This was mostly an experiment to learn go and test using closures to interpret a JSON path. You should use https://github.com/PaesslerAG/jsonpath instead.

jsonpath

a (partial) implementation in Go based on Stefan Goener JSON Path

Limitations

No support for subexpressions : $books[(@.length-1)]
No support for filters : $books[?(@.price > 10)]
Strings in brackets must use double quotes : $["bookstore"]
Cannot operate on struct fields

The third limitation comes from using the text/scanner package from the standard library. The last one could be overcome by using reflection.

JsonPath quick intro

All expressions start $.

Examples (supported by the current implementation) :

$ the current object (or array)
$.books access to the key of an object (or $["books"]with bracket syntax)
$.books[1] access to the index of an array
$.books[1].authors[1].name chaining of keys and index
$["books"][1]["authors"][1]["name"] the same with braket syntax
$.books[0,1,3] union on an array
$["books", "songs", "movies"] union on an object
$books[1:3] second and third items of an array
$books[:-2:2] every two items except the last two of an array
$books[::-1] all items in reversed order
$..authors all authors (recursive search)

Checkout the tests for more examples.

Install

go get github.com/yalp/jsonpath

Usage

A jsonpath applies to any JSON decoded data using interface{} when decoded with encoding/json :

var bookstore interface{}
err := json.Unmarshal(data, &bookstore)
authors, err := jsonpath.Read(bookstore, "$..authors")

A jsonpath expression can be prepared to be reused multiple times :

allAuthors, err = jsonpath.Prepare("$..authors")
...
var bookstore interface{}
err := json.Unmarshal(data, &bookstore)
authors, err := allAuthors(bookstore)

The type of the values returned by the Read method or Prepare functions depends on the jsonpath expression.