[kernel] Replace endpoint with new mailbox API

The new mailbox kernel object API offers asynchronous message-based IPC
for sending data and handles between threads, as opposed to endpoint's
synchronous model.

src/user/test_runner/test_runner.module

@@ -10,6 +10,7 @@ module("test_runner",
 
         "tests/constexpr_hash.cpp",
         "tests/linked_list.cpp",
+        "tests/mailbox.cpp",
         "tests/map.cpp",
         "tests/vector.cpp",
     ])

src/user/test_runner/tests/mailbox.cpp

@@ -0,0 +1,87 @@
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+
+#include <j6/errors.h>
+#include <j6/flags.h>
+#include <j6/types.h>
+#include <j6/syscalls.h>
+
+#include "test_case.h"
+#include "test_rng.h"
+
+struct mailbox_tests :
+    public test::fixture
+{
+};
+
+TEST_CASE( mailbox_tests, would_block )
+{
+    j6_handle_t mb = j6_handle_invalid;
+    j6_status_t s;
+
+    s = j6_mailbox_create(&mb);
+    CHECK( s == j6_status_ok, "Could not create a mailbox" );
+
+    uint64_t tag = 12345;
+    uint8_t buffer[128];
+    size_t buffer_size = 128;
+    j6_handle_t handles[10];
+    size_t handle_count = 10;
+    uint64_t reply_tag = 0;
+    uint64_t badge = 0;
+    uint64_t flags = 0;
+
+    s = j6_mailbox_receive( mb, &tag,
+            buffer, &buffer_size,
+            handles, &handle_count,
+            &reply_tag, &badge,
+            flags );
+    CHECK( s == j6_status_would_block, "Should have gotten would block error" );
+
+    j6_mailbox_close(mb);
+}
+
+TEST_CASE( mailbox_tests, send_receive )
+{
+    j6_handle_t mb = j6_handle_invalid;
+    j6_status_t s;
+
+    s = j6_mailbox_create(&mb);
+    CHECK( s == j6_status_ok, "Could not create a mailbox" );
+
+    uint64_t out_tag = 12345;
+    uint8_t out_buffer[128] = {2, 4, 6, 8, 10, 12, 14};
+    size_t out_buffer_size = 7;
+    j6_handle_t out_handles[10];
+    size_t out_handle_count = 0;
+
+    s = j6_mailbox_send( mb, out_tag,
+            out_buffer, out_buffer_size,
+            out_handles, out_handle_count );
+    CHECK( s == j6_status_ok, "Did not send successfully" );
+
+    uint64_t in_tag = 0;
+    uint8_t in_buffer[128];
+    size_t in_buffer_size = 128;
+    j6_handle_t in_handles[10];
+    size_t in_handle_count = 10;
+    uint64_t in_reply_tag = 0;
+    uint64_t in_badge = 0;
+    uint64_t in_flags = 0;
+
+    s = j6_mailbox_receive( mb, &in_tag,
+            in_buffer, &in_buffer_size,
+            in_handles, &in_handle_count,
+            &in_reply_tag, &in_badge,
+            in_flags );
+    CHECK( s == j6_status_ok, "Did not receive successfully" );
+
+    CHECK_BARE( in_tag == out_tag );
+    CHECK_BARE( in_buffer_size == out_buffer_size );
+    CHECK_BARE( in_handle_count == out_handle_count );
+
+    CHECK_BARE( memcmp(out_buffer, in_buffer, in_buffer_size) == 0 );
+
+    j6_mailbox_close(mb);
+}