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JSON External Templates

JSON-XT compresses JSON documents into short URIs, using eXternal Templates. Depending on the application, these URIs are 25 - 35% of the original JSON document size.

Great for constrained environments, such as encoding data in QR codes.

See jsonxt.io for more, as well as this paper for a lot more explanation.

Installation

Node.JS

npm install jsonxt

Python

pip install jsonxt

Use

Setup (Javascript)

const jsonxt = require("jsonxt")

// sample data…
const original = {
  "@context": {
    "ical": "http://www.w3.org/2002/12/cal/ical#",
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "ical:dtstart": {
      "@type": "xsd:dateTime"
    }
  },
  "ical:summary": "Lady Gaga Concert",
  "ical:location": "New Orleans Arena, New Orleans, Louisiana, USA",
  "ical:dtstart": "2011-04-09T20:00:00Z"
}
const templates = {
  "simple:1": {
    "columns": [
      {
        "path": "ical:summary", 
        "type": "string"
      }, 
      {
        "path": "ical:location", 
        "type": "string"
      }, 
      {
        "path": "ical:dtstart", 
        "type": "isodatetime-epoch-base32"
      }
    ], 
    "template": {
      "@context": {
        "ical": "http://www.w3.org/2002/12/cal/ical#", 
        "ical:dtstart": {
          "@type": "xsd:dateTime"
        }, 
        "xsd": "http://www.w3.org/2001/XMLSchema#"
      }
    }
  }
}
const TYPE = "simple"
const VERSION = "1"
  • An example original is here
  • An example templates is here

The templates can have multiple compression formats encoded, they will be selected by TYPE and VERSION.

Encoding

This will compress the original JSON payload into a URI

Javascript:

const packed = await jsonxt.pack(original, templates, TYPE, VERSION, "example.com")

Which yields (ignore newline)

jxt:jsonxt.io:simple:1:Lady~Gaga~Concert/
  New~Orleans~Arena%2C~New~Orleans%2C~Louisiana%2C~USA/16Q1EM0

This is a compression of 279 bytes to 101 bytes: 36% of the original size.

See test code for a more fully worked through example.

Decoding

This will decompress the packed URI into the original URI.

Javascript:

const unpacked = await jsonxt.unpack(packed, jsonxt.resolve)

Python (package details being worked out):

unpacked = jsonxt.unpack(packed, jsonxt.resolve)

Resolving

Resolving takes a "resolver name" like example.com embedded in the URI and a file name and retrieves a document.

The following rules are used:

  • if it has a slash or a colon, it's treated a a URL (https:// is assumed if no scheme)
  • otherwise we check https://resolver/.well-known/name

Generally you can just use jsonxt.resolve.

See Also

  • RFC2397 - The "data" URL scheme
  • RFC3986 - URI generic syntax
  • RFC4180 - Common Format and MIME Type for CSV Files
  • RFC8141 - Uniform Resource Names (URNs)

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