I got this patch from Rob Robertson <rob@gangrene.berkeley.edu>,
to fix a bug with XHDR returning incorrect data for non-existent
headers.

*** article.c.orig	Thu Mar 18 16:04:41 1993
--- article.c	Tue Sep  6 09:44:43 1994
***************
*** 29,34 ****
--- 29,35 ----
      char	*Header;
      int		Length;
      BOOL	HasHeader;
+     BOOL	NeedsHeader;
  } ARTOVERFIELD;
  
  
***************
*** 38,43 ****
--- 39,45 ----
  STATIC QIOSTATE		*ARTqp;
  STATIC ARTOVERFIELD	*ARTfields;
  STATIC int		ARTfieldsize;
+ STATIC int		ARTfirstfullfield = 0;
  STATIC SENDDATA		SENDbody = {
      STbody,	NNTP_BODY_FOLLOWS_VAL,		"body"
  };
***************
*** 93,102 ****
  	    continue;
  	if ((p = strchr(buff, ':')) != NULL) {
  	    *p++ = '\0';
! 	    fp->HasHeader = EQ(p, "full");
  	}
  	else
! 	    fp->HasHeader = FALSE;
  	fp->Header = COPY(buff);
  	fp->Length = strlen(buff);
  	fp++;
--- 95,106 ----
  	    continue;
  	if ((p = strchr(buff, ':')) != NULL) {
  	    *p++ = '\0';
! 	    fp->NeedsHeader = EQ(p, "full");
! 	    if (ARTfirstfullfield == 0)
! 	      ARTfirstfullfield = fp - ARTfields + 1;
  	}
  	else
! 	    fp->NeedsHeader = FALSE;
  	fp->Header = COPY(buff);
  	fp->Length = strlen(buff);
  	fp++;
***************
*** 648,662 ****
      ARTOVERFIELD	*fp;
      char		*next;
  
      /* Skip leading headers. */
!     for (fp = &ARTfields[field - 1]; --field >= 0 && *p; p++)
  	if ((p = strchr(p, '\t')) == NULL)
  	    return NULL;
      if (*p == '\0')
  	return NULL;
  
!     if (fp->HasHeader)
! 	p += fp->Length + 2;
  
      /* Figure out length; get space. */
      if ((next = strchr(p, '\t')) != NULL)
--- 652,677 ----
      ARTOVERFIELD	*fp;
      char		*next;
  
+     fp = &ARTfields[field - 1];
+ 
+     if (fp->NeedsHeader) 		/* we're going to need an exact match */
+       field = ARTfirstfullfield;
+ 
      /* Skip leading headers. */
!     for (; --field >= 0 && *p; p++)
  	if ((p = strchr(p, '\t')) == NULL)
  	    return NULL;
      if (*p == '\0')
  	return NULL;
  
!     if (fp->NeedsHeader) {		/* find an exact match */
! 	 while (strncmp(fp->Header, p, fp->Length) != 0) {
! 	      if ((p = strchr(p, '\t')) == NULL) 
! 		return NULL;
! 	      p++;
! 	 }
! 	 p += fp->Length + 2;
!     }
  
      /* Figure out length; get space. */
      if ((next = strchr(p, '\t')) != NULL)
***************
*** 781,788 ****
      /* Set up place to store headers. */
      if (Headers == NULL) {
  	Headers = NEW(ARTOVERFIELD, ARTfieldsize);
! 	for (hp = Headers, i = ARTfieldsize; --i >= 0; hp++)
  	    hp->Length = 0;
      }
      for (hp = Headers, i = ARTfieldsize; --i >= 0; hp++)
  	hp->HasHeader = FALSE;
--- 796,805 ----
      /* Set up place to store headers. */
      if (Headers == NULL) {
  	Headers = NEW(ARTOVERFIELD, ARTfieldsize);
! 	for (fp = ARTfields, hp = Headers, i = ARTfieldsize; --i >= 0; hp++, fp++) {
  	    hp->Length = 0;
+ 	    hp->NeedsHeader = fp->NeedsHeader;
+        }
      }
      for (hp = Headers, i = ARTfieldsize; --i >= 0; hp++)
  	hp->HasHeader = FALSE;
***************
*** 813,819 ****
  		continue;
  	    }
  	    *colon = ':';
! 	    if (fp->HasHeader)
  		p = line;
  	    else
  		/* Skip colon and whitespace, store value. */
--- 830,836 ----
  		continue;
  	    }
  	    *colon = ':';
! 	    if (fp->NeedsHeader)
  		p = line;
  	    else
  		/* Skip colon and whitespace, store value. */
***************
*** 887,892 ****
--- 904,911 ----
      /* Glue all the fields together. */
      p = buff + strlen(strcpy(buff, name));
      for (hp = Headers, i = ARTfieldsize; --i >= 0; hp++) {
+ 	 if (hp->NeedsHeader && !hp->HasHeader)
+ 	   continue;
  	*p++ = '\t';
  	if (hp->HasHeader)
  	    p += strlen(strcpy(p, hp->Header));
***************
*** 1080,1086 ****
  	}
  
      Printf("%d %s matches follow.\r\n", NNTP_HEAD_FOLLOWS_VAL, header);
!     for (pattern = Glom(&av[3]), i = range.Low; i < range.High; i++) {
  	if (ARTfind(i) < 0)
  	    continue;
  
--- 1099,1105 ----
  	}
  
      Printf("%d %s matches follow.\r\n", NNTP_HEAD_FOLLOWS_VAL, header);
!     for (pattern = Glom(&av[3]), i = range.Low; i <= range.High; i++) {
  	if (ARTfind(i) < 0)
  	    continue;