pngminus: Delete the incomplete output files upon premature termination

Defer the program termination on error until all files are closed and
(if applicable) all incompletely-written output files are deleted.

In addition, perform the following maintenance tasks:
 * Rename and document the internal helpers used by the functions
   `png2pnm` and `pnm2png`.
 * Unset the executable permission bits for the *.bat test programs.

contrib/pngminus/CHANGES.txt

@@ -11,4 +11,4 @@ version 1.0 - 1999.10.15 - First version.
         1.5 - 2018.08.05 - Fix buffer overflow in tokenizer (Cosmin Truta)
         1.6 - 2018.08.05 - Improve portability and fix style (Cosmin Truta)
         1.7 - 2019.01.22 - Change license to MIT (Willem van Schaik)
-        1.8 - 2024.01.08 - Fix, improve, modernize (Cosmin Truta)
+        1.8 - 2024.01.09 - Fix, improve, modernize (Cosmin Truta)

contrib/pngminus/png2pnm.c

@@ -28,7 +28,7 @@ int main (int argc, char *argv[]);
 void usage ();
 BOOL png2pnm (FILE *png_file, FILE *pnm_file, FILE *alpha_file,
               BOOL raw, BOOL alpha);
-BOOL png2pnm_internal (png_struct *png_ptr, png_info *info_ptr, 
+BOOL do_png2pnm (png_struct *png_ptr, png_info *info_ptr,
                  FILE *pnm_file, FILE *alpha_file,
                  BOOL raw, BOOL alpha);
 
@@ -41,9 +41,12 @@ int main (int argc, char *argv[])
   FILE *fp_rd = stdin;
   FILE *fp_wr = stdout;
   FILE *fp_al = NULL;
+  const char *fname_wr = NULL;
+  const char *fname_al = NULL;
   BOOL raw = TRUE;
   BOOL alpha = FALSE;
   int argi;
+  int ret;
 
   for (argi = 1; argi < argc; argi++)
   {
@@ -62,6 +65,7 @@ int main (int argc, char *argv[])
           argi++;
           if ((fp_al = fopen (argv[argi], "wb")) == NULL)
           {
+            fname_al = argv[argi];
             fprintf (stderr, "PNM2PNG\n");
             fprintf (stderr, "Error:  cannot create alpha-channel file %s\n",
                      argv[argi]);
@@ -92,6 +96,7 @@ int main (int argc, char *argv[])
     }
     else if (fp_wr == stdout)
     {
+      fname_wr = argv[argi];
       if ((fp_wr = fopen (argv[argi], "wb")) == NULL)
       {
         fprintf (stderr, "PNG2PNM\n");
@@ -117,12 +122,7 @@ int main (int argc, char *argv[])
 #endif
 
   /* call the conversion program itself */
-  if (png2pnm (fp_rd, fp_wr, fp_al, raw, alpha) == FALSE)
-  {
-    fprintf (stderr, "PNG2PNM\n");
-    fprintf (stderr, "Error:  unsuccessful conversion of PNG-image\n");
-    exit (1);
-  }
+  ret = png2pnm (fp_rd, fp_wr, fp_al, raw, alpha);
 
   /* close input file */
   fclose (fp_rd);
@@ -132,6 +132,17 @@ int main (int argc, char *argv[])
   if (alpha)
     fclose (fp_al);
 
+  if (!ret)
+  {
+    fprintf (stderr, "PNG2PNM\n");
+    fprintf (stderr, "Error:  unsuccessful conversion of PNG-image\n");
+    if (fname_wr)
+      remove (fname_wr); /* no broken output file shall remain behind */
+    if (fname_al)
+      remove (fname_al); /* ditto */
+    exit (1);
+  }
+
   return 0;
 }
 
@@ -165,7 +176,7 @@ BOOL png2pnm (FILE *png_file, FILE *pnm_file, FILE *alpha_file,
   png_info      *info_ptr;
   BOOL          ret;
 
-  /* initialize the libpng structures for reading from png_file */
+  /* initialize the libpng context for reading from png_file */
 
   png_ptr = png_create_read_struct (png_get_libpng_ver(NULL),
                                     NULL, NULL, NULL);
@@ -188,7 +199,7 @@ BOOL png2pnm (FILE *png_file, FILE *pnm_file, FILE *alpha_file,
   png_init_io (png_ptr, png_file);
 
   /* do the actual conversion */
-  ret = png2pnm_internal (png_ptr, info_ptr, pnm_file, alpha_file, raw, alpha);
+  ret = do_png2pnm (png_ptr, info_ptr, pnm_file, alpha_file, raw, alpha);
 
   /* clean up the libpng structures and their internally-managed data */
   png_destroy_read_struct (&png_ptr, &info_ptr, NULL);
@@ -197,10 +208,10 @@ BOOL png2pnm (FILE *png_file, FILE *pnm_file, FILE *alpha_file,
 }
 
 /*
- *  png2pnm_internal
+ *  do_png2pnm - does the conversion in a fully-initialized libpng context
  */
 
-BOOL png2pnm_internal (png_struct *png_ptr, png_info *info_ptr,
+BOOL do_png2pnm (png_struct *png_ptr, png_info *info_ptr,
                  FILE *pnm_file, FILE *alpha_file,
                  BOOL raw, BOOL alpha)
 {

contrib/pngminus/pnm2png.c

@@ -29,7 +29,7 @@ int main (int argc, char *argv[]);
 void usage ();
 BOOL pnm2png (FILE *pnm_file, FILE *png_file, FILE *alpha_file,
               BOOL interlace, BOOL alpha);
-BOOL pnm2png_internal (png_struct *png_ptr, png_info *info_ptr,
+BOOL do_pnm2png (png_struct *png_ptr, png_info *info_ptr,
                  FILE *pnm_file, FILE *alpha_file,
                  BOOL interlace, BOOL alpha);
 int fscan_pnm_magic (FILE *pnm_file, char *magic_buf, size_t magic_buf_size);
@@ -47,9 +47,11 @@ int main (int argc, char *argv[])
   FILE *fp_rd = stdin;
   FILE *fp_al = NULL;
   FILE *fp_wr = stdout;
+  const char *fname_wr = NULL;
   BOOL interlace = FALSE;
   BOOL alpha = FALSE;
   int argi;
+  int ret;
 
   for (argi = 1; argi < argc; argi++)
   {
@@ -95,6 +97,7 @@ int main (int argc, char *argv[])
     }
     else if (fp_wr == stdout)
     {
+      fname_wr = argv[argi];
       if ((fp_wr = fopen (argv[argi], "wb")) == NULL)
       {
         fprintf (stderr, "PNM2PNG\n");
@@ -122,12 +125,7 @@ int main (int argc, char *argv[])
 #endif
 
   /* call the conversion program itself */
-  if (pnm2png (fp_rd, fp_wr, fp_al, interlace, alpha) == FALSE)
-  {
-    fprintf (stderr, "PNM2PNG\n");
-    fprintf (stderr, "Error:  unsuccessful converting to PNG-image\n");
-    exit (1);
-  }
+  ret = pnm2png (fp_rd, fp_wr, fp_al, interlace, alpha);
 
   /* close input file */
   fclose (fp_rd);
@@ -137,6 +135,15 @@ int main (int argc, char *argv[])
   if (alpha)
     fclose (fp_al);
 
+  if (!ret)
+  {
+    fprintf (stderr, "PNM2PNG\n");
+    fprintf (stderr, "Error:  unsuccessful converting to PNG-image\n");
+    if (fname_wr)
+      remove (fname_wr); /* no broken output file shall remain behind */
+    exit (1);
+  }
+
   return 0;
 }
 
@@ -168,7 +175,7 @@ BOOL pnm2png (FILE *pnm_file, FILE *png_file, FILE *alpha_file,
   png_info      *info_ptr;
   BOOL          ret;
 
-  /* initialize the libpng structures for writing to png_file */
+  /* initialize the libpng context for writing to png_file */
 
   png_ptr = png_create_write_struct (png_get_libpng_ver(NULL),
                                      NULL, NULL, NULL);
@@ -191,8 +198,7 @@ BOOL pnm2png (FILE *pnm_file, FILE *png_file, FILE *alpha_file,
   png_init_io (png_ptr, png_file);
 
   /* do the actual conversion */
-  ret = pnm2png_internal (png_ptr, info_ptr,
-                          pnm_file, alpha_file, interlace, alpha);
+  ret = do_pnm2png (png_ptr, info_ptr, pnm_file, alpha_file, interlace, alpha);
 
   /* clean up the libpng structures and their internally-managed data */
   png_destroy_write_struct (&png_ptr, &info_ptr);
@@ -201,10 +207,10 @@ BOOL pnm2png (FILE *pnm_file, FILE *png_file, FILE *alpha_file,
 }
 
 /*
- *  pnm2png_internal
+ *  do_pnm2png - does the conversion in a fully-initialized libpng context
  */
 
-BOOL pnm2png_internal (png_struct *png_ptr, png_info *info_ptr,
+BOOL do_pnm2png (png_struct *png_ptr, png_info *info_ptr,
                  FILE *pnm_file, FILE *alpha_file,
                  BOOL interlace, BOOL alpha)
 {