Return agent response length. (#1170)

* Return agent response length.

* Return the actual payload along with its lenght rather than a copy turned into a null terminated string.

Author: hoolioh

data-pipeline-ffi/src/response.rs

@@ -4,10 +4,7 @@
 //! Define FFI compatible AgentResponse struct
 
 use data_pipeline::trace_exporter::agent_response::AgentResponse;
-use std::{
-    ffi::{c_char, CString},
-    ptr::null,
-};
+use std::ptr::null;
 
 /// Structure containing the agent response to a trace payload
 /// MUST be freed with `ddog_trace_exporter_response_free`
@@ -18,18 +15,16 @@ use std::{
 #[derive(Debug, Default)]
 pub struct ExporterResponse {
     /// The body of the response, which is a string containing the response from the agent.
-    pub body: CString,
+    pub body: Option<Vec<u8>>,
 }
 
 impl From<AgentResponse> for ExporterResponse {
     fn from(value: AgentResponse) -> Self {
         match value {
             AgentResponse::Changed { body } => ExporterResponse {
-                body: CString::new(body).unwrap_or_default(),
-            },
-            AgentResponse::Unchanged => ExporterResponse {
-                body: CString::new("").unwrap_or_default(),
+                body: Some(body.into_bytes()),
             },
+            AgentResponse::Unchanged => ExporterResponse { body: None },
         }
     }
 }
@@ -39,12 +34,22 @@ impl From<AgentResponse> for ExporterResponse {
 #[no_mangle]
 pub unsafe extern "C" fn ddog_trace_exporter_response_get_body(
     response: *const ExporterResponse,
-) -> *const c_char {
-    if response.is_null() {
+    out_len: Option<&mut usize>,
+) -> *const u8 {
+    let mut len: usize = 0;
+    let body = if response.is_null() {
         null()
+    } else if let Some(body) = &(*response).body {
+        len = body.len();
+        body.as_ptr()
     } else {
-        (*response).body.as_ptr()
+        null()
+    };
+
+    if let Some(out_len) = out_len {
+        *out_len = len;
     }
+    body
 }
 
 /// Free `response` and all its contents. After being called response will not point to a valid
@@ -59,28 +64,30 @@ pub unsafe extern "C" fn ddog_trace_exporter_response_free(response: *mut Export
 #[cfg(test)]
 mod tests {
     use super::*;
-    use std::ffi::CStr;
 
     #[test]
     fn constructor_test_changed() {
         let agent_response = AgentResponse::Changed {
             body: "res".to_string(),
         };
         let response = &ExporterResponse::from(agent_response) as *const ExporterResponse;
-        let body = unsafe {
-            CStr::from_ptr(ddog_trace_exporter_response_get_body(response)).to_string_lossy()
-        };
-        assert_eq!(body, "res".to_string());
+        let mut len = 0;
+        let body = unsafe { ddog_trace_exporter_response_get_body(response, Some(&mut len)) };
+        let response =
+            unsafe { std::str::from_utf8(std::slice::from_raw_parts(body, len)).unwrap() };
+        assert_eq!(response, "res");
+        assert_eq!(len, 3);
     }
 
     #[test]
     fn constructor_test_unchanged() {
         let agent_response = AgentResponse::Unchanged;
         let response = Box::into_raw(Box::new(ExporterResponse::from(agent_response)));
-        let body = unsafe {
-            CStr::from_ptr(ddog_trace_exporter_response_get_body(response)).to_string_lossy()
-        };
-        assert_eq!(body, "".to_string());
+        let mut len = usize::MAX;
+        let body = unsafe { ddog_trace_exporter_response_get_body(response, Some(&mut len)) };
+        assert!(body.is_null());
+        assert_eq!(len, 0);
+
         unsafe {
             ddog_trace_exporter_response_free(response);
         }
@@ -89,7 +96,7 @@ mod tests {
     #[test]
     fn handle_null_test() {
         unsafe {
-            let body = ddog_trace_exporter_response_get_body(null());
+            let body = ddog_trace_exporter_response_get_body(null(), None);
             assert!(body.is_null());
 
             ddog_trace_exporter_response_free(null::<ExporterResponse>() as *mut ExporterResponse);

data-pipeline-ffi/src/trace_exporter.rs

@@ -979,7 +979,7 @@ mod tests {
             );
             assert_eq!(ret, None);
             assert_eq!(
-                response.assume_init().body.to_string_lossy(),
+                String::from_utf8_lossy(&response.assume_init().body.unwrap()),
                 r#"{
                     "rate_by_service": {
                         "service:foo,env:staging": 1.0,
@@ -1048,7 +1048,10 @@ mod tests {
             );
             mock_traces.assert();
             assert_eq!(ret, None);
-            assert_eq!(response.assume_init().body.to_string_lossy(), response_body);
+            assert_eq!(
+                String::from_utf8_lossy(&response.assume_init().body.unwrap()),
+                response_body
+            );
 
             ddog_trace_exporter_free(exporter);
         }
@@ -1123,7 +1126,10 @@ mod tests {
             );
             mock_traces.assert();
             assert_eq!(ret, None);
-            assert_eq!(response.assume_init().body.to_string_lossy(), response_body);
+            assert_eq!(
+                String::from_utf8_lossy(&response.assume_init().body.unwrap()),
+                response_body
+            );
 
             ddog_trace_exporter_free(exporter);
             // It should receive 1 payloads: metrics