Set default exception Content-Type to text/html. Fixes #202

spec/common_exception_handler_spec.cr

@@ -34,11 +34,12 @@ describe "Kemal::CommonExceptionHandler" do
     io.rewind
     response = HTTP::Client::Response.from_io(io, decompress: false)
     response.status_code.should eq 403
+    response.headers["Content-Type"].should eq "text/html"
     response.body.should eq "403 error"
   end
 
   it "renders custom 500 error" do
-    error 500 do
+    error 500 do |env|
       "Something happened"
     end
     get "/" do |env|
@@ -54,6 +55,29 @@ describe "Kemal::CommonExceptionHandler" do
     io.rewind
     response = HTTP::Client::Response.from_io(io, decompress: false)
     response.status_code.should eq 500
+    response.headers["Content-Type"].should eq "text/html"
+    response.body.should eq "Something happened"
+  end
+
+  it "keeps the specified error Content-Type" do
+    error 500 do |env|
+      "Something happened"
+    end
+    get "/" do |env|
+      env.response.content_type = "application/json"
+      env.response.status_code = 500
+    end
+    request = HTTP::Request.new("GET", "/")
+    io = MemoryIO.new
+    response = HTTP::Server::Response.new(io)
+    context = HTTP::Server::Context.new(request, response)
+    Kemal::CommonExceptionHandler::INSTANCE.next = Kemal::RouteHandler::INSTANCE
+    Kemal::CommonExceptionHandler::INSTANCE.call(context)
+    response.close
+    io.rewind
+    response = HTTP::Client::Response.from_io(io, decompress: false)
+    response.status_code.should eq 500
+    response.headers["Content-Type"].should eq "application/json"
     response.body.should eq "Something happened"
   end
 end

src/kemal/common_exception_handler.cr

@@ -20,9 +20,9 @@ module Kemal
 
     def call_exception_with_status_code(context, status_code)
       if Kemal.config.error_handlers.has_key?(status_code)
-        context.response.status_code = status_code
+        context.response.content_type = "text/html" unless context.response.headers.has_key?("Content-Type")
         context.response.print Kemal.config.error_handlers[status_code].call(context)
-        return context
+        context
       end
     end
   end