Add spec for Socket#read_nonblock with a provided buffer

When provided a buffer MRI preserves the original encoding
but TruffleRuby sets the encoding to `Encoding::BINARY`

library/socket/basicsocket/read_nonblock_spec.rb

@@ -18,7 +18,37 @@
 
     it "receives data after it's ready" do
       IO.select([@r], nil, nil, 2)
-      @r.recv_nonblock(5).should == "aaa"
+      @r.read_nonblock(5).should == "aaa"
+    end
+
+    platform_is_not :windows do
+      it 'returned data is binary encoded regardless of the external encoding' do
+        IO.select([@r], nil, nil, 2)
+        @r.read_nonblock(1).encoding.should == Encoding::BINARY
+
+        @w.send("bbb", 0, @r.getsockname)
+        @r.set_encoding(Encoding::ISO_8859_1)
+        IO.select([@r], nil, nil, 2)
+        buffer = @r.read_nonblock(3)
+        buffer.should == "bbb"
+        buffer.encoding.should == Encoding::BINARY
+      end
+    end
+
+    it 'replaces the content of the provided buffer without changing its encoding' do
+      buffer = "initial data".dup.force_encoding(Encoding::UTF_8)
+
+      IO.select([@r], nil, nil, 2)
+      @r.read_nonblock(3, buffer)
+      buffer.should == "aaa"
+      buffer.encoding.should == Encoding::UTF_8
+
+      @w.send("bbb", 0, @r.getsockname)
+      @r.set_encoding(Encoding::ISO_8859_1)
+      IO.select([@r], nil, nil, 2)
+      @r.read_nonblock(3, buffer)
+      buffer.should == "bbb"
+      buffer.encoding.should == Encoding::UTF_8
     end
 
     platform_is :linux do

library/socket/basicsocket/read_spec.rb

@@ -0,0 +1,47 @@
+require_relative '../spec_helper'
+require_relative '../fixtures/classes'
+
+describe "BasicSocket#read" do
+  SocketSpecs.each_ip_protocol do |family, ip_address|
+    before :each do
+      @r = Socket.new(family, :DGRAM)
+      @w = Socket.new(family, :DGRAM)
+
+      @r.bind(Socket.pack_sockaddr_in(0, ip_address))
+      @w.send("aaa", 0, @r.getsockname)
+    end
+
+    after :each do
+      @r.close unless @r.closed?
+      @w.close unless @w.closed?
+    end
+
+    it "receives data after it's ready" do
+      @r.read(3).should == "aaa"
+    end
+
+    it 'returned data is binary encoded regardless of the external encoding' do
+      @r.read(3).encoding.should == Encoding::BINARY
+
+      @w.send("bbb", 0, @r.getsockname)
+      @r.set_encoding(Encoding::UTF_8)
+      buffer = @r.read(3)
+      buffer.should == "bbb"
+      buffer.encoding.should == Encoding::BINARY
+    end
+
+    it 'replaces the content of the provided buffer without changing its encoding' do
+      buffer = "initial data".dup.force_encoding(Encoding::UTF_8)
+
+      @r.read(3, buffer)
+      buffer.should == "aaa"
+      buffer.encoding.should == Encoding::UTF_8
+
+      @w.send("bbb", 0, @r.getsockname)
+      @r.set_encoding(Encoding::ISO_8859_1)
+      @r.read(3, buffer)
+      buffer.should == "bbb"
+      buffer.encoding.should == Encoding::UTF_8
+    end
+  end
+end