[io] Add TMemFile::DumpBin for debugging purposes

Author: silverweed

io/io/inc/TMemFile.h

@@ -105,6 +105,7 @@ class TMemFile : public TFile {
            void ResetErrno() const override;
 
            void        Print(Option_t *option="") const override;
+           void        DumpBin(FILE *out) const;
 
    ClassDefOverride(TMemFile, 0) // A ROOT file that reads/writes on a chunk of memory
 };

io/io/src/TMemFile.cxx

@@ -312,6 +312,26 @@ void TMemFile::Print(Option_t *option /* = "" */) const
    }
 }
 
+////////////////////////////////////////////////////////////////////////////////
+/// Writes the contents of the TMemFile to the given file. This is meant to be
+/// used mostly for debugging, as it dumps the current file's content as-is with
+/// no massaging (meaning the content might not be a valid ROOT file): for regular use cases, use Cp().
+/// Example usage:
+/// ~~~ {.cpp}
+/// FILE *out = fopen("memfile.root", "wb");
+/// memFile->DumpBin(out);
+/// fclose(out);
+/// ~~~
+void TMemFile::DumpBin(FILE *out) const
+{
+   const auto *cur = &fBlockList;
+   while (cur) {
+      fwrite(cur->fBuffer, cur->fSize, 1, out);
+      cur = cur->fNext;
+   }
+   fflush(out);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 /// Wipe all the data from the permanent buffer but keep, the in-memory object
 /// alive.