Fix multipart upload and back params.files (#499)

src/kemal/file_upload.cr

@@ -0,0 +1,24 @@
+module Kemal
+  struct FileUpload
+    getter tempfile : File
+    getter filename : String?
+    getter headers : HTTP::Headers
+    getter creation_time : Time?
+    getter modification_time : Time?
+    getter read_time : Time?
+    getter size : UInt64?
+
+    def initialize(upload)
+      @tempfile = File.tempfile
+      ::File.open(@tempfile.path, "w") do |file|
+        IO.copy(upload.body, file)
+      end
+      @filename = upload.filename
+      @headers = upload.headers
+      @creation_time = upload.creation_time
+      @modification_time = upload.modification_time
+      @read_time = upload.read_time
+      @size = upload.size
+    end
+  end
+end

src/kemal/param_parser.cr

@@ -9,15 +9,18 @@ module Kemal
     PARTS            = %w(url query body json)
     # :nodoc:
     alias AllParamTypes = Nil | String | Int64 | Float64 | Bool | Hash(String, JSON::Any) | Array(JSON::Any)
+    getter files
 
     def initialize(@request : HTTP::Request, @url : Hash(String, String) = {} of String => String)
       @query = HTTP::Params.new({} of String => Array(String))
       @body = HTTP::Params.new({} of String => Array(String))
       @json = {} of String => AllParamTypes
+      @files = {} of String => FileUpload
       @url_parsed = false
       @query_parsed = false
       @body_parsed = false
       @json_parsed = false
+      @files_parsed = false
     end
 
     private def unescape_url_param(value : String)
@@ -40,11 +43,17 @@ module Kemal
 
     private def parse_body
       content_type = @request.headers["Content-Type"]?
+
       return unless content_type
+
       if content_type.try(&.starts_with?(URL_ENCODED_FORM))
         @body = parse_part(@request.body)
         return
       end
+
+      if content_type.try(&.starts_with?(MULTIPART_FORM))
+        parse_files
+      end
     end
 
     private def parse_query
@@ -55,6 +64,24 @@ module Kemal
       @url.each { |key, value| @url[key] = unescape_url_param(value) }
     end
 
+    private def parse_files
+      return if @files_parsed
+
+      HTTP::FormData.parse(@request) do |upload|
+        next unless upload
+
+        filename = upload.filename
+
+        if !filename.nil?
+          @files[upload.name] = FileUpload.new(upload)
+        else
+          @body.add(upload.name, upload.body.gets_to_end)
+        end
+      end
+
+      @files_parsed = true
+    end
+
     # Parses JSON request body if Content-Type is `application/json`.
     #
     # - If request body is a JSON `Hash` then all the params are parsed and added into `params`.