Ensure pre-formatted JSON data doesn't contain trailing null bytes. (#…

…1332)

When serializing Python objects to JSON, `orjson` includes a trailing
null byte since it's producing a C-string which is null-terminated.

However, when sending HTTP multipart data, we send the JSON with an
explicit content length value, so the trailing null byte is neither
needed nor expected. So strip the trailing null (if present) before
sending `inputs` and `outputs`.

rust/crates/langsmith-tracing-client/src/client/blocking/processor.rs

@@ -117,11 +117,19 @@ impl RunProcessor {
                         to_vec(&run_create).unwrap(), // TODO: get rid of unwrap
                     ));
 
-                    if let Some(inputs) = io.inputs {
+                    // Ensure that pre-formatted JSON data represented as bytes
+                    // doesn't end in trailing null bytes, since we'll be pasting it verbatim
+                    // into an HTTP multipart request which carries an explicit length header.
+                    if let Some(mut inputs) = io.inputs {
+                        if inputs.last() == Some(&0) {
+                            inputs.pop().expect("popping trailing null byte failed");
+                        }
                         json_data.push((format!("post.{}.inputs", run_id), inputs));
                     }
-
-                    if let Some(outputs) = io.outputs {
+                    if let Some(mut outputs) = io.outputs {
+                        if outputs.last() == Some(&0) {
+                            outputs.pop().expect("popping trailing null byte failed");
+                        }
                         json_data.push((format!("post.{}.outputs", run_id), outputs));
                     }
 
@@ -150,7 +158,13 @@ impl RunProcessor {
                         to_vec(&run_update).unwrap(), // TODO: get rid of unwrap
                     ));
 
-                    if let Some(outputs) = io.outputs {
+                    // Ensure that pre-formatted JSON data represented as bytes
+                    // doesn't end in trailing null bytes, since we'll be pasting it verbatim
+                    // into an HTTP multipart request which carries an explicit length header.
+                    if let Some(mut outputs) = io.outputs {
+                        if outputs.last() == Some(&0) {
+                            outputs.pop().expect("popping trailing null byte failed");
+                        }
                         json_data.push((format!("patch.{}.outputs", run_id), outputs));
                     }