ji

ji is a JSON Inspector for the command line.

Input

ji handles its input much like grep. Data can be passed to it through stdin or by providing a list of filenames. Globbing works.

The Reader class reads from the standard input or a list of files, and emits events when a JSON document is read, and when it's finished reading documents.

{EventEmitter} = require 'events'
fs = require 'fs'
querystring = require 'querystring'

class Reader extends EventEmitter

Read the standard input, by resuming the standard input stream and calling @readStream on it.

  readStandardInput: ->
    process.stdin.setEncoding 'utf8'
    process.stdin.resume()
    @readStream '(standard input)', process.stdin, =>
      @emit 'end'

Read the next file from the @filenames array which contains the remaining files to be read.

  _readNextFile: () ->
    filename = @_filenames.shift()
    if filename
      stream = fs.createReadStream filename
      stream.setEncoding 'utf8'
      @readStream filename, stream, =>
        @_readNextFile()
    else
      @emit 'end'

Read a list of files. Makes a copy of the filenames so it can be modified without modifying the value passed in by reference.

  readFiles: (filenames) ->
    @_filenames = filenames.slice()
    @_readNextFile()

Read data from a stream. At present only one document per stream is permitted.

  readStream: (name, stream, done) ->
    data = ''
    stream.on 'data', (chunk) ->
      data += chunk
    stream.on 'end', =>
      document = JSON.parse(data)
      @emit 'data', name, document

Selecting Nodes

JSON Pointer is used for selecting nodes. It uses the same syntax as URLs. This differs from the spec in that you're allowed to omit the leading slash ('/').

class Pointer

To decode, split a string on slashes and unescape each component.

  @decode: (path) ->
    (querystring.unescape(component) for component in path.split '/')

To encode, escape each component and join it with a slash.

  @encode: (components) ->
    escaped = (querystring.escape(component) for component in components)
    escaped.join '/'

Get a value at a jsonpointer path.

  @get: (document, path) ->
    value = document
    components = Pointer.decode path
    for component in components
      if typeof value == 'object' and value != null
        value = value[component]
      else
        value = undefined
    value

Printing Data

class Printer
  print: (data) ->
    str = JSON.stringify data, null, 2
    console.log str

Gluing It Together

A Program class interprets the command-line arguments and runs commands.

class Program

Construct the object instances.

  constructor: ->
    @reader = new Reader
    @printer = new Printer
    @buildOptions()

The options are specified here. The key is both the key that will be set on the Program instance and the default long option name. A boolean option won't use a parameter; all other options will.

  options:
    path:
      short: 'p'
    #replace:
    #  short: 'r'
    #flat:
    #  short: 'f'
    #  boolean: true

Build the options into a more searchable format.

  buildOptions: ->
    @_options = {}
    for name, option of @options
      option.name = name
      option.long or= name
      @_options[option.long] = option
      @_options[option.short] = option if option.short

Parse the arguments using the options table. Make a lookup table for short options.

  parse: (argv) ->
    args = argv.slice(2)
    @filenames = []
    i = 0
    while i < args.length
      if /^-/.test(args[i])
        option = @_options[args[i][1]]
        @exitWithError 'unrecognized option: ' + args[i] unless option
        if option.boolean
          @[option.name] = true
        else
          if typeof args[i+1] == 'undefined'
            @exitWithError 'value required for option ' + args[i]
          @[option.name] = args[i+1]
          i += 1
      else
        @filenames.push args[i]
      i += 1

Parse the options and execute the command.

  run: ->
    @parse process.argv
    @reader.on 'data', (name, document) =>
      value = document
      if @path
        value = Pointer.get document, @path
      @printer.print value unless typeof value == 'undefined'
    if @filenames.length > 0
      @reader.readFiles @filenames
    else
      @reader.readStandardInput()

Display errors.

  showError: (message) ->
    console.error 'error: ' + message

  exitWithError: (message) ->
    @showError message
    process.exit 1

Run the program, unless this is being imported from another module.

unless module.parent
  program = new Program()
  program.run()

Export the classes.

exports.Reader = Reader
exports.Pointer = Pointer
exports.Printer = Printer
exports.Program = Program