py/stream: Introduce and use efficient mp_get_stream to access stream_p.

The existing mp_get_stream_raise() helper does explicit checks that the
input object is a real pointer object, has a non-NULL stream protocol, and
has the desired stream C method (read/write/ioctl).  In most cases it is
not necessary to do these checks because it is guaranteed that the input
object has the stream protocol and desired C methods.  For example, native
objects that use the stream wrappers (eg mp_stream_readinto_obj) in their
locals dict always have the stream protocol (or else they shouldn't have
these wrappers in their locals dict).

This patch introduces an efficient mp_get_stream() which doesn't do any
checks and just extracts the stream protocol struct.  This should be used
in all cases where the argument object is known to be a stream.  The
existing mp_get_stream_raise() should be used primarily to verify that an
object does have the correct stream protocol methods.

All uses of mp_get_stream_raise() in py/stream.c have been converted to use
mp_get_stream() because the argument is guaranteed to be a proper stream
object.

This patch improves efficiency of stream operations and reduces code size.

py/stream.c

@@ -1,3 +1,4 @@
+
 /*
  * This file is part of the MicroPython project, http://micropython.org/
  *
@@ -47,10 +48,9 @@ STATIC mp_obj_t stream_readall(mp_obj_t self_in);
 // be equal to input size).
 mp_uint_t mp_stream_rw(mp_obj_t stream, void *buf_, mp_uint_t size, int *errcode, byte flags) {
     byte *buf = buf_;
-    mp_obj_base_t* s = (mp_obj_base_t*)MP_OBJ_TO_PTR(stream);
     typedef mp_uint_t (*io_func_t)(mp_obj_t obj, void *buf, mp_uint_t size, int *errcode);
     io_func_t io_func;
-    const mp_stream_p_t *stream_p = s->type->protocol;
+    const mp_stream_p_t *stream_p = mp_get_stream(stream);
     if (flags & MP_STREAM_RW_WRITE) {
         io_func = (io_func_t)stream_p->write;
     } else {
@@ -99,8 +99,6 @@ const mp_stream_p_t *mp_get_stream_raise(mp_obj_t self_in, int flags) {
 }
 
 STATIC mp_obj_t stream_read_generic(size_t n_args, const mp_obj_t *args, byte flags) {
-    const mp_stream_p_t *stream_p = mp_get_stream_raise(args[0], MP_STREAM_OP_READ);
-
     // What to do if sz < -1?  Python docs don't specify this case.
     // CPython does a readall, but here we silently let negatives through,
     // and they will cause a MemoryError.
@@ -109,6 +107,8 @@ STATIC mp_obj_t stream_read_generic(size_t n_args, const mp_obj_t *args, byte fl
         return stream_readall(args[0]);
     }
 
+    const mp_stream_p_t *stream_p = mp_get_stream(args[0]);
+
     #if MICROPY_PY_BUILTINS_STR_UNICODE
     if (stream_p->is_text) {
         // We need to read sz number of unicode characters.  Because we don't have any
@@ -227,8 +227,6 @@ STATIC mp_obj_t stream_read1(size_t n_args, const mp_obj_t *args) {
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_read1_obj, 1, 2, stream_read1);
 
 mp_obj_t mp_stream_write(mp_obj_t self_in, const void *buf, size_t len, byte flags) {
-    mp_get_stream_raise(self_in, MP_STREAM_OP_WRITE);
-
     int error;
     mp_uint_t out_sz = mp_stream_rw(self_in, (void*)buf, len, &error, flags);
     if (error != 0) {
@@ -276,7 +274,6 @@ STATIC mp_obj_t stream_write1_method(mp_obj_t self_in, mp_obj_t arg) {
 MP_DEFINE_CONST_FUN_OBJ_2(mp_stream_write1_obj, stream_write1_method);
 
 STATIC mp_obj_t stream_readinto(size_t n_args, const mp_obj_t *args) {
-    mp_get_stream_raise(args[0], MP_STREAM_OP_READ);
     mp_buffer_info_t bufinfo;
     mp_get_buffer_raise(args[1], &bufinfo, MP_BUFFER_WRITE);
 
@@ -305,7 +302,7 @@ STATIC mp_obj_t stream_readinto(size_t n_args, const mp_obj_t *args) {
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_readinto_obj, 2, 3, stream_readinto);
 
 STATIC mp_obj_t stream_readall(mp_obj_t self_in) {
-    const mp_stream_p_t *stream_p = mp_get_stream_raise(self_in, MP_STREAM_OP_READ);
+    const mp_stream_p_t *stream_p = mp_get_stream(self_in);
 
     mp_uint_t total_size = 0;
     vstr_t vstr;
@@ -346,7 +343,7 @@ STATIC mp_obj_t stream_readall(mp_obj_t self_in) {
 
 // Unbuffered, inefficient implementation of readline() for raw I/O files.
 STATIC mp_obj_t stream_unbuffered_readline(size_t n_args, const mp_obj_t *args) {
-    const mp_stream_p_t *stream_p = mp_get_stream_raise(args[0], MP_STREAM_OP_READ);
+    const mp_stream_p_t *stream_p = mp_get_stream(args[0]);
 
     mp_int_t max_size = -1;
     if (n_args > 1) {
@@ -421,7 +418,7 @@ mp_obj_t mp_stream_unbuffered_iter(mp_obj_t self) {
 }
 
 mp_obj_t mp_stream_close(mp_obj_t stream) {
-    const mp_stream_p_t *stream_p = mp_get_stream_raise(stream, MP_STREAM_OP_IOCTL);
+    const mp_stream_p_t *stream_p = mp_get_stream(stream);
     int error;
     mp_uint_t res = stream_p->ioctl(stream, MP_STREAM_CLOSE, 0, &error);
     if (res == MP_STREAM_ERROR) {
@@ -432,8 +429,6 @@ mp_obj_t mp_stream_close(mp_obj_t stream) {
 MP_DEFINE_CONST_FUN_OBJ_1(mp_stream_close_obj, mp_stream_close);
 
 STATIC mp_obj_t stream_seek(size_t n_args, const mp_obj_t *args) {
-    const mp_stream_p_t *stream_p = mp_get_stream_raise(args[0], MP_STREAM_OP_IOCTL);
-
     struct mp_stream_seek_t seek_s;
     // TODO: Could be uint64
     seek_s.offset = mp_obj_get_int(args[1]);
@@ -447,6 +442,7 @@ STATIC mp_obj_t stream_seek(size_t n_args, const mp_obj_t *args) {
         mp_raise_OSError(MP_EINVAL);
     }
 
+    const mp_stream_p_t *stream_p = mp_get_stream(args[0]);
     int error;
     mp_uint_t res = stream_p->ioctl(args[0], MP_STREAM_SEEK, (mp_uint_t)(uintptr_t)&seek_s, &error);
     if (res == MP_STREAM_ERROR) {
@@ -467,7 +463,7 @@ STATIC mp_obj_t stream_tell(mp_obj_t self) {
 MP_DEFINE_CONST_FUN_OBJ_1(mp_stream_tell_obj, stream_tell);
 
 STATIC mp_obj_t stream_flush(mp_obj_t self) {
-    const mp_stream_p_t *stream_p = mp_get_stream_raise(self, MP_STREAM_OP_IOCTL);
+    const mp_stream_p_t *stream_p = mp_get_stream(self);
     int error;
     mp_uint_t res = stream_p->ioctl(self, MP_STREAM_FLUSH, 0, &error);
     if (res == MP_STREAM_ERROR) {
@@ -478,8 +474,6 @@ STATIC mp_obj_t stream_flush(mp_obj_t self) {
 MP_DEFINE_CONST_FUN_OBJ_1(mp_stream_flush_obj, stream_flush);
 
 STATIC mp_obj_t stream_ioctl(size_t n_args, const mp_obj_t *args) {
-    const mp_stream_p_t *stream_p = mp_get_stream_raise(args[0], MP_STREAM_OP_IOCTL);
-
     mp_buffer_info_t bufinfo;
     uintptr_t val = 0;
     if (n_args > 2) {
@@ -490,6 +484,7 @@ STATIC mp_obj_t stream_ioctl(size_t n_args, const mp_obj_t *args) {
         }
     }
 
+    const mp_stream_p_t *stream_p = mp_get_stream(args[0]);
     int error;
     mp_uint_t res = stream_p->ioctl(args[0], mp_obj_get_int(args[1]), val, &error);
     if (res == MP_STREAM_ERROR) {

py/stream.h

@@ -90,6 +90,11 @@ MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_ioctl_obj);
 #define MP_STREAM_OP_WRITE (2)
 #define MP_STREAM_OP_IOCTL (4)
 
+// Object is assumed to have a non-NULL stream protocol with valid r/w/ioctl methods
+static inline const mp_stream_p_t *mp_get_stream(mp_const_obj_t self) {
+    return (const mp_stream_p_t*)((const mp_obj_base_t*)MP_OBJ_TO_PTR(self))->type->protocol;
+}
+
 const mp_stream_p_t *mp_get_stream_raise(mp_obj_t self_in, int flags);
 mp_obj_t mp_stream_close(mp_obj_t stream);