DPL: add ability to get CCDB blobs without deserialization

Author: ktf

Framework/Core/include/Framework/DataRefUtils.h

@@ -23,6 +23,7 @@
 
 #include <gsl/gsl>
 
+#include <span>
 #include <type_traits>
 #include <typeinfo>
 
@@ -184,6 +185,10 @@ struct DataRefUtils {
   // Decode a CCDB object using the CcdbApi.
   static void* decodeCCDB(DataRef const& ref, std::type_info const& info);
   static std::map<std::string, std::string> extractCCDBHeaders(DataRef const& ref);
+  /// Return a span over the raw CCDB payload bytes, stripping the flattened HTTP
+  /// headers footer that CCDBFetcherHelper appends. Use this when the CCDB entry is
+  /// a binary blob rather than a ROOT-serialised object.
+  static std::span<const char> getCCDBPayloadBlob(DataRef const& ref);
 
   static o2::header::DataHeader::PayloadSizeType getPayloadSize(const DataRef& ref)
   {

Framework/Core/include/Framework/InputRecord.h

@@ -35,6 +35,7 @@
 #include <memory>
 #include <type_traits>
 #include <concepts>
+#include <span>
 
 #include <fairmq/FwdDecls.h>
 
@@ -45,6 +46,12 @@ namespace o2::framework
 struct CCDBMetadataExtractor {
 };
 
+/// Tag type to retrieve the raw binary payload of a CCDB entry without ROOT
+/// deserialization. The returned span is valid for the duration of the
+/// processing callback. Use as: inputs.get<CCDBBlob>("binding")
+struct CCDBBlob {
+};
+
 struct InputSpec;
 class InputSpan;
 class CallbackService;
@@ -522,6 +529,18 @@ class InputRecord
     return cache.idToMetadata[id];
   }
 
+  template <typename T = DataRef, typename R>
+  std::span<const char> get(R binding, int part = 0) const
+    requires std::same_as<T, CCDBBlob>
+  {
+    auto ref = getRef(binding, part);
+    auto header = DataRefUtils::getHeader<header::DataHeader*>(ref);
+    if (header->payloadSerializationMethod != header::gSerializationMethodCCDB) {
+      throw runtime_error("Attempt to extract CCDBBlob from a non-CCDB-serialized message");
+    }
+    return DataRefUtils::getCCDBPayloadBlob(ref);
+  }
+
   template <typename T>
     requires(std::same_as<T, DataRef>)
   decltype(auto) get(ConcreteDataMatcher matcher, int part = 0)

Framework/Core/src/DataRefUtils.cxx

@@ -9,6 +9,7 @@
 // granted to it by virtue of its status as an Intergovernmental Organization
 // or submit itself to any jurisdiction.
 
+#include <span>
 #include <typeinfo>
 #include <cstring>
 #include "Framework/DataRefUtils.h"
@@ -148,4 +149,19 @@ std::map<std::string, std::string> DataRefUtils::extractCCDBHeaders(DataRef cons
   return res;
 }
 
+std::span<const char> DataRefUtils::getCCDBPayloadBlob(DataRef const& ref)
+{
+  auto* dh = o2::header::get<o2::header::DataHeader*>(ref.header);
+  const char* buff = ref.payload;
+  size_t payloadSize = dh->payloadSize;
+  constexpr char FlatHeaderAnnot[] = "$HEADER$";
+  constexpr size_t Offset = sizeof(int) + sizeof(FlatHeaderAnnot);
+  int headerSize = 0;
+  if (payloadSize >= Offset &&
+      !std::strncmp(buff + payloadSize - sizeof(FlatHeaderAnnot), FlatHeaderAnnot, sizeof(FlatHeaderAnnot))) {
+    headerSize = *reinterpret_cast<const int*>(buff + payloadSize - Offset);
+  }
+  return {buff, payloadSize - headerSize};
+}
+
 } // namespace o2::framework