers some helpful settings that you can use to tweak its behavior.

There are few important and interesting things about this code to point out:

• When calling Decode() you must pass a non-nil pointer as the target decode destination. If you don’t use a pointer, it will return a json.InvalidUnmarshalError error at runtime.
• If the target decode destination is a struct — like in our case — the struct fields must be exported (start with a capital letter). Just like with encoding, they need to be exported so that they’re visible to the encoding/json package.
• When decoding a JSON object into a struct, the key/value pairs in the JSON are mapped to the struct fields based on the struct tag names. If there is no matching struct tag, Go will attempt to decode the value into a field that matches the key name (exact matches are preferred, but it will fall back to a case-insensitive match). Any JSON key/value pairs which cannot be successfully mapped to the struct fields will be silently ignored.
• There is no need to close r.Body after it has been read. This will be done automatically by Go’s http.Server, so you don’t have too.

Supported destination types

It’s important to mention that certain JSON types can be only be successfully decoded to certain Go types. For example, if you have the JSON string "foo" it can be decoded into a Go string, but trying to decode it into a Go int or bool will result in an error at runtime (as we’ll demonstrate in the next chapter).

The following table shows the supported target decode destinations for the different JSON types:

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