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JSONGen is a tool for generating native Golang types from JSON objects. This automates what is otherwise a very tedious and error prone task when working with JSON.

$ jsongen -h
Usage of jsongen:
  -dump="NUL": Dump tree structure to file.
  -normalize=true: Squash arrays of struct and determine primitive array type.
  -title=true: Convert identifiers to title case, treating '_' and '-' as word boundaries.

Reading from stdin can be done as follows:

$ cat test.json | jsongen

Or a filename can be passed:

$ jsongen test.json

Using test.json as input the example will produce:

type _ struct {
	Bool              bool          `json:"bool"`
	Boollist          []bool        `json:"boollist"`
	Float             float64       `json:"float"`
	Floatlist         []float64     `json:"floatlist"`
	Heterogeneouslist []interface{} `json:"heterogeneouslist"`
	Int               int64         `json:"int"`
	Intlist           []int64       `json:"intlist"`
	Nil               interface{}   `json:"nil"`
	Nillist           []interface{} `json:"nillist"`
	Sanitary          string        `json:"_Sanitary"`
	Sanitary          string
	Sanitary0         string
	String            string   `json:"string"`
	Stringlist        []string `json:"stringlist"`
	Struct            struct {
		Bool   bool        `json:"bool"`
		Float  float64     `json:"float"`
		Int    int64       `json:"int"`
		Nil    interface{} `json:"nil"`
		String string      `json:"string"`
	} `json:"struct"`
	Structlist []struct {
		Bool   bool    `json:"bool"`
		Float  float64 `json:"float"`
		Int    int64   `json:"int"`
		String string  `json:"string"`
	} `json:"structlist"`
	Structlistsquash []struct {
		Bool   bool    `json:"bool"`
		Float  float64 `json:"float"`
		Int    int64   `json:"int"`
		String string  `json:"string"`
	} `json:"structlistsquash"`
	Structlistsquashconflict []struct {
		Bool     bool        `json:"bool"`
		Conflict interface{} `json:"conflict"`
		Float    float64     `json:"float"`
		Int      int64       `json:"int"`
		String   string      `json:"string"`
	} `json:"structlistsquashconflict"`
	TitleCase  string `json:"title case"`
	TitleCase  string `json:"title_case"`
	TitleCase  string `json:"title-case"`
	Titlecase  string `json:"titlecase"`
	Unsanitary string `json:"0Unsanitary"`
	_          string `json:"123"`
}

• Field names are sanitized and written as exported fields of the generated type.
• If sanitizing produces an empty string the identifier is changed to _, this will need to be set by hand in order to properly decode the type.
• If sanitizing produces a field name different from the original value a JSON tag is added to the field.
• Spaces and - are converted to _.
• Field names are converted to title case treating _ and - as word boundaries along with spaces. This can be disabled using -title=false.

• Primitive types are parsed and stored as-is.
• Valid types are bool, int64, float64 and string.
• The JSON value null is translated to the empty interface.

• Object types are treated as structs.
• Fields of structures are sorted lexicographically by sanitized field name.
• If a structure contains duplicate fields of different types, the type will be chosen at random since Golang's map iteration order is undefined. This shouldn't be a problem since this is not permitted in JSON specification, but this is the expected behavior should it happen.

• A homogeneous list of primitive values are treated as a list of the primitive type e.g.: []float64
• Lists of heterogeneous types are treated as a list of the empty interface: []interface{}
• Lists containing both integers and floating point values are interpreted as []float64.
• Lists with object elements are treated as a list of structs.
  • Fields of each element are "squashed" into a single struct. The result is an array of a struct containing all encountered fields.
  • If a field in one element has a different type in another of the same list, the offending field is treated as an empty interface.

Examples of all of the above can be found in test.json.

• Currently sibling field names are not guaranteed to be unique.

The source of this project is licensed under GNU GPL v3.0, according to http://choosealicense.com/licenses/gpl-3.0/:

• Disclose Source: Source code must be made available when distributing the software. In the case of LGPL, the source for the library (and not the entire program) must be made available.
• License and copyright notice: Include a copy of the license and copyright notice with the code.
• State Changes: Indicate significant changes made to the code.

• Commercial Use: This software and derivatives may be used for commercial purposes.
• Distribution: You may distribute this software.
• Modification: This software may be modified.
• Patent Grant: This license provides an express grant of patent rights from the contributor to the recipient.
• Private Use: You may use and modify the software without distributing it.

• Hold Liable: Software is provided without warranty and the software author/license owner cannot be held liable for damages.
• Sublicensing: You may not grant a sublicense to modify and distribute this software to third parties not included in the license.

If you find a case that produces incorrect results or you have a feature suggestion, let me know: submit an issue.