From 7bb043aa26cd771e1ebf7fb824182a905de5a9f6 Mon Sep 17 00:00:00 2001
From: CyberLeo <cyberleo@cyberleo.net>
Date: Sun, 20 Oct 2013 01:21:02 -0500
Subject: [PATCH] Rework crc32 algorithm selection mechanism

---
 flag | 83 ++++++++++++++++++++++--------------------------------------
 1 file changed, 30 insertions(+), 53 deletions(-)

diff --git a/flag b/flag
index 587f4fe..38cbd4a 100755
--- a/flag
+++ b/flag
@@ -8,63 +8,40 @@
 # $HOME/.flag <- Local user's flag
 # Check them in that order.
 
-hash_string() {
-  # Hash the passed string into 8 hex characters
-  [ -z "${crc32_bin}" ] && find_crc32_bin
-  if [ -z "${crc32_bin}" ]
-  then
-    echo "No crc32 algo found!" >&2
-    echo "deadbeef"
-  else
-    echo -n "${*}" | eval "${crc32_bin}" | awk '{print $1}'
-  fi
-}
-
-find_crc32_bin() {
-  crc32=""
-  for bin in crc32sum crc32sum-linux crc32sum-freebsd
+# Name available algos as algo_something() and left-align for autodetection
+# Order the algos by priority: the first one that is correct will be used
+algo_cksum_linux() { printf '%08x\n' $(cksum) | head -n 1; }
+algo_cksum_freebsd() { printf '%08x\n' $(cksum -o 3) | head -n 1; }
+algo_crc32() { crc32 /dev/stdin; }
+algo_crc32sum() { crc32sum; }
+algo_crc32sum_linux() { crc32sum-linux; }
+algo_crc32sum_freebsd() { crc32sum-freebsd; }
+algo_ruby() { ruby -e 'require "zlib"; printf "%08x\n", Zlib.crc32(STDIN.readlines.join)'; }
+algo_php() { php -r 'printf("%08x\n", crc32(file_get_contents("/dev/stdin")));'; }
+algo_perl() { perl -e 'use String::CRC32; printf("%08x\n", crc32(*STDIN));'; }
+
+find_crc32_algo() {
+  sed -e '/^algo_[^(]*()/!d; s/().*$//' "${0}" | while read algo
   do
-    bin="$(which "${bin}" 2>/dev/null)"
-    if [ -x "${bin}" ]
+    if [ "$(printf "meow" | "${algo}" 2>/dev/null)" = "8a106afe" ]
     then
-      export crc32_bin="${bin}"
-      if [ "$(hash_string "meow" 2>/dev/null)" = "8a106afe" ]
-      then
-        crc32="${bin}"
-        break
-      fi
+      echo "${algo}"
+      break
     fi
   done
+}
 
-  if [ -z "${crc32}" ]
-  then
-    for bin in cksum ruby php perl
-    do
-      bin="$(which "${bin}" 2>/dev/null)"
-      if [ -x "${bin}" ]
-      then
-        case "${bin}" in
-        */cksum) bin="printf '%08x\n' \$(${bin} -o 3) | head -n 1" ;;
-        */ruby)  bin="${bin} -e 'require \"zlib\"; printf(\"%08x\n\", Zlib.crc32(STDIN.readlines.join))'" ;;
-        */php)   bin="${bin} -r 'printf(\"%08x\n\", crc32(file_get_contents(\"/dev/stdin\")));'" ;;
-        */perl)  bin="${bin} -e 'use String::CRC32; printf(\"%08x\n\", crc32(*STDIN));'" ;;
-        esac
-        export crc32_bin="${bin}"
-        if [ "$(hash_string "meow" 2>/dev/null)" = "8a106afe" ]
-        then
-          crc32="${bin}"
-          break
-        fi
-      fi
-    done
-  fi
-  if [ -n "${crc32}" ]
+hash_string() {
+  # Hash the passed string into 8 hex characters
+  [ "${crc32_algo}" ] || crc32_algo="$(find_crc32_algo)"
+  if [ -z "${crc32_algo}" ]
   then
-    export crc32_bin="${crc32}"
-  else
-    echo "Failed to locate usable crc32 algo" >&2
-    unset crc32_bin
+    echo "No crc32 algo found!" >&2
+    echo "deadbeef"
     return 1
+  else
+    echo -n "${*}" | "${crc32_algo}" 2>/dev/null | awk '{print $1}'
+    return 0
   fi
 }
 
@@ -77,9 +54,9 @@ flagcache(){
   fi
   if [ -z "${flag_hex}" ]
   then
-    flag_hex="$(hash_string "${myhost}")"
-    [ "${crc32_bin}" ] && echo -e "${myhost}\t${flag_hex}" >> "${cache}"
+    flag_hex="$(hash_string "${myhost}")" && echo -e "${myhost}\t${flag_hex}" >> "${cache}"
   fi
+  echo "${flag_hex}"
 }
 
 if [ -f "${HOME}/.flag" ]
@@ -94,7 +71,7 @@ fi
 
 if [ -z "${flag_hex}" ]
 then
-  flagcache
+  flag_hex="$(flagcache)"
 fi
 
 # Now we definitely have flag_hex
-- 
2.42.0