socketpool: make socket objects selectable

.. which will lead to them being usable in async contexts, pending
relevant changes in asyncio

ports/espressif/common-hal/socketpool/Socket.c

@@ -553,3 +553,27 @@ mp_uint_t common_hal_socketpool_socket_sendto(socketpool_socket_obj_t *self,
 void common_hal_socketpool_socket_settimeout(socketpool_socket_obj_t *self, uint32_t timeout_ms) {
     self->timeout_ms = timeout_ms;
 }
+
+bool common_hal_socketpool_readable(socketpool_socket_obj_t *self) {
+    struct timeval immediate = {0, 0};
+
+    fd_set fds;
+    FD_ZERO(&fds);
+    FD_SET(self->num, &fds);
+    int num_triggered = select(self->num + 1, &fds, NULL, &fds, &immediate);
+
+    // including returning true in the error case
+    return num_triggered != 0;
+}
+
+bool common_hal_socketpool_writable(socketpool_socket_obj_t *self) {
+    struct timeval immediate = {0, 0};
+
+    fd_set fds;
+    FD_ZERO(&fds);
+    FD_SET(self->num, &fds);
+    int num_triggered = select(self->num + 1, NULL, &fds, &fds, &immediate);
+
+    // including returning true in the error case
+    return num_triggered != 0;
+}

ports/raspberrypi/common-hal/socketpool/Socket.c

@@ -1163,3 +1163,46 @@ mp_uint_t common_hal_socketpool_socket_sendto(socketpool_socket_obj_t *socket,
 void common_hal_socketpool_socket_settimeout(socketpool_socket_obj_t *self, uint32_t timeout_ms) {
     self->timeout = timeout_ms;
 }
+
+bool common_hal_socketpool_readable(socketpool_socket_obj_t *self) {
+
+    MICROPY_PY_LWIP_ENTER;
+
+    bool result = self->incoming.pbuf != NULL;
+
+    if (self->state == STATE_PEER_CLOSED) {
+        result = true;
+    }
+
+    if (self->type == SOCKETPOOL_SOCK_STREAM && self->pcb.tcp->state == LISTEN) {
+        struct tcp_pcb *volatile *incoming_connection = &lwip_socket_incoming_array(self)[self->incoming.connection.iget];
+        result = (incoming_connection != NULL);
+    }
+
+    MICROPY_PY_LWIP_EXIT;
+
+    return result;
+}
+
+bool common_hal_socketpool_writable(socketpool_socket_obj_t *self) {
+    bool result = false;
+
+    MICROPY_PY_LWIP_ENTER;
+
+    switch (self->type) {
+        case SOCKETPOOL_SOCK_STREAM: {
+            result = tcp_sndbuf(self->pcb.tcp) != 0;
+            break;
+        }
+        case SOCKETPOOL_SOCK_DGRAM:
+        #if MICROPY_PY_LWIP_SOCK_RAW
+        case SOCKETPOOL_SOCK_RAW:
+        #endif
+            result = true;
+            break;
+    }
+
+    MICROPY_PY_LWIP_EXIT;
+
+    return result;
+}

shared-bindings/socketpool/Socket.c

@@ -30,13 +30,14 @@
 #include <stdio.h>
 #include <string.h>
 
-#include "shared/runtime/context_manager_helpers.h"
-#include "py/objtuple.h"
-#include "py/objlist.h"
-#include "py/runtime.h"
 #include "py/mperrno.h"
+#include "py/objlist.h"
+#include "py/objtuple.h"
+#include "py/runtime.h"
+#include "py/stream.h"
 
 #include "shared/netutils/netutils.h"
+#include "shared/runtime/context_manager_helpers.h"
 #include "shared/runtime/interrupt_char.h"
 
 //| class Socket:
@@ -422,6 +423,31 @@ STATIC const mp_rom_map_elem_t socketpool_socket_locals_dict_table[] = {
 
 STATIC MP_DEFINE_CONST_DICT(socketpool_socket_locals_dict, socketpool_socket_locals_dict_table);
 
+STATIC mp_uint_t socket_ioctl(mp_obj_t self_in, mp_uint_t request, mp_uint_t arg, int *errcode) {
+    socketpool_socket_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    mp_uint_t ret;
+    if (request == MP_STREAM_POLL) {
+        mp_uint_t flags = arg;
+        ret = 0;
+        if ((flags & MP_STREAM_POLL_RD) && common_hal_socketpool_readable(self) > 0) {
+            ret |= MP_STREAM_POLL_RD;
+        }
+        if ((flags & MP_STREAM_POLL_WR) && common_hal_socketpool_writable(self)) {
+            ret |= MP_STREAM_POLL_WR;
+        }
+    } else {
+        *errcode = MP_EINVAL;
+        ret = MP_STREAM_ERROR;
+    }
+    return ret;
+}
+
+STATIC const mp_stream_p_t socket_stream_p = {
+    MP_PROTO_IMPLEMENT(MP_QSTR_protocol_stream)
+    .ioctl = socket_ioctl,
+    .is_text = false,
+};
+
 const mp_obj_type_t socketpool_socket_type = {
     { &mp_type_type },
     .flags = MP_TYPE_FLAG_EXTENDED,
@@ -429,5 +455,6 @@ const mp_obj_type_t socketpool_socket_type = {
     .locals_dict = (mp_obj_dict_t *)&socketpool_socket_locals_dict,
     MP_TYPE_EXTENDED_FIELDS(
         .unary_op = mp_generic_unary_op,
+        .protocol = &socket_stream_p,
         )
 };

shared-bindings/socketpool/Socket.h

@@ -46,6 +46,8 @@ mp_uint_t common_hal_socketpool_socket_send(socketpool_socket_obj_t *self, const
 mp_uint_t common_hal_socketpool_socket_sendto(socketpool_socket_obj_t *self,
     const char *host, size_t hostlen, uint32_t port, const uint8_t *buf, uint32_t len);
 void common_hal_socketpool_socket_settimeout(socketpool_socket_obj_t *self, uint32_t timeout_ms);
+bool common_hal_socketpool_readable(socketpool_socket_obj_t *self);
+bool common_hal_socketpool_writable(socketpool_socket_obj_t *self);
 
 // Non-allocating versions for internal use.
 int socketpool_socket_accept(socketpool_socket_obj_t *self, uint8_t *ip, uint32_t *port);
@@ -53,5 +55,4 @@ void socketpool_socket_close(socketpool_socket_obj_t *self);
 int socketpool_socket_send(socketpool_socket_obj_t *self, const uint8_t *buf, uint32_t len);
 int socketpool_socket_recv_into(socketpool_socket_obj_t *self,
     const uint8_t *buf, uint32_t len);
-
 #endif // MICROPY_INCLUDED_SHARED_BINDINGS_SOCKETPOOL_SOCKET_H