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.

1 files changed, 20 insertions, 11 deletions

diff --git a/networking/tftp.c b/networking/tftp.c
index 6be265b4c..0b25f752d 100644
--- 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");