POSTing JSON body causes Rack::QueryParser::InvalidParameterError - ruby-on-rails

Question

I'm simply trying to POST a JSON content-type http request from one Rails server to another. Putting a % character in a value string in the JSON is causing the Rack::QueryParser::InvalidParameterError on the receiving server.
On Server A, I use the httparty gem to perform a POST request w/ a JSON body
obj = {"key":"<%= #results %>"}
resp = HTTParty.post('https://test-url.com/data',
:body => obj.to_json,
:options => { :headers => { 'Content-Type' => 'application/json', 'Accept' => 'application/json' } })
On Server B, I just parse the JSON from the request body
req_body = request.body.read()
req_body_json = JSON.parse req_body
# do work with json
This process works fine unless the obj = {"key":"<%= #results %>"} contains % chars, in which case this occurs on server B:
Started POST "/data" for 10.244.1.3 at 2018-01-02 19:27:04 +0000
F, [2018-01-02T19:27:04.245275 #1] FATAL -- :
F, [2018-01-02T19:27:04.245331 #1] FATAL -- : Rack::QueryParser::InvalidParameterError (invalid %-encoding ({"key":"\u003c%)):
F, [2018-01-02T19:27:04.245358 #1] FATAL -- :
F, [2018-01-02T19:27:04.245397 #1] FATAL -- : rack (2.0.3) lib/rack/query_parser.rb:72:in `rescue in parse_nested_query'
rack (2.0.3) lib/rack/query_parser.rb:60:in `parse_nested_query'
rack (2.0.3) lib/rack/request.rb:468:in `parse_query'
rack (2.0.3) lib/rack/request.rb:343:in `POST'
actionpack (5.1.4) lib/action_dispatch/http/request.rb:362:in `block (2 levels) in POST'
actionpack (5.1.4) lib/action_dispatch/http/parameters.rb:107:in `block in parse_formatted_parameters'
actionpack (5.1.4) lib/action_dispatch/http/parameters.rb:107:in `fetch'
actionpack (5.1.4) lib/action_dispatch/http/parameters.rb:107:in `parse_formatted_parameters'
actionpack (5.1.4) lib/action_dispatch/http/request.rb:361:in `block in POST'
rack (2.0.3) lib/rack/request.rb:57:in `fetch'
rack (2.0.3) lib/rack/request.rb:57:in `fetch_header'
actionpack (5.1.4) lib/action_dispatch/http/request.rb:360:in `POST'
...
When I change obj = {"key":"<%= #results %>"} to obj = {"key":"<= #results>"} the exception does not occur.
As far I know % is a valid in JSON, what am I missing here?

Answer 1

Considering they way how it's implemented here: https://github.com/jnunemaker/httparty/blob/38125db0d079d52a3b0da815150fa2135bb0110d/lib/httparty.rb#L559,
Your body and headers hash keys should be siblings, try the next:
resp = HTTParty.post('https://test-url.com/data',
:body => obj.to_json,
:headers => { 'Content-Type' => 'application/json',
'Accept' => 'application/json' }
)