Explain the chDB ABI

Author: auxten

bindings.md

@@ -17,6 +17,65 @@ Here is a table outlining the current status of language bindings for chDB:
 | PHP | n/a | Contributors Needed |
 | Ruby | n/a | Contributors Needed |
 
+
+### chDB stable ABI
+
+chDB provides several stable ABIs for other language bindings.
+
+
+
+The following is the definition of the `local_result` and `local_result_v2` structure:
+
+```c
+struct local_result
+{
+    char * buf;
+    size_t len;
+    void * _vec; // std::vector<char> *, for freeing
+    double elapsed;
+    uint64_t rows_read;
+    uint64_t bytes_read;
+};
+
+struct local_result_v2
+{
+    char * buf;
+    size_t len;
+    void * _vec; // std::vector<char> *, for freeing
+    double elapsed;
+    uint64_t rows_read;
+    uint64_t bytes_read;
+    char * error_message;
+};
+```
+
+The following is the definition of the `query_stable`, `free_result` and `query_stable_v2`, `free_result_v2` functions.
+
+```c
+// v1 API
+struct local_result * query_stable(int argc, char ** argv);
+void free_result(struct local_result * result);
+
+// v2 API added `char * error_message`.
+struct local_result_v2 * query_stable_v2(int argc, char ** argv);
+void free_result_v2(struct local_result_v2 * result);
+```
+
+#### Query
+`query_stable` and `query_stable_v2` accept the same parameters just like the `clickhouse-local` command line tool. You can check `queryToBuffer` function in [LocalChdb.cpp](programs/local/LocalChdb.cpp) as an example.
+
+The difference is that `query_stable_v2` adds the `char * error_message` field.
+You can check if the `error_message` field is `NULL` to determine if an error occurred.
+
+#### Free Result
+`free_result` and `free_result_v2` are used to free the `local_result` and `local_result_v2` memory. For GC languages, you can call `free_result` or `free_result_v2` in the destructor of the object.
+
+#### Known Issues
+
+- By chDB v1.2.0, the `query_stable_v2``
+ returns nil if the query(eg. CREATE TABLE) successes but returns no data. We will change this behavior in the future.
+
+
 ### Need Help?
 If you have already developed bindings for a language not listed above,