From 1aa183fd828c0456166b9c8834bfeb5618ef6911 Mon Sep 17 00:00:00 2001
From: Reini Urban <reini.urban@gmail.com>
Date: Fri, 16 Aug 2024 13:18:47 +0200
Subject: [PATCH] dxf: resolve empty BLOCK.name

which is mandatory in DXF.
Fixes GH #999
---
 src/dwg.spec  | 40 ++++++++++++++++++++++++++++++++--------
 src/out_dxf.c | 12 ++++++++++--
 2 files changed, 42 insertions(+), 10 deletions(-)

diff --git a/src/dwg.spec b/src/dwg.spec
index b3042fa17..a2ec9d58c 100644
--- a/src/dwg.spec
+++ b/src/dwg.spec
@@ -640,11 +640,8 @@ DWG_ENTITY (BLOCK)
     }
   }
 #endif
-  SINCE (R_13b1) {
-    BLOCK_NAME (name, 2) // special pre-R13 naming rules
-    COMMON_ENTITY_HANDLE_DATA;
-  }
 #ifdef IS_DXF
+  SINCE (R_13b1)
   {
     Dwg_Object_BLOCK_HEADER *_hdr = NULL;
     Dwg_Object *hdr
@@ -652,7 +649,25 @@ DWG_ENTITY (BLOCK)
               ? _ent->ownerhandle->obj : NULL;
     if (!hdr)
       hdr = dwg_ref_object (dwg, _ent->ownerhandle);
-    if (!hdr || hdr->fixedtype != DWG_TYPE_BLOCK_HEADER)
+    if (hdr && hdr->fixedtype == DWG_TYPE_BLOCK_HEADER)
+      _hdr = hdr->tio.object->tio.BLOCK_HEADER;
+    else if (_ent->entmode == 2) {
+      hdr = dwg_model_space_object (dwg);
+      _hdr = hdr ? hdr->tio.object->tio.BLOCK_HEADER : NULL;
+    }
+    else if (_ent->entmode == 1) {
+      hdr = dwg_paper_space_object (dwg);
+      _hdr = hdr ? hdr->tio.object->tio.BLOCK_HEADER : NULL;
+    }
+    if (_hdr && (bit_empty_T (dat, _obj->name) || bit_eq_T (dat, _obj->name, "*"))) {
+      VALUE_T (_hdr->name, 2);   // from BLOCK_HEADER
+    }
+    else {
+      BLOCK_NAME (name, 2);
+    }
+    COMMON_ENTITY_HANDLE_DATA;
+
+    if (!_hdr)
       {
         Dwg_Bitcode_3RD nullpt = { 0.0, 0.0, 0.0 };
         VALUE_BL (0, 70); // flags: anon, has_attribs, is_xref, is_overlaid, ...
@@ -660,12 +675,16 @@ DWG_ENTITY (BLOCK)
       }
     else
       {
-        _hdr = hdr->tio.object->tio.BLOCK_HEADER;
         VALUE_BL (_hdr->flag & 0x3f, 70);
         VALUE_3BD (_hdr->base_pt, 10);
       }
-    SINCE (R_13)
-      BLOCK_NAME (name, 3); // for entget() from BLOCK_HEADER
+    SINCE (R_13) {
+      if (_hdr && (bit_empty_T (dat, _obj->name) || bit_eq_T (dat, _obj->name, "*"))) {
+        VALUE_T (_hdr->name, 3);   // from BLOCK_HEADER
+      } else {
+        BLOCK_NAME (name, 3); // for entget() from BLOCK_HEADER
+      }
+    }
     if (_hdr) {
       VALUE_T (_hdr->xref_pname, 1);   // from BLOCK_HEADER
       VALUE_T0 (_hdr->description, 4); // from BLOCK_HEADER
@@ -673,6 +692,11 @@ DWG_ENTITY (BLOCK)
       VALUE_TFF ("", 1);
     }
   }
+#else
+  SINCE (R_13b1) {
+    BLOCK_NAME (name, 2) // special pre-R13 naming rules
+    COMMON_ENTITY_HANDLE_DATA;
+  }
 #endif
 
 DWG_ENTITY_END
diff --git a/src/out_dxf.c b/src/out_dxf.c
index ebc7be3fe..8fea0d4c3 100644
--- a/src/out_dxf.c
+++ b/src/out_dxf.c
@@ -1622,15 +1622,23 @@ dxf_cvt_tablerecord (Bit_Chain *restrict dat, const Dwg_Object *restrict obj,
 static void
 dxf_cvt_blockname (Bit_Chain *restrict dat, char *restrict name, const int dxf)
 {
+  static int gensym = 0;
   if (!name)
     {
-      fprintf (dat->fh, "%3i\r\n\r\n", dxf);
+      fprintf (dat->fh, "%3i\r\n*U%i\r\n", dxf, gensym++);
       return;
     }
   if (IS_FROM_TU (dat)) // r2007+ unicode names
     {
       name = bit_convert_TU ((BITCODE_TU)name);
     }
+  if (!name || !*name)
+    {
+      fprintf (dat->fh, "%3i\r\n*U%i\r\n", dxf, gensym++);
+      if (IS_FROM_TU (dat))
+        free (name);
+      return;
+    }
   if (dat->version == dat->from_version) // no conversion
     {
       fprintf (dat->fh, "%3i\r\n%s\r\n", dxf, name);
@@ -1648,7 +1656,7 @@ dxf_cvt_blockname (Bit_Chain *restrict dat, char *restrict name, const int dxf)
       else
         fprintf (dat->fh, "%3i\r\n%s\r\n", dxf, name);
     }
-  else if (dat->version >= R_13b1 && dat->from_version < R_13b1) // to newer
+  else if (dat->version >= R_13b1) // to newer
     {
       if (strlen (name) < 10)
         fprintf (dat->fh, "%3i\r\n%s\r\n", dxf, name);