if read-only, set recv_buff to zero too

on linux, this discards all data.  For others it doesn't work :(

diff --git a/src/lib/bio/fd.c b/src/lib/bio/fd.c
index fe298d4430a53eb33a97ae310ff7bfb5b9b5891c..d17d3eb20a5fd4560c4faf2d5e4dcda07cdf3815 100644 (file)
--- a/src/lib/bio/fd.c
+++ b/src/lib/bio/fd.c
@@ -1365,12 +1365,29 @@ int fr_bio_fd_write_only(fr_bio_t *bio)
        case FR_BIO_FD_CONNECTED:
        case FR_BIO_FD_ACCEPTED:
                /*
-                *      Further reads are disallowed.
+                *      Further reads are disallowed.  However, this likely has no effect for UDP sockets.
                 */
                if (shutdown(my->info.socket.fd, SHUT_RD) < 0) {
                        fr_strerror_printf("Failed shutting down connected socket - %s", fr_syserror(errno));
                        return -1;
                }
+
+#ifdef __linux__
+#ifdef SO_RCVBUF
+               /*
+                *      On Linux setting the receive buffer to zero has the effect of discarding all incoming
+                *      data in the kernel.  With macOS and others it's an invalid value.
+                */
+               {
+                       int opt = my->info.cfg->recv_buff;
+
+                       if (setsockopt(my->info.socket.fd, SOL_SOCKET, SO_RCVBUF, &opt, sizeof(opt)) < 0) {
+                               fr_strerror_printf("Failed setting SO_RCVBUF: %s", fr_syserror(errno));
+                               return -1;
+                       }
+               }
+#endif
+#endif
                break;
 
        case FR_BIO_FD_LISTEN:
@@ -1378,6 +1395,10 @@ int fr_bio_fd_write_only(fr_bio_t *bio)
                return -1;
        }
 
+       /*
+        *      No matter what the possibilities above, we replace the read function with a "discard"
+        *      function.
+        */
        my->bio.read = fr_bio_fd_read_discard;
        return 0;
 }