--- a/Framework/Common/DatabaseManager.cpp	Tue Apr 13 12:07:30 2021 +0200
+++ b/Framework/Common/DatabaseManager.cpp	Tue Apr 13 17:00:02 2021 +0200
@@ -269,7 +269,7 @@
     if (active_)
     {
       manager_.CommitTransaction();
-      active_ = true;
+      active_ = false;
     }
     else
     {
@@ -283,7 +283,7 @@
     if (active_)
     {
       manager_.RollbackTransaction();
-      active_ = true;
+      active_ = false;
     }
     else
     {

--- a/Framework/MySQL/MySQLStatement.cpp	Tue Apr 13 12:07:30 2021 +0200
+++ b/Framework/MySQL/MySQLStatement.cpp	Tue Apr 13 17:00:02 2021 +0200
@@ -153,6 +153,7 @@
         case MYSQL_TYPE_STRING:
         case MYSQL_TYPE_VAR_STRING:
         case MYSQL_TYPE_BLOB:
+        case MYSQL_TYPE_LONG_BLOB:
           // https://medium.com/@adamhooper/in-mysql-never-use-utf8-use-utf8mb4-11761243e434
           switch (field.charsetnr)
           {

--- a/Framework/Plugins/StorageBackend.cpp	Tue Apr 13 12:07:30 2021 +0200
+++ b/Framework/Plugins/StorageBackend.cpp	Tue Apr 13 17:00:02 2021 +0200
@@ -85,10 +85,10 @@
   }
     
 
-  void StorageBackend::Accessor::Create(const std::string& uuid,
-                                        const void* content,
-                                        size_t size,
-                                        OrthancPluginContentType type)
+  void StorageBackend::AccessorBase::Create(const std::string& uuid,
+                                            const void* content,
+                                            size_t size,
+                                            OrthancPluginContentType type)
   {
     DatabaseManager::Transaction transaction(manager_, TransactionType_ReadWrite);
 
@@ -113,9 +113,9 @@
   }
 
 
-  void StorageBackend::Accessor::Read(StorageBackend::IFileContentVisitor& visitor,
-                                      const std::string& uuid,
-                                      OrthancPluginContentType type) 
+  void StorageBackend::AccessorBase::ReadWhole(StorageBackend::IFileContentVisitor& visitor,
+                                               const std::string& uuid,
+                                               OrthancPluginContentType type) 
   {
     DatabaseManager::Transaction transaction(manager_, TransactionType_ReadOnly);
 
@@ -170,8 +170,18 @@
   }
 
 
-  void StorageBackend::Accessor::Remove(const std::string& uuid,
-                                        OrthancPluginContentType type)
+  void StorageBackend::AccessorBase::ReadRange(IFileContentVisitor& visitor,
+                                               const std::string& uuid,
+                                               OrthancPluginContentType type,
+                                               uint64_t start,
+                                               uint64_t length)
+  {
+    throw Orthanc::OrthancException(Orthanc::ErrorCode_NotImplemented);
+  }
+
+
+  void StorageBackend::AccessorBase::Remove(const std::string& uuid,
+                                            OrthancPluginContentType type)
   {
     DatabaseManager::Transaction transaction(manager_, TransactionType_ReadWrite);
 
@@ -212,8 +222,8 @@
       }
       else
       {
-        StorageBackend::Accessor accessor(*backend_);
-        accessor.Create(uuid, content, static_cast<size_t>(size), type);
+        std::unique_ptr<StorageBackend::IAccessor> accessor(backend_->CreateAccessor());
+        accessor->Create(uuid, content, static_cast<size_t>(size), type);
         return OrthancPluginErrorCode_Success;
       }
     }
@@ -237,6 +247,10 @@
         target_(target),
         success_(false)
       {
+        if (target == NULL)
+        {
+          throw Orthanc::OrthancException(Orthanc::ErrorCode_NullPointer);
+        }
       }
 
       virtual bool IsSuccess() const ORTHANC_OVERRIDE
@@ -269,24 +283,94 @@
         }
       }
     };
-    
+
+
     try
     {
       if (backend_.get() == NULL)
       {
         throw Orthanc::OrthancException(Orthanc::ErrorCode_BadSequenceOfCalls);
       }
-      else if (target == NULL)
+      else
+      {
+        Visitor visitor(target);
+
+        {
+          std::unique_ptr<StorageBackend::IAccessor> accessor(backend_->CreateAccessor());
+          accessor->ReadWhole(visitor, uuid, type);
+        }
+
+        return OrthancPluginErrorCode_Success;
+      }
+    }
+    ORTHANC_PLUGINS_DATABASE_CATCH;
+  }
+
+  
+  static OrthancPluginErrorCode StorageReadRange(OrthancPluginMemoryBuffer64* target,
+                                                 const char* uuid,
+                                                 OrthancPluginContentType type,
+                                                 uint64_t start)
+  {
+    class Visitor : public StorageBackend::IFileContentVisitor
+    {
+    private:
+      OrthancPluginMemoryBuffer64* target_;  // This buffer is already allocated by the Orthanc core
+      bool                         success_;
+      
+    public:
+      Visitor(OrthancPluginMemoryBuffer64* target) :
+        target_(target),
+        success_(false)
       {
-        throw Orthanc::OrthancException(Orthanc::ErrorCode_NullPointer);
+        if (target == NULL)
+        {
+          throw Orthanc::OrthancException(Orthanc::ErrorCode_NullPointer);
+        }
+      }
+
+      virtual bool IsSuccess() const ORTHANC_OVERRIDE
+      {
+        return success_;
+      }
+      
+      virtual void Assign(const std::string& content) ORTHANC_OVERRIDE
+      {
+        if (success_)
+        {
+          throw Orthanc::OrthancException(Orthanc::ErrorCode_InternalError);
+        }
+        else
+        {
+          if (content.size() != target_->size)
+          {
+            throw Orthanc::OrthancException(Orthanc::ErrorCode_InternalError);
+          }
+          
+          if (!content.empty())
+          {
+            memcpy(target_->data, content.c_str(), content.size());
+          }
+
+          success_ = true;
+        }
+      }
+    };
+
+
+    try
+    {
+      if (backend_.get() == NULL)
+      {
+        throw Orthanc::OrthancException(Orthanc::ErrorCode_BadSequenceOfCalls);
       }
       else
       {
         Visitor visitor(target);
 
         {
-          StorageBackend::Accessor accessor(*backend_);
-          accessor.Read(visitor, uuid, type);
+          std::unique_ptr<StorageBackend::IAccessor> accessor(backend_->CreateAccessor());
+          accessor->ReadRange(visitor, uuid, type, start, target->size);
         }
 
         return OrthancPluginErrorCode_Success;
@@ -377,8 +461,8 @@
         Visitor visitor(data, size);
 
         {
-          StorageBackend::Accessor accessor(*backend_);
-          accessor.Read(visitor, uuid, type);
+          std::unique_ptr<StorageBackend::IAccessor> accessor(backend_->CreateAccessor());
+          accessor->ReadWhole(visitor, uuid, type);
         }
 
         return OrthancPluginErrorCode_Success;
@@ -399,8 +483,8 @@
       }
       else
       {
-        StorageBackend::Accessor accessor(*backend_);
-        accessor.Remove(uuid, type);
+        std::unique_ptr<StorageBackend::IAccessor> accessor(backend_->CreateAccessor());
+        accessor->Remove(uuid, type);
         return OrthancPluginErrorCode_Success;
       }
     }
@@ -434,8 +518,13 @@
 #  if ORTHANC_PLUGINS_VERSION_IS_ABOVE(1, 9, 0)
       if (OrthancPluginCheckVersionAdvanced(context, 1, 9, 0) == 1)
       {
-        OrthancPluginRegisterStorageArea2(context_, StorageCreate, StorageReadWhole,
-                                          NULL /* TODO - StorageReadRange */, StorageRemove);
+        OrthancPluginStorageReadRange readRange = NULL;
+        if (backend_->HasReadRange())
+        {
+          readRange = StorageReadRange;
+        }
+        
+        OrthancPluginRegisterStorageArea2(context_, StorageCreate, StorageReadWhole, readRange, StorageRemove);
         hasLoadedV2 = true;
       }
 #  endif
@@ -456,44 +545,67 @@
   }
 
 
-  void StorageBackend::Accessor::ReadToString(std::string& target,
-                                              const std::string& uuid,
-                                              OrthancPluginContentType type)
+  class StorageBackend::StringVisitor : public StorageBackend::IFileContentVisitor
   {
-    class Visitor : public StorageBackend::IFileContentVisitor
+  private:
+    std::string&  target_;
+    bool          success_;
+      
+  public:
+    StringVisitor(std::string& target) :
+      target_(target),
+      success_(false)
     {
-    private:
-      std::string&  target_;
-      bool          success_;
-      
-    public:
-      Visitor(std::string& target) :
-        target_(target),
-        success_(false)
-      {
-      }
+    }
 
-      virtual bool IsSuccess() const ORTHANC_OVERRIDE
-      {
-        return success_;
-      }
+    virtual bool IsSuccess() const ORTHANC_OVERRIDE
+    {
+      return success_;
+    }
       
-      virtual void Assign(const std::string& content) ORTHANC_OVERRIDE
+    virtual void Assign(const std::string& content) ORTHANC_OVERRIDE
+    {
+      if (success_)
       {
-        if (success_)
-        {
-          throw Orthanc::OrthancException(Orthanc::ErrorCode_InternalError);
-        }
-        else
-        {
-          target_.assign(content);
-          success_ = true;
-        }
+        throw Orthanc::OrthancException(Orthanc::ErrorCode_InternalError);
       }
-    };
+      else
+      {
+        target_.assign(content);
+        success_ = true;
+      }
+    }
+  };
     
 
-    Visitor visitor(target);
-    Read(visitor, uuid, type);
+  void StorageBackend::ReadWholeToString(std::string& target,
+                                         IAccessor& accessor,
+                                         const std::string& uuid,
+                                         OrthancPluginContentType type)
+  {
+    StringVisitor visitor(target);
+    accessor.ReadWhole(visitor, uuid, type);
+
+    if (!visitor.IsSuccess())
+    {
+      throw Orthanc::OrthancException(Orthanc::ErrorCode_InternalError);
+    }
+  }
+    
+
+  void StorageBackend::ReadRangeToString(std::string& target,
+                                         IAccessor& accessor,
+                                         const std::string& uuid,
+                                         OrthancPluginContentType type,
+                                         uint64_t start,
+                                         uint64_t length)
+  {
+    StringVisitor visitor(target);
+    accessor.ReadRange(visitor, uuid, type, start, length);
+
+    if (!visitor.IsSuccess())
+    {
+      throw Orthanc::OrthancException(Orthanc::ErrorCode_InternalError);
+    }
   }
 }

--- a/Framework/Plugins/StorageBackend.h	Tue Apr 13 12:07:30 2021 +0200
+++ b/Framework/Plugins/StorageBackend.h	Tue Apr 13 17:00:02 2021 +0200
@@ -32,15 +32,6 @@
 {
   class StorageBackend : public boost::noncopyable
   {
-  private:
-    boost::mutex                       mutex_;
-    std::unique_ptr<DatabaseManager>   manager_;
-
-    DatabaseManager& GetManager();
-    
-  protected:
-    void SetDatabase(IDatabase* database);  // Takes ownership
-
   public:
     class IFileContentVisitor : public boost::noncopyable
     {
@@ -54,44 +45,109 @@
       virtual bool IsSuccess() const = 0;
     };
 
-    class Accessor : public boost::noncopyable
+    class IAccessor : public boost::noncopyable
+    {
+    public:
+      virtual ~IAccessor()
+      {
+      }
+
+      virtual void Create(const std::string& uuid,
+                          const void* content,
+                          size_t size,
+                          OrthancPluginContentType type) = 0;
+
+      virtual void ReadWhole(IFileContentVisitor& visitor,
+                             const std::string& uuid,
+                             OrthancPluginContentType type) = 0;
+
+      virtual void ReadRange(IFileContentVisitor& visitor,
+                             const std::string& uuid,
+                             OrthancPluginContentType type,
+                             uint64_t start,
+                             uint64_t length) = 0;
+      
+      virtual void Remove(const std::string& uuid,
+                          OrthancPluginContentType type) = 0;
+    };
+    
+  private:
+    class StringVisitor;
+    
+    boost::mutex                       mutex_;
+    std::unique_ptr<DatabaseManager>   manager_;
+
+    DatabaseManager& GetManager();
+    
+  protected:
+    class AccessorBase : public IAccessor
     {
     private:
       boost::mutex::scoped_lock  lock_;
       DatabaseManager&           manager_;
 
     public:
-      Accessor(StorageBackend& backend) :
+      AccessorBase(StorageBackend& backend) :
         lock_(backend.mutex_),
         manager_(backend.GetManager())
       {
       }
-        
-      void Create(const std::string& uuid,
-                  const void* content,
-                  size_t size,
-                  OrthancPluginContentType type);
+
+      DatabaseManager& GetManager() const
+      {
+        return manager_;
+      }
+
+      virtual void Create(const std::string& uuid,
+                          const void* content,
+                          size_t size,
+                          OrthancPluginContentType type);
 
-      void Read(IFileContentVisitor& visitor,
-                const std::string& uuid,
-                OrthancPluginContentType type);
+      virtual void ReadWhole(IFileContentVisitor& visitor,
+                             const std::string& uuid,
+                             OrthancPluginContentType type);
 
-      void Remove(const std::string& uuid,
-                  OrthancPluginContentType type);
-
-      // For unit tests
-      void ReadToString(std::string& target,
-                        const std::string& uuid,
-                        OrthancPluginContentType type);
+      virtual void ReadRange(IFileContentVisitor& visitor,
+                             const std::string& uuid,
+                             OrthancPluginContentType type,
+                             uint64_t start,
+                             uint64_t length);
+      
+      virtual void Remove(const std::string& uuid,
+                          OrthancPluginContentType type);
     };
     
+    void SetDatabase(IDatabase* database);  // Takes ownership
+
+    virtual bool HasReadRange() const = 0;
+
+  public:
     virtual ~StorageBackend()
     {
     }
 
+    virtual IAccessor* CreateAccessor()
+    {
+      return new AccessorBase(*this);
+    }
+
     static void Register(OrthancPluginContext* context,
                          StorageBackend* backend);   // Takes ownership
 
     static void Finalize();
+
+    // For unit tests
+    static void ReadWholeToString(std::string& target,
+                                  IAccessor& accessor,
+                                  const std::string& uuid,
+                                  OrthancPluginContentType type);
+
+    // For unit tests
+    static void ReadRangeToString(std::string& target,
+                                  IAccessor& accessor,
+                                  const std::string& uuid,
+                                  OrthancPluginContentType type,
+                                  uint64_t start,
+                                  uint64_t length);
   };
 }

--- a/Framework/PostgreSQL/PostgreSQLResult.cpp	Tue Apr 13 12:07:30 2021 +0200
+++ b/Framework/PostgreSQL/PostgreSQLResult.cpp	Tue Apr 13 17:00:02 2021 +0200
@@ -175,6 +175,10 @@
   {
     CheckColumn(column, OIDOID);
 
+    /**
+     * In PostgreSQL, the type "Oid" corresponds to "unsigned int", cf.
+     * /usr/include/postgresql/10/server/postgres_ext.h
+     **/
     Oid oid;
     assert(PQfsize(reinterpret_cast<PGresult*>(result_), column) == sizeof(oid));
 

--- a/MySQL/NEWS	Tue Apr 13 12:07:30 2021 +0200
+++ b/MySQL/NEWS	Tue Apr 13 17:00:02 2021 +0200
@@ -1,7 +1,8 @@
 Pending changes in the mainline
 ===============================
 
-* Support of "OrthancPluginRegisterStorageArea2()" from Orthanc SDK 1.9.0
+* Support of retries for collisions between multiple writers, from Orthanc SDK 1.9.2
+* Support of range reads for the storage area, from Orthanc SDK 1.9.0
 
 
 Release 3.0 (2020-12-16)

--- a/MySQL/Plugins/MySQLStorageArea.cpp	Tue Apr 13 12:07:30 2021 +0200
+++ b/MySQL/Plugins/MySQLStorageArea.cpp	Tue Apr 13 17:00:02 2021 +0200
@@ -21,6 +21,7 @@
 
 #include "MySQLStorageArea.h"
 
+#include "../../Framework/Common/BinaryStringValue.h"
 #include "../../Framework/MySQL/MySQLDatabase.h"
 #include "../../Framework/MySQL/MySQLTransaction.h"
 #include "MySQLDefinitions.h"
@@ -98,4 +99,94 @@
     ConfigureDatabase(*database, parameters, clearAll);
     SetDatabase(database.release());
   }
+
+
+  class MySQLStorageArea::Accessor : public StorageBackend::AccessorBase
+  {
+  public:
+    Accessor(MySQLStorageArea& backend) :
+      AccessorBase(backend)
+    {
+    }
+
+    virtual void ReadRange(IFileContentVisitor& visitor,
+                           const std::string& uuid,
+                           OrthancPluginContentType type,
+                           uint64_t start,
+                           uint64_t length) ORTHANC_OVERRIDE
+    {
+      DatabaseManager::Transaction transaction(GetManager(), TransactionType_ReadOnly);
+
+      {
+        // https://stackoverflow.com/a/6545557/881731
+        DatabaseManager::CachedStatement statement(
+          STATEMENT_FROM_HERE, GetManager(),
+          "SELECT SUBSTRING(content, ${start}, ${length}) FROM StorageArea WHERE uuid=${uuid} AND type=${type}");
+     
+        statement.SetParameterType("uuid", ValueType_Utf8String);
+        statement.SetParameterType("type", ValueType_Integer64);
+        statement.SetParameterType("start", ValueType_Integer64);
+        statement.SetParameterType("length", ValueType_Integer64);
+
+        Dictionary args;
+        args.SetUtf8Value("uuid", uuid);
+        args.SetIntegerValue("type", type);
+        args.SetIntegerValue("length", length);
+
+        /**
+         * "For all forms of SUBSTRING(), the position of the first
+         * character in the string from which the substring is to be
+         * extracted is reckoned as 1." => hence the "+ 1"
+         * https://dev.mysql.com/doc/refman/8.0/en/string-functions.html#function_substring
+         **/
+        args.SetIntegerValue("start", start + 1);
+     
+        statement.Execute(args);
+
+        if (statement.IsDone())
+        {
+          throw Orthanc::OrthancException(Orthanc::ErrorCode_UnknownResource);
+        }
+        else if (statement.GetResultFieldsCount() != 1)
+        {
+          throw Orthanc::OrthancException(Orthanc::ErrorCode_Database);        
+        }
+        else
+        {
+          const IValue& value = statement.GetResultField(0);
+      
+          if (value.GetType() == ValueType_BinaryString)
+          {
+            const std::string& content = dynamic_cast<const BinaryStringValue&>(value).GetContent();
+
+            if (static_cast<uint64_t>(content.size()) == length)
+            {
+              visitor.Assign(content);
+            }
+            else
+            {
+              throw Orthanc::OrthancException(Orthanc::ErrorCode_BadRange);
+            }
+          }
+          else
+          {
+            throw Orthanc::OrthancException(Orthanc::ErrorCode_Database);        
+          }
+        }
+      }
+
+      transaction.Commit();
+
+      if (!visitor.IsSuccess())
+      {
+        throw Orthanc::OrthancException(Orthanc::ErrorCode_Database, "Could not read range from the storage area");
+      }
+    }
+  };
+  
+
+  StorageBackend::IAccessor* MySQLStorageArea::CreateAccessor()
+  {
+    return new Accessor(*this);
+  }
 }

--- a/MySQL/Plugins/MySQLStorageArea.h	Tue Apr 13 12:07:30 2021 +0200
+++ b/MySQL/Plugins/MySQLStorageArea.h	Tue Apr 13 17:00:02 2021 +0200
@@ -30,12 +30,22 @@
   class MySQLStorageArea : public StorageBackend
   {
   private:
+    class Accessor;
+    
     void ConfigureDatabase(MySQLDatabase& db,
                            const MySQLParameters& parameters,
                            bool clearAll);
-    
+
+  protected:
+    virtual bool HasReadRange() const
+    {
+      return true;
+    }
+
   public:
     MySQLStorageArea(const MySQLParameters& parameters,
                      bool clearAll);
+
+    virtual IAccessor* CreateAccessor();
   };
 }

--- a/MySQL/UnitTests/UnitTestsMain.cpp	Tue Apr 13 12:07:30 2021 +0200
+++ b/MySQL/UnitTests/UnitTestsMain.cpp	Tue Apr 13 17:00:02 2021 +0200
@@ -162,7 +162,7 @@
   OrthancDatabases::MySQLStorageArea storageArea(globalParameters_, true /* clear database */);
 
   {
-    OrthancDatabases::MySQLStorageArea::Accessor accessor(storageArea);
+    std::unique_ptr<OrthancDatabases::StorageBackend::IAccessor> accessor(storageArea.CreateAccessor());
     
     ASSERT_EQ(0, CountFiles(*database));
   
@@ -170,15 +170,16 @@
     {
       std::string uuid = boost::lexical_cast<std::string>(i);
       std::string value = "Value " + boost::lexical_cast<std::string>(i * 2);
-      accessor.Create(uuid, value.c_str(), value.size(), OrthancPluginContentType_Unknown);
+      accessor->Create(uuid, value.c_str(), value.size(), OrthancPluginContentType_Unknown);
     }
 
     std::string buffer;
-    ASSERT_THROW(accessor.ReadToString(buffer, "nope", OrthancPluginContentType_Unknown), 
+    ASSERT_THROW(OrthancDatabases::StorageBackend::ReadWholeToString(
+                   buffer, *accessor, "nope", OrthancPluginContentType_Unknown), 
                  Orthanc::OrthancException);
   
     ASSERT_EQ(10, CountFiles(*database));
-    accessor.Remove("5", OrthancPluginContentType_Unknown);
+    accessor->Remove("5", OrthancPluginContentType_Unknown);
 
     ASSERT_EQ(9, CountFiles(*database));
 
@@ -190,19 +191,20 @@
 
       if (i == 5)
       {
-        ASSERT_THROW(accessor.ReadToString(buffer, uuid, OrthancPluginContentType_Unknown), 
+        ASSERT_THROW(OrthancDatabases::StorageBackend::ReadWholeToString(
+                       buffer, *accessor, uuid, OrthancPluginContentType_Unknown), 
                      Orthanc::OrthancException);
       }
       else
       {
-        accessor.ReadToString(buffer, uuid, OrthancPluginContentType_Unknown);
+        OrthancDatabases::StorageBackend::ReadWholeToString(buffer, *accessor, uuid, OrthancPluginContentType_Unknown);
         ASSERT_EQ(expected, buffer);
       }
     }
 
     for (int i = 0; i < 10; i++)
     {
-      accessor.Remove(boost::lexical_cast<std::string>(i), OrthancPluginContentType_Unknown);
+      accessor->Remove(boost::lexical_cast<std::string>(i), OrthancPluginContentType_Unknown);
     }
 
     ASSERT_EQ(0, CountFiles(*database));
@@ -210,6 +212,76 @@
 }
 
 
+TEST(MySQL, StorageReadRange)
+{
+  std::unique_ptr<OrthancDatabases::MySQLDatabase> database(
+    OrthancDatabases::MySQLDatabase::OpenDatabaseConnection(globalParameters_));
+  
+  OrthancDatabases::MySQLStorageArea storageArea(globalParameters_, true /* clear database */);
+
+  {
+    std::unique_ptr<OrthancDatabases::StorageBackend::IAccessor> accessor(storageArea.CreateAccessor());
+    ASSERT_EQ(0, CountFiles(*database));  
+    accessor->Create("uuid", "abcd\0\1\2\3\4\5", 10, OrthancPluginContentType_Unknown);
+    ASSERT_EQ(1u, CountFiles(*database));  
+  }
+
+  {
+    std::unique_ptr<OrthancDatabases::StorageBackend::IAccessor> accessor(storageArea.CreateAccessor());
+    ASSERT_EQ(1u, CountFiles(*database));
+
+    std::string s;
+    OrthancDatabases::StorageBackend::ReadWholeToString(s, *accessor, "uuid", OrthancPluginContentType_Unknown);
+    ASSERT_EQ(10u, s.size());
+    ASSERT_EQ('a', s[0]);
+    ASSERT_EQ('d', s[3]);
+    ASSERT_EQ('\0', s[4]);
+    ASSERT_EQ('\5', s[9]);
+
+    OrthancDatabases::StorageBackend::ReadRangeToString(s, *accessor, "uuid", OrthancPluginContentType_Unknown, 0, 0);
+    ASSERT_TRUE(s.empty());
+
+    OrthancDatabases::StorageBackend::ReadRangeToString(s, *accessor, "uuid", OrthancPluginContentType_Unknown, 0, 1);
+    ASSERT_EQ(1u, s.size());
+    ASSERT_EQ('a', s[0]);
+
+    OrthancDatabases::StorageBackend::ReadRangeToString(s, *accessor, "uuid", OrthancPluginContentType_Unknown, 4, 1);
+    ASSERT_EQ(1u, s.size());
+    ASSERT_EQ('\0', s[0]);
+
+    OrthancDatabases::StorageBackend::ReadRangeToString(s, *accessor, "uuid", OrthancPluginContentType_Unknown, 9, 1);
+    ASSERT_EQ(1u, s.size());
+    ASSERT_EQ('\5', s[0]);
+
+    OrthancDatabases::StorageBackend::ReadRangeToString(s, *accessor, "uuid", OrthancPluginContentType_Unknown, 10, 0);
+    ASSERT_TRUE(s.empty());
+
+    // Cannot read non-empty range after the end of the string
+    ASSERT_THROW(OrthancDatabases::StorageBackend::ReadRangeToString(
+                   s, *accessor, "uuid", OrthancPluginContentType_Unknown, 10, 1), Orthanc::OrthancException);
+
+    OrthancDatabases::StorageBackend::ReadRangeToString(s, *accessor, "uuid", OrthancPluginContentType_Unknown, 0, 4);
+    ASSERT_EQ(4u, s.size());
+    ASSERT_EQ('a', s[0]);
+    ASSERT_EQ('b', s[1]);
+    ASSERT_EQ('c', s[2]);
+    ASSERT_EQ('d', s[3]);
+
+    OrthancDatabases::StorageBackend::ReadRangeToString(s, *accessor, "uuid", OrthancPluginContentType_Unknown, 4, 6);
+    ASSERT_EQ(6u, s.size());
+    ASSERT_EQ('\0', s[0]);
+    ASSERT_EQ('\1', s[1]);
+    ASSERT_EQ('\2', s[2]);
+    ASSERT_EQ('\3', s[3]);
+    ASSERT_EQ('\4', s[4]);
+    ASSERT_EQ('\5', s[5]);
+
+    ASSERT_THROW(OrthancDatabases::StorageBackend::ReadRangeToString(
+                   s, *accessor, "uuid", OrthancPluginContentType_Unknown, 4, 7), Orthanc::OrthancException);
+  }
+}
+
+
 TEST(MySQL, ImplicitTransaction)
 {
   OrthancDatabases::MySQLDatabase::ClearDatabase(globalParameters_);  

--- a/PostgreSQL/Plugins/PostgreSQLStorageArea.h	Tue Apr 13 12:07:30 2021 +0200
+++ b/PostgreSQL/Plugins/PostgreSQLStorageArea.h	Tue Apr 13 17:00:02 2021 +0200
@@ -33,6 +33,12 @@
                            const PostgreSQLParameters& parameters,
                            bool clearAll);
 
+  protected:
+    virtual bool HasReadRange() const
+    {
+      return false;  // TODO
+    }
+
   public:
     PostgreSQLStorageArea(const PostgreSQLParameters& parameters,
                           bool clearAll);

--- a/PostgreSQL/UnitTests/PostgreSQLTests.cpp	Tue Apr 13 12:07:30 2021 +0200
+++ b/PostgreSQL/UnitTests/PostgreSQLTests.cpp	Tue Apr 13 17:00:02 2021 +0200
@@ -363,7 +363,7 @@
   PostgreSQLStorageArea storageArea(globalParameters_, true /* clear database */);
 
   {
-    PostgreSQLStorageArea::Accessor accessor(storageArea);
+    std::unique_ptr<OrthancDatabases::StorageBackend::IAccessor> accessor(storageArea.CreateAccessor());
     
     ASSERT_EQ(0, CountLargeObjects(*database));
   
@@ -371,15 +371,15 @@
     {
       std::string uuid = boost::lexical_cast<std::string>(i);
       std::string value = "Value " + boost::lexical_cast<std::string>(i * 2);
-      accessor.Create(uuid, value.c_str(), value.size(), OrthancPluginContentType_Unknown);
+      accessor->Create(uuid, value.c_str(), value.size(), OrthancPluginContentType_Unknown);
     }
 
     std::string buffer;
-    ASSERT_THROW(accessor.ReadToString(buffer, "nope", OrthancPluginContentType_Unknown), 
+    ASSERT_THROW(OrthancDatabases::StorageBackend::ReadWholeToString(buffer, *accessor, "nope", OrthancPluginContentType_Unknown), 
                  Orthanc::OrthancException);
   
     ASSERT_EQ(10, CountLargeObjects(*database));
-    accessor.Remove("5", OrthancPluginContentType_Unknown);
+    accessor->Remove("5", OrthancPluginContentType_Unknown);
 
     ASSERT_EQ(9, CountLargeObjects(*database));
 
@@ -390,19 +390,19 @@
 
       if (i == 5)
       {
-        ASSERT_THROW(accessor.ReadToString(buffer, uuid, OrthancPluginContentType_Unknown), 
+        ASSERT_THROW(OrthancDatabases::StorageBackend::ReadWholeToString(buffer, *accessor, uuid, OrthancPluginContentType_Unknown), 
                      Orthanc::OrthancException);
       }
       else
       {
-        accessor.ReadToString(buffer, uuid, OrthancPluginContentType_Unknown);
+        OrthancDatabases::StorageBackend::ReadWholeToString(buffer, *accessor, uuid, OrthancPluginContentType_Unknown);
         ASSERT_EQ(expected, buffer);
       }
     }
 
     for (int i = 0; i < 10; i++)
     {
-      accessor.Remove(boost::lexical_cast<std::string>(i), OrthancPluginContentType_Unknown);
+      accessor->Remove(boost::lexical_cast<std::string>(i), OrthancPluginContentType_Unknown);
     }
 
     ASSERT_EQ(0, CountLargeObjects(*database));