[DAP-17] TaskConf AAD Part 1: Add canonical TaskConfiguration builder and conversions

aggregator_core/src/task.rs

@@ -54,6 +54,22 @@ pub enum BatchMode {
     },
 }
 
+impl BatchMode {
+    /// Returns the [`BatchConfig`] message representation of this batch mode, for inclusion in a
+    /// [`TaskConfiguration`](janus_messages::TaskConfiguration).
+    ///
+    /// This is the inverse of [`BatchMode::try_from(&BatchConfig)`](TryFrom). The
+    /// `batch_time_window_size` of [`BatchMode::LeaderSelected`] is a Janus-specific parameter that
+    /// is not part of the DAP batch configuration, and is silently dropped. Therefore, the HPKE AAD
+    /// does not force the aggregators to agree on the `batch_time_window_size`.
+    pub fn to_batch_config(&self) -> BatchConfig {
+        match self {
+            BatchMode::TimeInterval => BatchConfig::TimeInterval,
+            BatchMode::LeaderSelected { .. } => BatchConfig::LeaderSelected,
+        }
+    }
+}
+
 impl TryFrom<batch_mode::Code> for BatchMode {
     type Error = Error;
 
@@ -1392,8 +1408,8 @@ mod tests {
         vdaf::vdaf_dp_strategies,
     };
     use janus_messages::{
-        Duration, HpkeAeadId, HpkeConfig, HpkeConfigId, HpkeKdfId, HpkeKemId, HpkePublicKey,
-        TaskId, Time, TimePrecision,
+        BatchConfig, Duration, HpkeAeadId, HpkeConfig, HpkeConfigId, HpkeKdfId, HpkeKemId,
+        HpkePublicKey, TaskId, Time, TimePrecision,
     };
     use rand::random;
     use serde_json::json;
@@ -1407,6 +1423,33 @@ mod tests {
         },
     };
 
+    #[test]
+    fn batch_mode_to_batch_config() {
+        assert_eq!(
+            BatchMode::TimeInterval.to_batch_config(),
+            BatchConfig::TimeInterval
+        );
+        // The Janus-specific batch_time_window_size is dropped, so both leader-selected variants
+        // map to the same BatchConfig.
+        assert_eq!(
+            BatchMode::LeaderSelected {
+                batch_time_window_size: None,
+            }
+            .to_batch_config(),
+            BatchConfig::LeaderSelected
+        );
+        assert_eq!(
+            BatchMode::LeaderSelected {
+                batch_time_window_size: Some(Duration::from_seconds(
+                    3600,
+                    &TimePrecision::from_seconds(3600)
+                )),
+            }
+            .to_batch_config(),
+            BatchConfig::LeaderSelected
+        );
+    }
+
     #[test]
     fn leader_task_serialization() {
         roundtrip_encoding(

core/src/lib.rs

@@ -12,6 +12,7 @@ pub mod hpke;
 pub mod http;
 pub mod report_id;
 pub mod retries;
+pub mod task_config;
 #[cfg(feature = "test-util")]
 #[cfg_attr(docsrs, doc(cfg(feature = "test-util")))]
 pub mod test_util;

core/src/task_config.rs

@@ -0,0 +1,200 @@
+//! Construction of canonical [`TaskConfiguration`] messages from a task's internal parameters.
+//!
+//! In DAP-18, the task's [`TaskConfiguration`] is bound into the HPKE additional authenticated data
+//! (AAD) for input shares and aggregate shares. Every party (both aggregators, the client, and the
+//! collector) must independently reconstruct *byte-identical* [`TaskConfiguration`] bytes, or all
+//! decryption fails. [`build_task_configuration`] is the single canonical construction path that
+//! maps internal representations onto the wire format in exactly one place.
+//!
+//! Endpoint URLs are kept as [`janus_messages::Url`] — the raw bytes from the wire — and
+//! bound directly, per DAP-18 §4.1.
+
+use janus_messages::{
+    BatchConfig, Error, Interval, TaskConfiguration, TaskExtension, TimePrecision, Url as DapUrl,
+    VdafConfig,
+};
+
+/// Construct a canonical [`TaskConfiguration`] from a task's parameters. Endpoints are bound
+/// verbatim from their wire bytes (no normalization — see the module docs).
+#[allow(clippy::too_many_arguments)]
+pub fn build_task_configuration(
+    task_info: Vec<u8>,
+    leader_aggregator_endpoint: DapUrl,
+    helper_aggregator_endpoint: DapUrl,
+    time_precision: TimePrecision,
+    min_batch_size: u64,
+    batch_config: BatchConfig,
+    vdaf_config: VdafConfig,
+    task_interval: Option<Interval>,
+) -> Result<TaskConfiguration, Error> {
+    // The optional task_interval becomes the lone extension, or none.
+    let extensions = Vec::from_iter(task_interval.map(TaskExtension::TaskInterval));
+
+    TaskConfiguration::new(
+        task_info,
+        leader_aggregator_endpoint,
+        helper_aggregator_endpoint,
+        time_precision,
+        min_batch_size,
+        batch_config,
+        vdaf_config,
+        extensions,
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use assert_matches::assert_matches;
+    use janus_messages::{
+        BatchConfig, Duration, Error, Interval, Time, TimePrecision, Url as DapUrl, VdafConfig,
+    };
+    use prio::codec::Encode as _;
+
+    use super::build_task_configuration;
+
+    fn leader() -> DapUrl {
+        DapUrl::try_from("https://leader.example.com/".as_bytes()).unwrap()
+    }
+
+    fn helper() -> DapUrl {
+        DapUrl::try_from("https://helper.example.com/".as_bytes()).unwrap()
+    }
+
+    #[test]
+    fn endpoints_bound_verbatim() {
+        // A path-bearing endpoint with no trailing slash must be bound exactly as given: this code
+        // performs no normalization (forbidden by DAP-18 §4.1).
+        let config = build_task_configuration(
+            b"task".to_vec(),
+            DapUrl::try_from("https://leader.example.com/dap".as_bytes()).unwrap(),
+            DapUrl::try_from("https://helper.example.com/dap".as_bytes()).unwrap(),
+            TimePrecision::from_seconds(3600),
+            100,
+            BatchConfig::TimeInterval,
+            VdafConfig::Prio3Count,
+            None,
+        )
+        .unwrap();
+        assert_eq!(
+            config.leader_aggregator_endpoint().to_string(),
+            "https://leader.example.com/dap"
+        );
+        assert_eq!(
+            config.helper_aggregator_endpoint().to_string(),
+            "https://helper.example.com/dap"
+        );
+    }
+
+    #[test]
+    fn no_task_interval() {
+        let config = build_task_configuration(
+            b"task".to_vec(),
+            leader(),
+            helper(),
+            TimePrecision::from_seconds(3600),
+            100,
+            BatchConfig::TimeInterval,
+            VdafConfig::Prio3Count,
+            None,
+        )
+        .unwrap();
+        assert!(config.extensions().is_empty());
+        assert_eq!(config.task_interval(), None);
+    }
+
+    #[test]
+    fn carries_task_interval() {
+        let interval = Interval::new(
+            Time::from_time_precision_units(1000),
+            Duration::from_time_precision_units(28),
+        )
+        .unwrap();
+        let config = build_task_configuration(
+            b"task".to_vec(),
+            leader(),
+            helper(),
+            TimePrecision::from_seconds(3600),
+            100,
+            BatchConfig::TimeInterval,
+            VdafConfig::Prio3Count,
+            Some(interval),
+        )
+        .unwrap();
+        assert_eq!(config.task_interval(), Some(interval));
+    }
+
+    #[test]
+    fn rejects_empty_task_info() {
+        assert_matches!(
+            build_task_configuration(
+                Vec::new(),
+                leader(),
+                helper(),
+                TimePrecision::from_seconds(3600),
+                100,
+                BatchConfig::TimeInterval,
+                VdafConfig::Prio3Count,
+                None,
+            ),
+            Err(Error::InvalidParameter(_))
+        );
+    }
+
+    /// Pins the exact encoded bytes produced by the canonical builder. Because DAP implementations
+    /// can be non-Janus, this synthesized encoding is a cross-implementation wire-compatibility
+    /// contract, so we assert the bytes directly rather than only round-tripping.
+    #[test]
+    fn encoded_test_vector() {
+        let time_precision = TimePrecision::from_seconds(3600);
+        let config = build_task_configuration(
+            b"foobar".to_vec(),
+            DapUrl::try_from("https://example.com/".as_bytes()).unwrap(),
+            DapUrl::try_from("https://another.example.com/".as_bytes()).unwrap(),
+            time_precision,
+            10000,
+            BatchConfig::TimeInterval,
+            VdafConfig::Prio3Count,
+            Some(
+                Interval::new(
+                    Time::from_time_precision_units(1000000),
+                    Duration::from_time_precision_units(28),
+                )
+                .unwrap(),
+            ),
+        )
+        .unwrap();
+
+        assert_eq!(
+            hex::encode(config.get_encoded().unwrap()),
+            concat!(
+                // task_info: length 0x06, "foobar"
+                "06",
+                "666f6f626172",
+                // leader_aggregator_endpoint: length 0x0014, "https://example.com/"
+                "0014",
+                "68747470733a2f2f6578616d706c652e636f6d2f",
+                // helper_aggregator_endpoint: length 0x001c, "https://another.example.com/"
+                "001c",
+                "68747470733a2f2f616e6f746865722e6578616d706c652e636f6d2f",
+                // time_precision: 3600
+                "0000000000000e10",
+                // min_batch_size: 10000
+                "0000000000002710",
+                // batch_config: TimeInterval (mode 0x01, empty config)
+                "01",
+                "0000",
+                // vdaf_config: Prio3Count (type 0x00000001, empty config)
+                "00000001",
+                "0000",
+                // extensions: u16 length prefix, then one task_interval extension
+                "0014",
+                // extension_type: task_interval (0x0001)
+                "0001",
+                // extension_data: u16 length 0x10, Interval{start: 1000000, duration: 28}
+                "0010",
+                "00000000000f4240",
+                "000000000000001c",
+            )
+        );
+    }
+}