How can I access the raw request body in ruby CGI scripts? - ruby

Question

In a ruby script that I run as a CGI program, I need to access the body of a HTTP POST request. The request body contains JSON data:
{"data":"a"}
I want to take the whole body and parse it with JSON.parse to process it. What's the canonical way to do this? The Ruby docs don't mention the request body.
I only found a hint in a blog post that
CGI tries to parse the request body as form parameters so a blob of JSON awkwardly ends up as the one and only parameter key.
This approach seems to work
puts cgi.params.keys.first # prints {"data":"a"}
but fails as soon as the value for data is a base64 encoded string that contains an = for padding: Using this body
{"data":"a="}
results in the following output (characters missing at the end):
puts cgi.params.keys.first # prints {"data":"a
What's the correct approach to solve this?

Answer 1

As you might already know, when parameters and their values are urlencoded they are delimited with an =: name=Theo&language=ruby and so on.
This is why the name of the first parameter stops at the character before the =. The approach of using the first key, as describe in that blog post, isn't really reliable.
Instead, in a CGI script you can read the request body directly from stdin e.g.
request_body = $stdin.read
Note, when you instantiate a CGI object it will read in everything from stdin and attempt to parse it into the params hash.
This means that if you'd still like to use the cgi library for building your response you'll need to read from stdin earlier in the code, before creating the CGI object. e.g.
# minimal example that just outputs the request body
require 'cgi'
request_body = $stdin.read
cgi = CGI.new
cgi.out("status" => "OK", "type" => "text/plain", "connection" => "close") do
request_body
end

Answer 2

Apparently there is no easy solution for this in Ruby.
But there are two ways you can achieve this.
Redefine CGI::parse(params) method.
This method in CGI module is responsible for parsing both POST and GET parameters into params hash. You can redefine this method in your code so that it add an extra parameter called RAW_DATA in params hash.
def CGI::parse(query)
params = {}
query.split(/[&;]/).each do |pairs |
key, value = pairs.split('=', 2).collect {
| v | CGI::unescape(v)
}
next unless key
params[key] || = []
params[key].push(value) if value
end
#Add RAW_DATA to params
params[:RAW_DATA] = query
params.default = [].freeze
params
end
Use $stdin.read() before creating CGI instance.
But this may prevent you from making use of other CGI features.
So you may replace $stdin temporarily with a StringIO object.
require 'cgi'
require 'stringio'
raw_data = $stdin.read()
real_stdin = $stdin
$stdin = StringIO.new(raw_data)
STDIN = $stdin
cgi = CGI.new
#Your CGI code here
#........
$stdin = real_stdin
STDIN = $stdin