1 files changed, 92 insertions, 46 deletions

diff --git a/common/iobuf.c b/common/iobuf.c
index 664db393f..fed98397a 100644
--- a/common/iobuf.c
+++ b/common/iobuf.c
@@ -1767,18 +1767,38 @@ underflow (iobuf_t a)
   size_t len;
   int rc;
 
-  assert (a->d.start == a->d.len);
-  if (a->use == IOBUF_TEMP)
-    return -1;			/* EOF because a temp buffer can't do an underflow */
+  if (DBG_IOBUF)
+    log_debug ("iobuf-%d.%d: underflow: buffer size: %d; still buffered: %d => space for %d bytes\n",
+	       a->no, a->subno,
+	       (int) a->d.size, (int) (a->d.len - a->d.start),
+	       (int) (a->d.size - (a->d.len - a->d.start)));
+
+  assert (a->use == IOBUF_INPUT);
+
+  /* If there is still some buffered data, then move it to the start
+     of the buffer and try to fill the end of the buffer.  (This is
+     useful if we are called from iobuf_peek().)  */
+  assert (a->d.start <= a->d.len);
+  a->d.len -= a->d.start;
+  memmove (a->d.buf, &a->d.buf[a->d.start], a->d.len);
+  a->d.start = 0;
 
-  if (a->filter_eof)
+  if (a->d.len == 0 && a->filter_eof)
+    /* The last time we tried to read from this filter, we got an EOF.
+       We couldn't return the EOF, because there was buffered data.
+       Since there is no longer any buffered data, return the
+       error.  */
     {
+      if (DBG_IOBUF)
+	log_debug ("iobuf-%d.%d: underflow: eof (pending eof)\n",
+		   a->no, a->subno);
       if (a->chain)
+	/* A filter follows this one.  Free this filter.  */
 	{
 	  iobuf_t b = a->chain;
 	  if (DBG_IOBUF)
-	    log_debug ("iobuf-%d.%d: pop '%s' in underflow\n",
-		       a->no, a->subno, iobuf_desc (a));
+	    log_debug ("iobuf-%d.%d: filter popped (pending EOF returned)\n",
+		       a->no, a->subno);
 	  xfree (a->d.buf);
 	  xfree (a->real_fname);
 	  memcpy (a, b, sizeof *a);
@@ -1787,82 +1807,108 @@ underflow (iobuf_t a)
 	}
       else
 	a->filter_eof = 0;	/* for the top level filter */
-      if (DBG_IOBUF)
-	log_debug ("iobuf-%d.%d: underflow: eof (due to filter eof)\n",
-		   a->no, a->subno);
       return -1;		/* return one(!) EOF */
     }
-  if (a->error)
+
+  if (a->d.len == 0 && a->error)
+    /* The last time we tried to read from this filter, we got an
+       error.  We couldn't return the error, because there was
+       buffered data.  Since there is no longer any buffered data,
+       return the error.  */
     {
       if (DBG_IOBUF)
-	log_debug ("iobuf-%d.%d: error\n", a->no, a->subno);
+	log_debug ("iobuf-%d.%d: pending error (%s) returned\n",
+		   a->no, a->subno, gpg_strerror (a->error));
       return -1;
     }
 
-  if (a->filter)
+  if (a->filter && ! a->filter_eof && ! a->error)
+    /* We have a filter function and the last time we tried to read we
+       didn't get an EOF or an error.  Try to fill the buffer.  */
     {
-      len = a->d.size;
+      /* Be careful to account for any buffered data.  */
+      len = a->d.size - a->d.len;
       if (DBG_IOBUF)
-	log_debug ("iobuf-%d.%d: underflow: req=%lu\n",
+	log_debug ("iobuf-%d.%d: underflow: A->FILTER (%lu bytes)\n",
 		   a->no, a->subno, (ulong) len);
-      rc = a->filter (a->filter_ov, IOBUFCTRL_UNDERFLOW, a->chain,
-		      a->d.buf, &len);
+      if (len == 0)
+	/* There is no space for more data.  Don't bother calling
+	   A->FILTER.  */
+	rc = 0;
+      else
+	rc = a->filter (a->filter_ov, IOBUFCTRL_UNDERFLOW, a->chain,
+			&a->d.buf[a->d.len], &len);
+      a->d.len += len;
+
       if (DBG_IOBUF)
-	{
-	  log_debug ("iobuf-%d.%d: underflow: got=%lu rc=%d\n",
-		     a->no, a->subno, (ulong) len, rc);
+	log_debug ("iobuf-%d.%d: A->FILTER() returned rc=%d (%s), read %lu bytes\n",
+		   a->no, a->subno,
+		   rc, rc == 0 ? "ok" : rc == -1 ? "EOF" : gpg_strerror (rc),
+		   (ulong) len);
 /*  	    if( a->no == 1 ) */
 /*                   log_hexdump ("     data:", a->d.buf, len); */
-	}
-      if (a->use == IOBUF_INPUT && rc == -1)
-	{			/* EOF: we can remove the filter */
+
+      if (rc == -1)
+	/* EOF.  */
+	{
 	  size_t dummy_len = 0;
 
-	  /* and tell the filter to free itself */
+	  /* Tell the filter to free itself */
 	  if ((rc = a->filter (a->filter_ov, IOBUFCTRL_FREE, a->chain,
 			       NULL, &dummy_len)))
 	    log_error ("IOBUFCTRL_FREE failed: %s\n", gpg_strerror (rc));
+
+	  /* Free everything except for the internal buffer.  */
 	  if (a->filter_ov && a->filter_ov_owner)
-	    {
-	      xfree (a->filter_ov);
-	      a->filter_ov = NULL;
-	    }
-	  a->filter = NULL;
+	    xfree (a->filter_ov);
 	  a->filter_ov = NULL;
+	  a->filter = NULL;
 	  a->filter_eof = 1;
-	  if (!len && a->chain)
+
+	  if (a->d.len == 0 && a->chain)
+	    /* We don't need to keep this filter around at all:
+
+	         - we got an EOF
+		 - we have no buffered data
+		 - a filter follows this one.
+
+	      Unlink this filter.  */
 	    {
 	      iobuf_t b = a->chain;
 	      if (DBG_IOBUF)
-		log_debug ("iobuf-%d.%d: pop in underflow (!len)\n",
+		log_debug ("iobuf-%d.%d: pop in underflow (nothing buffered, got EOF)\n",
 			   a->no, a->subno);
 	      xfree (a->d.buf);
 	      xfree (a->real_fname);
 	      memcpy (a, b, sizeof *a);
 	      xfree (b);
+
 	      print_chain (a);
+
+	      return -1;
 	    }
+	  else if (a->d.len == 0)
+	    /* We can't unlink this filter (it is the only one in the
+	       pipeline), but we can immediately return EOF.  */
+	    return -1;
 	}
       else if (rc)
-	a->error = rc;
-
-      if (!len)
+	/* Record the error.  */
 	{
-	  if (DBG_IOBUF)
-	    log_debug ("iobuf-%d.%d: underflow: eof\n", a->no, a->subno);
-	  return -1;
+	  a->error = rc;
+
+	  if (a->d.len == 0)
+	    /* There is no buffered data.  Immediately return EOF.  */
+	    return -1;
 	}
-      a->d.len = len;
-      a->d.start = 0;
-      return a->d.buf[a->d.start++];
-    }
-  else
-    {
-      if (DBG_IOBUF)
-	log_debug ("iobuf-%d.%d: underflow: eof (no filter)\n",
-		   a->no, a->subno);
-      return -1;		/* no filter; return EOF */
     }
+
+  assert (a->d.start <= a->d.len);
+  if (a->d.start < a->d.len)
+    return a->d.buf[a->d.start++];
+
+  /* EOF.  */
+  return -1;
 }