Skip serialization of field Span.error if equals to 0 (#500)

* Skip serialization of field Span.error if equals to 0

* Add tests

* Move serde_json in dev-dependencies

* Fix clippy

LICENSE-3rdparty.yml

@@ -19251,7 +19251,7 @@ third_party_libraries:
 
       END OF TERMS AND CONDITIONS
 - package_name: serde_json
-  package_version: 1.0.115
+  package_version: 1.0.117
   repository: https://github.com/serde-rs/json
   license: MIT OR Apache-2.0
   licenses:

trace-protobuf/Cargo.toml

@@ -11,6 +11,9 @@ prost = "0.11.6"
 serde = { version = "1.0.145", features = ["derive"] }
 serde_bytes = "0.11.9"
 
+[dev-dependencies]
+serde_json = "1.0.117"
+
 [build-dependencies]
 prost-build = { version = "0.11.9", optional = true  }
 protoc-bin-vendored = { version = "3.0.0", optional = true }

trace-protobuf/build.rs

@@ -63,6 +63,10 @@ fn generate_protobuf() {
         ".pb.Span.spanLinks",
         "#[serde(skip_serializing_if = \"::prost::alloc::vec::Vec::is_empty\")]",
     );
+    config.field_attribute(
+        ".pb.Span.error",
+        "#[serde(skip_serializing_if = \"is_default\")]",
+    );
 
     config.type_attribute("StatsPayload", "#[derive(Deserialize, Serialize)]");
     config.type_attribute("StatsPayload", "#[serde(rename_all = \"PascalCase\")]");
@@ -141,6 +145,10 @@ where
     Ok(opt.unwrap_or_default())
 }
 
+pub fn is_default<T: Default + PartialEq>(t: &T) -> bool {
+    t == &T::default()
+}
+
 "
     .as_bytes();
 

trace-protobuf/src/lib.rs

@@ -3,3 +3,6 @@
 
 #[rustfmt::skip]
 pub mod pb;
+
+#[cfg(test)]
+mod pb_test;

trace-protobuf/src/pb.rs

@@ -12,6 +12,10 @@ where
     Ok(opt.unwrap_or_default())
 }
 
+pub fn is_default<T: Default + PartialEq>(t: &T) -> bool {
+    t == &T::default()
+}
+
 #[derive(Deserialize, Serialize)]
 #[allow(clippy::derive_partial_eq_without_eq)]
 #[derive(Clone, PartialEq, ::prost::Message)]
@@ -107,6 +111,7 @@ pub struct Span {
     #[prost(int32, tag = "9")]
     #[serde(default)]
     #[serde(deserialize_with = "deserialize_null_into_default")]
+    #[serde(skip_serializing_if = "is_default")]
     pub error: i32,
     /// meta is a mapping from tag name to tag value for string-valued tags.
     /// @gotags: json:"meta,omitempty" msg:"meta,omitempty"

trace-protobuf/src/pb_test.rs

@@ -0,0 +1,36 @@
+// Copyright 2023-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+#[cfg(test)]
+mod tests {
+    use crate::pb::{is_default, Span};
+
+    #[test]
+    fn test_is_default() {
+        assert!(is_default(&false));
+        assert!(!is_default(&true));
+
+        assert!(is_default(&0));
+        assert!(!is_default(&1));
+
+        assert!(is_default(&""));
+        assert!(!is_default(&"foo"));
+    }
+
+    #[test]
+    fn test_serialize_span() {
+        let mut span = Span {
+            name: "test".to_string(),
+            ..Default::default()
+        };
+
+        let json = serde_json::to_string(&span).unwrap();
+        let expected = "{\"service\":\"\",\"name\":\"test\",\"resource\":\"\",\"trace_id\":0,\"span_id\":0,\"parent_id\":0,\"start\":0,\"duration\":0,\"meta\":{},\"metrics\":{},\"type\":\"\"}";
+        assert_eq!(expected, json);
+
+        span.error = 42;
+        let json = serde_json::to_string(&span).unwrap();
+        let expected = "{\"service\":\"\",\"name\":\"test\",\"resource\":\"\",\"trace_id\":0,\"span_id\":0,\"parent_id\":0,\"start\":0,\"duration\":0,\"error\":42,\"meta\":{},\"metrics\":{},\"type\":\"\"}";
+        assert_eq!(expected, json);
+    }
+}