stream: Make non-blcoking stream support configurable.

Enable only on unix. To avoid unpleasant surprises with error codes.

py/mpconfig.h

@@ -249,6 +249,11 @@ typedef double mp_float_t;
 #define MICROPY_PATH_MAX (512)
 #endif
 
+// Whether POSIX-semantics non-blocking streams are supported
+#ifndef MICROPY_STREAMS_NON_BLOCK
+#define MICROPY_STREAMS_NON_BLOCK (0)
+#endif
+
 // Whether to use computed gotos in the VM, or a switch
 // Computed gotos are roughly 10% faster, and increase VM code size by a little
 #ifndef MICROPY_USE_COMPUTED_GOTO

py/stream.c

@@ -25,7 +25,6 @@
  */
 
 #include <string.h>
-#include <errno.h>
 
 #include "mpconfig.h"
 #include "nlr.h"
@@ -33,6 +32,9 @@
 #include "qstr.h"
 #include "obj.h"
 #include "stream.h"
+#if MICROPY_STREAMS_NON_BLOCK
+#include <errno.h>
+#endif
 
 // This file defines generic Python stream read/write methods which
 // dispatch to the underlying stream interface of an object.
@@ -42,9 +44,13 @@
 
 STATIC mp_obj_t stream_readall(mp_obj_t self_in);
 
+#if MICROPY_STREAMS_NON_BLOCK
 // TODO: This is POSIX-specific (but then POSIX is the only real thing,
 // and anything else just emulates it, right?)
 #define is_nonblocking_error(errno) ((errno) == EAGAIN || (errno) == EWOULDBLOCK)
+#else
+#define is_nonblocking_error(errno) (0)
+#endif
 
 STATIC mp_obj_t stream_read(uint n_args, const mp_obj_t *args) {
     struct _mp_obj_base_t *o = (struct _mp_obj_base_t *)args[0];

unix/mpconfigport.h

@@ -39,6 +39,7 @@
 #define MICROPY_FLOAT_IMPL          (MICROPY_FLOAT_IMPL_DOUBLE)
 #define MICROPY_LONGINT_IMPL        (MICROPY_LONGINT_IMPL_MPZ)
 #define MICROPY_PATH_MAX            (PATH_MAX)
+#define MICROPY_STREAMS_NON_BLOCK   (1)
 #define MICROPY_USE_COMPUTED_GOTO   (1)
 #define MICROPY_MOD_SYS_STDFILES    (1)
 #define MICROPY_ENABLE_MOD_CMATH    (1)