h3: Support additional settings in C API

quiche/include/quiche.h

@@ -1120,6 +1120,20 @@ void quiche_h3_config_set_qpack_blocked_streams(quiche_h3_config *config, uint64
 // Sets the `SETTINGS_ENABLE_CONNECT_PROTOCOL` setting.
 void quiche_h3_config_enable_extended_connect(quiche_h3_config *config, bool enabled);
 
+// Sets an additional HTTP/3 setting.
+//
+// Returns 0 on success. Returns `QUICHE_H3_ERR_SETTINGS_ERROR` if the setting
+// is already present in the config or if it is one of the settings already
+// handled by the library:
+//
+// - SETTINGS_QPACK_MAX_TABLE_CAPACITY
+// - SETTINGS_MAX_FIELD_SECTION_SIZE
+// - SETTINGS_QPACK_BLOCKED_STREAMS
+// - SETTINGS_ENABLE_CONNECT_PROTOCOL
+// - SETTINGS_H3_DATAGRAM
+int quiche_h3_config_set_additional_setting(quiche_h3_config *config,
+                                            uint64_t setting, uint64_t value);
+
 // Frees the HTTP/3 config object.
 void quiche_h3_config_free(quiche_h3_config *config);
 

quiche/src/h3/ffi.rs

@@ -77,6 +77,17 @@ pub extern "C" fn quiche_h3_config_enable_extended_connect(
     config.enable_extended_connect(enabled);
 }
 
+#[no_mangle]
+pub extern "C" fn quiche_h3_config_set_additional_setting(
+    config: &mut h3::Config, setting: u64, value: u64,
+) -> c_int {
+    let settings = vec![(setting, value)];
+    match config.set_additional_settings(settings) {
+        Ok(()) => 0,
+        Err(err) => err.to_c() as c_int,
+    }
+}
+
 #[no_mangle]
 pub extern "C" fn quiche_h3_config_free(config: *mut h3::Config) {
     drop(unsafe { Box::from_raw(config) });