File atftp-0.7-ack_heuristic.patch of Package atftp

Index: tftpd_file.c
===================================================================
--- tftpd_file.c.orig
+++ tftpd_file.c
@@ -406,7 +406,6 @@ int tftpd_send_file(struct thread_data *
      int timeout_state = state;
      int result;
      long block_number = 0;
-     long last_requested_block = -1;
      long last_block = -1;
      int data_size;
      struct sockaddr_storage *sa = &data->client_info->client;
@@ -434,6 +433,11 @@ int tftpd_send_file(struct thread_data *
      long prev_file_pos = 0;
      int temp = 0;
 
+     long prev_sent_block = -1;
+     int prev_sent_count = 0;
+     int prev_ack_count = 0;
+     int curr_sent_count = 0;
+
      /* look for mode option */
      if (strcasecmp(data->tftp_options[OPT_MODE].value, "netascii") == 0)
      {
@@ -819,8 +823,8 @@ int tftpd_send_file(struct thread_data *
                                                &client_info->client));
                                    sa = &client_info->client;
 
-                                   /* rewind the last_requested_block counter */
-                                   last_requested_block = -1;
+                                   /* rewind the prev_sent_block counter */
+                                   prev_sent_block = -1;
 
                                    state = S_SEND_OACK;
                                    break;
@@ -895,6 +899,7 @@ int tftpd_send_file(struct thread_data *
                                           "source port mismatch, check bypassed");
                          }
                     }
+
                     /* The ACK is from the current client */
                     number_of_timeout = 0;
 		    if (multicast)
@@ -908,24 +913,82 @@ int tftpd_send_file(struct thread_data *
                          logger(LOG_DEBUG, "received ACK <block: %ld>",
                                 block_number);
 
-                    /* if turned on, check whether the block request isn't already fulfilled */
-                    if (tftpd_prevent_sas) {
-                         /* multicast, block numbers could contain gaps */
-                         if (multicast) {
-                              if (last_requested_block >= block_number) {
+                    /* Now check the ACK number and possibly ignore the request */
+
+                    /* multicast, block numbers could contain gaps */
+                    if (multicast) {
+                         /* if turned on, check whether the block request isn't already fulfilled */
+                         if (tftpd_prevent_sas) {
+                              if (prev_sent_block >= block_number) {
                                    if (data->trace)
-                                        logger(LOG_DEBUG, "received duplicated ACK <block: %d >= %d>", last_requested_block, block_number);
+                                        logger(LOG_DEBUG, "received duplicated ACK <block: %d >= %d>", prev_sent_block, block_number);
                                    break;
                               } else
-                                   last_requested_block = block_number;
-                              /* unicast, blocks should be requested one after another */
-                         } else {
-                              if (last_requested_block + 1 != block_number && last_requested_block != -1) {
+                                   prev_sent_block = block_number;
+                         }
+                         /* don't prevent thes SAS */
+                         /* use a heuristic suggested by Vladimir Nadvornik */
+                         else {
+                              /* here comes the ACK again */
+                              if (prev_sent_block == block_number) {
+                                   /* drop if number of ACKs == times of previous block sending */
+                                   if (++prev_ack_count == prev_sent_count) {
+                                        logger(LOG_DEBUG, "ACK count (%d) == previous block transmission count -> dropping ACK", prev_ack_count);
+                                        break;
+                                   }
+                                   /* else resend the block */
+                                   logger(LOG_DEBUG, "resending block %d", block_number + 1);
+                              }
+                              /* received ACK to sent block -> move on to next block */
+                              else if (prev_sent_block < block_number) {
+                                   prev_sent_block = block_number;
+                                   prev_sent_count = curr_sent_count;
+                                   curr_sent_count = 0;
+                                   prev_ack_count = 1;
+                              }
+                              /* block with low number -> ignore it completely */
+                              else {
+                                   logger(LOG_DEBUG, "ignoring ACK %d", block_number);
+                                   break;
+                              }
+                         }
+                         /* unicast, blocks should be requested one after another */
+                    } else {
+                         /* if turned on, check whether the block request isn't already fulfilled */
+                         if (tftpd_prevent_sas) {
+                              if (prev_sent_block + 1 != block_number) {
+                                   logger(LOG_WARNING, "timeout: retrying...");
                                    if (data->trace)
-                                        logger(LOG_DEBUG, "received out of order ACK <block: %d != %d>", last_requested_block + 1, block_number);
+                                        logger(LOG_DEBUG, "received out of order ACK <block: %d != %d>", prev_sent_block + 1, block_number);
                                    break;
-                              } else
-                                   last_requested_block = block_number;
+                              } else {
+                                   prev_sent_block = block_number;
+                              }
+                              /* don't prevent thes SAS */
+                              /* use a heuristic suggested by Vladimir Nadvornik */
+                              } else {
+                              /* here comes the ACK again */
+                              if (prev_sent_block == block_number) {
+                                   /* drop if number of ACKs == times of previous block sending */
+                                   if (++prev_ack_count == prev_sent_count) {
+                                        logger(LOG_DEBUG, "ACK count (%d) == previous block transmission count -> dropping ACK", prev_ack_count);
+                                        break;
+                                   }
+                                   /* else resend the block */
+                                   logger(LOG_DEBUG, "resending block %d", block_number + 1);
+                              }
+                              /* received ACK to sent block -> move on to next block */
+                              else if (prev_sent_block < block_number) {
+                                   prev_sent_block = block_number;
+                                   prev_sent_count = curr_sent_count;
+                                   curr_sent_count = 0;
+                                   prev_ack_count = 1;
+                              }
+                              /* nor previous nor current block number -> ignore it completely */
+                              else {
+                                   logger(LOG_DEBUG, "ignoring ACK %d", block_number);
+                                   break;
+                              }
                          }
                     }
 
@@ -934,6 +997,8 @@ int tftpd_send_file(struct thread_data *
                          state = S_END;
                          break;
                     }
+
+                    curr_sent_count++;
                     state = S_SEND_DATA;
                     break;
                case GET_ERROR:
@@ -1028,7 +1093,7 @@ int tftpd_send_file(struct thread_data *
                          state = S_SEND_OACK;                
                          fseek(fp, 0, SEEK_SET);
 			 /* reset the last block received counter */
-			 last_requested_block = -1;
+			 prev_sent_block = -1;
                     }
                     else
                     {