Add JANET_MARSH_UNSAFE flag.

This allows unmarshal to optional marshal raw
pointers and cfunctions and send them across threads.
This flag is only exposed in the C API as it is very easy
to misuse and cause segfaults.

src/core/marsh.c

@@ -61,7 +61,9 @@ enum {
     LB_ABSTRACT, /* 217 */
     LB_REFERENCE, /* 218 */
     LB_FUNCENV_REF, /* 219 */
-    LB_FUNCDEF_REF /* 220 */
+    LB_FUNCDEF_REF, /* 220 */
+    LB_UNSAFE_CFUNCTION, /* 221 */
+    LB_UNSAFE_POINTER /* 222 */
 } LeadBytes;
 
 /* Helper to look inside an entry in an environment */
@@ -563,9 +565,25 @@ static void marshal_one(MarshalState *st, Janet x, int flags) {
             marshal_one_fiber(st, janet_unwrap_fiber(x), flags + 1);
             return;
         }
+        case JANET_CFUNCTION: {
+            if (!(flags & JANET_MARSHAL_UNSAFE)) goto no_registry;
+            MARK_SEEN();
+            pushbyte(st, LB_UNSAFE_CFUNCTION);
+            JanetCFunction cfn = janet_unwrap_cfunction(x);
+            pushbytes(st, (uint8_t *) &cfn, sizeof(JanetCFunction));
+            return;
+        }
+        case JANET_POINTER: {
+            if (!(flags & JANET_MARSHAL_UNSAFE)) goto no_registry;
+            MARK_SEEN();
+            pushbyte(st, LB_UNSAFE_POINTER);
+            void *ptr = janet_unwrap_pointer(x);
+            pushbytes(st, (uint8_t *) &ptr, sizeof(void *));
+            return;
+        }
+    no_registry:
         default: {
             janet_panicf("no registry value and cannot marshal %p", x);
-            return;
         }
     }
 #undef MARK_SEEN
@@ -1293,6 +1311,42 @@ static const uint8_t *unmarshal_one(
             }
             return data;
         }
+        case LB_UNSAFE_POINTER: {
+            MARSH_EOS(st, data + sizeof(void *));
+            data++;
+            if (!(flags & JANET_MARSHAL_UNSAFE)) {
+                janet_panicf("unsafe flag not given, "
+                             "will not unmarshal raw pointer at index %d",
+                             (int)(data - st->start));
+            }
+            union {
+                void *ptr;
+                uint8_t bytes[sizeof(void *)];
+            } u;
+            memcpy(u.bytes, data, sizeof(void *));
+            data += sizeof(void *);
+            *out = janet_wrap_pointer(u.ptr);
+            janet_v_push(st->lookup, *out);
+            return data;
+        }
+        case LB_UNSAFE_CFUNCTION: {
+            MARSH_EOS(st, data + sizeof(JanetCFunction));
+            data++;
+            if (!(flags & JANET_MARSHAL_UNSAFE)) {
+                janet_panicf("unsafe flag not given, "
+                             "will not unmarshal function pointer at index %d",
+                             (int)(data - st->start));
+            }
+            union {
+                JanetCFunction ptr;
+                uint8_t bytes[sizeof(JanetCFunction)];
+            } u;
+            memcpy(u.bytes, data, sizeof(JanetCFunction));
+            data += sizeof(JanetCFunction);
+            *out = janet_wrap_cfunction(u.ptr);
+            janet_v_push(st->lookup, *out);
+            return data;
+        }
         default: {
             janet_panicf("unknown byte %x at index %d",
                          *data,

src/core/thread.c

@@ -329,7 +329,7 @@ int janet_thread_send(JanetThread *thread, Janet msg, double timeout) {
         msgbuf->count = 0;
 
         /* Start panic zone */
-        janet_marshal(msgbuf, msg, thread->encode, 0);
+        janet_marshal(msgbuf, msg, thread->encode, JANET_MARSHAL_UNSAFE);
         /* End panic zone */
 
         mailbox->messageNext = (mailbox->messageNext + 1) % mailbox->messageCapacity;
@@ -379,7 +379,7 @@ int janet_thread_receive(Janet *msg_out, double timeout) {
                 const uint8_t *nextItem = NULL;
                 Janet item = janet_unmarshal(
                                  msgbuf->data, msgbuf->count,
-                                 0, janet_thread_get_decode(), &nextItem);
+                                 JANET_MARSHAL_UNSAFE, janet_thread_get_decode(), &nextItem);
                 *msg_out = item;
 
                 /* Cleanup */

src/include/janet.h

@@ -1310,6 +1310,8 @@ typedef JanetBuildConfig(*JanetModconf)(void);
 JANET_API JanetModule janet_native(const char *name, JanetString *error);
 
 /* Marshaling */
+#define JANET_MARSHAL_UNSAFE 0x20000
+
 JANET_API void janet_marshal(
     JanetBuffer *buf,
     Janet x,