Receiving posted JSON with Sinatra

small tricks to make things easier

Published July 27, 2015 #ruby #sinatra #toys

Here’s some simple code to accept a JSON string posted to a Sinatra end point rather than a form. I switched from using jQueries $.ajax method to superagent as part of my exploration of the node javascript package universe, and it has a different way of serializing nest objects when posting as a form. Specifically, it doesn’t.

I needed something that could do both.

Code to use form encoding or JSON blob

This first tries and loads the parameters using the normal form encoding methods. If it doesn’t find the path parameter, it attempts to parse the body’s payload, found in, using JSON.parse:

  post '/post' do
    payload = params
    payload = JSON.parse( unless params[:path] "Saving #{payload[:path]} with #{payload[:meta]}"

    file = load_app.sitemap.find_resource_by_path payload[:path]


The coffeescript that calls this is: "/api/post"
  .set('Content-Type', 'application/json')
  .send path: @state.path, meta: @state.metadata, body: @state.markdown
  .end (err, response) =>
    if response.ok
      @state.saving = false
      @state.dirty = false
      @trigger @state

In this case, @state.metadata is also a complex object, and posting it as JSON ensures that it’s marshalled correctly.

Not too complicated.

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