Add support for writing commit metadata.

rdkafka-sys/src/helpers.rs

@@ -1,5 +1,7 @@
 //! Utility functions.
 
+use libc::c_char;
+
 use crate::types::RDKafkaErrorCode;
 use crate::types::RDKafkaErrorCode::*;
 use crate::types::RDKafkaRespErr;
@@ -175,3 +177,7 @@ pub fn rd_kafka_resp_err_t_to_rdkafka_error(err: RDKafkaRespErr) -> RDKafkaError
         RD_KAFKA_RESP_ERR_END_ALL => EndAll,
     }
 }
+
+extern "C" {
+    pub fn rd_strndup(_: *const c_char, _: isize) -> *mut c_char;
+}

src/topic_partition_list.rs

@@ -141,6 +141,18 @@ impl<'a> TopicPartitionListElem<'a> {
         let slice: &[u8] = unsafe { ptr_to_slice(self.ptr.metadata, self.ptr.metadata_size) };
         from_utf8(slice).expect("metadata is not UTF-8")
     }
+
+    /// Set the metadata.
+    pub fn set_metadata(&mut self, metadata: impl AsRef<str>) {
+        let metadata = metadata.as_ref();
+        let c_metadata = CString::new(metadata).expect("metadat is not UTF-8");
+
+        unsafe {
+            self.ptr.metadata =
+                rdsys::helpers::rd_strndup(c_metadata.as_ptr(), metadata.len() as isize) as *mut _;
+            self.ptr.metadata_size = libc::strlen(self.ptr.metadata as *const _);
+        }
+    }
 }
 
 impl<'a> PartialEq for TopicPartitionListElem<'a> {