allow not passing an ntuple name

src/argparse.cpp

@@ -4,13 +4,15 @@ void print_help(const char *argv0)
   fprintf(stderr,
     "rntviewer v" V_MAJOR "." V_MINOR " by silverweed"
     "\n"
-    "\nUsage: %s [-t] [-s START] [-l LEN] [-w WIDTH] [-e] <ntuple_name> <ntuple_file.root>"   
+    "\nUsage: %s [-t] [-s START] [-l LEN] [-w WIDTH] [-e] <ntuple_file.root> [ntuple_name]"
     "\n\t-t: no graphics, output to terminal"
     "\n\t-s: set first displayed byte to START"
     "\n\t-l: display LEN bytes (only in terminal mode)"
     "\n\t-w: display WIDTH bytes per column"
     "\n\t-e: display some extended info (may slow down the startup)"
     "\n"
+    "\nNOTE: if `ntuple_name' is not passed, rntviewer will look for the first RNTuple in the TFile."
+    "\n"
   , argv0);
 }
 
@@ -89,7 +91,7 @@ internal
 Cmdline_Args parse_args(i32 argc, char **argv)
 {
   Cmdline_Args args {};
-  if (argc < 3) {
+  if (argc < 2) {
     args.show_help_and_exit = true;
     return args;
   }
@@ -117,13 +119,13 @@ Cmdline_Args parse_args(i32 argc, char **argv)
       } else {
         args.show_help_and_exit = true;   
       }
-    } else if (args.ntpl_name.size) {
-      if (args.file_name.size)
+    } else if (args.file_name.size) {
+      if (args.ntpl_name.size)
         args.show_help_and_exit = true;
       else
-        args.file_name = arg;
-    } else {
         args.ntpl_name = arg;
+    } else {
+      args.file_name = arg;
     }
   }
   return args;

src/rntuple.cpp

@@ -385,8 +385,9 @@ u64 calc_page_uncomp_size(const u8 *fmem, const Page_Info_Node *page_head)
   return tot_size;
 }
 
+// NOTE: ntpl_name may be empty
 internal
-RNTuple_Data get_rntuple_data(Arena *arena, const Inspected_File &file, String8 ntpl_name, b8 extended_info)
+RNTuple_Data get_rntuple_data(Arena *arena, const Inspected_File &file, String8 &ntpl_name, b8 extended_info)
 {
   RNTuple_Data rndata {};
   
@@ -409,6 +410,9 @@ RNTuple_Data get_rntuple_data(Arena *arena, const Inspected_File &file, String8
     rndata.rblob_header_size = file_info.rblob_key_header_nbytes;
     rndata.rng_tkeys_list.start = file_info.tkeys_list_seek;
     rndata.rng_tkeys_list.len = file_info.tkeys_list_nbytes;
+    if (!ntpl_name.size) {
+      ntpl_name = push_str8f(arena, "%s", file_info.ntuple_name.c_str());
+    }
 
     gather_ntuple_metadata(arena, file_reader, file_info, rndata);
     if (extended_info)

src/rntviewer.cpp

@@ -104,7 +104,7 @@ int main(int argc, char **argv)
 
   // Parse cmdline
   Cmdline_Args args = parse_args(argc, argv);
-  if (args.show_help_and_exit || !args.ntpl_name.size || !args.file_name.size) {
+  if (args.show_help_and_exit || !args.file_name.size) {
     print_help(argv[0]);
     return 1;
   }
@@ -131,10 +131,10 @@ int main(int argc, char **argv)
       os_start_file_watch(args.file_name, app);
   }
 
-  app.ntpl_name = args.ntpl_name;
+  app.ntpl_name = args.ntpl_name; // may be null
   app.base_display_addr = args.start_addr;
-  app.tfile_data = get_tfile_data(app.inspected_file, app.ntpl_name);
   app.rndata = get_rntuple_data(arena, app.inspected_file, app.ntpl_name, args.extended_info);
+  app.tfile_data = get_tfile_data(app.inspected_file, app.ntpl_name);
 
   if (args.print_to_terminal) {
     u64 nbytes_displayed = args.nbytes_displayed;

src/root/RMicroFileReader.cxx

@@ -1187,15 +1187,20 @@ RMicroFileReader::GetNTupleProper(const char *ntupleName)
       offset += name.GetSize();
       ReadBuffer(&name, 1, offset);
       ReadBuffer(&name, name.GetSize(), offset);
-      if (std::string_view(name.fData, name.fLName) == std::string_view(ntupleName)) {
+      if (!ntupleName || ntupleName[0] == 0 || std::string_view(name.fData, name.fLName) == std::string_view(ntupleName)) {
+         fileInfo.ntuple_name = { name.fData, name.fLName };
          found = true;
          break;
       }
       offset = offsetNextKey;
    }
    if (!found) {
+      if (!ntupleName || ntupleName[0] == 0) {
+         FAIL("no RNTuple found in file '" + impl->fRawFile->GetUrl() + "'");
+      } else {
          FAIL("no RNTuple named '" + std::string(ntupleName) + "' in file '" + impl->fRawFile->GetUrl() + "'");
       }
+   }
 
    offset = key.GetSeekKey() + key.fKeyLen;
 

src/root/RMicroFileReader.hxx

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <cstdint>
+#include <string>
 
 // We are forced to use our own RNTuple anchor struct because we cannot
 // write into the private members of the real RNTuple class from RMicroFileReader.
@@ -42,6 +43,7 @@ struct RNTuple_File_Info {
   std::uint64_t rblob_key_header_nbytes;
   std::uint64_t tkeys_list_seek;
   std::uint64_t tkeys_list_nbytes;
+  std::string ntuple_name; // useful when not passing an explicit name to GetNTupleProper
 };
 
 struct Root_File_Info {
@@ -64,6 +66,7 @@ public:
   explicit RMicroFileReader(const char *fname);
   ~RMicroFileReader();
 
+  // if ntupleName == "", look for the first RNTuple in the file.
   RNTuple_File_Info GetNTupleProper(const char *ntupleName);
 
   void ReadBuffer(void *buffer, std::size_t nbytes, std::uint64_t offset);