Improve the --skip-empty-attachment functionality

This also includes small bugfixes in the MIME library code.

The --skip-empty-attachment option now affects the original
body as well.  If the option is in effect, and the body is empty,
it will not be included to the composed message.

* libmailutils/mime/mime.c (_mime_body_stream_read): Return EOF
if there are no parts in the message.
(mu_mime_get_num_parts): If message is not multipart, report 1 part
without setting mime->nmtp_parts.  Setting it caused coredump in
other MIME functions (namely, in mu_mime_add_part.
* mail/send.c (add_body): New function.  Adds original body to
the MIME, honoring the --skip-empty-attachment option.
* doc/texinfo/programs.texi: Update.

@@ -3048,7 +3048,9 @@ Sets the return email address for outgoing mail.
 @itemx --no-skip-empty-attachments
 Don't create attachments that would have zero-size body.  This
 option affects all attachments created by @option{--attach} and
-@option{--attach-fd} options appearing after it in the command line.
+@option{--attach-fd} options appearing after it in the command line,
+as well as the body of the original message.
+
 To cancel its effect, use the @option{--no-skip-empty-attachments} option.
 
 @item -s @var{subj}
@@ -3542,7 +3544,38 @@ The option @option{--skip-empty-attachments} instructs @command{mail}
 to skip creating attachments that would have zero-size body.  This
 option affects all attachments created by @option{--attach} and
 @option{--attach-fd} options appearing after it in the command line.
-To cancel its effect, use the @option{--no-skip-empty-attachments} option.
+It also affects the handling of the original message body.  To cancel
+its effect, use the @option{--no-skip-empty-attachments} option. 
+
+Here are some examples illustrating how it works.
+
+First, consider the following command line
+
+@example
+$ mail --attach=archive.tar </dev/null
+@end example
+
+Assume that @file{archive.tar} is not empty.
+
+This will create a MIME message of two parts: the first part having
+@samp{text/html} type and empty body, and the second part of type
+@samp{application/octet-stream}, with the content copied from the file
+@file{archive.tar}.
+
+Now, if you do:
+
+@example
+$ mail --attach=archive.tar --skip-empty-attachments </dev/null
+@end example
+
+@noindent
+then the created MIME message will contain only one part: that
+containing @file{archive.tar}.
+
+If the file @file{archive.tar} has zero length, the resulting archive
+will still contain the @samp{application/octet-stream} part of zero
+length.  However, if you place the @option{--skip-empty-attachments}
+option before @option{--attach}, then the produced message will be empty.
 
 The following Perl program serves as an example of using
 @command{mail} from a script to construct a MIME message on the fly.

@@ -662,7 +662,10 @@ _mime_body_stream_read (mu_stream_t stream, char *buf, size_t buflen, size_t *nb
   size_t             total = 0;
   
   if (mime->nmtp_parts == 0)
-    return EINVAL;
+    {
+      *nbytes = 0;
+      return 0;
+    }
   
   if ((ret = _mime_set_content_type (mime)) == 0)
     {
@@ -1055,7 +1058,10 @@ mu_mime_get_num_parts (mu_mime_t mime, size_t *nmtp_parts)
 	    return (ret);
 	}
       else
-	mime->nmtp_parts = 1;
+	{
+	  *nmtp_parts = 1;
+	  return 0;
+	}
     }
   *nmtp_parts = mime->nmtp_parts;
   return (ret);

@@ -408,50 +408,52 @@ saveatt (void *item, void *data)
 }
 
 static int
-add_attachments (mu_message_t *pmsg, mu_mime_t *pmime)
+add_body (mu_message_t inmsg, mu_iterator_t itr, mu_mime_t mime)
 {
-  mu_message_t inmsg, outmsg, part;
   mu_body_t body;
-  mu_header_t inhdr, outhdr;
-  mu_iterator_t itr;
-  mu_mime_t mime;
+  mu_message_t part;
   mu_stream_t str, output;
-  int rc;
+  mu_header_t outhdr;
   char *p;
+  int rc;
   
-  if (mu_list_is_empty (attlist))
+  mu_message_get_body (inmsg, &body);
+  if (skip_empty_attachments)
     {
-      *pmime = NULL;
-      return 0;
+      size_t size;
+      rc = mu_body_size (body, &size);
+      if (rc)
+	{
+	  mu_diag_funcall (MU_DIAG_ERROR, "mu_body_size", NULL, rc);
+	  return -1;
+	}
+      if (size == 0)
+	return 0;
     }
+    
+  /* Add original message as the first part */
   
-  inmsg = *pmsg;
-
-  /* Create a mime object */
-  rc = mu_mime_create (&mime, NULL, 0);
-  if (rc)
+  /* 1. Create the part and obtain a reference to its stream */
+  if ((rc = mu_message_create (&part, NULL)) == 0)
     {
-      mu_diag_funcall (MU_DIAG_ERROR, "mu_mime_create", NULL, rc);
-      return 1;
+      mu_body_t pbody;
+      
+      mu_message_get_body (part, &pbody);
+      mu_body_get_streamref (pbody, &output);
     }
-
-  /* Add original message as its first part */
-  /* 1. Create the part and obtain a reference to its stream */
-  mu_message_create (&part, NULL);
-  mu_message_get_body (part, &body);
-  mu_body_get_streamref (body, &output);
-
+  else
+    {
+      mu_diag_funcall (MU_DIAG_ERROR, "mu_message_create", NULL, rc);
+      return -1;
+    }
+  
   /* 2. Get original body stream and copy it out to the part's body */
-  mu_message_get_body (inmsg, &body);
   mu_body_get_streamref (body, &str);
   mu_stream_copy (output, str, 0, NULL);
 
   mu_stream_close (output);
   mu_stream_destroy (&output);
 
-  mu_message_get_header (inmsg, &inhdr);
-  mu_header_get_iterator (inhdr, &itr);
-
   /* 3. Copy "Content-*" headers from the original message */
   mu_message_get_header (part, &outhdr);
   for (mu_iterator_first (itr); !mu_iterator_is_done (itr);
@@ -477,11 +479,50 @@ add_attachments (mu_message_t *pmsg, mu_mime_t *pmime)
   mu_mime_add_part (mime, part);
   mu_message_unref (part);
 
+  return 0;
+}  
+
+static int
+add_attachments (mu_message_t *pmsg, mu_mime_t *pmime)
+{
+  mu_message_t inmsg, outmsg;
+  mu_header_t inhdr, outhdr;
+  mu_iterator_t itr;
+  mu_mime_t mime;  
+  int rc;
+  
+  if (mu_list_is_empty (attlist))
+    {
+      *pmime = NULL;
+      return 0;
+    }
+  
+  inmsg = *pmsg;
+
+  /* Create a mime object */
+  rc = mu_mime_create (&mime, NULL, 0);
+  if (rc)
+    {
+      mu_diag_funcall (MU_DIAG_ERROR, "mu_mime_create", NULL, rc);
+      return 1;
+    }
+
+  mu_message_get_header (inmsg, &inhdr);
+  mu_header_get_iterator (inhdr, &itr);
+
+  if (add_body (inmsg, itr, mime))
+    {
+      mu_mime_destroy (&mime);
+      mu_iterator_destroy (&itr);
+      return 1;
+    }
+
   /* Add the respective attachments */
   rc = mu_list_foreach (attlist, saveatt, mime);
   if (rc)
     {
       mu_mime_destroy (&mime);
+      mu_iterator_destroy (&itr);
       return 1;
     }
 
@@ -492,6 +533,7 @@ add_attachments (mu_message_t *pmsg, mu_mime_t *pmime)
     {
       mu_diag_funcall (MU_DIAG_ERROR, "mu_mime_get_message", NULL, rc);
       mu_mime_destroy (&mime);
+      mu_iterator_destroy (&itr);
       return 1;
     }
 
@@ -515,6 +557,7 @@ add_attachments (mu_message_t *pmsg, mu_mime_t *pmime)
 
   mu_message_unref (outmsg);
   mu_message_unref (inmsg);
+
   *pmsg = outmsg;
   *pmime = mime;
   return 0;
@@ -1193,6 +1236,7 @@ mail_send0 (compose_env_t *env, int save_to)
 	  status = mu_message_create (&msg, NULL);
 	  if (status)
 	    break;
+	  
 	  /* Fill the body. */
 	  mu_stream_seek (env->compstr, 0, MU_SEEK_SET, NULL);
 	  status = fill_body (msg, env->compstr);