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From afine <...@git.apache.org>
Subject [GitHub] zookeeper pull request #150: ZOOKEEPER-2184: Zookeeper Client should re-reso...
Date Tue, 17 Jan 2017 21:22:09 GMT
Github user afine commented on a diff in the pull request:

    https://github.com/apache/zookeeper/pull/150#discussion_r96512625
  
    --- Diff: src/java/main/org/apache/zookeeper/client/StaticHostProvider.java ---
    @@ -87,15 +73,69 @@ public StaticHostProvider(Collection<InetSocketAddress> serverAddresses)
             Collections.shuffle(this.serverAddresses);
         }
     
    +    /**
    +     * In Java 7, we have a method getHostString, but earlier versions do not support
it.
    +     * This method is to provide a replacement for InetSocketAddress.getHostString().
    +     *
    +     * It evaluates to a hostname if one is available and otherwise it returns the
    +     * string representation of the IP address.
    +     *
    +     * @param addr
    +     * @return Hostname string of address parameter
    +     */
    +    private String getHostString(InetSocketAddress addr) {
    +        String hostString;
    +        InetAddress ia = addr.getAddress();
    +
    +        if (ia != null) {
    +            // If the string starts with '/', then it has no hostname
    +            // and we want to avoid the reverse lookup, so we return
    +            // the string representation of the address.
    +            if (ia.toString().startsWith("/")) {
    +                hostString = ia.getHostAddress();
    +            } else {
    +                hostString = addr.getHostName();
    +            }
    +        } else {
    +            // According to the Java 6 documentation, if the hostname is
    +            // unresolved, then the string before the colon is the hostname.
    +            String addrString = addr.toString();
    +            hostString = addrString.substring(0, addrString.lastIndexOf(':'));
    +        }
    +
    +        return hostString;
    +    }
    +
         public int size() {
             return serverAddresses.size();
         }
     
         public InetSocketAddress next(long spinDelay) {
    -        ++currentIndex;
    -        if (currentIndex == serverAddresses.size()) {
    -            currentIndex = 0;
    +        // Handle possible connection error by re-resolving hostname if possible
    +        if (!connectedSinceNext) {
    +            InetSocketAddress curAddr = serverAddresses.get(currentIndex);
    +            if (!curAddr.getHostString().equals(curAddr.getAddress().getHostAddress()))
{
    +                try {
    +                    int thePort = curAddr.getPort();
    +                    InetAddress resolvedAddresses[] = InetAddress.getAllByName(getHostString(curAddr));
    +                    if (resolvedAddresses.length == 1) {
    +                        serverAddresses.set(currentIndex, new InetSocketAddress(resolvedAddresses[0],
thePort));
    +                    } else {
    +                        serverAddresses.remove(currentIndex);
    --- End diff --
    
    In the case where during the construction of the `StaticHostProvider` we add a host H1
which resolves to addresses A,B,C. Then at some point in the future A goes offline and the
DNS system has changed H1 to resolve to hosts D,E,F. With the current code wouldn't `serverAddresses`
now contain hosts B,C,D,E,F instead of only hosts D,E,F?
    
    Is this something even worth fixing?


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