Fallback to existing server file when getbukkit retrieval fails (#2721)

scripts/start-deployBukkitSpigot

@@ -76,35 +76,48 @@ function downloadSpigot {
   fi
 
   setServerVar
+  curlArgs=()
   if [ -f "$SERVER" ] && ! isTrue "$FORCE_REDOWNLOAD"; then
     # tell curl to only download when newer
-    curlArgs="-z $SERVER"
+    curlArgs+=(-z "$SERVER")
   fi
   if isDebugging; then
-    curlArgs="$curlArgs -v"
+    curlArgs+=(-v)
   fi
   log "Downloading $match from $downloadUrl ..."
-  curl -fsSL -o "$SERVER" $curlArgs "$downloadUrl"
-  if [[ $? != 0 || $(grep -c "DOCTYPE html" "$SERVER") != 0 ]]; then
+
+  tempFile="$SERVER.$$"
+
+  # HTTP error or download site responded with an HTML error page
+  if ! curl -fsSL -o "$tempFile" "${curlArgs[@]}" "$downloadUrl" || grep -iq "doctype html" "$tempFile"; then
+
     cat <<EOF
 
 ERROR: failed to download from $downloadUrl
        Visit https://getbukkit.org/download/${getbukkitFlavor} to lookup the
-       exact version, such as 1.4.6-R0.4-SNAPSHOT or 1.8-R0.1-SNAPSHOT-latest.
-       Click into the version entry to find the **exact** version, because something
-       like "1.8" is not sufficient according to their download naming.
+       exact version or see if download site is unavailable.
+       Click into the version entry to find the **exact** version.
 
 EOF
 
-    if isDebugging && [[ $(grep -c "DOCTYPE html" "$SERVER") != 0 ]]; then
-      cat "$SERVER"
+    if isDebugging && grep -iq "doctype html" "$tempFile"; then
+      cat "$tempFile"
     fi
 
-    # remove invalid download
-    rm "$SERVER"
-    exit 3
+    if [ -f "$SERVER" ]; then
+      log "Continuing with existing $SERVER file"
+    else
+      # remove invalid download
+      rm "$tempFile"
+      exit 3
+    fi
+
+  else
+    mv "$tempFile" "$SERVER"
+
   fi
 
+
   JVM_OPTS="${JVM_OPTS} -DIReallyKnowWhatIAmDoingISwear"
   export JVM_OPTS
 }