ShowException only serves HTML Accept header contains text/html

Rather than be concerned with whether a request is an asynchronous browser
request or not it is better to simply consider the Accept header and only serve
HTML to clients that specifically ask for it.

This way you will not find your pure JSON API application splitting out HTML
error messages to your console when using curl :)

lib/rack/showexceptions.rb

@@ -28,12 +28,12 @@ def call(env)
       env["rack.errors"].puts(exception_string)
       env["rack.errors"].flush
 
-      if prefers_plain_text?(env)
-        content_type = "text/plain"
-        body = [exception_string]
-      else
+      if accepts_html?(env)
         content_type = "text/html"
         body = pretty(env, e)
+      else
+        content_type = "text/plain"
+        body = [exception_string]
       end
 
       [500,
@@ -42,8 +42,8 @@ def call(env)
        body]
     end
 
-    def prefers_plain_text?(env)
-      env["HTTP_X_REQUESTED_WITH"] == "XMLHttpRequest" && (!env["HTTP_ACCEPT"] || !env["HTTP_ACCEPT"].include?("text/html"))
+    def accepts_html?(env)
+      env["HTTP_ACCEPT"] && env["HTTP_ACCEPT"].include?("text/html")
     end
 
     def dump_exception(exception)

test/spec_showexceptions.rb

@@ -16,7 +16,7 @@ def show_exceptions(app)
     ))
 
     lambda{
-      res = req.get("/")
+      res = req.get("/", "HTTP_ACCEPT" => "text/html")
     }.should.not.raise
 
     res.should.be.a.server_error
@@ -26,7 +26,7 @@ def show_exceptions(app)
     res.should =~ /ShowExceptions/
   end
 
-  it "responds with plain text on AJAX requests accepting anything but HTML" do
+  it "responds with plain text to requests not specifically accepting HTML" do
     res = nil
 
     req = Rack::MockRequest.new(
@@ -35,7 +35,7 @@ def show_exceptions(app)
     ))
 
     lambda{
-      res = req.get("/", "HTTP_X_REQUESTED_WITH" => "XMLHttpRequest")
+      res = req.get( "/", "HTTP_ACCECPT" => "*/*")
     }.should.not.raise
 
     res.should.be.a.server_error
@@ -47,7 +47,7 @@ def show_exceptions(app)
     res.body.should.include __FILE__
   end
 
-  it "responds with HTML on AJAX requests accepting HTML" do
+  it "responds with HTML to requests specifically accepting HTML" do
     res = nil
 
     req = Rack::MockRequest.new(
@@ -56,7 +56,7 @@ def show_exceptions(app)
     ))
 
     lambda{
-      res = req.get("/", "HTTP_X_REQUESTED_WITH" => "XMLHttpRequest", "HTTP_ACCEPT" => "text/html")
+      res = req.get("/", "HTTP_ACCEPT" => "text/html")
     }.should.not.raise
 
     res.should.be.a.server_error
@@ -79,7 +79,7 @@ def show_exceptions(app)
     )
 
     lambda{
-      res = req.get("/")
+      res = req.get("/", "HTTP_ACCEPT" => "text/html")
     }.should.not.raise
 
     res.should.be.a.server_error