Expose the build epoch via the Swift bindings

Author: jakepetroules

products/libllbuild/BuildDB-C-API.cpp

@@ -162,6 +162,10 @@ class CAPIBuildDB: public BuildDBDelegate {
     buildUpKeyCache(keys_out);
     return success;
   }
+
+  Epoch getCurrentEpoch(bool *success_out, std::string *error_out) {
+    return _db.get()->getCurrentEpoch(success_out, error_out);
+  }
 };
 
 const llb_data_t mapData(std::vector<uint8_t> input) {
@@ -372,3 +376,14 @@ bool llb_database_get_keys_and_results(llb_database_t *database, llb_database_fe
   return success;
 }
 
+uint64_t llb_database_get_epoch(llb_database_t *database, llb_data_t *_Nullable error_out) {
+  auto db = (CAPIBuildDB *)database;
+  bool success;
+  std::string error;
+  auto epoch = db->getCurrentEpoch(&success, &error);
+  if (!success && error_out) {
+    error_out->length = error.size();
+    error_out->data = (const uint8_t *)strdup(error.c_str());
+  }
+  return epoch;
+}

products/libllbuild/include/llbuild/db.h

@@ -105,6 +105,8 @@ llb_database_get_keys(llb_database_t *database, llb_database_fetch_result_t *_Nu
 
 LLBUILD_EXPORT bool llb_database_get_keys_and_results(llb_database_t *database, llb_database_fetch_result_t *_Nullable *_Nonnull keysAndResults_out, llb_data_t *_Nullable error_out);
 
+LLBUILD_EXPORT uint64_t llb_database_get_epoch(llb_database_t *database, llb_data_t *_Nullable error_out);
+
 LLBUILD_ASSUME_NONNULL_END
 
 #endif

products/llbuildSwift/BuildDBBindings.swift

@@ -309,4 +309,15 @@ public final class BuildDB {
         llb_database_destroy_result(&result)
         return mappedResult
     }
+
+    public func currentBuildEpoch() throws -> UInt64 {
+        let errorPtr = MutableStringPointer()
+        let epoch = llb_database_get_epoch(_database, &errorPtr.ptr)
+
+        if let error = errorPtr.msg {
+            throw Error.operationDidFail(error: error)
+        }
+
+        return epoch
+    }
 }