The problem in my case was that I wanted to connect to Github but, SSH
traffic was blocked on the network where I was working. So what to do?
I quick mail to the Jayway tech mailing list, lets me know that in Linux
there is a route command, that can solve this problem. (Un)Fortunately
I am not using Linux on my development machine, but it turns out there
is a route(8) command in BSD too, with slightly different syntax.

Find the IP-address of the host I wish to connect to

# Find the IP-address of the host I wish to connect to
$ nslookup github.com
Server:		195.58.103.21
Address:	195.58.103.21#53 

Non-authoritative answer:
Name:	github.com
Address: 207.97.227.239 

Find out the gateway of the interface of the cell phone

# Find out the gateway of the interface of the cell phone
$ ifconfig
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
	inet 127.0.0.1 netmask 0xff000000
	inet6 ::1 prefixlen 128
	inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1
...
vmnet8: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	ether 00:50:56:c0:00:08
	inet 192.168.105.1 netmask 0xffffff00 broadcast 192.168.105.255
en3: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	ether 06:1e:64:00:34:1a
	inet6 fe80::41e:64ff:fe00:341a%en3 prefixlen 64 scopeid 0xa
	inet 172.20.10.3 netmask 0xfffffff0 broadcast 172.20.10.15
	media: 10baseT/UTP
	status: active

In my case the interface I want to use is the last one, en3 with inet
172.20.10.3 but if you are unsure, you can open the network preference
pane and look it up there.

Now I need to find out what the gateway for this interface is. I can
do this with netstat -r.

# Show the routing table
$ netstat -r
Routing tables

Internet:
Destination        Gateway            Flags        Refs      Use   Netif Expire
default            10.67.10.254       UGSc           10        0     en1
default            172.20.10.1        UGScI           0        0     en3
10.67.10/24        link#5             UCS             3        0     en1
10.67.10.88        localhost          UHS             1      811     lo0
10.67.10.254       0:14:4f:69:da:13   UHLWI          10       41     en1    661
10.67.10.255       link#5             UHLWbI          1       78     en1
127                localhost          UCS             0        0     lo0
... 

Internet6:
Destination        Gateway            Flags         Netif Expire
localhost          localhost          UH              lo0
fe80::%lo0         localhost          Uc              lo0
localhost          link#1             UHL             lo0
... 

Close to the top we find the entry for our interface en3.

default            172.20.10.1        UGScI           0        0     en3

Now we have the ip to the gateway that we wanted. So now the last step
is to make sure that access to github.com is routed via this gateway.

#route command -host destination gateway
$ sudo route add -host 207.97.227.239 172.20.10.1
add host 207.97.227.239: gateway 172.20.10.1 

That's it, I'm done. To make sure the routing is changed I check the
routing table with netstat -r again, to make sure the new entry is in it.

$ netstat -r
Routing tables

Internet:
Destination        Gateway            Flags        Refs      Use   Netif Expire
default            10.67.10.254       UGSc           30        0     en1
default            172.20.10.1        UGScI           0        0     en3
10.67.10/24        link#5             UCS             4        0     en1
10.67.10.88        localhost          UHS             0      973     lo0
10.67.10.254       0:14:4f:69:da:13   UHLWI          27       11     en1    708
10.67.10.255       ff:ff:ff:ff:ff:ff  UHLWbI          1       14     en1
127                localhost          UCS             0        0     lo0
...
github.com         172.20.10.1        UGHS            0       43     en3

Internet6:
Destination        Gateway            Flags         Netif Expire
localhost          localhost          UH              lo0
fe80::%lo0         localhost          Uc              lo0
localhost          link#1             UHL             lo0
fe80::%en0         link#4             UC              en0 

Sure enough, there it is, github.com. Finally I can now git pull
and everything works .

If I want to remove the entry, when I'm working elsewhere, I do that with

$ sudo route delete -host 207.97.227.239 172.20.10.1 

NSOperation do not have any facilities for returning a result when done as the Future do, you are left to implement this on your own. Which I have done a few times, and as a rule of thumb, make the solution generic when needed for the third time.

Operations works perfectly for background network activities. One common network activity is search-as-you-type, in this case you need to also cancel the previous operation if it has not yet been completed, so lets built this behavior into the generic solution as well.

API Design

What we want is an subclass of NSOperation that provides a future result, lets call this class CWFutureOperation. It is abstract, so users are supposed to subclass and implement main method just as for NSOperation, only difference is that the main method implementation must call setResult: before exiting.

The result that is set in the main method implementation can then be fetched using the blocking method result, equivalent to get() from the Java Future. As an alternative we would also like to be handed the method upon completion via a target-action pair. If the target-action pair is only called for finished operations that are not cancelled, then we get the search-as-you-type behavior for free.

It is also nice to be able to wrap up any method returning an object in a future operation as a convenience, so lets add that as well to our class interface:

@interface CWFutureOperation : NSOperation {
@private
    id _result;
    BOOL _isResultSet;
    id _completionTarget;
    SEL _completionSelector;
}

-(id)result;
-(void)setCompletionTarget:(id)target selector:(SEL)selector;
-(void)setResult:(id)result;

+(CWFutureOperation*)operationWithTarget:(id)target
                                selector:(SEL)selector
                                  object:(id)object;

+(CWFutureOperation*)operationWithInvocation:(NSInvocation*)invocation;

@end

Implementation

The client of the code must be able to fetch the result and the CWFutureOperation subclass must be able to set the result. The result method should block until the operation is finished if needed, and must properly return a result that can survive the operation that might be in a release pool. The implementation for this is straight forward, only minor complexity added in order to allow the result to be set multiple times:

-(id)result;
{
    if (![self isFinished]) {
        [self waitUntilFinished];
    }
    if ([self isCancelled]) {
        return nil;
    }
    return [[_result retain] autorelease];
}

-(void)setResult:(id)result;
{
    _isResultSet = YES;
    if (_result != result) {
        [_result autorelease];
        _result = [result retain];
    }
}

The reason that we flag if the result has been set is because we want to throw an exception if the subclass implementation of the main method failes to set the result before exiting, we add this behavior by overriding the start method in CWFutureOperation.

The start method will also call the target-action pair upon completion if the operation has not been cancelled. The target selector is always called on the main thread, this is so that we safely can update any UI using the calculated result without adding even more threading code.

-(void)start;
{
    [super start];
    if (![self isCancelled]) {
        if (!_isResultSet) {
            [NSException raise:NSInternalInconsistencyException
                        format:@"%@ did not set result.", self];
        }
        [_completionTarget performSelectorOnMainThread:_completionSelector
                                            withObject:self
                                         waitUntilDone:NO];
    }
}

Conclusion

The total amount of code is not muFuturesch, but this generic class adds a pattern to follow making design decisions for new application easy and consistent.

Solving the age old search-as-you-type problem can be as simple as this (Many assumptions, but you get the idea):

-(NSArray*)performSearchWithString:(NSString*)str;
{
    NSMutableArray* searchResults = nil;
    // Do actual search over the interwebz.
    return searchResults;
}

-(void)searchOperationDidComplete:(CWFutureOperation*)op;
{
    self.currentSearchOperation = nil;
    self.currentSearchResult = [op result];
    [self.searchDisplayController.searchResultsTableView reloadData];
}

-(BOOL)searchDisplayController:(UISearchDisplayController*)controller
  shouldReloadTableForSearchString:(NSString*)searchString;
{
	CWFutureOperation* op = [CWFutureOperation operationWithTarget:self
                                                          selector:@selector(performSearchWithString:) object:searchString];
    [op setCompletionTarget:self
                   selector:@selector(searchOperationDidComplete:)];
    [[NSOperationQueue defaultQueue]
    		replaceOperation:self.currentSearchOperation
               withOperation:op];
    self.currentSearchOperation = op;
    return NO;
}

The full source code including unit tests, and some additional categories for making operation queue life easier, can be downloaded here.

Any sane developer avoids premature optimization, so the task we later want to execute in a separate thread is almost always available in our current context. I am sure all Java-developers has seen something like this:

 new Thread() {
    public void run() {
        OuterClass.this.someMethod(arg);
    }
}.start();

And often an anonymous Runnable is involved as well. Executing a task in a separate thread with Cocoa and Cocoa Touch is ridiculously easy given the dynamic nature of Objective-C. This is done with Cocoa with this one-liner:

[self performSelectorInBackground:@selector(someMethod:) withObject:arg];

The performSelectorInBackground:withObject: is a companion method for performSelector:withObject:, and will create a new NSThread instance, and execute the specified method there. There are more companions such as performSelectorOnMainThread:withObject: that is used to execute a method on the main UI thread.

This easy access to executing in new threads often can result in code that spawns too many threads. In Cocoa on Mac OS X this is seldom a problem, not for Cocoa Touch applications under development when running in the iPhone simulator either. But on the more resource constrained iPhone and iPod Touch devices this will be a problem. Spawning a dozen background threads to download images will bring the iPhone OS to a staggering mess.

Update: I have removed CWSelectorOperation from this post, since using NSInvocationOperation is preferred.

Operation Queues

The solution is to use a NSOperationQueue, that as the name implies handles a queue of operations. The max number of concurrent operations can be set, as well as dependencies and priority. The downside is that NSOperationQueue can only handle instances of NSOperation.

NSOperation is an abstract class, where you as a developer override the main method to execute your task. In short NSOperation is programatically the equivalent of the Java Runnable interface. It is even worse as Objective-C do not support anonymous classes, so we will be required to actually implement our queued tasks as separate classes.

Not as neat as one would like, and definitely not even very Cocoa-like.

What is Missing

As a Cocoa developer I expect that executing a task on background queue, would be just as easy as executing a task on a background thread. The expected needed code is something like this:

[self performSelectorOnBackgroundQueue:@selector(someMethod:) withObject:arg];

To make this work we need:

1. A category on NSObject to add performSelectorOnBackgroundQueue:withObject:.
2. Implement a concrete subclass of NSOperation to support execution of a selector on any target.Use NSInvocationOperation to perform selector.
3. A category on NSOperationQueue to add a shared operation queue.

This is in the order of how a client developer would see it (most developers will only care for the NSObject category). For us this is the reverse order when implement this functionality.

A Shared Operation Queue

Cocoa and Cocoa Touch used many shared instances, for example a shared UIAccelerometer instance, and a shared NSURLCache instance. So this pattern of single point dependency injection is common in Cocoa and works very well. So let us follow suit by introducing an interface like this:

@interface NSOperationQueue (CWSharedQueue)
+(NSOperationQueue*)sharedOperationQueue;
+(void)setSharedOperationQueue:(NSOperationQueue*)operationQueue;
@end

The shared operation queue will be created lazily if it do not exist, and the client can easily swap it out at startup if needed. The implementation is very small, and a good example of how we should implement class variables with proper memory handling.

@implementation NSOperationQueue (CWSharedQueue)
 
static NSOperationQueue* cw_sharedOperationQueue = nil;
 
+(NSOperationQueue*)sharedOperationQueue;
{
  if (cw_sharedOperationQueue == nil) {
    cw_sharedOperationQueue = [[NSOperationQueue alloc] init];
    [cw_sharedOperationQueue setMaxConcurrentOperationCount:3];
  }
  return cw_sharedOperationQueue;
}
 
+(void)setSharedOperationQueue:(NSOperationQueue*)operationQueue;
{
  if (operationQueue != cw_sharedOperationQueue) {
    [cw_sharedOperationQueue release];
    cw_sharedOperationQueue = [operationQueue retain];
  }
}
 
@end

Enter CWSelectorOperation

Update: CWSelectorOperation is no longer needed, our implementation instead uses NSInvocationOperation.

Wrapping up NSObject

And at last we reach the category on NSObject, that is what we initially wanted, and what 95% of all use cases will be limited to.

@interface NSObject (CWSharedQueue)
 
-(NSInvocationOperation*)performSelectorInBackgroundQueue:(SEL)aSelector
    withObject:(id)arg;
-(NSInvocationOperation*)performSelectorInBackgroundQueue:(SEL)aSelector
    withObject:(id)arg dependencies:(NSArray*)dependencies
    priority:(NSOperationQueuePriority)priority;
 
@end

Most performSelector* methods do not have a return value, I have chosen to return the resulting NSInvocationOperation so that it can be used to setup dependencies for future queued operations. I have also added a second method performSelectorInBackgroundQueue:withObject:dependencies:priority: so that such dependencies can easily be setup, as well as prioritisation of operations.

The actual implementation is a simple wrapper around the NSInvocationOperation class, and category on NSOperationQueue that we implemented above:

@implementation NSObject (CWSharedQueue)
 
-(NSInvocationOperation*)performSelectorInBackgroundQueue:(SEL)aSelector
    withObject:(id)arg;
{
  NSInvocationOperation* operation = [[NSInvocationOperation alloc]
      initWithTarget:self selector:aSelector object:arg];
  [[NSOperationQueue sharedOperationQueue] addOperation:operation];
  return [operation autorelease];
}
 
-(NSInvocationOperation*)performSelectorInBackgroundQueue:(SEL)aSelector
    withObject:(id)arg dependencies:(NSArray*)dependencies
    priority:(NSOperationQueuePriority)priority;
{
  NSInvocationOperation* operation = [[NSInvocationOperation alloc]
      initWithTarget:self selector:aSelector object:arg];
  [operation setQueuePriority:priority];
  for (NSOperation* dependency in dependencies) {
    [operation addDependency:dependency];
  }
  [[NSOperationQueue sharedOperationQueue] addOperation:operation];
  return [operation autorelease];
}
 
@end

And that is it, if you want to avoid cut and paste of all this code to your own project just download the source code here. And happy concurrent hacking.

Download the older source code here, with a concrete subclass of NSOperation called CWSelectorOperation.

On the Mac it was easy to get running (if you have MacPorts):

% sudo port install squid
% sudo squid -z (initialize stuff if you never ran Squid before)
% sudo squid -N -d 1 (no daemon, debug level 1)

Then it was running on the console, and you could test it like this:

% squidclient http://google.com
...
X-Cache: MISS from myhostname
Via: 1.0 myhostname:3128 (squid/2.7.STABLE2)

And again, this time fetching from the cache:

% squidclient http://google.com
...
X-Cache: HIT from myhostname
Via: 1.0 myhostname:3128 (squid/2.7.STABLE2)

You configure your browser by simply setting proxy server to localhost:3128, if you are running your Squid locally, that is.

Maven is probably best configured in ~/.m2/settings.xml:

<settings xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/xmlSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
    http://maven.apache.org/xsd/settings-1.0.0.xsd">
  <proxies>
    <proxy>
      <active>true</active>
      <protocol>http</protocol>
      <host>localhost</host>
      <port>3128</port>
    </proxy>
  </proxies>
</settings>

I used the Jungle Disk software to provide the mapping from the S3 web service interface to a network drive. You give Jungle Disk your S3 account information, and it provides a network disk which you can use as the backup device. I first tried my existing backup software (Synchronize! Pro X) and it happily began creating directories and copying files. I then tried the backup feature built into Jungle Disk, and it works fine too. It's not fast compared to a local FireWire disk. It's limited to your upload bandwidth, which often is substantially smaller than the download bandwidth.

Anyway, it has been tugging along today storing 5 GB of by digital photos. It feels pretty good to know that my photos are now stored encrypted and with 99.99% availability somewhere far far away, costing me only 75 cents per month after the initial $2 for the transfer.

Setup

Cable modem from ISP, network cable to a firewall, the private end of the firewall via network cable on to a switch. Pretty basic, I guess. No wireless base stations or anything. Just an iMac connected via network cable to the switch.

Problem

Share the iMac's network cable connection through its Airport wireless capability. The client is a MacBook Pro. Basically, I just want to get Internet access on my laptop via the iMac. Sounds simple, but hey, it took me half a day and plenty of research to figure out.

Useful pieces of information gathered during this adventure

1. Turning on Internet Connection Sharing (ICS) will start a DHCP server.
2. Turning on ICS will create a full Airport network (not a computer-to-computer network).
3. Turning on ICS will create a new network configuration for 10.0.2.1, which I understand is the same address as the Airport base stations use.

Solution

1. On the iMac, set the Airport network to "Use DHCP with manual address" and set the IP to 10.0.2.1. Set the DNS servers to the ones recommended by your ISP. Apply.
2. On the iMac, go to Sharing|Internet and choose AirPort Options. Enable WEP encryption (I chose 40-bit with a 5 character password). The default network name is your computer name. I added a postfix to the network name ("-ics") so I can distinguish it from the computer-to-computer network. Apply.
3. Now start sharing your Built-in Ethernet connection to computers using Airport. As I mentioned previously, this will create the new network and also start a DHCP server.
4. On the MacBook, set the Airport network to "Use DHCP". Leave all fields blank.
5. On the MacBook, connect to the newly created network, which should be named "hostname-ics" if you followed my naming advice earlier. Watch the network configuration. Eventually it shows the IP 10.0.2.2.

That's it. You should now have access to your other machines on your private network, but also to Internet.

I had seen somewhere that you could get the 403 error if you were using SSL (which I was) and the Sourceforge server svn.sourceforge.net. The correct server is the PROJECTNAME.svn.sourceforge.net, where PROJECTNAME in my case was springframework. So the correct URL to use is https://springframework.svn.sourceforge.net/svnroot/springframework/. This meant changing the checkout URL, which Subversion can do on an already checked-out working copy, using the switch command. Cool. When I tried this, it failed because it couldn't find the new server. The problem was that the DNS servers I was using at some point didn't find this server, and probably cached this negative hit. Eventually I found a DNS that could locate this server and performed the switch. Things have been working much better since.

Using the incorrect server, which most likely is a proxy server of some sort, could possibly have resulted in different physical servers being used for different requests during the Subversion transaction. It's not allowed to perform a svn copy operation between repositories. You'll get a 403 if you try it. Perhaps that rule applied to my situation as well.

Note that although this follows the Internet standard for email addresses (RFC 822), some sites simply ignore this and incorrectly disallows addresses with plus signs.

Read more here. More cool mail tips can be found here.