1 files changed, 40 insertions, 5 deletions
diff --git a/ext/pty/lib/expect.rb b/ext/pty/lib/expect.rb
index aa9ab895d3..22cbf54115 100644
--- a/ext/pty/lib/expect.rb
+++ b/ext/pty/lib/expect.rb
@@ -1,27 +1,63 @@
+# frozen_string_literal: true
 $expect_verbose = false
 
 class IO
+  # call-seq:
+  #   IO#expect(pattern,timeout=9999999)                  ->  Array
+  #   IO#expect(pattern,timeout=9999999) { |result| ... } ->  nil
+  #
+  # The +expect+ library adds instance method IO#expect,
+  # which is similar to the
+  # {TCL expect extension}[https://www.tcl.tk/man/expect5.31/expect.1.html].
+  #
+  # To use this method, you must require +expect+:
+  #
+  #   require 'expect'
+  #
+  # Reads from the IO until the given +pattern+ matches or the +timeout+ is over.
+  #
+  # It returns an array with the read buffer, followed by the matches.
+  # If a block is given, the result is yielded to the block and returns nil.
+  #
+  # When called without a block, it waits until the input that matches the
+  # given +pattern+ is obtained from the IO or the time specified as the
+  # timeout passes. An array is returned when the pattern is obtained from the
+  # IO. The first element of the array is the entire string obtained from the
+  # IO until the pattern matches, followed by elements indicating which the
+  # pattern which matched to the anchor in the regular expression.
+  #
+  # The optional timeout parameter defines, in seconds, the total time to wait
+  # for the pattern.  If the timeout expires or eof is found, nil is returned
+  # or yielded.  However, the buffer in a timeout session is kept for the next
+  # expect call.  The default timeout is 9999999 seconds.
   def expect(pat,timeout=9999999)
-    buf = ''
+    buf = ''.dup
     case pat
     when String
       e_pat = Regexp.new(Regexp.quote(pat))
     when Regexp
       e_pat = pat
+    else
+      raise TypeError, "unsupported pattern class: #{pat.class}"
     end
+    @unusedBuf ||= ''
     while true
-      if IO.select([self],nil,nil,timeout).nil? then
+      if not @unusedBuf.empty?
+        c = @unusedBuf.slice!(0)
+      elsif !IO.select([self],nil,nil,timeout) or eof? then
         result = nil
+        @unusedBuf = buf
         break
+      else
+        c = getc
       end
-      c = getc.chr
       buf << c
       if $expect_verbose
         STDOUT.print c
         STDOUT.flush
       end
       if mat=e_pat.match(buf) then
-        result = [buf,*mat.to_a[1..-1]]
+        result = [buf,*mat.captures]
         break
       end
     end
@@ -33,4 +69,3 @@ class IO
     nil
   end
 end
-