IO:::Sized: don't peek underlying IO if read_remaining is zero. Fixes #4261

Ary Borenszweig · Ary Borenszweig · commit 3eef15a18a61 · 2017-04-09T16:18:00.000-03:00
diff --git a/spec/std/io/sized_spec.cr b/spec/std/io/sized_spec.cr
@@ -1,5 +1,21 @@
 require "spec"
 
+private class NoPeekIO
+  include IO
+
+  def read(bytes : Bytes)
+    0
+  end
+
+  def write(bytes : Bytes)
+    0
+  end
+
+  def peek
+    raise "shouldn't be invoked"
+  end
+end
+
 describe "IO::Sized" do
   describe "#read" do
     it "doesn't read past the limit when reading char-by-char" do
@@ -117,6 +133,11 @@ describe "IO::Sized" do
     sized.peek.should eq(Bytes.empty)
   end
 
+  it "doesn't peek when remaining = 0 (#4261)" do
+    sized = IO::Sized.new(NoPeekIO.new, read_size: 0)
+    sized.peek.should eq(Bytes.empty)
+  end
+
   it "skips" do
     io = IO::Memory.new "123456789"
     sized = IO::Sized.new(io, read_size: 6)
diff --git a/src/io/sized.cr b/src/io/sized.cr
@@ -52,6 +52,8 @@ module IO
     def peek
       check_open
 
+      return Bytes.empty if @read_remaining == 0 # EOF
+
       peek = @io.peek
       return nil unless peek
 
