Improve header stream write method.

* libmailutils/mailbox/header.c (HEADER_STREAMMOD): New flag.
(mu_header_fill): Read data back from mstream if it was
modified.
(mu_header_destroy): Destroy mstream.
(header_write): Rewrite from scratch. Allow for writing at
arbitrary offsets.
* examples/header.c: New commands: "overwrite" and "append",
for testing the new functionality.

@@ -283,7 +283,7 @@ cmd_write (int argc, char **argv)
       mu_error ("%u: cannot get stream: %s", line_num, mu_strerror (status));
       return;
     }
-  printf("[reading headers; end with an empty line]\n");
+  printf ("[reading headers; end with an empty line]\n");
   mu_stream_seek (str, 0, SEEK_SET, NULL);
   while (prompt (1), fgets(buf, sizeof buf, stdin))
     {
@@ -296,6 +296,71 @@ cmd_write (int argc, char **argv)
 }
 
 void
+cmd_overwrite (int argc, char **argv)
+{
+  char buf[512];
+  mu_stream_t str;
+  int status;
+  mu_off_t off;
+  
+  if (check_args (argv[0], argc, 2, 2))
+    return;
+
+  off = strtoul (argv[1], NULL, 0);
+  
+  status = mu_header_get_streamref (header, &str);
+  if (status)
+    {
+      mu_error ("%u: cannot get stream: %s", line_num, mu_strerror (status));
+      return;
+    }
+  status = mu_stream_seek (str, off, SEEK_SET, NULL);
+  if (status)
+    {
+      mu_error ("seek error: %s", mu_strerror (status));
+      return;
+    }
+
+  printf ("[reading headers; end with an empty line]\n");
+  while (prompt (1), fgets(buf, sizeof buf, stdin))
+    {
+      if (buf[0] == '\n')
+	break;
+      mu_stream_write (str, buf, strlen (buf), NULL);
+    }
+  mu_stream_destroy (&str);
+  mu_stream_destroy (&hstream);
+}
+
+void
+cmd_append (int argc, char **argv)
+{
+  char buf[512];
+  mu_stream_t str;
+  int status;
+  
+  if (check_args (argv[0], argc, 1, 1))
+    return;
+
+  status = mu_header_get_streamref (header, &str);
+  if (status)
+    {
+      mu_error ("%u: cannot get stream: %s", line_num, mu_strerror (status));
+      return;
+    }
+  printf ("[reading headers; end with an empty line]\n");
+  mu_stream_seek (str, 0, SEEK_END, NULL);
+  while (prompt (1), fgets(buf, sizeof buf, stdin))
+    {
+      mu_stream_write (str, buf, strlen (buf), NULL);
+      if (buf[0] == '\n')
+	break;
+    }
+  mu_stream_destroy (&str);
+  mu_stream_destroy (&hstream);
+}
+
+void
 cmd_iterate (int argc, char **argv)
 {
   if (check_args (argv[0], argc, 1, 2))
@@ -379,7 +444,7 @@ static struct cmdtab cmdtab[] = {
   { "free", cmd_free, NULL, "discard all headers" },
   { "print", cmd_print, "NAME [N]",
     "find and print the Nth (by default, 1st) instance of header named NAME" },
-  { "dump", cmd_dump, NULL, "dump all headers on screen" },
+  { "dump", cmd_dump, "[OFF]", "dump all headers on screen" },
   { "itr", cmd_iterate, "[first|1|next|n]", "iterate over headers" },
   { "readline", cmd_readline, "[SIZE]", "read line" },
   { "remove", cmd_remove, "NAME [N]",
@@ -387,6 +452,8 @@ static struct cmdtab cmdtab[] = {
   { "insert", cmd_insert, "NAME VALUE [REF [NUM] [before|after] [replace]]",
     "insert new header" },
   { "write", cmd_write, NULL, "accept headers from raw stream" },
+  { "overwrite", cmd_overwrite, "OFF", "overwrite raw data from offset OFF" },
+  { "append", cmd_append, NULL, "append raw data" },
   { "help", cmd_help, "[COMMAND]", "print short usage message" },
   { NULL }
 };

@@ -50,6 +50,7 @@
 
 #define HEADER_MODIFIED   0x01
 #define HEADER_INVALIDATE 0x02
+#define HEADER_STREAMMOD  0x04
 
 #define HEADER_SET_MODIFIED(h) \
   ((h)->flags |= (HEADER_MODIFIED|HEADER_INVALIDATE))
@@ -412,6 +413,33 @@ mu_header_fill (mu_header_t header)
   size_t blurb_len = 0;
   char *blurb = NULL;
   
+  if (header->mstream && header->flags & HEADER_STREAMMOD)
+    {
+      mu_off_t end;
+
+      mu_header_invalidate (header);
+      status = mu_stream_size (header->mstream, &end);
+      if (status)
+	return status;
+      status = mu_stream_seek (header->mstream, 0, MU_SEEK_SET, NULL);
+      if (status)
+	return status;      
+      blurb_len = end;
+      blurb = malloc (blurb_len + 1);
+      if (!blurb)
+	return ENOMEM;
+      status = mu_stream_read (header->mstream, blurb, blurb_len, NULL);
+      if (status)
+	{
+	  free (blurb);
+	  return status;
+	}
+      status = header_parse (header, blurb, blurb_len);
+      free (blurb);
+      if (status == 0)
+	header->flags &= ~HEADER_STREAMMOD;
+      return status;
+    }
   if (header->spool_used)
     return 0;
   
@@ -452,6 +480,7 @@ mu_header_destroy (mu_header_t *ph)
     {  
       mu_header_t header = *ph;
 
+      mu_stream_destroy (&header->mstream);
       mu_stream_destroy (&header->stream);
       mu_hdrent_free_list (header);
       free (header->spool);
@@ -1091,68 +1120,50 @@ _header_readline (mu_stream_t is, char *buffer, size_t buflen, size_t *pnread)
 static int
 header_write (mu_stream_t os, const char *buf, size_t buflen, size_t *pnwrite)
 {
-  struct _mu_header_stream *hstr;
+  struct _mu_header_stream *hstr = (struct _mu_header_stream *) os;
   mu_header_t header;
-  int status;
-  mu_off_t mstream_size;
+  int rc;
   
-  if (!os || !buf)
+  if (os == NULL)
     return EINVAL;
-
-  hstr = (struct _mu_header_stream *) os;
   header = hstr->hdr;
-  if (header == NULL)
-    return EINVAL;
-  
-  /* Skip the obvious.  */
-  if (*buf == '\0' || buflen == 0)
-    {
-      if (pnwrite)
-        *pnwrite = 0;
-      return 0;
-    }
-
-  if (!header->mstream)
+  if (!(header->flags & HEADER_STREAMMOD))
     {
-      status = mu_memory_stream_create (&header->mstream, MU_STREAM_RDWR);
-      if (status)
-	return status;
-    }
-
-  status = mu_stream_write (header->mstream, buf, buflen, NULL);
-  if (status)
-    {
-      mu_stream_destroy (&header->mstream);
-      return status;
-    }
-
-  status = mu_stream_size (header->mstream, &mstream_size);
-  if (status == 0 && mstream_size > 1)
-    {
-      char nlbuf[2];
+      struct mu_hdrent *ent;
+	
+      rc = mu_header_fill (header);
+      if (rc)
+	return rc;
 
-      status = mu_stream_seek (header->mstream, -2, MU_SEEK_END, NULL);
-      if (status == 0)
-	status = mu_stream_read (header->mstream, nlbuf, 2, NULL);
-      if (status == 0 && memcmp (nlbuf, "\n\n", 2) == 0)
+      if (!header->mstream)
 	{
-	  char *blurb;
-
-	  blurb = calloc (1, mstream_size + 1);
-	  if (blurb)
-	    {
-	      mu_stream_read (header->mstream, blurb, mstream_size, NULL);
-	      status = header_parse (header, blurb, mstream_size);
-	    }
-	  free (blurb);
-	  mu_stream_destroy (&header->mstream);
+	  rc = mu_memory_stream_create (&header->mstream, MU_STREAM_RDWR);
+	  if (rc)
+	    return rc;
 	}
+      mu_stream_seek (header->mstream, 0, MU_SEEK_SET, NULL);
+      if (header->spool_used)
+	{
+	  for (ent = header->head; ent; ent = ent->next)
+	    mu_hdrent_fixup (header, ent);
+	  rc = mu_stream_write (header->mstream, header->spool,
+				header->spool_used, NULL);
+	  for (ent = header->head; ent; ent = ent->next)
+	    mu_hdrent_unroll_fixup (header, ent);
+	  if (rc)
+	    return rc;
+	  mu_stream_truncate (header->mstream, header->spool_used);
+	  if (hstr->off > header->spool_used)
+	    hstr->off = header->spool_used;
+	}
+      header->flags |= HEADER_STREAMMOD;
     }
+
+  rc = mu_stream_seek (header->mstream, hstr->off, MU_SEEK_SET, NULL);
+  if (rc)
+    return rc;
   
-  if (pnwrite)
-    *pnwrite = buflen;
-  
-  return status;
+  return mu_stream_write (header->mstream, buf, buflen, pnwrite);
 }
 
 static int