Using backup server when original download server fails

Until now, the main download script could only check one server for the
given URL. However, ultimately the actual server that a file is downloaded
from is irrelevant for this project: we actually check its
checksum. Especially in the case of software (which are distributed over
many servers), this can usually be very annoying: the servers may not
properly communicate with the running system and even the 10 trials won't
be enough.

With this commit, the download script
`reproduce/analysis/bash/download-multi-try' can take a new optional
argument (a 5th argument). It assumes this argument is a space-separated
list of server(s) to use as backup for the original URL. When downloading
from the original URL fails, it will look into this list and try
downloading the same file from each given server.

1 files changed, 21 insertions, 1 deletions

diff --git a/reproduce/analysis/bash/download-multi-try b/reproduce/analysis/bash/download-multi-try
index dec2539..7a5f8f2 100755
--- a/reproduce/analysis/bash/download-multi-try
+++ b/reproduce/analysis/bash/download-multi-try
@@ -51,11 +51,13 @@ set -e
 
 
 
-# Input arguments and necessary sanity checks.
+# Input arguments and necessary sanity checks. Note that the 5th argument
+# (backup servers) isn't mandatory.
 inurl="$3"
 outname="$4"
 lockfile="$2"
 downloader="$1"
+backupservers="$5"
 if [ "x$downloader" = x ]; then
     echo "$0: downloader (first argument) not given."; exit 1;
 fi
@@ -73,6 +75,13 @@ fi
 
 
 
+# Separate the actual filename, to possibly use backup server.
+urlfile=$(echo "$inurl" | awk -F "/" '{print $NF}')
+
+
+
+
+
 # Try downloading multiple times before crashing.
 counter=0
 maxcounter=10
@@ -107,8 +116,19 @@ while [ ! -f "$outname" ]; do
     if [ x"$lockfile" = xnolock ]; then
         if ! $downloader $outname $inurl; then rm -f $outname; fi
     else
+        # Try downloading from the requested URL.
         flock "$lockfile" bash -c \
               "if ! $downloader $outname $inurl; then rm -f $outname; fi"
+
+        # If it failed, try the backup server(s).
+        if [ ! -f "$outname" ]; then
+            if [ x"$backupservers" != x ]; then
+                for bs in "$backupservers"; do
+                    flock "$lockfile" bash -c \
+                          "if ! $downloader $outname $bs/$urlfile; then rm -f $outname; fi"
+                done
+            fi
+        fi
     fi
 
 done