Yield error in custom error handlers

CHANGELOG.md

@@ -44,6 +44,13 @@ end
 
 - Close response on `halt`. (thanks @samueleaton).
 - Update `Radix` to `v0.3.4`.
+- `error` handler now also yields error. For example you can get the error mesasage like
+
+```crystal
+  error 500 do |env, err|
+    err.message
+  end
+```
 
 # 0.16.1 (12-10-2016)
 

spec/common_exception_handler_spec.cr

@@ -80,4 +80,26 @@ describe "Kemal::CommonExceptionHandler" do
     response.headers["Content-Type"].should eq "application/json"
     response.body.should eq "Something happened"
   end
+
+  it "renders custom error with env and error" do
+    error 500 do |env, err|
+      err.message
+    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 "Rendered error with 500"
+  end
 end

src/kemal/common_exception_handler.cr

@@ -6,22 +6,22 @@ module Kemal
     def call(context)
       begin
         call_next(context)
-      rescue Kemal::Exceptions::RouteNotFound
+      rescue ex : Kemal::Exceptions::RouteNotFound
-        call_exception_with_status_code(context, 404)
+        call_exception_with_status_code(context, ex, 404)
-      rescue Kemal::Exceptions::CustomException
+      rescue ex : Kemal::Exceptions::CustomException
-        call_exception_with_status_code(context, context.response.status_code)
+        call_exception_with_status_code(context, ex, context.response.status_code)
       rescue ex : Exception
         Kemal.config.logger.write("Exception: #{ex.inspect_with_backtrace}\n")
-        return call_exception_with_status_code(context, 500) if Kemal.config.error_handlers.has_key?(500)
+        return call_exception_with_status_code(context, ex, 500) if Kemal.config.error_handlers.has_key?(500)
         verbosity = Kemal.config.env == "production" ? false : true
         return render_500(context, ex.inspect_with_backtrace, verbosity)
       end
     end
 
-    def call_exception_with_status_code(context, status_code)
+    def call_exception_with_status_code(context, exception, status_code)
       if Kemal.config.error_handlers.has_key?(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)
+        context.response.print Kemal.config.error_handlers[status_code].call(context, exception)
         context
       end
     end

src/kemal/config.cr

@@ -7,7 +7,7 @@ module Kemal
   class Config
     INSTANCE       = Config.new
     HANDLERS       = [] of HTTP::Handler
-    ERROR_HANDLERS = {} of Int32 => HTTP::Server::Context -> String
+    ERROR_HANDLERS = {} of Int32 => HTTP::Server::Context, Exception -> String
     {% if flag?(:without_openssl) %}
     @ssl : Bool?
     {% else %}
@@ -72,8 +72,8 @@ module Kemal
       ERROR_HANDLERS
     end
 
-    def add_error_handler(status_code, &handler : HTTP::Server::Context -> _)
+    def add_error_handler(status_code, &handler : HTTP::Server::Context, Exception -> _)
-      ERROR_HANDLERS[status_code] = ->(context : HTTP::Server::Context) { handler.call(context).to_s }
+      ERROR_HANDLERS[status_code] = ->(context : HTTP::Server::Context, error : Exception) { handler.call(context, error).to_s }
     end
 
     def extra_options(&@extra_options : OptionParser ->)

src/kemal/dsl.cr

@@ -15,6 +15,6 @@ def ws(path, &block : HTTP::WebSocket, HTTP::Server::Context -> Void)
   Kemal::WebSocketHandler.new path, &block
 end
 
-def error(status_code, &block : HTTP::Server::Context -> _)
+def error(status_code, &block : HTTP::Server::Context, Exception -> _)
   Kemal.config.add_error_handler status_code, &block
 end