Automatically set the Host header from the URI

Closes #32.

lib/http/request.rb

@@ -42,6 +42,7 @@ def initialize(method, uri, headers = {}, proxy = {}, body = nil, version = "1.1
         key ||= Http.canonicalize_header(name)
         @headers[key] = value
       end
+      @headers["Host"] ||= @uri.host
 
       @proxy, @body, @version = proxy, body, version
     end

spec/http/request_spec.rb

@@ -0,0 +1,19 @@
+require 'spec_helper'
+
+describe Http::Request do
+  describe "headers" do
+    subject { Http::Request.new(:get, "http://example.com/", :accept => "text/html") }
+
+    it "sets explicit headers" do
+      subject["Accept"].should eq("text/html")
+    end
+
+    it "sets implicit headers" do
+      subject["Host"].should eq("example.com")
+    end
+
+    it "provides a #headers accessor" do
+      subject.headers.should eq("Accept" => "text/html", "Host" => "example.com")
+    end
+  end
+end