Ensure correct Faraday JSON parsing/response body for invalid response header

CHANGELOG.md

@@ -1,5 +1,6 @@
 ### (Next)
 * Your contribution here.
+* [#110](https://github.com/ashkan18/graphlient/pull/110): Ensure correct Faraday JSON response body parsing with invalid response header - [@taylorthurlow](https://github.com/taylorthurlow).
 * [#107](https://github.com/ashkan18/graphlient/pull/107): Pass in initialized schema as an option - [@kbaum](https://github.com/kbaum).
 * [#106](https://github.com/ashkan18/graphlient/pull/106): Add 3.2 to the list of ruby ci versions - [@igor-drozdov](https://github.com/igor-drozdov).
 * [#102](https://github.com/ashkan18/graphlient/pull/102): Update ci to test latest jruby - [@ashkan18](https://github.com/ashkan18).

lib/graphlient/adapters/http/faraday_adapter.rb

@@ -1,4 +1,5 @@
 require 'faraday'
+require 'json'
 
 module Graphlient
   module Adapters
@@ -13,7 +14,8 @@ def execute(document:, operation_name:, variables:, context:)
               variables: variables
             }.to_json
           end
-          response.body
+
+          parse_body(response.body)
         rescue Faraday::ConnectionFailed => e
           raise Graphlient::Errors::ConnectionFailedError, e
         rescue Faraday::TimeoutError => e
@@ -39,6 +41,38 @@ def connection
             end
           end
         end
+
+        private
+
+        # Faraday 2.x's JSON response middleware will only parse a JSON
+        # response body into a Hash (or Array) object if the response headers
+        # match a specific content type regex. See Faraday's response JSON
+        # middleware definition for specifics on what the datatype of the
+        # response body will be. This method will handle the situation where
+        # the response header is not set appropriately, but contains JSON
+        # anyways. If the body cannot be parsed as JSON, an exception will be
+        # raised.
+        def parse_body(body)
+          case body
+          when Hash, Array
+            body
+          when String
+            begin
+              JSON.parse(body)
+            rescue JSON::ParserError
+              raise Graphlient::Errors::ServerError, 'Failed to parse response body as JSON'
+            end
+          else
+            inner_exception = StandardError.new <<~ERR.strip.tr("\n", ' ')
+              Unexpected response body type '#{body.class}'. Graphlient doesn't
+              know how to handle a response body of this type, but Faraday is
+              returning it. Please open an issue, particularly if the response
+              body does actually contain valid JSON.
+            ERR
+
+            raise Graphlient::Errors::ClientError, inner_exception
+          end
+        end
       end
     end
   end

spec/graphlient/adapters/http/faraday_adapter_spec.rb

@@ -75,6 +75,61 @@
     end
   end
 
+  context 'a non-error response without an appropriate JSON header' do
+    let(:url) { 'http://example.com/graphql' }
+    let(:headers) { { 'Content-Type' => 'application/notjson' } }
+    let(:client) { Graphlient::Client.new(url) }
+    let(:response_headers) { { 'Content-Type' => 'application/notjson' } }
+
+    context 'when the response body is valid JSON' do
+      before do
+        stub_request(:post, url).to_return(
+          status: 200,
+          headers: response_headers,
+          body: DummySchema.execute(GraphQL::Introspection::INTROSPECTION_QUERY).to_json
+        )
+      end
+
+      it 'retrieves schema' do
+        expect(client.schema).to be_a Graphlient::Schema
+      end
+    end
+
+    context 'when the response body is not valid JSON' do
+      before do
+        stub_request(:post, url).to_return(
+          status: 200,
+          headers: response_headers,
+          body: ''
+        )
+      end
+
+      it 'raises Graphlient::Errors::ServerError' do
+        expect { client.schema }.to raise_error(Graphlient::Errors::ServerError) { |error|
+          expect(error.message).to include('Failed to parse response body as JSON')
+        }
+      end
+    end
+
+    context 'when the Faraday response body object is not a type we expect from Faraday' do
+      before do
+        stub_request(:post, url).to_return(
+          status: 200,
+          headers: response_headers
+        )
+      end
+
+      it 'raises Graphlient::Errors::ClientError' do
+        mock_response = double('response', body: nil)
+        allow(client.http.connection).to receive(:post).and_return(mock_response)
+
+        expect { client.schema }.to raise_error(Graphlient::Errors::ClientError) { |error|
+          expect(error.message).to include "Unexpected response body type 'NilClass'"
+        }
+      end
+    end
+  end
+
   context 'Failed to open TCP connection error' do
     let(:url) { 'http://example.com/graphql' }
     let(:client) { Graphlient::Client.new(url) }