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

Author: jepler

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;
-
-    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;
-    }
+    mp_pin_p_t *pin_p = (mp_pin_t*)mp_proto_get(QSTR_pin_protocol, pin);
 
     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

@@ -67,15 +67,15 @@ 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;
 }
 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_RGB565] = {rgb565_setpixel, rgb565_getpixel, rgb565_fill_rect},
-    [FRAMEBUF_GS2_HMSB] = {gs2_hmsb_setpixel, gs2_hmsb_getpixel, gs2_hmsb_fill_rect},
-    [FRAMEBUF_GS4_HMSB] = {gs4_hmsb_setpixel, gs4_hmsb_getpixel, gs4_hmsb_fill_rect},
-    [FRAMEBUF_GS8] = {gs8_setpixel, gs8_getpixel, gs8_fill_rect},
-    [FRAMEBUF_MHLSB] = {mono_horiz_setpixel, mono_horiz_getpixel, mono_horiz_fill_rect},
-    [FRAMEBUF_MHMSB] = {mono_horiz_setpixel, mono_horiz_getpixel, mono_horiz_fill_rect},
+    [FRAMEBUF_MVLSB] = {MP_PROTO_IMPLEMENT(MP_QSTR_protocol_framebuf) mvlsb_setpixel, mvlsb_getpixel, mvlsb_fill_rect},
+    [FRAMEBUF_RGB565] = {MP_PROTO_IMPLEMENT(MP_QSTR_protocol_framebuf) rgb565_setpixel, rgb565_getpixel, rgb565_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] = {MP_PROTO_IMPLEMENT(MP_QSTR_protocol_framebuf) gs4_hmsb_setpixel, gs4_hmsb_getpixel, gs4_hmsb_fill_rect},
+    [FRAMEBUF_GS8] = {MP_PROTO_IMPLEMENT(MP_QSTR_protocol_framebuf) gs8_setpixel, gs8_getpixel, gs8_fill_rect},
+    [FRAMEBUF_MHLSB] = {MP_PROTO_IMPLEMENT(MP_QSTR_protocol_framebuf) 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,