This is a video using the mouse as input:

Shares

In addition to being an Amazon S3 client, 3Hub offers a cool decentralized sharing feature. Shares are a way to let your friends more easily keep track of what S3 buckets you have shared (for them).

Sharing on 3Hub

Shares can be read only or both read and write. Permissions on files you upload to these shares are handled automatically.

When you make a bucket a ‘Share’, that bucket will show up when they browse you in their Friends list. To view what buckets your friend has given you permissions, you’ll need to add them in the Friends tab (using their email address). Selecting a friend in the friends tab will show you a list of buckets they have shared for you.

Friends on 3Hub

Sharing works without contacting any 3rd-party server or “middleman” and works by storing meta-data information in certain expected file locations on S3 that are readable only by those you share with. It is essentially a private and distributed way to share files without having to use a Dropbox or other service that operates on top of S3.

And shares are just buckets with permissions, nothing special. You can remove a bucket as a share at any time without having to update any files within those buckets. You can make an existing bucket a share by selecting the ‘Add as a Share’ option.

And more features are coming soon to make sharing files with your friends on S3 even easier. Try it from the App Store.

The SBJSON test ran NSString#JSONValue, and the equivalent YAJL test ran NSData#yajl_JSON. The YAJL bindings operate directly on NSData, and this makes a bit more sense since we usually have NSData first, whereas for SBJSON you have to decode to a string before parsing. I didn’t include this difference in my tests though.

These are tests of parsing only (and not loading of any data or strings) of the 4 APIs datasets run 100 times on the original iPhone, 3G and 3GS:

So the YAJL framework gives about a 60% speed increase. The YAJL Objective-C bindings can be found on github.

Be sure to thank @lloydhilaiel for making YAJL full of so much awesomeness.

Update: The project used to do the perf test can be found here.

Hopefully, sometime soon I will do some performance comparisons. In the meantime, if you try these bindings, let me know how it goes. You can find it on github at: http://github.com/gabriel/yajl-objc.

This limitation can be really frustrating, particularly when you are using NSOperation or threading in general and need your delegates to call back onto the main (UI) thread.

A possible solution is to use NSInvocation with performSelector to deal with multiple arguments and primitives, for example:

NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:[self methodSignatureForSelector:@selector(listWithOffset:limit:)]];
[theInvocation setSelector:@selector(listWithOffset:limit:)];
[theInvocation setTarget:self];
NSInteger offset = 40;
[theInvocation setArgument:&offset atIndex:2];
NSInteger limit = 20;
[theInvocation setArgument:&limit atIndex:3];
[invocation performSelector:@selector(invoke) onThread:thread withObject:nil waitUntilDone:NO];

but it gets cumbersome, especially setting up the invocation instance. (BTW, the first argument is at index 2 because of the hidden arguments self and _cmd.) Also you would need to call retainArguments if your arguments were objects, that may be released by the calling thread.

Thankfully there is a better way. In a post called ‘Grab that Invocation‘ and later at Dave Dribbin’s post ‘Invoke on Main Thread‘ we can see how to get an NSInvocation instance from an NSProxy/forwardInvocation: automatically; and now we can combine the proxy with performSelector:onThread: or any of the other peformSelector methods to invoke back on the main thread, invoke on other threads, delay invocation, or other more general aspects like timing methods, debugging, logging, or security.

You can find Dave Dribbins original DDInvocationGrabber implementation in his DDFoundation library.

I’ve expanded on it a bit in GHKit, (see GHNSInvocationProxy) and plan on adding more features. If you use it with the GHNSObject+Invocation category, it gets even better:

// Invoke after 2 second delay (useful for simulating slow operations)
[[self gh_proxyAfterDelay:2.0] listWithOffset:40 limit:20];

// Invoke on main thread (if you ran on a separate thread or NSOperation
// and wanted to call back the delegate on the main thread)
[self listWithOffset:40 limit:20 delegate:[delegate_ gh_proxyOnMainThread:YES]];
// Later, after listing, the connection invokes the delegate back on the 
// main thread
[delegate_ connection:self didListWithOffset:40 limit:20];

// Invoke on thread
[[self gh_proxyOnThread:thread waitUntilDone:NO] listWithOffset:40 limit:20];

// Time the invocation
NSTimeInterval time;
[[self gh_timedProxy:&time] listWithOffset:40 limit:20];
NSLog(@"Took %0.2fs", time);

This category also includes other performSelector helpers (supporting var args and argument lists).

What might be some other ways to use this? Maybe an NSOperationProxy that allows you to queue and prioritize invocations, or more complex debugging or analytics proxies that can keep stats of certain activities.

GHUnit (pronounced ˈgü-ˈnit, I guess?), hosted at gabriel/gh-unit, is meant to be installed as a framework, and run as an application in a separate Test target. The idea being that you can run and crash into the XCode debugger directly and utilize all the debugging techniques that you normally use. The test GUI should allow you to see test failures more clearly, view timings / stats and not have to go fishing for the build console window. And an automated way to view stack traces.

Details on how to use the framework are included in the README.

GHUnit Test GUI for Mac OS X App

Unit Test GUI for iPhone App

For the iPhone side, I included a similar GUI that runs the tests in the simulator.

GHUnit can be used as a standalone test framework (by subclassing GHTestCase), or with your existing SenTestCase tests or GTMTestCase tests.

So far its pretty basic, but I am using it on a couple projects and its been helping my development a bunch and letting me to write tests as I go without completely destroying my workflow or sanity.

Any feedback is appreciated and let me know if you have any problems with the install/embed instructions or in general. Also thanks to the GTM peeps, on which much of this is based.

Maybe the next step is an XCode plugin?

Thanks!

As far as I could work out, traditional methods of grabbing a symbolic stack trace don’t work on the iPhone. (If I am remembering right, I don’t think NSStackTraceKey exists in UIKit.)

A little while ago I hacked the GTMStackTrace from google-toolbox-for-mac, to lookup the symbolic stack trace from the call stack return addresses (NSException#callStackReturnAddresses introduced in 10.5) and print it out using NSSetUncaughtExceptionHandler. Life has been a little bit easier ever since. Thankfully, the awesome people who work on GTM added it in themselves (see GTMStackTrace.h#61). Here is how you might set it up, in main.m:

#ifdef DEBUG
#import 
#import "GTMStackTrace.h"

void exceptionHandler(NSException *exception) {
	NSLog(@"%@", GTMStackTraceFromException(exception));
}
#endif

int main(int argc, char *argv[]) {
    
#ifdef DEBUG
	NSLog(@"Debug enabled");	
	NSDebugEnabled = YES;
	NSZombieEnabled = YES;
	NSDeallocateZombies = NO;
	NSHangOnUncaughtException = YES;
	[NSAutoreleasePool enableFreedObjectCheck:YES];
	NSSetUncaughtExceptionHandler(&exceptionHandler);
#endif	

	NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
	int retVal = UIApplicationMain(argc, argv, nil, nil);
	[pool release];
	return retVal;
}

For me, DEBUG is set in GCC_PREPROCESSOR_DEFINITIONS via the awesome GTM xcconfg files, which you should also be using. Hopefully, you should get a trace that looks like:

[Session started at 2008-12-30 00:10:13 -0800.]
2008-12-30 00:10:15.772 TestExceptionIPhone[8493:20b] Debug enabled
2008-12-30 00:10:15.830 TestExceptionIPhone[8493:20b] #0  0x92c5614b _NSExceptionSetRubyToken()  (/System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation)
#1  0x9657ce3b objc_exception_throw()  (/usr/lib/libobjc.A.dylib)
#2  0x92c55f2b +[NSException raise:format:arguments:]  (/System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation)
#3  0x92c55f6a +[NSException raise:format:]  (/System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation)
#4  0x002350 +[TestExceptionIPhoneAppDelegate applicationDidFinishLaunching:]  (/Users/gabe/Library/Application Support/iPhone Simulator/User/Applications/586E48B6-B758-4DBD-A534-D6927DA74583/TestExceptionIPhone.app/TestExceptionIPhone)
#5  0x30a4e01a +[UIApplication performInitializationWithURL:asPanel:]  (/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator2.2.sdk/System/Library/Frameworks/UIKit.framework/UIKit)
#6  0x30a57363 +[UIApplication _runWithURL:]  (/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator2.2.sdk/System/Library/Frameworks/UIKit.framework/UIKit)
#7  0x900425ee +[NSRunLoop runMode:beforeDate:]  (/System/Library/Frameworks/Foundation.framework/Versions/C/Foundation)
#8  0x92bdcb45 CFRunLoopRunSpecific()  (/System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation)
#9  0x92bdccf8 CFRunLoopRunInMode()  (/System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation)
#10 0x31564600 GSEventRunModal()  (/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator2.2.sdk/System/Library/PrivateFrameworks/GraphicsServices.framework/GraphicsServices)
#11 0x315646c5 GSEventRun()  (/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator2.2.sdk/System/Library/PrivateFrameworks/GraphicsServices.framework/GraphicsServices)
#12 0x30a4ec98 +[UIApplication _run]  (/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator2.2.sdk/System/Library/Frameworks/UIKit.framework/UIKit)
#13 0x30a5a094 UIApplicationMain()  (/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator2.2.sdk/System/Library/Frameworks/UIKit.framework/UIKit)
2008-12-30 00:10:15.834 TestExceptionIPhone[8493:20b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Give me a good stack trace'

And the source of the exception usually starts around the 5th line.

Me and my friends have been using it for a little while to keep track of when we are uploading files (via RSS) and it seems to work pretty well.

Last week, I was playing around with the idea of a MuxTape/OpenTape type format where you could point it at a directory of mp3′s and you could play them straight from the browser. I have a preliminary version, an example of it, at: http://shrub.appspot.com/m1xes/sub-pop-mix-1/?format=tape (songs from the official Subpop Records free downloads page). So it seems like an OK way to share mixtapes by hosting them on your own S3 account, or to just stream mp3′s that you have backed up from a web browser.

In order to get it to show the track information, I wrote a handler to pull ID3v2 tag info from the mp3s by doing a request using the Range header (which S3 supports) of the first 1024 bytes (Range: bytes=0-1024). I think most ID3v2 taggings are at the beginning of the mp3 (I think ID3v1 was at the end). For example, if you have the S3 file:

sub-pop-mix-1/01-Dntel-The_Distance_(ft._Arthur&Yu).mp3

in the m1xes bucket, you can do an ID3 lookup using format=id3-json:

http://shrub.appspot.com/m1xes/sub-pop-mix-1/01-Dntel-The_Distance_%28ft._Arthur%26Yu%29.mp3?format=id3-json:

{ "album": "Dumb Luck",
  "performer": "Dntel",
  "title": "The Distance (Ft. Arthur & Yu)",
  "track": "5/9",
  "year": null,
  "isTruncated": false }

It will parse as much as it can from the first 1024 bytes of the mp3 (and isTruncated will be true, if there was more data after that). ID3 lookups are cached for 5 minutes.

Right now it doesn’t do any authentication (not sure if I want to store secret keys), so its only useful for public buckets and files. I think it makes sense to open source it and then add auth capability, and then people can configure it with their own keys and host it on their own app engine space. I will try to throw some code up on github really soon, after I re-factor some of my noobish python code.

Mainly, its just an excuse to help me learn python and play with mako and google app engine.

All this, and more detailed info is at: http://shrub.appspot.com/. If you see anything wacky, let me know.

Update: The source is now available on github: gabriel/shrub

• GHNSDate+Parsing.m: Various RFC and ISO date formatting and parsing
• GHNSString+TimeInterval.m: Time ago in words
• GHViewAnimation.m: View animation helper.
• GHNSString+HMAC.m: HMAC-SHA1 implementation which works on iPhone

And other stuff for generating uuids, mime types, etc. I blogged earlier about the date parsing and time ago in words.

Also, be sure to checkout the Google Toolbox For Mac which is way comprehensive (definately check there first). Feel free to pick and choose stuff at will. All files from other sources should have their original licenses which should all be MIT-like.

PS, sorry about the crazy feed crossing before. If you want to switch to a “cleaner” feed you can use this url: feeds.feedburner.com/gabrielh. Google reader caches the feed entries on the other one, so those will likely live forever.

HTTP Date

Some quick background on HTTP dates first. S3 requires sending a ‘Date’ header field as part of an authenticated request. (This and signing the request is a common countermeasure against a replay attack.) The spec says, the format of the date should be “one of the RFC 2616 formats (http://www.ietf.org/rfc/rfc2616.txt)”.

HTTP applications have historically allowed three different formats
for the representation of date/time stamps:

Sun, 06 Nov 1994 08:49:37 GMT ; RFC 822, updated by RFC 1123
Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036
Sun Nov 6 08:49:37 1994 ; ANSI C’s asctime() format

The first format is preferred as an Internet standard and represents
a fixed-length subset of that defined by RFC 1123 [8] (an update to
RFC 822 [9]). The second format is in common use, but is based on the
obsolete RFC 850 [12] date format and lacks a four-digit year.
HTTP/1.1 clients and servers that parse the date value MUST accept
all three formats (for compatibility with HTTP/1.0), though they MUST
only generate the RFC 1123 format for representing HTTP-date values
in header fields. See section 19.3 for further information.

So these are the standard formats. When sending a formatted date you should only use RFC1123 but should be able to handle any of the formats listed. This is just a way to maintain compatibility while trying to move everything to the latest format. If you are wondering what the difference is, RFC 1123 updated 822 by changing the time zone from hour format (±0000) to GMT format (GMT).

For example, the ‘Date’ or ‘Expires’ header fields for requests have this (RFC1123) format. Replies might have an HTTP date format in a Last-Modified or Date header as well.

ISO Date

XML data which has formatted date fields might use a date format which is defined by the ISO8601 standard and looks like ’2006-02-03T16:45:09.000Z’.

Date parsing in Cocoa

Prior to 10.4, the Cocoa API supported “strftime-style conversion specifiers”. In 10.4, they added support for the Unicode Technical Standard #35 (version tr35-6).

The pre-10.4 strftime patterns look like: “%m/%d/%y” and the Unicode standard looks like “MM/dd/yyyy”. The default behavior (for backwards compatibility) is strftime format. In order to use the Unicode standard (which you will, its way better), you need to set the formatter behavior to NSDateFormatterBehavior10_4 either by calling setFormatterBehavior or setting the classes formatter behavior globally. Do NOT use the initWithDateFormat:allowNaturalLanguage: constructor, because it will give you a pre-10.4 date formatter. Using the strftime style of pattern when configured for the 10.4 (Unicode) behavior will fail silently.

So fast forward a few weeks, an S3Hub user told me he was getting authentication errors (invalid signing) trying to connect. I couldn’t replicate the problem but I eventually got the raw HTTP request header it was sending and the Date header looked like.

Fr, 06 Jun 2008 08:49:37 GMT.

Turns out the user is in Germany and when I change my locale to something German, I can reproduce the problem. Date formatters themselves can have specific styles (and symbols) that are modified by the locale. In the German locale the weekday symbol for friday is ‘Fr’ instead of English locale which is ‘Fri’. So when you use a date formatter in this way (with day or month symbols, for example) make sure to set the locale to en_US. The final date formatter looks like:

NSDateFormatter *rfc1123DateFormatter = [[[NSDateFormatter alloc] init] autorelease];
[rfc1123DateFormatter setFormatterBehavior:NSDateFormatterBehavior10_4];
[rfc1123DateFormatter setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"en_US"] autorelease]];
[rfc1123DateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
[rfc1123DateFormatter setDateFormat:@"EEE, dd MMM yyyy HH:mm:ss zzz"];

Update: See GHNSDate+Parsing gh-kit category on github for a collection of these date formatters.