Fix gets on Windows. Fixes #2959

* Don't unwrap stdin streams; the direct FileChannel does not seem
  to be usable and reads result in IOException: Not enough storage
  is available to process this command.
* Tweaks for argf logic.
* Always treat FileChannel as ready for read, since files always
  select immediately and processes can't be selected without
  native support.

Author: headius

core/src/main/java/org/jruby/RubyArgsFile.java

@@ -36,6 +36,7 @@
 import java.io.IOException;
 import static org.jruby.RubyEnumerator.enumeratorize;
 
+import org.jruby.anno.FrameField;
 import org.jruby.anno.JRubyMethod;
 import org.jruby.exceptions.RaiseException;
 import jnr.posix.FileStat;
@@ -239,6 +240,7 @@ public static IRubyObject external_encoding(ThreadContext context, IRubyObject r
         return ((RubyIO) getData(context, recv, "no stream to set encoding").currentFile).external_encoding(context);
     }    
 
+    // MRI: argf_getline
     private static IRubyObject argf_getline(ThreadContext context, IRubyObject recv, IRubyObject[] args) {
         ArgsFileData data = ArgsFileData.getDataFrom(recv);
 
@@ -269,21 +271,10 @@ private static IRubyObject argf_getline(ThreadContext context, IRubyObject recv,
     /** Read a line.
      * 
      */
-    @JRubyMethod(name = "gets", optional = 1)
+    @JRubyMethod(name = "gets", optional = 1, writes = FrameField.LASTLINE)
     public static IRubyObject gets(ThreadContext context, IRubyObject recv, IRubyObject[] args) {
-        ArgsFileData data = ArgsFileData.getDataFrom(recv);
-
-        if (!data.next_argv(context)) return context.runtime.getNil();
-
-        IRubyObject line;
-        if (!(data.currentFile instanceof RubyIO)) {
-            line = data.currentFile.callMethod(context, "gets", args);
-        } else {
-            line = argf_getline(context, recv, args);
-        }
-
+        IRubyObject line = argf_getline(context, recv, args);
         context.setLastLine(line);
-        context.runtime.getGlobalVariables().set("$_", line);
 
         return line;
     }

core/src/main/java/org/jruby/RubyGlobal.java

@@ -286,19 +286,9 @@ private static Channel prepareStdioChannel(Ruby runtime, STDIO stdio, Object str
         } else {
             switch (stdio) {
                 case IN:
-                    stream = ShellLauncher.unwrapFilterInputStream((InputStream)stream);
-                    if (stream instanceof FileInputStream) {
-                        return ((FileInputStream)stream).getChannel();
-                    }
-
                     return Channels.newChannel((InputStream)stream);
                 case OUT:
                 case ERR:
-                    stream = ShellLauncher.unwrapFilterOutputStream((OutputStream)stream);
-                    if (stream instanceof FileOutputStream) {
-                        return ((FileOutputStream)stream).getChannel();
-                    }
-
                     return Channels.newChannel((OutputStream)stream);
                 default: throw new RuntimeException("invalid stdio: " + stdio);
             }

core/src/main/java/org/jruby/RubyKernel.java

@@ -318,9 +318,15 @@ public static IRubyObject getc(ThreadContext context, IRubyObject recv) {
         return defin.callMethod(context, "getc");
     }
 
+    // MRI: rb_f_gets
     @JRubyMethod(optional = 1, module = true, visibility = PRIVATE)
     public static IRubyObject gets(ThreadContext context, IRubyObject recv, IRubyObject[] args) {
-        return RubyArgsFile.gets(context, context.runtime.getArgsFile(), args);
+        Ruby runtime = context.runtime;
+
+        if (recv == runtime.getArgsFile()) {
+            return RubyArgsFile.gets(context, runtime.getArgsFile(), args);
+        }
+        return runtime.getArgsFile().callMethod(context, "gets", args);
     }
 
     @JRubyMethod(optional = 1, module = true, visibility = PRIVATE)

core/src/main/java/org/jruby/util/io/OpenFile.java

@@ -1398,18 +1398,17 @@ boolean waitReadable(ThreadContext context, ChannelFD fd) {
                 }
             }
 
-            // kinda-hacky way to see if there's more data to read from a seekable channel
+            /*
+            Seekable channels (usually FileChannel) are treated as ready always. There are
+            three kinds we typically see:
+            1. files, which always select(2) as ready
+            2. stdio, which we can't select and can't check .size for available data
+            3. subprocess stdio, which we can't select and can't check .size either
+            In all three cases, without native fd logic, we can't do anything to determine
+            if the stream is ready, so we just assume it is and hope for the best.
+             */
             if (fd.chSeek != null) {
-                FileChannel fdSeek = fd.chSeek;
-                try {
-                    // not a real file, can't get size...we'll have to just read and block
-                    if (fdSeek.size() < 0) return true;
-
-                    // if current position is less than file size, read should not block
-                    return fdSeek.position() < fdSeek.size();
-                } catch (IOException ioe) {
-                    throw context.runtime.newIOErrorFromException(ioe);
-                }
+                return true;
             }
         } finally {
             if (locked) unlock();