How do I make Ruby's RestClient gem respect content_type on post?

You might want to put json as string as your payload instead of hash. For example, do:

RestClient.post 'http://localhost:5001','{"a":"b"}',:content_type => 'application/json'

If you look at the payload.rb, it shows that it will use the Base clase instead of UrlEncoded class if the payload is string. Try that and see if that work for you.

Fact:

For :post request, when payload is a Hash, the Content-Type header will be always overridden to application/x-www-form-urlencoded.

Reproduciable with rest-client (2.0.0).

Solution:

Convert the hash payload to json string.

require 'json'

payload.to_json

There is a ticket in rest-client's repo:

I'd like to add that my issue was when using RestClient::Request.execute (as opposed to RestClient.post or RestClient.get).

The problem was with how I was setting :content_type and :accept. From the examples I saw it felt like they should be top level options like this:

res = RestClient::Request.execute(
  :method => :get,
  :url => url,
  :verify_ssl =>  false,
  :content_type => :json,
  :accept => :json,
  :headers => { 
    :Authorization => "Bearer #{token}", 
  },
  :payload => '{"a":"b"}'
)

But you actually have to put them within :headers like this:

res = RestClient::Request.execute(
  :method => :get,
  :url => url,
  :verify_ssl =>  false,
  :headers => { 
    :Authorization => "Bearer #{token}", 
    :content_type => :json,
    :accept => :json
  },
  :payload => '{"a":"b"}'
)