login-common: Add preproxy pool

preproxy pool can be used to do allocations that are released
once proxying starts.

src/login-common/client-common.c

@@ -174,6 +174,7 @@ client_create(int fd, bool ssl, pool_t pool,
 	client->refcount = 1;
 
 	client->pool = pool;
+	client->preproxy_pool = pool_alloconly_create(MEMPOOL_GROWING"preproxy pool", 256);
 	client->set = set;
 	client->ssl_set = ssl_set;
 	p_array_init(&client->module_contexts, client->pool, 5);
@@ -224,6 +225,9 @@ void client_destroy(struct client *client, const char *reason)
 		return;
 	client->destroyed = TRUE;
 
+	if (client->preproxy_pool != NULL)
+		pool_unref(&client->preproxy_pool);
+
 	if (!client->login_success && reason != NULL) {
 		reason = t_strconcat(reason, " ",
 			client_get_extra_disconnect_reason(client), NULL);

src/login-common/client-common.h

@@ -107,6 +107,8 @@ struct client_vfuncs {
 struct client {
 	struct client *prev, *next;
 	pool_t pool;
+	/* this pool gets free'd once proxying starts */
+	pool_t preproxy_pool;
 	struct client_vfuncs v;
 	struct client_vfuncs *vlast;
 

src/login-common/login-proxy.c

@@ -705,6 +705,9 @@ void login_proxy_detach(struct login_proxy *proxy)
 	const unsigned char *data;
 	size_t size;
 
+	if (proxy->client->preproxy_pool != NULL)
+		pool_unref(&proxy->client->preproxy_pool);
+
 	i_assert(proxy->client_fd == -1);
 	i_assert(proxy->server_input != NULL);
 	i_assert(proxy->server_output != NULL);