fix infinite retry bug. also, reduce per-packet receive timeout

to something more reasonable than 5 seconds, and add simple
exponential backoff to compensate.  improves performance on
marginal networks.

diff --git a/networking/tftp.c b/networking/tftp.c
index 6be265b4cdd0ef7a29b5d90ff2a61580611ccc43..0b25f752d25bae3d568c7c8212c91380191ecd1f 100644 (file)
--- a/networking/tftp.c
+++ b/networking/tftp.c
@@ -21,12 +21,12 @@
 
 #include "libbb.h"
 
-
 #if ENABLE_FEATURE_TFTP_GET || ENABLE_FEATURE_TFTP_PUT
 
 #define TFTP_BLOCKSIZE_DEFAULT 512     /* according to RFC 1350, don't change */
-#define TFTP_TIMEOUT 5 /* seconds */
-#define TFTP_NUM_RETRIES 5 /* number of retries */
+#define TFTP_TIMEOUT 50000             /* 50ms, in microseconds */
+#define TFTP_MAXTIMEOUT 999000         /* about 1 second, in microseconds */
+#define TFTP_NUM_RETRIES 12            /* number of backed-off retries */
 
 /* opcodes we support */
 #define TFTP_RRQ   1
@@ -124,7 +124,7 @@ static int tftp( USE_GETPUT(const int cmd,)
        uint16_t opcode;
        uint16_t block_nr = 1;
        uint16_t recv_blk;
-       int timeout = TFTP_NUM_RETRIES;
+       int retries, waittime;
        char *cp;
 
        unsigned org_port;
@@ -206,6 +206,10 @@ static int tftp( USE_GETPUT(const int cmd,)
                send_len = cp - xbuf;
                /* NB: send_len value is preserved in code below
                 * for potential resend */
+
+               retries = TFTP_NUM_RETRIES;     /* re-initialize */
+               waittime = TFTP_TIMEOUT;
+
  send_again:
 #if ENABLE_DEBUG_TFTP
                fprintf(stderr, "sending %u bytes\n", send_len);
@@ -218,11 +222,10 @@ static int tftp( USE_GETPUT(const int cmd,)
                if (finished && (opcode == TFTP_ACK))
                        goto ret;
 
-               timeout = TFTP_NUM_RETRIES;     /* re-initialize */
  recv_again:
                /* Receive packet */
-               tv.tv_sec = TFTP_TIMEOUT;
-               tv.tv_usec = 0;
+               tv.tv_sec = 0;
+               tv.tv_usec = waittime;
                FD_ZERO(&rfds);
                FD_SET(socketfd, &rfds);
                switch (select(socketfd + 1, &rfds, NULL, NULL, &tv)) {
@@ -248,12 +251,18 @@ static int tftp( USE_GETPUT(const int cmd,)
                                goto recv_again;
                        goto process_pkt;
                case 0:
-                       timeout--;
-                       if (timeout == 0) {
-                               bb_error_msg("last timeout");
+                       retries--;
+                       if (retries == 0) {
+                               bb_error_msg("timeout");
                                goto ret;
                        }
-                       bb_error_msg("last timeout" + 5);
+
+                       /* exponential backoff with limit */
+                       waittime += waittime/2;
+                       if (waittime > TFTP_MAXTIMEOUT) {
+                               waittime = TFTP_MAXTIMEOUT;
+                       }
+
                        goto send_again; /* resend last sent pkt */
                default:
                        bb_perror_msg("select");