Serialize OCSP Redis snapshots with CBOR

ocsp-responder/src/snapshot.rs

@@ -3,7 +3,7 @@
 use std::collections::HashMap;
 
 use chrono::{DateTime, Utc};
-use serde::Deserialize;
+use serde::{Deserialize, Serialize};
 use sha1::{Digest as _, Sha1};
 use sha2::Sha256;
 use x509_cert::ext::pkix::CrlReason;
@@ -28,7 +28,7 @@ pub struct Snapshot {
     pub entries: HashMap<Vec<u8>, StatusEntry>,
 }
 
-#[derive(Debug, Deserialize)]
+#[derive(Debug, Deserialize, Serialize)]
 struct RawSnapshot {
     schema: String,
     issuer: RawIssuer,
@@ -36,7 +36,7 @@ struct RawSnapshot {
     entries: Vec<RawEntry>,
 }
 
-#[derive(Debug, Deserialize)]
+#[derive(Debug, Deserialize, Serialize)]
 struct RawIssuer {
     #[serde(default)]
     id: String,
@@ -44,7 +44,7 @@ struct RawIssuer {
     sha256: String,
 }
 
-#[derive(Debug, Deserialize)]
+#[derive(Debug, Deserialize, Serialize)]
 struct RawEntry {
     serial_hex: String,
     status: String,
@@ -61,7 +61,9 @@ impl Snapshot {
         expected_sha256: &str,
         expected_ca_id: &str,
     ) -> Result<Self, SnapshotError> {
-        let raw: RawSnapshot = serde_json::from_slice(bytes)?;
+        cbor2::validate_slice(bytes).map_err(|error| SnapshotError::Cbor(error.to_string()))?;
+        let raw: RawSnapshot =
+            cbor2::from_slice(bytes).map_err(|error| SnapshotError::Cbor(error.to_string()))?;
         if raw.schema != SCHEMA {
             return Err(SnapshotError::Schema(raw.schema));
         }
@@ -166,8 +168,8 @@ pub fn hash_sha256(bytes: &[u8]) -> Vec<u8> {
 
 #[derive(Debug, thiserror::Error)]
 pub enum SnapshotError {
-    #[error("invalid JSON: {0}")]
-    Json(#[from] serde_json::Error),
+    #[error("invalid CBOR: {0}")]
+    Cbor(String),
     #[error("unsupported snapshot schema {0:?}")]
     Schema(String),
     #[error("snapshot issuer ID {actual} does not match configured CA ID {expected}")]
@@ -184,27 +186,64 @@ pub enum SnapshotError {
     DuplicateSerial(String),
 }
 
+#[cfg(test)]
+pub(crate) fn test_body(sha: &str) -> Vec<u8> {
+    let raw = RawSnapshot {
+        schema: SCHEMA.to_string(),
+        issuer: RawIssuer {
+            id: "ca".to_string(),
+            sha256: sha.to_string(),
+        },
+        entries: vec![RawEntry {
+            serial_hex: "01".to_string(),
+            status: "valid".to_string(),
+            revoked_at: None,
+            reason: None,
+        }],
+    };
+    cbor2::to_vec(&raw).unwrap()
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
 
-    fn body(sha: &str) -> String {
-        format!(
-            r#"{{
-              "schema": "kca-ocsp-status/v2",
-              "issuer": {{"id": "ca", "sha256": "{sha}", "subject": "CN=CA"}},
-              "entries": [
-                {{"serial_hex": "01ab", "status": "valid", "not_after": "2027-01-01T00:00:00Z"}},
-                {{"serial_hex": "00ff", "status": "revoked", "revoked_at": "2026-02-03T04:05:06Z", "reason": "keyCompromise"}}
-              ]
-            }}"#
-        )
+    fn raw_body(sha: &str, schema: &str) -> RawSnapshot {
+        RawSnapshot {
+            schema: schema.to_string(),
+            issuer: RawIssuer {
+                id: "ca".to_string(),
+                sha256: sha.to_string(),
+            },
+            entries: vec![
+                RawEntry {
+                    serial_hex: "01ab".to_string(),
+                    status: "valid".to_string(),
+                    revoked_at: None,
+                    reason: None,
+                },
+                RawEntry {
+                    serial_hex: "00ff".to_string(),
+                    status: "revoked".to_string(),
+                    revoked_at: Some(
+                        DateTime::parse_from_rfc3339("2026-02-03T04:05:06Z")
+                            .unwrap()
+                            .with_timezone(&Utc),
+                    ),
+                    reason: Some("keyCompromise".to_string()),
+                },
+            ],
+        }
+    }
+
+    fn body(sha: &str) -> Vec<u8> {
+        cbor2::to_vec(&raw_body(sha, SCHEMA)).unwrap()
     }
 
     #[test]
     fn parses_statuses_and_reasons() {
         let sha = sha256_hex(b"ca");
-        let snapshot = Snapshot::parse(body(&sha).as_bytes(), &sha, "ca").unwrap();
+        let snapshot = Snapshot::parse(&body(&sha), &sha, "ca").unwrap();
         let good = snapshot.status_for_serial(&[0x01, 0xab]).unwrap();
         assert_eq!(good.status, Status::Good);
         let revoked = snapshot.status_for_serial(&[0xff]).unwrap();
@@ -216,15 +255,28 @@ mod tests {
     #[test]
     fn rejects_wrong_issuer_schema_and_duplicates() {
         let sha = sha256_hex(b"ca");
-        assert!(Snapshot::parse(body(&sha).as_bytes(), "wrong", "ca").is_err());
+        assert!(Snapshot::parse(&body(&sha), "wrong", "ca").is_err());
         assert!(matches!(
-            Snapshot::parse(body(&sha).as_bytes(), &sha, "other"),
+            Snapshot::parse(&body(&sha), &sha, "other"),
             Err(SnapshotError::IssuerIdMismatch { .. })
         ));
-        let wrong_schema = body(&sha).replace(SCHEMA, "other");
-        assert!(Snapshot::parse(wrong_schema.as_bytes(), &sha, "ca").is_err());
-        let duplicate = body(&sha).replace("\"00ff\"", "\"01ab\"");
-        assert!(Snapshot::parse(duplicate.as_bytes(), &sha, "ca").is_err());
+        let wrong_schema = cbor2::to_vec(&raw_body(&sha, "other")).unwrap();
+        assert!(Snapshot::parse(&wrong_schema, &sha, "ca").is_err());
+        let mut duplicate = raw_body(&sha, SCHEMA);
+        duplicate.entries[1].serial_hex = duplicate.entries[0].serial_hex.clone();
+        let duplicate = cbor2::to_vec(&duplicate).unwrap();
+        assert!(Snapshot::parse(&duplicate, &sha, "ca").is_err());
+    }
+
+    #[test]
+    fn rejects_legacy_json() {
+        let sha = sha256_hex(b"ca");
+        let legacy =
+            br#"{"schema":"kca-ocsp-status/v2","issuer":{"id":"ca","sha256":"sha"},"entries":[]}"#;
+        assert!(matches!(
+            Snapshot::parse(legacy, &sha, "ca"),
+            Err(SnapshotError::Cbor(_))
+        ));
     }
 
     #[test]