proxy: -o proxy_arg to pass cmdline to lua

Assigned to `mcp.start_arg` and available in all threads.

If argument is a normal string, it is assigned as a string.

If the argument contains ':' then it is split into a table. If sections
of the string contain '_' then they are treated as key/value.

`proxy_arg=foo` -> foo.

`proxy_arg=foo_bar:baz' -> { foo = "bar", baz = true }

memcached.c

@@ -4202,7 +4202,8 @@ static void usage(void) {
     verify_default("ext_item_age", settings.ext_item_age == UINT_MAX);
 #endif
 #ifdef PROXY
-    printf("   - proxy_config:        path to lua config file.\n");
+    printf("   - proxy_config:        path to lua library file. separate with ':' for multiple files\n");
+    printf("   - proxy_arg:           string to pass to lua library\n");
 #endif
 #ifdef TLS
     printf("   - ssl_chain_cert:      certificate chain file in PEM format\n"
@@ -4850,6 +4851,7 @@ int main (int argc, char **argv) {
 #endif
 #ifdef PROXY
         PROXY_CONFIG,
+        PROXY_ARG,
         PROXY_URING,
         PROXY_MEMPROFILE,
 #endif
@@ -4913,6 +4915,7 @@ int main (int argc, char **argv) {
 #endif
 #ifdef PROXY
         [PROXY_CONFIG] = "proxy_config",
+        [PROXY_ARG] = "proxy_arg",
         [PROXY_URING] = "proxy_uring",
         [PROXY_MEMPROFILE] = "proxy_memprofile",
 #endif
@@ -5685,6 +5688,9 @@ int main (int argc, char **argv) {
                 settings.binding_protocol = proxy_prot;
                 protocol_specified = true;
                 break;
+            case PROXY_ARG:
+                settings.proxy_startarg = strdup(subopts_value);
+                break;
             case PROXY_URING:
                 settings.proxy_uring = true;
                 break;

memcached.h

@@ -548,6 +548,7 @@ struct settings {
     bool proxy_uring; /* if the proxy should use io_uring */
     bool proxy_memprofile; /* output detail of lua allocations */
     char *proxy_startfile; /* lua file to run when workers start */
+    char *proxy_startarg; /* string argument to pass to proxy */
     void *proxy_ctx; /* proxy's state context */
 #endif
 #ifdef SOCK_COOKIE_ID

proto_proxy.c

@@ -263,7 +263,7 @@ void process_proxy_funcstats(void *arg, ADD_STAT add_stats, conn *c) {
 void *proxy_init(bool use_uring, bool proxy_memprofile) {
     proxy_ctx_t *ctx = calloc(1, sizeof(proxy_ctx_t));
     ctx->use_uring = use_uring;
-    ctx->memprofile = proxy_memprofile; // FIXME: take from argument.
+    ctx->memprofile = proxy_memprofile;
 
     pthread_mutex_init(&ctx->config_lock, NULL);
     pthread_cond_init(&ctx->config_cond, NULL);

proxy_lua.c

@@ -1377,6 +1377,44 @@ static void proxy_register_defines(lua_State *L) {
     lua_setfield(L, -2, "WAIT_RESUME");
 }
 
+// TODO: low priority malloc error handling.
+static void proxy_register_startarg(lua_State *L) {
+    int idx = lua_absindex(L, -1); // remember 'mcp' table.
+    if (settings.proxy_startarg == NULL) {
+        // no argument given.
+        lua_pushboolean(L, 0);
+        lua_setfield(L, idx, "start_arg");
+        return;
+    }
+
+    char *sarg = strdup(settings.proxy_startarg);
+    if (strchr(sarg, ':') == NULL) {
+        // just upload the string
+        lua_pushstring(L, sarg);
+    } else {
+        // split into a table and set that instead.
+        lua_newtable(L);
+        int nidx = lua_absindex(L, -1);
+        char *b = NULL;
+        for (char *p = strtok_r(sarg, ":", &b);
+                p != NULL;
+                p = strtok_r(NULL, ":", &b)) {
+            char *e = NULL;
+            char *name = strtok_r(p, "_", &e);
+            lua_pushstring(L, name); // table -> key
+            char *value = strtok_r(NULL, "_", &e);
+            if (value == NULL) {
+                lua_pushboolean(L, 1); // table -> key -> True
+            } else {
+                lua_pushstring(L, value); // table -> key -> value
+            }
+            lua_settable(L, nidx);
+        }
+    }
+    free(sarg);
+    lua_setfield(L, idx, "start_arg");
+}
+
 // Creates and returns the top level "mcp" module
 int proxy_register_libs(void *ctx, LIBEVENT_THREAD *t, void *state) {
     lua_State *L = state;
@@ -1627,6 +1665,9 @@ int proxy_register_libs(void *ctx, LIBEVENT_THREAD *t, void *state) {
         luaL_setfuncs(L, mcplib_f_config, 1); // store upvalues.
     }
 
+    // every VM gets a copy of the start arguments to work with.
+    proxy_register_startarg(L);
+
     lua_setglobal(L, "mcp"); // set the lib table to mcp global.
     return 1;
 }