Optional serde support for SpanContext

opentelemetry-api/CHANGELOG.md

@@ -6,6 +6,7 @@
 
 - Fix `SpanRef::set_attributes` mutability requirement. [#1038](https://github.com/open-telemetry/opentelemetry-rust/pull/1038)
 - Move OrderMap module to root of otel-api crate. [#1061](https://github.com/open-telemetry/opentelemetry-rust/pull/1061)
+- Fix `SpanContext` should implement serde::Serialize, Deserialize. [#1074](https://github.com/open-telemetry/opentelemetry-rust/issues/1074)
 
 ## v0.19.0
 ### Added

opentelemetry-api/Cargo.toml

@@ -16,6 +16,7 @@ futures-util = { version = "0.3", default-features = false, features = ["std", "
 indexmap = "1.8"
 once_cell = "1.12.0"
 pin-project-lite = { version = "0.2", optional = true }
+serde = { version = "1.0", optional = true, features = ["derive"] }
 thiserror = "1"
 tokio-stream = { version = "0.1", optional = true }
 urlencoding = "2.1.2"

opentelemetry-api/src/trace/span_context.rs

@@ -1,4 +1,6 @@
 use crate::trace::{TraceError, TraceResult};
+#[cfg(feature = "serde")]
+use serde::{self, Deserialize, Serialize};
 use std::collections::VecDeque;
 use std::fmt;
 use std::hash::Hash;
@@ -17,6 +19,7 @@ use thiserror::Error;
 ///
 /// [trace-flags]: https://www.w3.org/TR/trace-context/#trace-flags
 #[derive(Clone, Debug, Default, PartialEq, Eq, Copy, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct TraceFlags(u8);
 
 impl TraceFlags {
@@ -87,6 +90,7 @@ impl fmt::LowerHex for TraceFlags {
 ///
 /// The id is valid if it contains at least one non-zero byte.
 #[derive(Clone, PartialEq, Eq, Copy, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct TraceId(u128);
 
 impl TraceId {
@@ -148,6 +152,7 @@ impl fmt::LowerHex for TraceId {
 ///
 /// The id is valid if it contains at least one non-zero byte.
 #[derive(Clone, PartialEq, Eq, Copy, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct SpanId(u64);
 
 impl SpanId {
@@ -213,6 +218,7 @@ impl fmt::LowerHex for SpanId {
 ///
 /// [W3C specification]: https://www.w3.org/TR/trace-context/#tracestate-header
 #[derive(Clone, Debug, Default, Eq, PartialEq, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct TraceState(Option<VecDeque<(String, String)>>);
 
 impl TraceState {
@@ -448,10 +454,15 @@ impl From<TraceStateError> for TraceError {
 /// [`Span`]: crate::trace::Span
 /// [W3C TraceContext specification]: https://www.w3.org/TR/trace-context
 #[derive(Clone, Debug, PartialEq, Hash, Eq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct SpanContext {
     trace_id: TraceId,
     span_id: SpanId,
     trace_flags: TraceFlags,
+    #[cfg_attr(
+        feature = "serde",
+        serde(skip, default = "SpanContext::deserialize_is_remote")
+    )]
     is_remote: bool,
     trace_state: TraceState,
 }
@@ -525,6 +536,15 @@ impl SpanContext {
     pub fn trace_state(&self) -> &TraceState {
         &self.trace_state
     }
+
+    /// Provides the value for self.is_remote when deserializing.
+    /// Since deserializing implies the span context was propagated, this
+    /// value is always true.
+    /// See https://serde.rs/field-attrs.html#default--path
+    #[cfg(feature = "serde")]
+    fn deserialize_is_remote() -> bool {
+        true
+    }
 }
 
 #[cfg(test)]

opentelemetry/Cargo.toml

@@ -36,3 +36,4 @@ testing = ["opentelemetry_api/testing", "opentelemetry_sdk/testing"]
 rt-tokio = ["opentelemetry_sdk/rt-tokio"]
 rt-tokio-current-thread = ["opentelemetry_sdk/rt-tokio-current-thread"]
 rt-async-std = ["opentelemetry_sdk/rt-async-std"]
+serde = ["opentelemetry_api/serde"]