Add IO#readable?, BasicSocket#readable? and StringIO#readable?.

ext/socket/basicsocket.c

@@ -735,6 +735,39 @@ bsock_do_not_rev_lookup_set(VALUE self, VALUE val)
     return val;
 }
 
+static VALUE
+bsock_readable_p(VALUE self)
+{
+    VALUE result = rb_call_super(0, NULL);
+
+    if (RTEST(result)) {
+        rb_io_t *fptr;
+        RB_IO_POINTER(self, fptr);
+
+        char buffer[1];
+#ifdef MSG_DONTWAIT
+        int result = recv(fptr->fd, buffer, 1, MSG_PEEK | MSG_DONTWAIT);
+#else
+        rb_io_set_nonblock(fptr);
+        int result = recv(fptr->fd, buffer, 1, MSG_PEEK);
+#endif
+
+        if (result > 0) {
+            return Qtrue;
+        }
+
+        if (result == 0) {
+            return Qfalse;
+        }
+
+        if (result == -1 && (errno == EAGAIN || errno == EWOULDBLOCK)) {
+            return Qtrue;
+        }
+    } else {
+        return Qfalse;
+    }
+}
+
 void
 rsock_init_basicsocket(void)
 {
@@ -768,6 +801,8 @@ rsock_init_basicsocket(void)
     rb_define_method(rb_cBasicSocket, "do_not_reverse_lookup", bsock_do_not_reverse_lookup, 0);
     rb_define_method(rb_cBasicSocket, "do_not_reverse_lookup=", bsock_do_not_reverse_lookup_set, 1);
 
+    rb_define_method(rb_cBasicSocket, "readable?", bsock_readable_p, 0);
+
     /* for ext/socket/lib/socket.rb use only: */
     rb_define_private_method(rb_cBasicSocket,
                              "__recv_nonblock", bsock_recv_nonblock, 4);

ext/stringio/stringio.c

@@ -638,6 +638,14 @@ strio_eof(VALUE self)
     return Qtrue;
 }
 
+static VALUE
+strio_readable_p(VALUE self)
+{
+    if (strio_to_read(self)) return Qtrue;
+    return Qfalse;
+
+}
+
 /* :nodoc: */
 static VALUE
 strio_copy(VALUE copy, VALUE orig)
@@ -1936,6 +1944,7 @@ Init_stringio(void)
     rb_define_method(StringIO, "closed_write?", strio_closed_write, 0);
     rb_define_method(StringIO, "eof", strio_eof, 0);
     rb_define_method(StringIO, "eof?", strio_eof, 0);
+    rb_define_method(StringIO, "readable?", strio_readable_p, 0);
     /* call-seq: strio.fcntl */
     rb_define_method(StringIO, "fcntl", strio_fcntl, -1);
     /* call-seq: strio.flush -> strio */

io.c

@@ -2623,6 +2623,20 @@ io_fillbuf(rb_io_t *fptr)
     return 0;
 }
 
+VALUE
+rb_io_readable_p(VALUE io)
+{
+    rb_io_t *fptr;
+    RB_IO_POINTER(io, fptr);
+
+    rb_io_check_char_readable(fptr);
+
+    if (READ_CHAR_PENDING(fptr)) return Qtrue;
+    if (READ_DATA_PENDING(fptr)) return Qtrue;
+
+    return RBOOL(fptr->fd >= 0);
+}
+
 /*
  *  call-seq:
  *    eof -> true or false
@@ -15707,6 +15721,7 @@ Init_IO(void)
     rb_define_method(rb_cIO, "rewind", rb_io_rewind, 0);
     rb_define_method(rb_cIO, "pos", rb_io_tell, 0);
     rb_define_method(rb_cIO, "pos=", rb_io_set_pos, 1);
+    rb_define_method(rb_cIO, "readable?", rb_io_readable_p, 0);
     rb_define_method(rb_cIO, "eof", rb_io_eof, 0);
     rb_define_method(rb_cIO, "eof?", rb_io_eof, 0);