feat(ffe): support serial id (#1951)

# What does this PR do?

Support serial id propagation from UFC to assignment. Ported from our internal repo.


Co-authored-by: oleksii.shmalko <oleksii.shmalko@datadoghq.com>

Author: dd-oleksii

datadog-ffe-ffi/cbindgen.toml

@@ -23,6 +23,7 @@ renaming_overrides_prefixing = true
 [export.rename]
 "Error" = "ddog_Error"
 "Vec_U8" = "ddog_Vec_U8"
+"Option_I32" = "ddog_Option_I32"
 "ArrayMap_BorrowedStr__BorrowedStr" = "ddog_ffe_ArrayMap_BorrowedStr"
 "KeyValue_BorrowedStr__BorrowedStr" = "ddog_ffe_KeyValue_BorrowedStr"
 

datadog-ffe-ffi/src/assignment.rs

@@ -432,6 +432,23 @@ pub unsafe extern "C" fn ddog_ffe_assignment_get_error_message(
     }
 }
 
+/// Get the serial_id produced by evaluation.
+///
+/// Returns `None` if the assignment has no serial_id or evaluation did not produce any value.
+///
+/// # Safety
+/// `assignment` must be a valid handle.
+#[no_mangle]
+pub unsafe extern "C" fn ddog_ffe_assignment_get_serial_id(
+    assignment: Handle<ResolutionDetails>,
+) -> libdd_common_ffi::Option<i32> {
+    // SAFETY: the caller must ensure that assignment handle is valid.
+    match unsafe { assignment.as_ref() }.as_ref() {
+        Ok(a) => a.serial_id.into(),
+        Err(_) => libdd_common_ffi::Option::None,
+    }
+}
+
 /// # Safety
 /// `assignment` must be a valid handle.
 #[no_mangle]

datadog-ffe/src/rules_based/eval/eval_assignment.rs

@@ -105,6 +105,7 @@ impl Flag {
             variation_key: split.variation_key.clone(),
             allocation_key: allocation.key.clone(),
             reason,
+            serial_id: split.serial_id,
             do_log: allocation.do_log,
         })
     }

datadog-ffe/src/rules_based/ufc/assignment.rs

@@ -30,7 +30,8 @@ pub struct Assignment {
     pub allocation_key: Str,
     /// The reason for this assignment.
     pub reason: AssignmentReason,
-
+    /// Serial id for the selected split.
+    pub serial_id: Option<i32>,
     /// Whether this assignment is part of an experiment and should be logged.
     pub do_log: bool,
 }

datadog-ffe/src/rules_based/ufc/compiled_flag_config.rs

@@ -53,6 +53,7 @@ pub(crate) struct Split {
     pub shards: Vec<Shard>,
     pub variation_key: Str,
     pub value: AssignmentValue,
+    pub serial_id: Option<i32>,
 }
 
 #[derive(Debug, Clone)]
@@ -168,6 +169,7 @@ fn compile_split(
         shards,
         variation_key: split.variation_key,
         value: result,
+        serial_id: split.serial_id,
     })
 }
 

datadog-ffe/src/rules_based/ufc/models.rs

@@ -528,6 +528,8 @@ impl From<Vec<String>> for ConditionValue {
 pub(crate) struct SplitWire {
     pub shards: Vec<ShardWire>,
     pub variation_key: Str,
+    #[serde(default)]
+    pub serial_id: Option<i32>,
 }
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]

examples/ffi/ffe.c

@@ -154,6 +154,14 @@ void evaluate_and_print_flag(
     bool do_log = ddog_ffe_assignment_get_do_log(assignment);
     printf("  Do Log: %s\n", do_log ? "true" : "false");
 
+    // Get and print serial_id
+    struct ddog_Option_I32 serial_id = ddog_ffe_assignment_get_serial_id(assignment);
+    if (serial_id.tag == DDOG_OPTION_I32_SOME_I32) {
+        printf("  Serial ID: %d\n", serial_id.some);
+    } else {
+        printf("  Serial ID: (none)\n");
+    }
+
     // Get and print flag metadata
     struct ddog_ffe_ArrayMap_BorrowedStr metadata = ddog_ffe_assignnment_get_flag_metadata(assignment);
     if (metadata.count > 0) {