Add RFC7233 support (#299)

Add RFC7233 support a.k.a "Range" headers support

spec/static_file_handler.cr

@@ -12,7 +12,9 @@ private def handle(request, fallthrough = true)
 end
 
 describe Kemal::StaticFileHandler do
-  file_text = File.read "#{__DIR__}/static/dir/test.txt"
+  file = File.open "#{__DIR__}/static/dir/test.txt"
+  file_size = file.size
+  file_text = file.to_s
 
   it "should serve a file with content type and etag" do
     response = handle HTTP::Request.new("GET", "/dir/test.txt")
@@ -99,4 +101,33 @@ describe Kemal::StaticFileHandler do
       response.headers["Allow"].should eq("GET, HEAD")
     end
   end
+
+  it "should send part of files when requested (RFC7233)" do
+    %w(POST PUT DELETE HEAD).each do |method|
+      headers = HTTP::Headers{"Range" => "0-100"}
+      response = handle HTTP::Request.new(method, "/dir/test.txt", headers)
+      response.status_code.should_not eq(206)
+      response.headers.has_key?("Content-Range").should eq(false)
+    end
+
+    %w(GET).each do |method|
+      headers = HTTP::Headers{"Range" => "0-100"}
+      response = handle HTTP::Request.new(method, "/dir/test.txt", headers)
+      response.status_code.should eq(206 || 200)
+      if response.status_code == 206
+        response.headers.has_key?("Content-Range").should eq true
+        match = response.headers["Content-Range"].match(/bytes (\d+)-(\d+)\/(\d+)/)
+        match.should_not be nil
+        if match
+          start_range = match[1].to_i {0}
+          end_range = match[2].to_i {0}
+          range_size = match[3].to_i {0}
+
+          range_size.should eq file_size
+          (end_range < file_size).should eq true
+          (start_range < end_range).should eq true
+        end
+      end
+    end
+  end
 end

src/kemal/response.cr

@@ -0,0 +1,14 @@
+class HTTP::Server::Response
+  class Output
+    def close
+
+      unless response.wrote_headers? && !response.headers.has_key?("Content-Range")
+        response.content_length = @out_count
+      end
+
+      ensure_headers_written
+
+      super
+    end
+  end
+end

src/kemal/static_file_handler.cr

@@ -56,6 +56,9 @@ module Kemal
         request_headers = context.request.headers
         filesize = File.size(file_path)
         File.open(file_path) do |file|
+          if context.request.headers.has_key?("Range") && context.request.method == "GET"
+            next multipart(file, context)
+          end
           if request_headers.includes_word?("Accept-Encoding", "gzip") && config.is_a?(Hash) && config["gzip"] == true && filesize > minsize && Utils.zip_types(file_path)
             context.response.headers["Content-Encoding"] = "gzip"
             Zlib::Deflate.gzip(context.response) do |deflate|
@@ -76,6 +79,58 @@ module Kemal
       end
     end
 
+    def multipart(file, env)
+      #See http://httpwg.org/specs/rfc7233.html
+      fileb = file.size
+
+      range = env.request.headers["Range"]
+      match = range.match(/bytes=(\d{1,})-(\d{0,})/)
+
+      startb = 0
+      endb = 0
+
+      if match
+        if match.size >= 2
+          startb = match[1].to_i { 0 }
+        end
+
+        if match.size >= 3
+          endb = match[2].to_i { 0 }
+        end
+      end
+
+      if endb == 0
+          endb = fileb
+      end
+
+      if startb < endb && endb <= fileb
+        env.response.status_code = 206
+        env.response.content_length = endb - startb
+        env.response.headers["Accept-Ranges"] = "bytes"
+        env.response.headers["Content-Range"] = "bytes #{startb}-#{endb - 1}/#{fileb}" # MUST
+
+        if startb > 1024
+          skipped = 0
+          # file.skip only accepts values less or equal to 1024 (buffer size, undocumented)
+          until skipped + 1024 > startb
+            file.skip(1024)
+            skipped += 1024
+          end
+          if skipped - startb > 0
+            file.skip(skipped - startb)
+          end
+        else
+          file.skip(startb)
+        end
+
+        IO.copy(file, env.response, endb - startb)
+      else
+        env.response.content_length = fileb
+        env.response.status_code = 200 # Range not satisfable, see 4.4 Note
+        IO.copy(file, env.response)
+      end
+    end
+
     def etag(context, file_path)
       etag = %{W/"#{File.lstat(file_path).mtime.epoch.to_s}"}
       context.response.headers["ETag"] = etag