make secure_join flow more readable by using and adding a few macros, tiny api changes

src/dc_token.rs

@@ -10,20 +10,17 @@ pub const DC_TOKEN_INVITENUMBER: dc_tokennamespc_t = 100;
 
 // Functions to read/write token from/to the database. A token is any string associated with a key.
 
-pub fn dc_token_save(
-    context: &Context,
-    namespc: dc_tokennamespc_t,
-    foreign_id: u32,
-    token: &str,
-) -> bool {
+pub fn dc_token_save(context: &Context, namespc: dc_tokennamespc_t, foreign_id: u32) -> String {
     // foreign_id may be 0
+    let token = dc_create_id();
     sql::execute(
         context,
         &context.sql,
         "INSERT INTO tokens (namespc, foreign_id, token, timestamp) VALUES (?, ?, ?, ?);",
-        params![namespc as i32, foreign_id as i32, token, time()],
+        params![namespc as i32, foreign_id as i32, &token, time()],
     )
-    .is_ok()
+    .ok();
+    token
 }
 
 pub fn dc_token_lookup(
@@ -39,6 +36,15 @@ pub fn dc_token_lookup(
     )
 }
 
+pub fn dc_token_lookup_or_new(
+    context: &Context,
+    namespc: dc_tokennamespc_t,
+    foreign_id: u32,
+) -> String {
+    dc_token_lookup(context, namespc, foreign_id)
+        .unwrap_or_else(|| dc_token_save(context, namespc, foreign_id))
+}
+
 pub fn dc_token_exists(context: &Context, namespc: dc_tokennamespc_t, token: &str) -> bool {
     context
         .sql