fix: Report slash- and tilde-prefixed redacted attributes as escaped references

src/contexts/attribute_reference.rs

@@ -145,6 +145,17 @@ impl Reference {
         }
     }
 
+    /// Constructs a [Reference] from a literal top-level attribute name, escaping it per the
+    /// backwards-compatibility rules so a name beginning with '/' is not read as pointer syntax.
+    pub(crate) fn from_literal_name(name: &str) -> Self {
+        if !name.starts_with('/') {
+            return Self::new(name);
+        }
+        let mut escaped = name.replace('~', "~0").replace('/', "~1");
+        escaped.insert(0, '/');
+        Self::new(escaped)
+    }
+
     /// Returns true if the reference is valid.
     pub fn is_valid(&self) -> bool {
         !matches!(&self.variant, Variant::Error(_))
@@ -303,12 +314,7 @@ impl From<AttributeName> for Reference {
     /// string passed into the Reference constructor, not the original AttributeName. This
     /// is desirable since data should be "upgraded" into the new format as it is encountered.
     fn from(name: AttributeName) -> Self {
-        if !name.0.starts_with('/') {
-            return Self::new(name.0);
-        }
-        let mut escaped = name.0.replace('~', "~0").replace('/', "~1");
-        escaped.insert(0, '/');
-        Self::new(escaped)
+        Reference::from_literal_name(&name.0)
     }
 }
 

src/contexts/context.rs

@@ -603,7 +603,7 @@ impl ContextAttributes {
             self.all_attributes_private || (self.redact_anonymous && context.anonymous);
 
         for key in optional_attribute_names.iter() {
-            let reference = Reference::new(key);
+            let reference = Reference::from_literal_name(key);
             if let Some(value) = context.get_value(&reference) {
                 // If redact_all is true, then there's no complex filtering or
                 // recursing to be done: all of these values are by definition private, so just add
@@ -867,9 +867,10 @@ mod tests {
     use crate::{AttributeValue, ContextBuilder, MultiContextBuilder, Reference};
     use maplit::hashmap;
     use proptest::proptest;
+    use std::collections::HashSet;
     use test_case::test_case;
 
-    use super::Kind;
+    use super::{ContextAttributes, Kind};
 
     proptest! {
         #[test]
@@ -1144,4 +1145,70 @@ mod tests {
 
         assert!(context.is_err());
     }
+
+    // Collects the strings in an event context's redactedAttributes as a set, since their order is
+    // not significant.
+    fn redacted_attributes(json: &serde_json::Value) -> HashSet<String> {
+        json["_meta"]["redactedAttributes"]
+            .as_array()
+            .expect("redactedAttributes should be an array")
+            .iter()
+            .map(|v| v.as_str().unwrap().to_string())
+            .collect()
+    }
+
+    #[test_case("/ssn", "/~1ssn"; "slash prefix is escaped")]
+    #[test_case("/a~b", "/~1a~0b"; "slash prefix with tilde escapes both")]
+    fn all_attributes_private_reports_escaped_references(name: &str, expected_ref: &str) {
+        let context = ContextBuilder::new("my-key")
+            .set_string(name, "secret")
+            .build()
+            .expect("Failed to build context");
+
+        let attributes = ContextAttributes::from_context(context, true, HashSet::new());
+        let json = serde_json::to_value(&attributes).expect("Failed to serialize");
+
+        assert_eq!(
+            redacted_attributes(&json),
+            HashSet::from([expected_ref.to_string()])
+        );
+        // The attribute value must not be leaked into the serialized output.
+        assert!(json.get(name).is_none());
+    }
+
+    #[test]
+    fn anonymous_redaction_reports_slash_prefixed_names_as_escaped_references() {
+        let context = ContextBuilder::new("my-key")
+            .anonymous(true)
+            .set_string("/ssn", "123-45-6789")
+            .build()
+            .expect("Failed to build context");
+
+        let attributes = ContextAttributes::from_context_with_anonymous_redaction(
+            context,
+            false,
+            HashSet::new(),
+        );
+        let json = serde_json::to_value(&attributes).expect("Failed to serialize");
+
+        assert_eq!(
+            redacted_attributes(&json),
+            HashSet::from(["/~1ssn".to_string()])
+        );
+        assert!(json.get("/ssn").is_none());
+    }
+
+    #[test]
+    fn slash_prefixed_attribute_is_serialized_under_its_literal_name_when_not_private() {
+        let context = ContextBuilder::new("my-key")
+            .set_string("/ssn", "123-45-6789")
+            .build()
+            .expect("Failed to build context");
+
+        let attributes = ContextAttributes::from_context(context, false, HashSet::new());
+        let json = serde_json::to_value(&attributes).expect("Failed to serialize");
+
+        assert_eq!(json["/ssn"], serde_json::json!("123-45-6789"));
+        assert!(json.get("_meta").is_none());
+    }
 }