protocols: Allow them to be (optionally) type-safe

Protocols are nice, but there is no way for C code to verify whether
a type's "protocol" structure actually implements some particular
protocol.  As a result, you can pass an object that implements the
"vfs" protocol to one that expects the "stream" protocol, and the
opposite of awesomeness ensues.

This patch adds an OPTIONAL (but enabled by default) protocol identifier
as the first member of any protocol structure.  This identifier is
simply a unique QSTR chosen by the protocol designer and used by each
protocol implementer.  When checking for protocol support, instead of
just checking whether the object's type has a non-NULL protocol field,
use `mp_proto_get` which implements the protocol check when possible.

The existing protocols are now named:
    protocol_framebuf
    protocol_i2c
    protocol_pin
    protocol_stream
    protocol_spi
    protocol_vfs
(most of these are unused in CP and are just inherited from MP; vfs and
stream are definitely used though)

I did not find any crashing examples, but here's one to give a flavor of what
is improved, using `micropython_coverage`.  Before the change,
the vfs "ioctl" protocol is invoked, and the result is not intelligible
as json (but it could have resulted in a hard fault, potentially):

    >>> import uos, ujson
    >>> u = uos.VfsPosix('/tmp')
    >>> ujson.load(u)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ValueError: syntax error in JSON

After the change, the vfs object is correctly detected as not supporting
the stream protocol:
    >>> ujson.load(p)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    OSError: stream operation not supported

extmod/machine_i2c.c

@@ -318,7 +318,7 @@ MP_DEFINE_CONST_FUN_OBJ_KW(machine_i2c_init_obj, 1, machine_i2c_obj_init);
 
 STATIC mp_obj_t machine_i2c_scan(mp_obj_t self_in) {
     mp_obj_base_t *self = MP_OBJ_TO_PTR(self_in);
-    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)self->type->protocol;
+    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)mp_proto_get(self, QSTR_protocol_i2c);
     mp_obj_t list = mp_obj_new_list(0, NULL);
     // 7-bit addresses 0b0000xxx and 0b1111xxx are reserved
     for (int addr = 0x08; addr < 0x78; ++addr) {
@@ -333,7 +333,7 @@ MP_DEFINE_CONST_FUN_OBJ_1(machine_i2c_scan_obj, machine_i2c_scan);
 
 STATIC mp_obj_t machine_i2c_start(mp_obj_t self_in) {
     mp_obj_base_t *self = (mp_obj_base_t*)MP_OBJ_TO_PTR(self_in);
-    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)self->type->protocol;
+    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)mp_proto_get(self, QSTR_protocol_i2c);
     if (i2c_p->start == NULL) {
         mp_raise_msg(&mp_type_OSError, translate("I2C operation not supported"));
     }
@@ -347,7 +347,7 @@ MP_DEFINE_CONST_FUN_OBJ_1(machine_i2c_start_obj, machine_i2c_start);
 
 STATIC mp_obj_t machine_i2c_stop(mp_obj_t self_in) {
     mp_obj_base_t *self = (mp_obj_base_t*)MP_OBJ_TO_PTR(self_in);
-    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)self->type->protocol;
+    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)mp_proto_get(self, QSTR_protocol_i2c);
     if (i2c_p->stop == NULL) {
         mp_raise_msg(&mp_type_OSError, translate("I2C operation not supported"));
     }
@@ -361,7 +361,7 @@ MP_DEFINE_CONST_FUN_OBJ_1(machine_i2c_stop_obj, machine_i2c_stop);
 
 STATIC mp_obj_t machine_i2c_readinto(size_t n_args, const mp_obj_t *args) {
     mp_obj_base_t *self = (mp_obj_base_t*)MP_OBJ_TO_PTR(args[0]);
-    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)self->type->protocol;
+    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)mp_proto_get(self, QSTR_protocol_i2c);
     if (i2c_p->read == NULL) {
         mp_raise_msg(&mp_type_OSError, translate("I2C operation not supported"));
     }
@@ -385,7 +385,7 @@ MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(machine_i2c_readinto_obj, 2, 3, machine_i2c_
 
 STATIC mp_obj_t machine_i2c_write(mp_obj_t self_in, mp_obj_t buf_in) {
     mp_obj_base_t *self = (mp_obj_base_t*)MP_OBJ_TO_PTR(self_in);
-    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)self->type->protocol;
+    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)mp_proto_get(self, QSTR_protocol_i2c);
     if (i2c_p->write == NULL) {
         mp_raise_msg(&mp_type_OSError, translate("I2C operation not supported"));
     }
@@ -407,7 +407,7 @@ MP_DEFINE_CONST_FUN_OBJ_2(machine_i2c_write_obj, machine_i2c_write);
 
 STATIC mp_obj_t machine_i2c_readfrom(size_t n_args, const mp_obj_t *args) {
     mp_obj_base_t *self = (mp_obj_base_t*)MP_OBJ_TO_PTR(args[0]);
-    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)self->type->protocol;
+    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)mp_proto_get(self, QSTR_protocol_i2c);
     mp_int_t addr = mp_obj_get_int(args[1]);
     vstr_t vstr;
     vstr_init_len(&vstr, mp_obj_get_int(args[2]));
@@ -422,7 +422,7 @@ MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(machine_i2c_readfrom_obj, 3, 4, machine_i2c_
 
 STATIC mp_obj_t machine_i2c_readfrom_into(size_t n_args, const mp_obj_t *args) {
     mp_obj_base_t *self = (mp_obj_base_t*)MP_OBJ_TO_PTR(args[0]);
-    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)self->type->protocol;
+    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)mp_proto_get(self, QSTR_protocol_i2c);
     mp_int_t addr = mp_obj_get_int(args[1]);
     mp_buffer_info_t bufinfo;
     mp_get_buffer_raise(args[2], &bufinfo, MP_BUFFER_WRITE);
@@ -437,7 +437,7 @@ MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(machine_i2c_readfrom_into_obj, 3, 4, machine
 
 STATIC mp_obj_t machine_i2c_writeto(size_t n_args, const mp_obj_t *args) {
     mp_obj_base_t *self = (mp_obj_base_t*)MP_OBJ_TO_PTR(args[0]);
-    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)self->type->protocol;
+    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)mp_proto_get(self, QSTR_protocol_i2c);
     mp_int_t addr = mp_obj_get_int(args[1]);
     mp_buffer_info_t bufinfo;
     mp_get_buffer_raise(args[2], &bufinfo, MP_BUFFER_READ);
@@ -453,7 +453,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(machine_i2c_writeto_obj, 3, 4, machin
 
 STATIC int read_mem(mp_obj_t self_in, uint16_t addr, uint32_t memaddr, uint8_t addrsize, uint8_t *buf, size_t len) {
     mp_obj_base_t *self = (mp_obj_base_t*)MP_OBJ_TO_PTR(self_in);
-    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)self->type->protocol;
+    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)mp_proto_get(self, QSTR_protocol_i2c);
     uint8_t memaddr_buf[4];
     size_t memaddr_len = 0;
     for (int16_t i = addrsize - 8; i >= 0; i -= 8) {
@@ -473,7 +473,7 @@ STATIC int read_mem(mp_obj_t self_in, uint16_t addr, uint32_t memaddr, uint8_t a
 
 STATIC int write_mem(mp_obj_t self_in, uint16_t addr, uint32_t memaddr, uint8_t addrsize, const uint8_t *buf, size_t len) {
     mp_obj_base_t *self = (mp_obj_base_t*)MP_OBJ_TO_PTR(self_in);
-    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)self->type->protocol;
+    mp_machine_i2c_p_t *i2c_p = (mp_machine_i2c_p_t*)mp_proto_get(self, QSTR_protocol_i2c);
 
     // need some memory to create the buffer to send; try to use stack if possible
     uint8_t buf2_stack[MAX_MEMADDR_SIZE + BUF_STACK_SIZE];
@@ -621,6 +621,7 @@ int mp_machine_soft_i2c_write(mp_obj_base_t *self_in, const uint8_t *src, size_t
 }
 
 STATIC const mp_machine_i2c_p_t mp_machine_soft_i2c_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_i2c)
     .start = (int(*)(mp_obj_base_t*))mp_hal_i2c_start,
     .stop = (int(*)(mp_obj_base_t*))mp_hal_i2c_stop,
     .read = mp_machine_soft_i2c_read,

extmod/machine_i2c.h

@@ -27,10 +27,12 @@
 #define MICROPY_INCLUDED_EXTMOD_MACHINE_I2C_H
 
 #include "py/obj.h"
+#include "py/proto.h"
 
 // I2C protocol
 // the first 4 methods can be NULL, meaning operation is not supported
 typedef struct _mp_machine_i2c_p_t {
+    MP_PROTOCOL_HEAD
     int (*start)(mp_obj_base_t *obj);
     int (*stop)(mp_obj_base_t *obj);
     int (*read)(mp_obj_base_t *obj, uint8_t *dest, size_t len, bool nack);

extmod/machine_pinbase.c

@@ -74,6 +74,7 @@ mp_uint_t pinbase_ioctl(mp_obj_t obj, mp_uint_t request, uintptr_t arg, int *err
 }
 
 STATIC const mp_pin_p_t pinbase_pin_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_pin)
     .ioctl = pinbase_ioctl,
 };
 

extmod/machine_signal.c

@@ -47,12 +47,7 @@ STATIC mp_obj_t signal_make_new(const mp_obj_type_t *type, size_t n_args, const
     bool invert = false;
 
     #if defined(MICROPY_PY_MACHINE_PIN_MAKE_NEW)
-    mp_pin_p_t *pin_p = NULL;
+    mp_pin_p_t *pin_p = (mp_pin_t*)mp_proto_get(QSTR_pin_protocol, pin);
-
-    if (MP_OBJ_IS_OBJ(pin)) {
-        mp_obj_base_t *pin_base = (mp_obj_base_t*)MP_OBJ_TO_PTR(args[0]);
-        pin_p = (mp_pin_p_t*)pin_base->type->protocol;
-    }
 
     if (pin_p == NULL) {
         // If first argument isn't a Pin-like object, we filter out "invert"
@@ -170,6 +165,7 @@ STATIC const mp_rom_map_elem_t signal_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(signal_locals_dict, signal_locals_dict_table);
 
 STATIC const mp_pin_p_t signal_pin_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_pin)
     .ioctl = signal_ioctl,
 };
 

extmod/machine_spi.c

@@ -67,7 +67,7 @@ mp_obj_t mp_machine_spi_make_new(const mp_obj_type_t *type, size_t n_args, const
 
 STATIC mp_obj_t machine_spi_init(size_t n_args, const mp_obj_t *args, mp_map_t *kw_args) {
     mp_obj_base_t *s = (mp_obj_base_t*)MP_OBJ_TO_PTR(args[0]);
-    mp_machine_spi_p_t *spi_p = (mp_machine_spi_p_t*)s->type->protocol;
+    mp_machine_spi_p_t *spi_p = (mp_machine_spi_p_t*)mp_proto_get(QSTR_protocol_spi, s);
     spi_p->init(s, n_args - 1, args + 1, kw_args);
     return mp_const_none;
 }
@@ -75,7 +75,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_KW(machine_spi_init_obj, 1, machine_spi_init);
 
 STATIC mp_obj_t machine_spi_deinit(mp_obj_t self) {
     mp_obj_base_t *s = (mp_obj_base_t*)MP_OBJ_TO_PTR(self);
-    mp_machine_spi_p_t *spi_p = (mp_machine_spi_p_t*)s->type->protocol;
+    mp_machine_spi_p_t *spi_p = (mp_machine_spi_p_t*)mp_proto_get(QSTR_protocol_spi, s);
     if (spi_p->deinit != NULL) {
         spi_p->deinit(s);
     }
@@ -85,7 +85,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_1(machine_spi_deinit_obj, machine_spi_deinit);
 
 STATIC void mp_machine_spi_transfer(mp_obj_t self, size_t len, const void *src, void *dest) {
     mp_obj_base_t *s = (mp_obj_base_t*)MP_OBJ_TO_PTR(self);
-    mp_machine_spi_p_t *spi_p = (mp_machine_spi_p_t*)s->type->protocol;
+    mp_machine_spi_p_t *spi_p = (mp_machine_spi_p_t*)mp_proto_get(QSTR_protocol_spi, s);
     spi_p->transfer(s, len, src, dest);
 }
 
@@ -268,6 +268,7 @@ STATIC void mp_machine_soft_spi_transfer(mp_obj_base_t *self_in, size_t len, con
 }
 
 const mp_machine_spi_p_t mp_machine_soft_spi_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_spi)
     .init = mp_machine_soft_spi_init,
     .deinit = NULL,
     .transfer = mp_machine_soft_spi_transfer,

extmod/machine_spi.h

@@ -27,11 +27,13 @@
 #define MICROPY_INCLUDED_EXTMOD_MACHINE_SPI_H
 
 #include "py/obj.h"
+#include "py/proto.h"
 #include "py/mphal.h"
 #include "drivers/bus/spi.h"
 
 // SPI protocol
 typedef struct _mp_machine_spi_p_t {
+    MP_PROTOCOL_HEAD
     void (*init)(mp_obj_base_t *obj, size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args);
     void (*deinit)(mp_obj_base_t *obj); // can be NULL
     void (*transfer)(mp_obj_base_t *obj, size_t len, const uint8_t *src, uint8_t *dest);

extmod/modframebuf.c

@@ -28,6 +28,7 @@
 #include <string.h>
 
 #include "py/runtime.h"
+#include "py/proto.h"
 
 #if MICROPY_PY_FRAMEBUF
 
@@ -46,6 +47,7 @@ typedef uint32_t (*getpixel_t)(const mp_obj_framebuf_t*, int, int);
 typedef void (*fill_rect_t)(const mp_obj_framebuf_t *, int, int, int, int, uint32_t);
 
 typedef struct _mp_framebuf_p_t {
+    MP_PROTOCOL_HEAD
     setpixel_t setpixel;
     getpixel_t getpixel;
     fill_rect_t fill_rect;
@@ -227,13 +229,13 @@ STATIC void gs8_fill_rect(const mp_obj_framebuf_t *fb, int x, int y, int w, int
 }
 
 STATIC mp_framebuf_p_t formats[] = {
-    [FRAMEBUF_MVLSB] = {mvlsb_setpixel, mvlsb_getpixel, mvlsb_fill_rect},
+    [FRAMEBUF_MVLSB] = {MP_PROTO_IMPLEMENT(MP_QSTR_protocol_framebuf) mvlsb_setpixel, mvlsb_getpixel, mvlsb_fill_rect},
-    [FRAMEBUF_RGB565] = {rgb565_setpixel, rgb565_getpixel, rgb565_fill_rect},
+    [FRAMEBUF_RGB565] = {MP_PROTO_IMPLEMENT(MP_QSTR_protocol_framebuf) rgb565_setpixel, rgb565_getpixel, rgb565_fill_rect},
-    [FRAMEBUF_GS2_HMSB] = {gs2_hmsb_setpixel, gs2_hmsb_getpixel, gs2_hmsb_fill_rect},
+    [FRAMEBUF_GS2_HMSB] = {MP_PROTO_IMPLEMENT(MP_QSTR_protocol_framebuf) gs2_hmsb_setpixel, gs2_hmsb_getpixel, gs2_hmsb_fill_rect},
-    [FRAMEBUF_GS4_HMSB] = {gs4_hmsb_setpixel, gs4_hmsb_getpixel, gs4_hmsb_fill_rect},
+    [FRAMEBUF_GS4_HMSB] = {MP_PROTO_IMPLEMENT(MP_QSTR_protocol_framebuf) gs4_hmsb_setpixel, gs4_hmsb_getpixel, gs4_hmsb_fill_rect},
-    [FRAMEBUF_GS8] = {gs8_setpixel, gs8_getpixel, gs8_fill_rect},
+    [FRAMEBUF_GS8] = {MP_PROTO_IMPLEMENT(MP_QSTR_protocol_framebuf) gs8_setpixel, gs8_getpixel, gs8_fill_rect},
-    [FRAMEBUF_MHLSB] = {mono_horiz_setpixel, mono_horiz_getpixel, mono_horiz_fill_rect},
+    [FRAMEBUF_MHLSB] = {MP_PROTO_IMPLEMENT(MP_QSTR_protocol_framebuf) mono_horiz_setpixel, mono_horiz_getpixel, mono_horiz_fill_rect},
-    [FRAMEBUF_MHMSB] = {mono_horiz_setpixel, mono_horiz_getpixel, mono_horiz_fill_rect},
+    [FRAMEBUF_MHMSB] = {MP_PROTO_IMPLEMENT(MP_QSTR_protocol_framebuf) mono_horiz_setpixel, mono_horiz_getpixel, mono_horiz_fill_rect},
 };
 
 static inline void setpixel(const mp_obj_framebuf_t *fb, int x, int y, uint32_t col) {

extmod/modlwip.c

@@ -1261,6 +1261,7 @@ STATIC const mp_rom_map_elem_t lwip_socket_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(lwip_socket_locals_dict, lwip_socket_locals_dict_table);
 
 STATIC const mp_stream_p_t lwip_socket_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = lwip_socket_read,
     .write = lwip_socket_write,
     .ioctl = lwip_socket_ioctl,

extmod/modussl_axtls.c

@@ -221,6 +221,7 @@ STATIC const mp_rom_map_elem_t ussl_socket_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(ussl_socket_locals_dict, ussl_socket_locals_dict_table);
 
 STATIC const mp_stream_p_t ussl_socket_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = socket_read,
     .write = socket_write,
     .ioctl = socket_ioctl,

extmod/modussl_mbedtls.c

@@ -305,6 +305,7 @@ STATIC const mp_rom_map_elem_t ussl_socket_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(ussl_socket_locals_dict, ussl_socket_locals_dict_table);
 
 STATIC const mp_stream_p_t ussl_socket_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = socket_read,
     .write = socket_write,
     .ioctl = socket_ioctl,

extmod/moduzlib.c

@@ -134,6 +134,7 @@ STATIC const mp_rom_map_elem_t decompio_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(decompio_locals_dict, decompio_locals_dict_table);
 
 STATIC const mp_stream_p_t decompio_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = decompio_read,
 };
 

extmod/modwebrepl.c

@@ -331,6 +331,7 @@ STATIC const mp_rom_map_elem_t webrepl_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(webrepl_locals_dict, webrepl_locals_dict_table);
 
 STATIC const mp_stream_p_t webrepl_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = webrepl_read,
     .write = webrepl_write,
     .ioctl = webrepl_ioctl,

extmod/modwebsocket.c

@@ -286,6 +286,7 @@ STATIC const mp_rom_map_elem_t websocket_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(websocket_locals_dict, websocket_locals_dict_table);
 
 STATIC const mp_stream_p_t websocket_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = websocket_read,
     .write = websocket_write,
     .ioctl = websocket_ioctl,

extmod/vfs.c

@@ -126,7 +126,7 @@ mp_import_stat_t mp_vfs_import_stat(const char *path) {
     }
 
     // If the mounted object has the VFS protocol, call its import_stat helper
-    const mp_vfs_proto_t *proto = mp_obj_get_type(vfs->obj)->protocol;
+    const mp_vfs_proto_t *proto = (mp_vfs_proto_t*)mp_proto_get(MP_QSTR_protocol_vfs, vfs->obj);
     if (proto != NULL) {
         return proto->import_stat(MP_OBJ_TO_PTR(vfs->obj), path_out);
     }

extmod/vfs.h

@@ -28,6 +28,7 @@
 
 #include "py/lexer.h"
 #include "py/obj.h"
+#include "py/proto.h"
 
 // return values of mp_vfs_lookup_path
 // ROOT is 0 so that the default current directory is the root directory
@@ -47,6 +48,7 @@
 
 // At the moment the VFS protocol just has import_stat, but could be extended to other methods
 typedef struct _mp_vfs_proto_t {
+    MP_PROTOCOL_HEAD
     mp_import_stat_t (*import_stat)(void *self, const char *path);
 } mp_vfs_proto_t;
 

extmod/vfs_fat.c

@@ -488,6 +488,7 @@ STATIC const mp_rom_map_elem_t fat_vfs_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(fat_vfs_locals_dict, fat_vfs_locals_dict_table);
 
 STATIC const mp_vfs_proto_t fat_vfs_proto = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_vfs)
     .import_stat = fat_vfs_import_stat,
 };
 

extmod/vfs_fat_file.c

@@ -254,6 +254,7 @@ STATIC MP_DEFINE_CONST_DICT(rawfile_locals_dict, rawfile_locals_dict_table);
 
 #if MICROPY_PY_IO_FILEIO
 STATIC const mp_stream_p_t fileio_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = file_obj_read,
     .write = file_obj_write,
     .ioctl = file_obj_ioctl,
@@ -272,6 +273,7 @@ const mp_obj_type_t mp_type_vfs_fat_fileio = {
 #endif
 
 STATIC const mp_stream_p_t textio_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = file_obj_read,
     .write = file_obj_write,
     .ioctl = file_obj_ioctl,

extmod/vfs_posix.c

@@ -350,6 +350,7 @@ STATIC const mp_rom_map_elem_t vfs_posix_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(vfs_posix_locals_dict, vfs_posix_locals_dict_table);
 
 STATIC const mp_vfs_proto_t vfs_posix_proto = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_vfs)
     .import_stat = mp_vfs_posix_import_stat,
 };
 

extmod/vfs_posix_file.c

@@ -220,6 +220,7 @@ STATIC MP_DEFINE_CONST_DICT(rawfile_locals_dict, rawfile_locals_dict_table);
 
 #if MICROPY_PY_IO_FILEIO
 STATIC const mp_stream_p_t fileio_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = vfs_posix_file_read,
     .write = vfs_posix_file_write,
     .ioctl = vfs_posix_file_ioctl,
@@ -238,6 +239,7 @@ const mp_obj_type_t mp_type_vfs_posix_fileio = {
 #endif
 
 STATIC const mp_stream_p_t textio_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = vfs_posix_file_read,
     .write = vfs_posix_file_write,
     .ioctl = vfs_posix_file_ioctl,

extmod/virtpin.c

@@ -25,15 +25,16 @@
  */
 
 #include "extmod/virtpin.h"
+#include "py/proto.h"
 
 int mp_virtual_pin_read(mp_obj_t pin) {
     mp_obj_base_t* s = (mp_obj_base_t*)MP_OBJ_TO_PTR(pin);
-    mp_pin_p_t *pin_p = (mp_pin_p_t*)s->type->protocol;
+    const mp_pin_p_t *pin_p = mp_proto_get(MP_QSTR_protocol_pin, s);
     return pin_p->ioctl(pin, MP_PIN_READ, 0, NULL);
 }
 
 void mp_virtual_pin_write(mp_obj_t pin, int value) {
     mp_obj_base_t* s = (mp_obj_base_t*)MP_OBJ_TO_PTR(pin);
-    mp_pin_p_t *pin_p = (mp_pin_p_t*)s->type->protocol;
+    const mp_pin_p_t *pin_p = mp_proto_get(MP_QSTR_protocol_pin, s);
     pin_p->ioctl(pin, MP_PIN_WRITE, value, NULL);
 }

extmod/virtpin.h

@@ -27,6 +27,7 @@
 #define MICROPY_INCLUDED_EXTMOD_VIRTPIN_H
 
 #include "py/obj.h"
+#include "py/proto.h"
 
 #define MP_PIN_READ   (1)
 #define MP_PIN_WRITE  (2)
@@ -35,6 +36,7 @@
 
 // Pin protocol
 typedef struct _mp_pin_p_t {
+    MP_PROTOCOL_HEAD
     mp_uint_t (*ioctl)(mp_obj_t obj, mp_uint_t request, uintptr_t arg, int *errcode);
 } mp_pin_p_t;
 

lib/utils/sys_stdio_mphal.c

@@ -123,6 +123,7 @@ STATIC const mp_rom_map_elem_t stdio_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(stdio_locals_dict, stdio_locals_dict_table);
 
 STATIC const mp_stream_p_t stdio_obj_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = stdio_read,
     .write = stdio_write,
     .ioctl = stdio_ioctl,
@@ -158,6 +159,7 @@ STATIC mp_uint_t stdio_buffer_write(mp_obj_t self_in, const void *buf, mp_uint_t
 }
 
 STATIC const mp_stream_p_t stdio_buffer_obj_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = stdio_buffer_read,
     .write = stdio_buffer_write,
     .is_text = false,

ports/unix/coverage.c

@@ -96,6 +96,7 @@ STATIC const mp_rom_map_elem_t rawfile_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(rawfile_locals_dict, rawfile_locals_dict_table);
 
 STATIC const mp_stream_p_t fileio_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = stest_read,
     .write = stest_write,
     .ioctl = stest_ioctl,
@@ -123,6 +124,7 @@ STATIC const mp_rom_map_elem_t rawfile_locals_dict_table2[] = {
 STATIC MP_DEFINE_CONST_DICT(rawfile_locals_dict2, rawfile_locals_dict_table2);
 
 STATIC const mp_stream_p_t textio_stream_p2 = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = stest_read2,
     .write = NULL,
     .is_text = true,

ports/unix/file.c

@@ -230,6 +230,7 @@ STATIC MP_DEFINE_CONST_DICT(rawfile_locals_dict, rawfile_locals_dict_table);
 
 #if MICROPY_PY_IO_FILEIO
 STATIC const mp_stream_p_t fileio_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = fdfile_read,
     .write = fdfile_write,
     .ioctl = fdfile_ioctl,
@@ -248,6 +249,7 @@ const mp_obj_type_t mp_type_fileio = {
 #endif
 
 STATIC const mp_stream_p_t textio_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = fdfile_read,
     .write = fdfile_write,
     .ioctl = fdfile_ioctl,

ports/unix/modusocket.c

@@ -374,6 +374,7 @@ STATIC const mp_rom_map_elem_t usocket_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(usocket_locals_dict, usocket_locals_dict_table);
 
 STATIC const mp_stream_p_t usocket_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = socket_read,
     .write = socket_write,
     .ioctl = socket_ioctl,

py/modio.c

@@ -90,6 +90,7 @@ STATIC mp_uint_t iobase_ioctl(mp_obj_t obj, mp_uint_t request, uintptr_t arg, in
 }
 
 STATIC const mp_stream_p_t iobase_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = iobase_read,
     .write = iobase_write,
     .ioctl = iobase_ioctl,
@@ -185,6 +186,7 @@ STATIC const mp_rom_map_elem_t bufwriter_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(bufwriter_locals_dict, bufwriter_locals_dict_table);
 
 STATIC const mp_stream_p_t bufwriter_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .write = bufwriter_write,
 };
 

py/objstringio.c

@@ -240,6 +240,7 @@ STATIC const mp_rom_map_elem_t stringio_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(stringio_locals_dict, stringio_locals_dict_table);
 
 STATIC const mp_stream_p_t stringio_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = stringio_read,
     .write = stringio_write,
     .ioctl = stringio_ioctl,
@@ -247,6 +248,7 @@ STATIC const mp_stream_p_t stringio_stream_p = {
 };
 
 STATIC const mp_stream_p_t bytesio_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = stringio_read,
     .write = stringio_write,
     .ioctl = stringio_ioctl,

py/proto.c

@@ -0,0 +1,50 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2019 Jeff Epler for Adafruit Industries
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "py/obj.h"
+#include "py/proto.h"
+#include "py/runtime.h"
+
+#ifndef MICROPY_UNSAFE_PROTO
+const void *mp_proto_get(uint16_t name, mp_const_obj_t obj) {
+    mp_obj_type_t *type = mp_obj_get_type(obj);
+    if (!type->protocol) return NULL;
+    uint16_t proto_name = *(const uint16_t*) type->protocol;
+    if (proto_name == name) {
+        return type->protocol;
+    }
+    return NULL;
+}
+#endif
+
+const void *mp_proto_get_or_throw(uint16_t name, mp_const_obj_t obj) {
+    const void *proto = mp_proto_get(name, obj);
+    if (proto) {
+        return proto;
+    }
+    mp_raise_TypeError_varg(translate("'%s' object does not support '%s'"), 
+        mp_obj_get_type_str(obj), qstr_str(name));
+}

py/proto.h

@@ -0,0 +1,43 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2019 Jeff Epler for Adafruit Industries
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef MICROPY_INCLUDED_PY_PROTO_H
+#define MICROPY_INCLUDED_PY_PROTO_H
+
+#ifdef MICROPY_UNSAFE_PROTO
+#define MP_PROTOCOL_HEAD /* NOTHING */
+#define MP_PROTO_IMPLEMENT(name) /* NOTHING */
+static inline void *mp_proto_get(uint16_t name, mp_const_obj_type_t obj) { return mp_obj_get_type(obj)->protocol; }
+#else
+#define MP_PROTOCOL_HEAD \
+    uint16_t name; // The name of this protocol, a qstr
+#define MP_PROTO_IMPLEMENT(n) .name = n,
+const void *mp_proto_get(uint16_t name, mp_const_obj_t obj);
+const void *mp_proto_get_or_throw(uint16_t name, mp_const_obj_t obj);
+#endif
+
+#endif
+

py/py.mk

@@ -214,6 +214,7 @@ PY_CORE_O_BASENAME = $(addprefix py/,\
 	objtype.o \
 	objzip.o \
 	opmethods.o \
+	proto.o \
 	reload.o \
 	sequence.o \
 	stream.o \

py/stream.c

@@ -86,8 +86,7 @@ mp_uint_t mp_stream_rw(mp_obj_t stream, void *buf_, mp_uint_t size, int *errcode
 }
 
 const mp_stream_p_t *mp_get_stream_raise(mp_obj_t self_in, int flags) {
-    mp_obj_type_t *type = mp_obj_get_type(self_in);
+    const mp_stream_p_t *stream_p = mp_proto_get(MP_QSTR_protocol_stream, self_in);
-    const mp_stream_p_t *stream_p = type->protocol;
     if (stream_p == NULL
         || ((flags & MP_STREAM_OP_READ) && stream_p->read == NULL)
         || ((flags & MP_STREAM_OP_WRITE) && stream_p->write == NULL)
@@ -522,7 +521,7 @@ int mp_stream_errno;
 
 ssize_t mp_stream_posix_write(mp_obj_t stream, const void *buf, size_t len) {
     mp_obj_base_t* o = (mp_obj_base_t*)MP_OBJ_TO_PTR(stream);
-    const mp_stream_p_t *stream_p = o->type->protocol;
+    const mp_stream_p_t *stream_p = mp_get_stream(o);
     mp_uint_t out_sz = stream_p->write(stream, buf, len, &mp_stream_errno);
     if (out_sz == MP_STREAM_ERROR) {
         return -1;
@@ -533,7 +532,7 @@ ssize_t mp_stream_posix_write(mp_obj_t stream, const void *buf, size_t len) {
 
 ssize_t mp_stream_posix_read(mp_obj_t stream, void *buf, size_t len) {
     mp_obj_base_t* o = (mp_obj_base_t*)MP_OBJ_TO_PTR(stream);
-    const mp_stream_p_t *stream_p = o->type->protocol;
+    const mp_stream_p_t *stream_p = mp_get_stream(o);
     mp_uint_t out_sz = stream_p->read(stream, buf, len, &mp_stream_errno);
     if (out_sz == MP_STREAM_ERROR) {
         return -1;
@@ -544,7 +543,7 @@ ssize_t mp_stream_posix_read(mp_obj_t stream, void *buf, size_t len) {
 
 off_t mp_stream_posix_lseek(mp_obj_t stream, off_t offset, int whence) {
     const mp_obj_base_t* o = (mp_obj_base_t*)MP_OBJ_TO_PTR(stream);
-    const mp_stream_p_t *stream_p = o->type->protocol;
+    const mp_stream_p_t *stream_p = mp_get_stream(o);
     struct mp_stream_seek_t seek_s;
     seek_s.offset = offset;
     seek_s.whence = whence;
@@ -557,7 +556,7 @@ off_t mp_stream_posix_lseek(mp_obj_t stream, off_t offset, int whence) {
 
 int mp_stream_posix_fsync(mp_obj_t stream) {
     mp_obj_base_t* o = (mp_obj_base_t*)MP_OBJ_TO_PTR(stream);
-    const mp_stream_p_t *stream_p = o->type->protocol;
+    const mp_stream_p_t *stream_p = mp_get_stream(o);
     mp_uint_t res = stream_p->ioctl(stream, MP_STREAM_FLUSH, 0, &mp_stream_errno);
     if (res == MP_STREAM_ERROR) {
         return -1;

py/stream.h

@@ -27,6 +27,7 @@
 #define MICROPY_INCLUDED_PY_STREAM_H
 
 #include "py/obj.h"
+#include "py/proto.h"
 #include "py/mperrno.h"
 
 #define MP_STREAM_ERROR ((mp_uint_t)-1)
@@ -64,6 +65,7 @@ struct mp_stream_seek_t {
 
 // Stream protocol
 typedef struct _mp_stream_p_t {
+    MP_PROTOCOL_HEAD
     // On error, functions should return MP_STREAM_ERROR and fill in *errcode (values
     // are implementation-dependent, but will be exposed to user, e.g. via exception).
     mp_uint_t (*read)(mp_obj_t obj, void *buf, mp_uint_t size, int *errcode);
@@ -93,7 +95,7 @@ MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_stream_ioctl_obj);
 
 // 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;
+    return mp_proto_get(MP_QSTR_protocol_stream, self); 
 }
 
 const mp_stream_p_t *mp_get_stream_raise(mp_obj_t self_in, int flags);

shared-bindings/_bleio/CharacteristicBuffer.c

@@ -230,6 +230,7 @@ STATIC const mp_rom_map_elem_t bleio_characteristic_buffer_locals_dict_table[] =
 STATIC MP_DEFINE_CONST_DICT(bleio_characteristic_buffer_locals_dict, bleio_characteristic_buffer_locals_dict_table);
 
 STATIC const mp_stream_p_t characteristic_buffer_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = bleio_characteristic_buffer_read,
     .write = bleio_characteristic_buffer_write,
     .ioctl = bleio_characteristic_buffer_ioctl,

shared-bindings/busio/UART.c

@@ -398,6 +398,7 @@ STATIC const mp_rom_map_elem_t busio_uart_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(busio_uart_locals_dict, busio_uart_locals_dict_table);
 
 STATIC const mp_stream_p_t uart_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = busio_uart_read,
     .write = busio_uart_write,
     .ioctl = busio_uart_ioctl,

shared-bindings/socket/__init__.c

@@ -500,6 +500,7 @@ mp_uint_t socket_ioctl(mp_obj_t self_in, mp_uint_t request, uintptr_t arg, int *
 }
 
 STATIC const mp_stream_p_t socket_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .ioctl = socket_ioctl,
     .is_text = false,
 };

shared-bindings/terminalio/Terminal.c

@@ -112,6 +112,7 @@ STATIC const mp_rom_map_elem_t terminalio_terminal_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(terminalio_terminal_locals_dict, terminalio_terminal_locals_dict_table);
 
 STATIC const mp_stream_p_t terminalio_terminal_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = NULL,
     .write = terminalio_terminal_write,
     .ioctl = terminalio_terminal_ioctl,

shared-bindings/usb_midi/PortIn.c

@@ -107,6 +107,7 @@ STATIC const mp_rom_map_elem_t usb_midi_portin_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(usb_midi_portin_locals_dict, usb_midi_portin_locals_dict_table);
 
 STATIC const mp_stream_p_t usb_midi_portin_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = usb_midi_portin_read,
     .write = NULL,
     .ioctl = usb_midi_portin_ioctl,

shared-bindings/usb_midi/PortOut.c

@@ -89,6 +89,7 @@ STATIC const mp_rom_map_elem_t usb_midi_portout_locals_dict_table[] = {
 STATIC MP_DEFINE_CONST_DICT(usb_midi_portout_locals_dict, usb_midi_portout_locals_dict_table);
 
 STATIC const mp_stream_p_t usb_midi_portout_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
     .read = NULL,
     .write = usb_midi_portout_write,
     .ioctl = usb_midi_portout_ioctl,