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App & Service
Benjamin Ragheb
CocoaHeads, New York City
9 May 2013
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In cloud computing the people are served by two
separate, yet equally important parts.
The applications which interact with the users
and the services which process their data.
These are their stories.
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Make Setup Easier
• User snaps photo of blank log sheet
• A sophisticated neural network
(a.k.a. “Mike”) interprets photo
• Send email to user when we’re done
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Constraints
• Will anybody use it?
• I hate writing web services
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To the Cloud!
Amazon S3
(obviously)
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Amazon SNS
• You create a topic
• Use HTTP to publish something to the
topic
• Amazon forwards the something to the
topic’s subscribers
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Amazon SNS
• Message is up to 64KB of whatever you like
• Can forward to email, text message, HTTP,
or SQS
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Separation of Concerns
• App doesn’t need to know where message
is going
• Amazon keeps track of subscriptions
• Official Objective-C SDK available
• I can procrastinate!
• I hate writing web services
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Workflow
• Read instructions
• Take photo
• Answer questions
• Submit to service
• Photo to S3
• Metadata to SNS
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Lingering Worry
• AWS credentials baked into app
• What if a malicious user extracts them?
• New credentials requires App Store review
• A token-vending machine is server-side
code
• I hate writing web services
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Let’s work on the app
• Let’s use a web view to present
instructions
• Why not load content from the network?
• Feature requires network access anyway
• Now we can revise any time
• “Out of Order”
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Buttons in HTML
• Links that look like buttons
• URL like “action:///takePhoto”
• To disable feature, remove buttons
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- (BOOL)webView:(UIWebView *)webView
shouldStartLoadWithRequest:(NSURLRequest *)request
navigationType:(UIWebViewNavigationType)navigationType
{
NSURL *URL = [request URL];
if ([[URL scheme] isEqualToString:@"action"]) {
if ([[URL path] isEqualToString:@"/takePhoto"]) {
[self takePhoto:nil];
return NO;
}
else if ([[URL path] isEqualToString:@"/choosePhoto"]) {
[self choosePhoto:nil];
return NO;
}
}
if (navigationType == UIWebViewNavigationTypeLinkClicked) {
[[UIApplication sharedApplication] openURL:URL];
return NO;
}
return YES;
}
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Serendipity
• If I can transmit information to the user…
• …surely I can transmit to my code
• Use Javascript to embed metadata
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var access = {
key: 'AKIAJV3BLV6Z3Y7FKURQ',
secret: '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',
bucket: 'logbook-capture',
topic: 'arn:aws:sns:us-east-1:693923277227:logbooks-topic'
}
var jpegQuality = 0.5;
var facilityTypes = ["",
"Commercial",
"Healthcare",
"Hotel",
"Industrial/Manufacturing",
"Maritime",
"Multifamily Residential",
"Power Plant/Generation",
"University/School",
"Warehouse",
"Other"];
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• “document.body.id” to see if this is the
page you want
• “javascriptVariableName” to read a scalar
value
• “javascriptArrayName.join(‘\0’)” to read an
array
stringByEvaluatingJavaScriptFromString:
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- (void)webViewDidFinishLoad:(UIWebView *)webView
{
NSString *bodyID = [webView stringByEvaluatingJavaScriptFromString:@"document.body.id"];
if ([bodyID isEqualToString:@"start"]) {
SGLogbookCaptureSession *session = [[SGLogbookCaptureSession alloc] init];
session.amazonAccessKey = [webView stringByEvaluatingJavaScriptFromString:@"access.key
session.amazonSecretKey = [webView stringByEvaluatingJavaScriptFromString:@"access.sec
session.amazonBucketName = [webView stringByEvaluatingJavaScriptFromString:@"access.bu
session.amazonTopicARN = [webView stringByEvaluatingJavaScriptFromString:@"access.topi
session.logbookImageQuality = [[webView stringByEvaluatingJavaScriptFromString:@"jpegQ
NSString *facilityTypes = [webView stringByEvaluatingJavaScriptFromString:@"facilityTy
session.facilityTypes = [facilityTypes componentsSeparatedByString:@"\0"];
SGAccountController *accountController = [SGAccountController sharedController];
if (![accountController isGuest]) {
session.emailAddress = accountController.emailAddress;
}
self.session = session;
}
}
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Success
• Lines of server code written: 0
• Token vending machine? Do it later!
• Submission handler? Do it later!
• I hate writing web services
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Executive Producer
Dick Wolf
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Benjamin Ragheb
Keep in touch!
@benzado
http://www.benzado.com
[email protected]