Basically working reading

needed also support for availableChunks

Author: franzpoeschel

include/openPMD/toolkit/ExternalBlockStorage.hpp

@@ -101,7 +101,7 @@ class ExternalBlockStorage
     void read(
         Offset blockOffset,
         Extent blockExtent,
-        nlohmann::json &fullJsonDataset,
+        nlohmann::json const &fullJsonDataset,
         nlohmann::json::json_pointer const &path,
         T *data);
 

src/IO/JSON/JSONIOHandlerImpl.cpp

@@ -1104,9 +1104,44 @@ void JSONIOHandlerImpl::availableChunks(
 {
     refreshFileFromParent(writable);
     auto filePosition = setAndGetFilePosition(writable);
-    auto &j = obtainJsonContents(writable)["data"];
-    *parameters.chunks = chunksInJSON(j);
-    chunk_assignment::mergeChunks(*parameters.chunks);
+    auto &j = obtainJsonContents(writable);
+
+    auto [extent, datasetmode] = getExtent(j, m_datasetMode.m_mode);
+
+    std::visit(
+        auxiliary::overloaded{
+            [&](DatasetMode::Dataset_t const &) {
+                *parameters.chunks = chunksInJSON(j.at("data"));
+                chunk_assignment::mergeChunks(*parameters.chunks);
+            },
+            [&](DatasetMode::Template_t const &) {
+                /* no-op, no chunks to be loaded */
+            },
+            [&](DatasetMode::External_t &) {
+                auto external_blocks = j.at("external_blocks");
+                auto &res = *parameters.chunks;
+                res.reserve(external_blocks.size());
+                for (auto it = external_blocks.begin();
+                     it != external_blocks.end();
+                     ++it)
+                {
+                    auto const &block = it.value();
+                    try
+                    {
+                        auto const &o = block.at("offset").get<Offset>();
+                        auto const &e = block.at("extent").get<Extent>();
+                        res.emplace_back(o, e);
+                    }
+                    catch (nlohmann::json::exception const &e)
+                    {
+                        std::cerr << "[JSONIOHandlerImpl::availableChunks] "
+                                     "Could not parse block '"
+                                  << it.key() << "'. Original error was:\n"
+                                  << e.what();
+                    }
+                }
+            }},
+        datasetmode.as_base());
 }
 
 void JSONIOHandlerImpl::openFile(

src/toolkit/ExternalBlockStorage.cpp

@@ -167,7 +167,7 @@ template <typename DatatypeHandling, typename T>
 void ExternalBlockStorage::read(
     Offset blockOffset,
     Extent blockExtent,
-    nlohmann::json &fullJsonDataset,
+    nlohmann::json const &fullJsonDataset,
     nlohmann::json::json_pointer const &path,
     T *data)
 {
@@ -176,7 +176,7 @@ void ExternalBlockStorage::read(
     {
         throw std::runtime_error("Inconsistent chunk storage in datatype.");
     }
-    auto external_blocks = dataset["external_blocks"];
+    auto external_blocks = dataset.at("external_blocks");
     bool found_a_precise_match = false;
     for (auto it = external_blocks.begin(); it != external_blocks.end(); ++it)
     {
@@ -247,7 +247,7 @@ void ExternalBlockStorage::sanitizeString(std::string &s)
     template void ExternalBlockStorage::read<datatypehandling, type>(          \
         Offset blockOffset,                                                    \
         Extent blockExtent,                                                    \
-        nlohmann::json & fullJsonDataset,                                      \
+        nlohmann::json const &fullJsonDataset,                                 \
         nlohmann::json::json_pointer const &path,                              \
         type *data);
 #define OPENPMD_INSTANTIATE(type)                                              \