From 86b2ccc6577579f7abbc22d73721858f15e51ac3 Mon Sep 17 00:00:00 2001
From: Mikhail Burakov <mburakov@mailbox.org>
Date: Sat, 7 Jan 2023 14:52:15 +0100
Subject: Implement subscribing to topics from lua

---
 main.c    | 71 +++++++++++++++++++++++++++++++++++++++++++++++++++++----------
 message.c |  2 ++
 message.h |  1 +
 3 files changed, 63 insertions(+), 11 deletions(-)

diff --git a/main.c b/main.c
index 9b760eb..dac79fb 100644
--- a/main.c
+++ b/main.c
@@ -192,6 +192,13 @@ static void GatherMessages(const void* nodep, VISIT which, int depth) {
   g_twalk_closure.ptr++->iov_len = 8;
 }
 
+static void UnrefLuaCallbacks(const void* nodep, VISIT which, int depth) {
+  (void)depth;
+  struct Message* message = *(void* const*)nodep;
+  if (which == preorder || which == endorder) return;
+  luaL_unref(g_service.lua_state, LUA_REGISTRYINDEX, message->lua_callback);
+}
+
 static bool ServeHttpGet(int fd, const char* target) {
   if (!strcmp(target, "/favicon.ico"))
     return SendHttpReply(fd, "404 Not Found", NULL, NULL, 0);
@@ -368,9 +375,9 @@ static void OnMqttConnectAck(void* user, bool success) {
 
 static int LuaPublish(lua_State* lua_state) {
   int result = 0;
-  size_t topic_length;
-  const char* topic = luaL_checklstring(lua_state, 1, &topic_length);
-  if (!topic || topic_length > UINT16_MAX) {
+  size_t topic_size;
+  const char* topic = luaL_checklstring(lua_state, 1, &topic_size);
+  if (!topic || topic_size > UINT16_MAX) {
     LOGW("Invalid topic argument for publish call");
     goto bail_out;
   }
@@ -380,8 +387,8 @@ static int LuaPublish(lua_State* lua_state) {
     LOGW("Invalid payload argument for publish call");
     goto bail_out;
   }
-  LOGD("%.*s -> %.*s", (int)topic_length, topic, (int)payload_length, payload);
-  if (!MqttPublish(g_service.mqtt, topic, (uint16_t)topic_length, payload,
+  LOGD("%.*s -> %.*s", (int)topic_size, topic, (int)payload_length, payload);
+  if (!MqttPublish(g_service.mqtt, topic, (uint16_t)topic_size, payload,
                    payload_length)) {
     LOGW("Failed to publish mqtt message (%s)", strerror(errno));
     goto bail_out;
@@ -394,8 +401,44 @@ bail_out:
 }
 
 static int LuaSubscribe(lua_State* lua_state) {
-  // TODO(mburakov): Implement me!
-  return 0;
+  int result = 0;
+  size_t topic_size;
+  const char* topic = luaL_checklstring(lua_state, 1, &topic_size);
+  if (!topic) {
+    LOGW("Invalid topic argument for subscribe call");
+    goto bail_out;
+  }
+  luaL_checkany(lua_state, 2);
+  if (!lua_isfunction(lua_state, -1)) {
+    LOGW("Invalid callback argument for subscribe call");
+    goto bail_out;
+  }
+  struct Message key = {
+      .topic = *(void**)(void*)&topic,
+      .topic_size = topic_size,
+  };
+  struct Message** node = tsearch(&key, &g_service.messages, MessageCompare);
+  if (!node) {
+    LOGW("Failed to create message node (%s)", strerror(errno));
+    goto bail_out;
+  }
+  if (*node == &key) {
+    struct Message* message = MessageCreate(topic, topic_size);
+    if (!message) {
+      LOGW("Failed to create message (%s)", strerror(errno));
+      tdelete(&key, &g_service.messages, MessageCompare);
+      goto bail_out;
+    }
+    *node = message;
+    g_service.messages_count++;
+  }
+  luaL_unref(lua_state, LUA_REGISTRYINDEX, (*node)->lua_callback);
+  (*node)->lua_callback = luaL_ref(lua_state, LUA_REGISTRYINDEX);
+  result = 1;
+
+bail_out:
+  lua_pushboolean(lua_state, result);
+  return 1;
 }
 
 static void OnMqttSubscribeAck(void* user, bool success) {
@@ -414,10 +457,8 @@ static void OnMqttSubscribeAck(void* user, bool success) {
   }
 
   luaL_openlibs(g_service.lua_state);
-  lua_pushcfunction(g_service.lua_state, LuaPublish);
-  lua_setglobal(g_service.lua_state, "publish");
-  lua_pushcfunction(g_service.lua_state, LuaSubscribe);
-  lua_setglobal(g_service.lua_state, "subscribe");
+  lua_register(g_service.lua_state, "publish", LuaPublish);
+  lua_register(g_service.lua_state, "subscribe", LuaSubscribe);
 
   DIR* current_dir = opendir(".");
   if (!current_dir) {
@@ -471,6 +512,13 @@ static void OnMqttPublish(void* user, const char* topic, size_t topic_size,
   free((*node)->payload);
   (*node)->payload = payload_copy;
   (*node)->payload_size = payload_size;
+  if ((*node)->lua_callback != LUA_REFNIL) {
+    // TODO(mburakov): Handle lua errors.
+    lua_rawgeti(g_service.lua_state, LUA_REGISTRYINDEX, (*node)->lua_callback);
+    lua_pushlstring(g_service.lua_state, (*node)->payload,
+                    (*node)->payload_size);
+    lua_pcall(g_service.lua_state, 1, 0, 0);
+  }
   return;
 
 delete_node:
@@ -591,6 +639,7 @@ int main(int argc, char* argv[]) {
       OnSignal(SIGABRT);
     }
   }
+  twalk(g_service.messages, UnrefLuaCallbacks);
   tdestroy(g_service.messages, MessageDestroy);
   while (g_service.clients) DropClientContext(g_service.clients);
   if (g_service.lua_state) lua_close(g_service.lua_state);
diff --git a/message.c b/message.c
index 657c759..dcee14e 100644
--- a/message.c
+++ b/message.c
@@ -18,6 +18,7 @@
 #include "message.h"
 
 #include <errno.h>
+#include <lauxlib.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -38,6 +39,7 @@ struct Message* MessageCreate(const char* topic, size_t topic_size) {
   message->topic_size = topic_size;
   message->payload = NULL;
   message->payload_size = 0;
+  message->lua_callback = LUA_REFNIL;
   return message;
 
 free_message:
diff --git a/message.h b/message.h
index 6ba9e1a..fb4a7ad 100644
--- a/message.h
+++ b/message.h
@@ -25,6 +25,7 @@ struct Message {
   size_t topic_size;
   void* payload;
   size_t payload_size;
+  int lua_callback;
 };
 
 struct Message* MessageCreate(const char* topic, size_t topic_size);
-- 
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