Allow CSV.open with StringIO argument

lib/csv.rb

@@ -1508,10 +1508,8 @@ def generate_lines(rows, **options)
 
     #
     # :call-seq:
-    #   open(file_path, mode = "rb", **options ) -> new_csv
-    #   open(io, mode = "rb", **options ) -> new_csv
-    #   open(file_path, mode = "rb", **options ) { |csv| ... } -> object
-    #   open(io, mode = "rb", **options ) { |csv| ... } -> object
+    #   open(path_or_io, mode = "rb", **options ) -> new_csv
+    #   open(path_or_io, mode = "rb", **options ) { |csv| ... } -> object
     #
     # possible options elements:
     #   keyword form:
@@ -1520,7 +1518,7 @@ def generate_lines(rows, **options)
     #     :undef => :replace   # replace undefined conversion
     #     :replace => string   # replacement string ("?" or "\uFFFD" if not specified)
     #
-    # * Argument +path+, if given, must be the path to a file.
+    # * Argument +path_or_io+, must be a file path or an \IO stream.
     # :include: ../doc/csv/arguments/io.rdoc
     # * Argument +mode+, if given, must be a \File mode.
     #   See {Access Modes}[https://docs.ruby-lang.org/en/master/File.html#class-File-label-Access+Modes].
@@ -1544,6 +1542,9 @@ def generate_lines(rows, **options)
     #   path = 't.csv'
     #   File.write(path, string)
     #
+    #   string_io = StringIO.new
+    #   string_io << "foo,0\nbar,1\nbaz,2\n"
+    #
     # ---
     #
     # With no block given, returns a new \CSV object.
@@ -1556,6 +1557,9 @@ def generate_lines(rows, **options)
     #   csv = CSV.open(File.open(path))
     #   csv # => #<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">
     #
+    # Create a \CSV object using a \StringIO:
+    #   csv = CSV.open(string_io)
+    #   csv # => #<CSV io_type:StringIO encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">
     # ---
     #
     # With a block given, calls the block with the created \CSV object;
@@ -1573,16 +1577,24 @@ def generate_lines(rows, **options)
     # Output:
     #   #<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">
     #
+    # Using a \StringIO:
+    #   csv = CSV.open(string_io) {|csv| p csv}
+    #   csv # => #<CSV io_type:StringIO encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">
+    # Output:
+    #   #<CSV io_type:StringIO encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">
     # ---
     #
     # Raises an exception if the argument is not a \String object or \IO object:
     #   # Raises TypeError (no implicit conversion of Symbol into String)
     #   CSV.open(:foo)
-    def open(filename, mode="r", **options)
+    def open(filename_or_io, mode="r", **options)
       # wrap a File opened with the remaining +args+ with no newline
       # decorator
       file_opts = {}
-      may_enable_bom_deletection_automatically(mode, options, file_opts)
+      may_enable_bom_detection_automatically(filename_or_io,
+                                             mode,
+                                             options,
+                                             file_opts)
       file_opts.merge!(options)
       unless file_opts.key?(:newline)
         file_opts[:universal_newline] ||= false
@@ -1592,14 +1604,23 @@ def open(filename, mode="r", **options)
       options.delete(:replace)
       options.delete_if {|k, _| /newline\z/.match?(k)}
 
-      begin
-        f = File.open(filename, mode, **file_opts)
-      rescue ArgumentError => e
-        raise unless /needs binmode/.match?(e.message) and mode == "r"
-        mode = "rb"
-        file_opts = {encoding: Encoding.default_external}.merge(file_opts)
-        retry
+      if filename_or_io.is_a?(StringIO)
+        f = if RUBY_VERSION >= "2.7"
+          StringIO.new(filename_or_io.string, **file_opts)
+        else
+          StringIO.new(filename_or_io.string)
+        end
+      else
+        begin
+          f = File.open(filename_or_io, mode, **file_opts)
+        rescue ArgumentError => e
+          raise unless /needs binmode/.match?(e.message) and mode == "r"
+          mode = "rb"
+          file_opts = {encoding: Encoding.default_external}.merge(file_opts)
+          retry
+        end
       end
+
       begin
         csv = new(f, **options)
       rescue Exception
@@ -1886,10 +1907,15 @@ def table(path, **options)
     private_constant :ON_WINDOWS
 
     private
-    def may_enable_bom_deletection_automatically(mode, options, file_opts)
-      # "bom|utf-8" may be buggy on Windows:
-      # https://bugs.ruby-lang.org/issues/20526
-      return if ON_WINDOWS
+    def may_enable_bom_detection_automatically(filename_or_io,
+                                               mode,
+                                               options,
+                                               file_opts)
+      unless filename_or_io.is_a?(StringIO)
+        # "bom|utf-8" may be buggy on Windows:
+        # https://bugs.ruby-lang.org/issues/20526
+        return if ON_WINDOWS
+      end
       return unless Encoding.default_external == Encoding::UTF_8
       return if options.key?(:encoding)
       return if options.key?(:external_encoding)

test/csv/interface/test_read.rb

@@ -32,6 +32,24 @@ def test_foreach
     assert_equal(@rows, rows)
   end
 
+  def test_foreach_stringio
+    string_io = StringIO.new(@data)
+    rows = CSV.foreach(string_io, col_sep: "\t", row_sep: "\r\n").to_a
+    assert_equal(@rows, rows)
+  end
+
+  def test_foreach_stringio_with_bom
+    if RUBY_VERSION < "2.7"
+      # Support to StringIO was dropped for Ruby 2.6 and earlier without BOM support:
+      # https://github.com/ruby/stringio/pull/47
+      omit("StringIO's BOM support isn't available with Ruby < 2.7")
+    end
+
+    string_io = StringIO.new("\ufeff#{@data}") # U+FEFF ZERO WIDTH NO-BREAK SPACE
+    rows = CSV.foreach(string_io, col_sep: "\t", row_sep: "\r\n").to_a
+    assert_equal(@rows, rows)
+  end
+
   if respond_to?(:ractor)
     ractor
     def test_foreach_in_ractor