Sat, 10 Feb 2024

Reframing Multi-factor Authentication

In December, I was the victim of a domain hijacking attack in which Google Domains transferred control of all of my domains from my Google account to an attacker's Google account. These domains are used for my personal and business email, and all of my online accounts were associated with my email addresses at these domains. By gaining control of my domains, the attacker was able direct email sent to my domains to a mail server under his control so that he could intercept incoming email for my domains.

With control of incoming email, the attacker was able to gain control of some of the accounts registered using these email addresses. He was able to compromise those accounts that did not have multi-factor authentication enabled, requiring that, after password authentication, a one-time password sent by SMS or a generated time-based one-time password (TOTP) using a shared secret.

As a result of this attack, I have a new perspective on the value of multi-factor authentication. Re-framing how multi-factor authentication is described, in terms of possessions that one is unlikely to concurrently lose control over, makes its value clearer and provides a better way of thinking about the risks of an account being compromised.

A list of recommendations is provided at the end.

Traditional Framing of MFA

The traditional description of multi-factor authentication is a mechanism that requires two things in order to authenticate oneself:

The "something the user knows" is typically a password. The "something the user has" is often a mobile phone, which either can receive SMS messages or has an application installed such as Google Authenticator, which stores shared keys used to generate one-time codes.

Describing of MFA in these terms is misleading for a few reasons:

  1. the password is no longer something the user knows
  2. "something the user has" is too abstract
  3. suggests there are only two distinct things which the user must have

It is no longer common nor recommended for users to know the password used to access each online service. Most people use tens to hundreds of services. It's not feasible to remember separate passwords for each service. Since users do not have control over how services store passwords, it's also not recommended to use the same password for multiple services. There have been numerous cases of passwords being leaked due to security compromises.

Because it's impractical to know your passwords, a password manager must be used. To make use of a password manager, you will typically want it to be available on the computers you are using regularly. These are probably your laptop/desktop and your phone. Storing your web application passwords in your Google account or your iCloud keychain, for example, keep your passwords where you need to access them.

Similarly, when you need to generate TOTP codes, it makes to do so on your phone or on your computer using an application like 1Password.

Multi-factor authentication, using a password manager and a TOTP generator therefore is better described as "something the user has" (a password manager) and "something else the user has" (a TOTP generator). If both of these are available on the same device, an attacker gaining control of one will likely gain control of the other.

So prior to the attack I underestimated the value of multi-factor authentication because I thought of it primarily in terms of what would happen if an attacker gained control of my computer. If gaining control gave them access to all of the factors needed to access an account, multi-factor authentication wasn't better than one-factor authentication.

Better Framing As Possessions

A better way to think about multi-factor authentication is:

In the domain hijacking attack, my computer wasn't compromised. None of my account passwords were compromised. None of the keys used to generate TOTP codes were compromised. What was compromised was the possession that can be described as control over incoming email (COIE), and COIE is often equivalent to a password.

Some applications make the equivalence of a password and COIE explicit. Slack, for example, will email you a one-time code to log in by default. (Authenticating using a password is also possible.)

Most other applications will allow you to reset your password if you have COIE, implicitly making the password and COIE equivalent with respect to authentication.

Equivalent Possessions

When authenticating using a service that makes a password and COIE equivalent, one of the required factors is therefore one of two possessions. If your account also has MFA configured to require a TOTP code, you need these two possessions to authenticate:

Some services may allow email to be used to receive one-time codes after authenticating using a password. If the service also allows resetting the password through email verification, these two factors are effectively reduced to one.

Similarly, if a service allows you to reset your password by verifying control over incoming SMS and also allows you to receive one-time codes via SMS, two-factor authentication would effectively be reduced to a single factor.

Now consider a scenario in which your passwords are stored in Google Chrome on your laptop computer and one-time passwords are sent via SMS to your phone. This ostensibly requires two distinct possessions to authenticate, your laptop and your phone. But you can inadvertently reduce this to a single possession if your SMS messages are available on your computer through iMessage or Google's Messages web client (, for example. (Google has recently started trying mitigate this risk by displaying messages such as "Use the Google Messages app on your phone to chat with Microsoft" when viewing messages from Microsoft or Google on the Messages web client. The browser notifications still show the full messages so this is apparently still a work-in-progress.)

Additional Considerations

Account Access Chaining

Often, one service will grant access to possessions that can be used as one or more factors to authenticate to another service. For example, if you use Gmail for email and your Google account is compromised, that grants access to the COIE possession used for authentication for many other services.

Delegated Authentication

Some services allow using another service's account to authenticate. For example, a service may allow you to sign in with your Google or Facebook account. There is a trade-off here. If you are using your Facebook to authenticate to multiple other services, and your Facebook account is compromised, the attacker can use it to gain access to all of those other services.

On the other hand, providing robust multi-factor authentication for a service is non-trivial. Facebook certainly devotes more resources to account security than many other services so it may be easier to maintain control of one Facebook account than a multitude of services with their own authentication mechanisms.

Segregation of Possessions

You may also want to segregate your possessions such that you have multiple instances of the same type of possession which are used to access different accounts. For example, you can use one email address for your bank accounts, and a different email address that's used for correspondence and to register for social media accounts or the marketing emails from your e-commerce accounts.

You could use a separate phone to generate your TOTP codes. It can be an old phone that doesn't have service that is kept at your desk. This makes access to your desk, in effect, a required possession for authentication (assuming the recovery codes that are treated as equivalent possessions are printed out and kept at the desk as well). There is a trade-off in that you will only be able to log into these accounts while at your desk, but it may be worthwhile or even desirable for certain types of accounts.


You want to be notified when one of your factors is used unexpectedly. Even if the second factor fails, you want to be notified if someone enters your password unexpected from a new location, for example.

This is analogous to having a deadbolt lock on your front door, the key to which is factor 1, along with a safe in your home to protect valuables, the code to which is factor 2 (unless you have lots of safes, you probably can keep this password in your head). It's useful to have an alarm on the front door that goes off even if a thief can't successfully break into your safe on their first try.


When evaluating the security of existing online accounts and when setting up accounts with new services, I offer the following suggestions.

In addition to securing access to your accounts, you may want to take additional precautions in securing your financial accounts. In the US, you can place a fraud alert on your credit file at each of the three main credit reporting agencies. You can do this prior to being a victim of fraud. You have to renew it annually, but it notifies potential creditors to take extra precautions in verifying your identity. You can also put a freeze on your credit reports, which should prevent any new creditors from issuing new credit using your name and social security number until you lift the freeze.

To reduce the likelihood of credit card fraud, you might consider not storing your credit card details with e-commerce sites. Large sites like Amazon will require that credit cards be re-entered when shipping orders to a new address, but smaller retailers may not. As with delegated authentication, consider delegating paying by credit card to Google Pay, Apple Pay, or Amazon Pay when available.

tech | Permanent Link

Wed, 16 Mar 2022

Experience Buying Residential Real Estate Without a Buyer's Agent

In response to

I think buyers without agents are pretty rare. In Portland, a listing agent refused to present my initial offer to the seller, despite a legal obligation to do so, because it wasn't on the customary form created by the local Realtor association. I ended up buying a license for the forms, plus a license for the software to complete the forms. I resubmitted the offer, and the rest of the closing process went smoothly. The seller's agent had to a little extra work that a buyer's agent might typically do, being present for the inspection and appraisal. The sale price was about 9% below the asking price. I don't know if the listing agent reduced his commission, about $13k that was saved by not paying a buyer's agent commission.

I made an offer on another property without a buyer's agent, contingent on me being able to see it, and the listing agent refused to schedule time to show me the property. That one received multiple offers above asking so she didn't feel obliged to deal with an unusual situation, I guess.

The second property I bought without a buyer's agent was in Chicago. The seller was a real estate agent. He was fine using the purchase agreement form created by an Illinois lawywers association, which is publicly available. I believe the Chicago Realtors association has their own forms as well that aren't available to non-Realtors/lawyers. In Chicago, buyers and sellers typically use lawyers in addition to real estate agents, but close through escrow at a title company. I didn't bother hiring a lawyer for this transaction. (The lawyer we used on the purchase of our primary residence was about $800.)

I haven't sold a property without an agent, but if you have time to do showings/open houses, I don't see any reason not to. The buyer will likely have an agent, and the agent will probably expect the customary commission from you. I know someone who came to an agreement with a buyer's agent for a 1% commission.

misc | Permanent Link

Wed, 12 Jan 2022

A Proposal for NFTs with Actual Property Rights

I'd like to propose a project that makes use of the technology behind NFTs while solving real problems: digital concert tickets

As of early 2022, none of the popular NFT projects provide any actual property rights. The only right associated with each token is the right to transfer the token to someone else. This includes projects like the Bored Apes Yacht Club, where the cost of membership in the yacht club is comparable to lifetime membership at an actual yacht club; you get the exclusivity without access to an actual yacht club.

There are applications where being able to verify and trade property rights in unique assets could potentially be done at lower cost through the technology introduced with blockchains. I've previously argued that efficient replacements for rights licensing organizations like ASCAP and BMI, real estate title search/insurance companies, and ownership or shareholder tracking like MERS or ProxyVote are areas that could be fruitful for exploration.

Any of these would be large a undertaking so I'll propose a more tractable problem in concert ticket NFTs.

Concert tickets have characteristics and associated problems that make them well-suited for being represented as NFTs. They are

Here's how concert tickets as NFTs would work.

  1. The venue (or venue's agent) selects a network on which the tickets will be issued
  2. The venue owner issues one Entrance Ticket as an NFT for each seat at the venue for an upcoming concert
  3. The venue owner either sets prices for each Entrance Ticket or auctions the tickets
  4. The Entrance Ticket is transferred to the buyer, completing the initial sale
  5. The buyer can resell the Entrance Ticket until the end of the concert
  6. On their way into the venue before the concert, the owner of the Entrance Ticket exchanges with the ticket collector their Entrance Ticket for a Seat Ticket

This solves a few problems with current ticketing solutions.

Buyers can verify that they are buying an authenticate ticket. They would verify that the issuer is the venue owner off-chain. The venue owner should publish the the public key of the issuer. They can simply publish it on their web site, or they could make use of a identity-linking mechanism like Keybase to link their public key to multiple identities such as a twitter profile, a domain in DNS that they own, and a website that they manage to provide buyers greater confidence that they are buying from the legitimate seller.

When one concertgoer wants to buy a ticket from a previous buyer in a secondary transaction, buyers can verify on-chain that the ticket they are buying was originally issued by the venue by verifying the identity of the original issuer.

This solves the problem with buyers potentially buying counterfeit tickets from third-party sellers using Craigslist, for example. It also can reduce the transaction costs associated with buying tickets on the secondary market through trusted intermediaries like Ticketmaster.

Venues, i.e. ticket issuers, also benefit by eliminating the possibility of counterfeiting tickets. Apart from the costs of mediating disputes when two people show up with the same ticket in the form of a bar code or two people claim the same seat number based on a printed ticket or screenshot, there will be a greater demand for tickets from buyers who know that they can resell their tickets. Therefore some of the benefit should accrue to ticket issuers in the form of higher initial ticket sale prices.

Up above, I described how Entrance Tickets are exchanged for Seat Tickets at the door. This solves the double-spend problem. A ticket holder could share their private key with another person, allowing two people to prove ownership of the same ticket if ticket ownership is simply checked at the door.

This may be minor problem, but since the tickets need to be checked at the door anyway, we can have the ticket collector and ticket holder perform a trade on-chain at the door.

The ticket holder transfers their Entrance Ticket for a Seat Ticket. The Seat Ticket is issued for the same seat at the same venue for the same duration, but is not valid for entering the venue. Now, a second holder of the private key can no longer enter the venue, but the ticket holder can still ensure show the usher which seat they own for the show.

A note about implementation:
At the moment, transaction costs on the popular networks for trading NFTs would make secondary sales and my proposed Entrance-Ticket-for-Seat-Ticket transactions cost prohibitive so there's work to be done. There are nascent NFT projects on the stellar and ripple networks, where transaction settlement time and costs are low. It may be worth exploring funding options from the Stellar Enterprise Fund or Ripple's Creator Fund.

tech | Permanent Link

Thu, 07 Sep 2017

Cost Accounting as a Poorly Defined Constrained Optimization Model

I recently read The Goal, a business novel that introduces the Theory of Constraints as a toolset for managing a business in order to "more money now and in the future". One of the criticisms the book makes of the way businesses are often run is that their use of cost accounting to guide decisions fails to maximize the amount of money the business can make. An alternative called throughput accounting is proposed, but after having completed The Goal, I didn't have a clear understanding of how and why cost accounting fails.

So I bought Throughput Accounting to dig in deeper. The book starts with a great example of a simple decision made using cost accounting.

A factory makes mens and womens shirts. To make a shirt, you need some raw materials, plus the labor to cut fabric and sew fabric.

Raw Materials$45$50
Cutting Time2 minutes10 minutes
Sewing Time15 minutes10 minutes
Total Time17 minutes20 minutes
Weekly Demand120 shirts120 shirts

Making all 120 womens shirts and 120 mens shirts requires 1,440 minutes (10 min/shirt * 120 mens shirts + 2 min/shirt * 120 womens shirts) of cutting time and 3,000 minutes (10 min/shirt * 120 mens shirts + 15 min/shirt * 120 womens shirts) of sewing time. Since we only have 2,400 minutes of sewing time available, we can't make all of the shirts. How many mens shirts and womens shirts should we make?

Gross profit for mens shirts is $50 ($100 sales price - $50 for raw materials). Gross profit for womens shirts is $60 ($105 sales price - $45 for raw materials). Mens shirts require a total of 20 minutes of labor. Womens shirts require a total of 17 minutes of labor.

Since womens shirts bring in more revenue, have a higher gross margin, and require less labor, it seems like a reasonable answer is to produce 120 womens shirts, and then as many mens shirts as we can with the remaining time we have available.

120 womens shirts take 1,800 minutes on the sewing machine, so we can make 60 mens shirts with the remaining 600 minutes available on the sewing machine. (We're not constrained by cutting.) This results in a net profit of $-300, i.e. a loss.

Raw Materials$8,400
Gross Margin$10,200
Operating Expense-$10,500
Net Profit-$300

Throughput Accounting then explains how to calculate the amount of money (throughput) being made on the constrained resource per minute, the sewing machine, to decide how many of each product to make. But I'm going to use MiniZinc to use a contrained optimization solver to maximize net profit, which will give us the same result.

The constraints above, and the goal of trying to maximize net profit, can be translated into a MiniZinc model as follows (this would be done in a more concise manner if there were many products):

int: womens_sewing_minutes = 15;
int: womens_cutting_minutes = 2;
int: mens_sewing_minutes = 10;
int: mens_cutting_minutes = 10;

int: womens_price = 105;
int: mens_price = 100;

int: womens_raw_costs = 45;
int: mens_raw_costs = 50;

int: max_sewing_minutes = 2400;
int: max_cutting_minutes = 2400;

int: operating_expense = 10500;

int: womens_demand = 120;
int: mens_demand = 120;

var 0..mens_demand: mens_produced;
var 0..womens_demand: womens_produced;

var int: total_sewing_minutes = womens_produced * womens_sewing_minutes + mens_produced * mens_sewing_minutes;
var int: total_cutting_minutes = womens_produced * womens_cutting_minutes + mens_produced * mens_cutting_minutes;

var int: revenue = womens_price * womens_produced + mens_price * mens_produced;
var int: raw_materials_cost = (womens_raw_costs * womens_produced + mens_raw_costs * mens_produced);
var int: gross_margin = revenue - raw_materials_cost;

var int: total_cost = raw_materials_cost + operating_expense;

var int: net_profit = gross_margin - operating_expense;

constraint total_sewing_minutes <= max_sewing_minutes;
constraint total_cutting_minutes <= max_cutting_minutes;
solve maximize net_profit;

output ["mens: \(mens_produced)\n", "womens: \(womens_produced)\n", "net profit: \(net_profit)\n", "total cost: \(total_cost)"];

And solving the model tells us that we should produce 120 mens shirts and 80 womens shirts for a net profit of $300, rather than a loss.

$ minizinc clothes.mzn
mens: 120
womens: 80
net profit: 300
total cost: 20100

Intuitively, what's going wrong in the cost accounting solution is that we're lumping together all of the labor and not taking into consideration that the sewing machine is our bottleneck, and that we need to maximize the amount of value we're getting out of the bottleneck. Nonetheless, I struggled to translate this mistake into a MiniZinc model that also gave the wrong answer.

Below is an incorrectly defined constrained optimization model that I think reflects where we go wrong when trying to use cost accounting for decision making. The goal is changed from maximizing net profit to minimizing cost. But we don't want to just minimize cost; we could do that by producing zero shirts. We also want to produce as many shirts as we can. I modelled this as a constraint that says that producing one more mens shirt or one more womens shirt should cause us to exceed our cutting or sewing constraints.

int: womens_sewing_minutes = 15;
int: womens_cutting_minutes = 2;
int: mens_sewing_minutes = 10;
int: mens_cutting_minutes = 10;

int: womens_processing = womens_cutting_minutes + womens_sewing_minutes;
int: mens_processing = mens_cutting_minutes + mens_sewing_minutes;

int: womens_price = 105;
int: mens_price = 100;

int: womens_raw_costs = 45;
int: mens_raw_costs = 50;

int: max_sewing_minutes = 2400;
int: max_cutting_minutes = 2400;

int: operating_expense = 10500;

int: womens_demand = 120;
int: mens_demand = 120;

var 0..mens_demand: mens_produced;
var 0..womens_demand: womens_produced;

var int: total_sewing_minutes = womens_produced * womens_sewing_minutes + mens_produced * mens_sewing_minutes;
var int: total_cutting_minutes = womens_produced * womens_cutting_minutes + mens_produced * mens_cutting_minutes;

var int: womens_revenue = womens_price * womens_produced;
var int: womens_raw_materials_cost = womens_raw_costs * womens_produced;
var int: womens_operating_expenses = operating_expense * womens_produced div (womens_produced + mens_produced);
var int: womens_net_profit = womens_revenue - womens_raw_materials_cost - womens_operating_expenses;

var int: mens_revenue = mens_price * mens_produced;
var int: mens_raw_materials_cost = mens_raw_costs * mens_produced;
var int: mens_operating_expenses = operating_expense * mens_produced div (womens_produced + mens_produced);
var int: mens_net_profit = mens_revenue - mens_raw_materials_cost - mens_operating_expenses;

var int: total_cost = womens_operating_expenses + womens_raw_materials_cost + mens_operating_expenses + mens_raw_materials_cost;

var int: net_profit = womens_net_profit + mens_net_profit;

constraint total_sewing_minutes <= max_sewing_minutes;
constraint total_cutting_minutes <= max_cutting_minutes;

% Maximize the number of items produced by ensuring that it must not be
% possible to produce another item
   ((mens_produced + 1) * mens_sewing_minutes + womens_produced * womens_sewing_minutes > max_sewing_minutes \/
   (mens_produced + 1) * mens_cutting_minutes + womens_produced * womens_cutting_minutes > max_cutting_minutes)
   (mens_produced * mens_sewing_minutes + (womens_produced + 1) * womens_sewing_minutes > max_sewing_minutes \/
   mens_produced * mens_cutting_minutes + (womens_produced + 1) * womens_cutting_minutes > max_cutting_minutes);

solve minimize total_cost;

output ["mens: \(mens_produced)\n", "womens: \(womens_produced)\n", "net profit: \(net_profit)\n", "total cost: \(total_cost)"];

Solving this model gives us the original cost accounting result.

$ minizinc clothes-cost.mzn
mens: 60
womens: 120
net profit: -300
total cost: 18900

business | Permanent Link

Fri, 07 Jul 2017

Cast Iron Studio 7 on Linux

There's a shell script on the IBM DeveloperWorks forum describing how to run Cast Iron Studio on Linux, but it's from 2010. This describes the steps I followed to get Cast Iron Studio 7.5 running on Linux.

Download the latest version of Cast Iron Studio, as of 2017-07-07:

The installation file is distributed as a Windows executable self-extracting zip file. The paths within the zip file contain backslashes rather than path-independent directory delimiters so the zip file needs to be fixed up before extracting it.

Use Info-ZIP's zip to strip the self-extracting stub from the zip file and to fix the structure:

$ zip -F -J --out

Then use 7z's rename function to convert the backslashes to slashes within the archive.

$ 7z rn $(7z l | grep '\\' | awk '{ print $6, gensub(/\\/, "/", "g", $6); }' | paste -s)

Now you can unzip

Finally, here's the modified version of the shell script I found above used to start Cast Iron Studio. Put it in the directory where you unzipped


# Tell Java that the window manager is LG3D to avoid grey window
/usr/bin/wmname LG3D

THIS=$(readlink -f $0)
DIST_HOME=$(dirname "$THIS")



for f in `find plugins -type f -name '*.jar'`; do

export OSGI_FRAMEWORK_JAR=org.eclipse.osgi_3.10.1.v20140909-1633.jar
export SET MAIN_CLASS=org.eclipse.core.runtime.adaptor.EclipseStarter
export IH_LOGGING_PROPS="resources/"
export ENDORSED="-Djava.endorsed.dirs=endorsed-lib"
export KEYSTORE=""
export TRUSTSTORE=""
export LOGIN_CTX=""
export JAAS_CONFIG=""

export JVM_DIRECTIVES=" -Djava.util.logging.config.file=$IH_LOGGING_PROPS -Djgoodies.fontSizeHints=SMALL "-Dinstall4j.launcherId=10" -Dinstall4j.swt=false"

export JAVA_HOME=/usr/lib/jvm/ibm-java-x86_64-80

"$JAVA_HOME/bin/java" -client $ENDORSED $KEYSTORE $TRUSTSTORE $LOGIN_CTX $JAAS_CONFIG $YP_AGENT $PROFILINGAGENT $JVM_DIRECTIVES -Dcom.approuter.maestro.opera.sessionFactory=com.approuter.maestro.opera.ram.RamSessionFactory -Djgoodies.fontSizeHints=SMALL -Xmx2048M -Xms512M -Xbootclasspath/p:$LIB_PATH -jar $OSGI_FRAMEWORK_JAR

Update JAVA_HOME to the path to your jvm. Performance seems to be better with the IBM jvm than the Oracle jvm.

tech | Permanent Link

Mon, 18 Jan 2016

Gold Almost at $500

Gold almost hit $500/oz today.

business | Permanent Link

Requirements in Micro-purchasing

I recently completed an 18F micro-purchase task. It turned out to be a very simple task, tweaking some CSS. I spent more time on bidding, setting up the development environment, and figuring out how to receive payment than on the actual work.

My pull request was accepted, and 18F paid me quickly, but after my changes were merged, Maya Benari pointed out that a simpler solution may have been acceptable, or perhaps even preferable.

It turns out that 18F have drafted U.S. Web Design Standards, and have already given a lot of thought to things like vertical spacing, the subject of my change.

As an independent contractor with no previous experience working with 18F, I didn't know there was a U.S. Web Design Standards document, much less its contents. Had this task been assigned to an internal staff member, they probably would have known that the page being updated should follow the standards, or that if the standards didn't adequately address the requirements for the task, that perhaps a future update to the standards should be planned.

Getting the right level of details in task requirements is often tricky. One doesn't want to spend days writing requirements for a task that can be completed in hours. But one also doesn't want what could have been an hour-long task drag on for days because the requirements were ambiguous.

When working within a long-lived team structure, there is some shared institutional knowledge that doesn't need to be made explicit in every task, like the fact that U.S. Web Design Standards exist. Usually when bringing in an outside contractor or new employee, one is starting a relationship that will last weeks, months, or years, and knowledge transfer is an expected part of the on-boarding. This investment makes sense given the size of the overall engagement.

Micro-purchasing of software development work is unique in this respect. Neither party is committing to a long-term relationship, and therefore unlikely to bear significant knowledge transfer costs. Had the acceptance criteria for my spacing fix task included compliance with the U.S. Web Design Standards, I would have had to bid more to cover the time to read and understand the document. And 18F wouldn't want to bear the cost of making me an expert on U.S. Web Design Standards if I were only going to complete a single task.

It's still early in 18F's micro-purchasing experiment, but if the experiment continues or if other organizations want to try it out, it's worth thinking about what types of tasks are best suited for micro-purchasing, and what level of detail in the requirements is optimal.

Some possible questions to ask about tasks you are considering outsourcing as micro-purchases:

As always when discussing project management, I suggest ordinal prioritization of tasks and confidence interval based estimates. If your existing tools don't support these, I recommend checking out LiquidPlanner (affiliate link).

I like the micro-purchasing model, and I hope that it succeeds and is adopted by commercial organizations.

I've gotten multiple emails from grad students doing research on Github. If you're an economics student interested in industrial organization or open source, micro-purchasing of open source software could be an interesting research project.

business | Permanent Link

Thu, 24 Sep 2015

Debugging Salesforce Apps with Flame Graphs

Salesforce applications can sometimes be difficult to debug. The debug log often has the information you need, but finding it isn't always easy.

For example, in a recent project, I needed to figure out why performing an action from a Visualforce page was causing more SOQL queries than expected, generating warning emails as we neared the governor limit. This was a large application that had been under development for about eight years; many different developers had been involved in various phases of its development.

As with many Salesforce applications that have been through many phases of development, it wasn't obvious how multiple triggers, workflow rules, and Process Builder flows were interrelated.

It was easy enough to figure out which SOQL queries were running multiple times by grepping the debug log, but it wasn't obvious why the method containing the query was being called repeatedly.

In researching ways to analyze call paths, I found Brendan Gregg's work on flame graphs, which visualizes call stacks with stacked bar charts. (You might also be familiar with Chrome's flame charts.)

Visualizing the call path through stacked bar charts turned out to be a good way to make sense of the Salesforce debug log.

So I created Apex Flame to visualize Salesforce debug logs using flame charts or flame graphs.

Here's an example based on the debug log generated from running one of the tests included in the Declarative Lookup Rollup Summaries tool.

Example Flame Graph Reset Zoom Search RollupSummariesSelector.RollupSummariesSelector() (1235996 ns, 0.10%) SObjectSelector.assertIsAccessible() (235478 ns, 0.02%) RollupSummariesSelector.getSObjectFieldList() (1036673 ns, 0.09%) StringBuilder.CSVBuilder.add(String) (4611602 ns, 0.38%) SObjectSelector.getFieldListBuilder() (6141498 ns, 0.51%) SObjectSelector.getFieldListString() (6768212 ns, 0.56%) select Name,Active__c,AggregateOperation__c,AggregateResultField__c,CalculationMode__c,ChildObject__c,ConcatenateDelimiter__c,FieldToAggregate__c,FieldToOrderBy__c,ParentObject__c,RelationshipCriteria__c,RelationshipCriteriaFields__c,RelationshipField__c,CalculateJobId__c,UniqueName__c,CalculationSharingMode__c from LookupRollupSummary__c where CalculationMode__c in :calculationModeNames and ChildObject__c in :childObjectNames and Active__c = true order by ParentObject__c, RelationshipField__c (17721838 ns, 1.47%) RollupSummariesSelector.selectActiveByChildObject(List<RollupSummaries.CalculationMode>, Set<String>) (25244446 ns, 2.09%) RollupService.describeRollups(Schema.SObjectType) (27229671 ns, 2.26%) RollupService.triggerHandler() (28183993 ns, 2.34%) RollupServiceTest3Trigger on Account trigger event AfterInsert for [0011a00000CUUaT] (216806872 ns, 17.98%) RollupServiceTest.. RollupService.RollupService() (4998569 ns, 0.41%) RollupServiceTest3Trigger on Account trigger event BeforeInsert for [new] (111753618 ns, 9.27%) RollupS.. Insert:Account (331363950 ns, 27.48%) Insert:Account SObjectDomain.MockDatabase.hasRecords() (318698 ns, 0.03%) RollupSummaries.Constructor.construct(List<SObject>) (252746 ns, 0.02%) ApexTriggersSelector.getSObjectFieldList() (494428 ns, 0.04%) StringBuilder.CSVBuilder.add(String) (2209819 ns, 0.18%) SObjectSelector.getFieldListBuilder() (2910150 ns, 0.24%) SObjectSelector.getFieldListString() (3082568 ns, 0.26%) select Name,UsageIsBulk,UsageBeforeUpdate,UsageBeforeInsert,UsageBeforeDelete,UsageAfterUpdate,UsageAfterUndelete,UsageAfterInsert,UsageAfterDelete,TableEnumOrId,SystemModstamp,Status,NamespacePrefix,LengthWithoutComments,LastModifiedDate,LastModifiedById,IsValid,Id,CreatedDate,CreatedById,BodyCrc,Body,ApiVersion from ApexTrigger where Name in :names order by Name (6633886 ns, 0.55%) ApexTriggersSelector.selectByName(Set<String>) (10219683 ns, 0.85%) LREngine.RollupSummaryField.isAggregateBasedRollup() (253205 ns, 0.02%) LREngine.RollupSummaryField.isQueryBasedRollup() (333290 ns, 0.03%) LREngine.Context.add(LREngine.RollupSummaryField) (683669 ns, 0.06%) LREngine.RollupSummaryField.isDateOrTime(Schema.DisplayType) (557102 ns, 0.05%) LREngine.RollupSummaryField.isNumber(Schema.DisplayType) (851243 ns, 0.07%) LREngine.RollupSummaryField.isText(Schema.DisplayType) (642769 ns, 0.05%) LREngine.RollupSummaryField.validate() (431676 ns, 0.04%) RollupSummaries.makeTriggerName(LookupRollupSummary__c) (18859039 ns, 1.56%) RollupSummaries.onValidate() (57860434 ns, 4.80%) Rol.. SObjectDomain.handleAfterInsert() (57952353 ns, 4.81%) SO.. SObjectDomain.triggerHandler(SObjectDomain.IConstructable, Boolean, Boolean, Boolean, Boolean, Boolean, List<SObject>, Map<Id,SObject>) (58249145 ns, 4.83%) SO.. SObjectDomain.triggerHandler(System.Type) (59311227 ns, 4.92%) SO.. RollupSummariesTrigger on LookupRollupSummary trigger event AfterInsert for [a051a000002ly2F] (115241071 ns, 9.56%) RollupS.. SObjectDomain.SObjectDomain() (10311621 ns, 0.86%) SObjectDomain.MockDatabase.hasRecords() (3485995 ns, 0.29%) RollupSummaries.RollupSummaries() (2235961 ns, 0.19%) RollupSummaries.Constructor.construct(List<SObject>) (2968808 ns, 0.25%) SObjectDomain.triggerHandler(SObjectDomain.IConstructable, Boolean, Boolean, Boolean, Boolean, Boolean, List<SObject>, Map<Id,SObject>) (3215443 ns, 0.27%) SObjectDomain.triggerHandler(System.Type) (6785400 ns, 0.56%) RollupSummariesTrigger on LookupRollupSummary trigger event BeforeInsert for [new] (48017934 ns, 3.98%) Ro.. Insert:LookupRollupSummary__c (166856163 ns, 13.84%) Insert:Looku.. RollupSummariesSelector.getSObjectFieldList() (452150 ns, 0.04%) StringBuilder.CSVBuilder.add(String) (1558019 ns, 0.13%) SObjectSelector.getFieldListBuilder() (2293678 ns, 0.19%) SObjectSelector.getFieldListString() (2649104 ns, 0.22%) select Name,Active__c,AggregateOperation__c,AggregateResultField__c,CalculationMode__c,ChildObject__c,ConcatenateDelimiter__c,FieldToAggregate__c,FieldToOrderBy__c,ParentObject__c,RelationshipCriteria__c,RelationshipCriteriaFields__c,RelationshipField__c,CalculateJobId__c,UniqueName__c,CalculationSharingMode__c from LookupRollupSummary__c where CalculationMode__c in :calculationModeNames and ChildObject__c in :childObjectNames and Active__c = true order by ParentObject__c, RelationshipField__c (7340162 ns, 0.61%) RollupSummariesSelector.selectActiveByChildObject(List<RollupSummaries.CalculationMode>, Set<String>) (10460284 ns, 0.87%) RollupService.describeRollups(Schema.SObjectType) (10976812 ns, 0.91%) RollupService.triggerHandler() (11852139 ns, 0.98%) RollupServiceTestTrigger on Opportunity trigger event AfterInsert for [0061a00000AjNjf] (377149414 ns, 31.28%) RollupServiceTestTrigger on Oppo.. RollupService.triggerHandler() (1149884 ns, 0.10%) RollupServiceTestTrigger on Opportunity trigger event BeforeInsert for [new] (188822108 ns, 15.66%) RollupServiceTe.. Insert:Opportunity (568896270 ns, 47.19%) Insert:Opportunity RollupActionCalculate.RollupActionCalculate() (1229813 ns, 0.10%) RollupActionCalculate.RollupToCalculate.toServiceRollupToCalculate() (914554 ns, 0.08%) LREngine.LREngine() (11705510 ns, 0.97%) LREngine.IsMultiCurrencyOrg() (1174095 ns, 0.10%) SELECT AccountId, Sum(Amount) lre0 FROM Opportunity WHERE AccountId in :masterIds GROUP BY AccountId (19113729 ns, 1.59%) LREngine.QueryExecutor.query(String, Set<Id>) (19272499 ns, 1.60%) LREngine.WithSharingQueryExecutor.query(String, Set<Id>) (19329423 ns, 1.60%) User Debug: New aggregarte value 100.0 for master 0011a00000CUUaTAAX (971765 ns, 0.08%) User Debug: SOQL is SELECT AccountId, Sum(Amount) lre0 FROM Opportunity WHERE AccountId in :masterIds GROUP BY AccountId (218734 ns, 0.02%) LREngine.rollUp(LREngine.Context, Set<Id>, Boolean) (23289994 ns, 1.93%) LREngine.rollUp(LREngine.Context, Set<Id>) (23341264 ns, 1.94%) LREngine.RollupSummaryField.isAggregateBasedRollup() (172964 ns, 0.01%) LREngine.RollupSummaryField.isQueryBasedRollup() (235926 ns, 0.02%) LREngine.Context.add(LREngine.RollupSummaryField) (520645 ns, 0.04%) LREngine.RollupSummaryField.isAggregateBasedRollup() (213647 ns, 0.02%) LREngine.RollupSummaryField.isDateOrTime(Schema.DisplayType) (433093 ns, 0.04%) LREngine.RollupSummaryField.isNumber(Schema.DisplayType) (291409 ns, 0.02%) LREngine.RollupSummaryField.isText(Schema.DisplayType) (527450 ns, 0.04%) LREngine.RollupSummaryField.validate() (296564 ns, 0.02%) RollupService.createLREngineContexts(List<LookupRollupSummary__c>) (7423909 ns, 0.62%) RollupSummariesSelector.getSObjectFieldList() (439088 ns, 0.04%) StringBuilder.CSVBuilder.add(String) (1518768 ns, 0.13%) SObjectSelector.getFieldListBuilder() (2216018 ns, 0.18%) SObjectSelector.getFieldListString() (2394601 ns, 0.20%) select Name,Active__c,AggregateOperation__c,AggregateResultField__c,CalculationMode__c,ChildObject__c,ConcatenateDelimiter__c,FieldToAggregate__c,FieldToOrderBy__c,ParentObject__c,RelationshipCriteria__c,RelationshipCriteriaFields__c,RelationshipField__c,CalculateJobId__c,UniqueName__c,CalculationSharingMode__c from LookupRollupSummary__c where UniqueName__c in :uniqueNames and Active__c = true order by ParentObject__c, RelationshipField__c (9208942 ns, 0.76%) RollupSummariesSelector.selectActiveByUniqueName(Set<String>) (12026548 ns, 1.00%) RollupSummariesSelector.getSObjectFieldList() (418751 ns, 0.03%) StringBuilder.CSVBuilder.add(String) (1555555 ns, 0.13%) SObjectSelector.getFieldListBuilder() (2244164 ns, 0.19%) SObjectSelector.getFieldListString() (2566370 ns, 0.21%) select Name,Active__c,AggregateOperation__c,AggregateResultField__c,CalculationMode__c,ChildObject__c,ConcatenateDelimiter__c,FieldToAggregate__c,FieldToOrderBy__c,ParentObject__c,RelationshipCriteria__c,RelationshipCriteriaFields__c,RelationshipField__c,CalculateJobId__c,UniqueName__c,CalculationSharingMode__c from LookupRollupSummary__c where CalculationMode__c in :calculationModeNames and ChildObject__c in :childObjectNames and Active__c = true order by ParentObject__c, RelationshipField__c (3684774 ns, 0.31%) RollupSummariesSelector.selectActiveByChildObject(List<RollupSummaries.CalculationMode>, Set<String>) (6684942 ns, 0.55%) RollupService.describeRollups(Schema.SObjectType) (6975134 ns, 0.58%) RollupService.triggerHandler() (7631690 ns, 0.63%) RollupServiceTest3Trigger on Account trigger event AfterUpdate for [0011a00000CUUaT] (21000032 ns, 1.74%) RollupService.triggerHandler() (689974 ns, 0.06%) RollupServiceTest3Trigger on Account trigger event BeforeUpdate for [0011a00000CUUaT] (7372667 ns, 0.61%) Update:SObject (28865245 ns, 2.39%) RollupService.rollup(List<RollupService.RollupToCalculate>) (83997802 ns, 6.97%) Rollu.. RollupActionCalculate.calculate(List<RollupActionCalculate.RollupToCalculate>) (85011182 ns, 7.05%) Rollu.. RollupActionCalculateTest.RollupActionCalculateTest() (3130766 ns, 0.26%) SELECT AnnualRevenue FROM Account WHERE Id = :tmpVar1 (5357048 ns, 0.44%) TestContext.TestContext() (1580402 ns, 0.13%) ApexTriggersSelector.ApexTriggersSelector() (1565665 ns, 0.13%) ApexTriggersSelector.getSObjectType() (246508 ns, 0.02%) SObjectSelector.assertIsAccessible() (746409 ns, 0.06%) ApexTriggersSelector.getSObjectFieldList() (807801 ns, 0.07%) StringBuilder.CSVBuilder.add(String) (9477382 ns, 0.79%) SObjectSelector.getFieldListBuilder() (10872873 ns, 0.90%) StringBuilder.CSVBuilder.getStringValue(String) (236619 ns, 0.02%) StringBuilder.CSVBuilder.getStringValue() (268153 ns, 0.02%) SObjectSelector.getFieldListString() (11221683 ns, 0.93%) SObjectSelector.getSObjectName() (197176 ns, 0.02%) select Name,UsageIsBulk,UsageBeforeUpdate,UsageBeforeInsert,UsageBeforeDelete,UsageAfterUpdate,UsageAfterUndelete,UsageAfterInsert,UsageAfterDelete,TableEnumOrId,SystemModstamp,Status,NamespacePrefix,LengthWithoutComments,LastModifiedDate,LastModifiedById,IsValid,Id,CreatedDate,CreatedById,BodyCrc,Body,ApiVersion from ApexTrigger where Name in :names order by Name (23913926 ns, 1.98%) ApexTriggersSelector.selectByName(Set<String>) (37030248 ns, 3.07%) SObjectSelector.SObjectSelector() (409239 ns, 0.03%) TestContext.isSupported() (41196903 ns, 3.42%) T.. RollupActionCalculateTest.testCalculateAction (1205664192 ns, 100.00%) RollupActionCalculateTest.testCalculateAction all (1205664192 ns, 100%) all

You can drill in by clicking on a statement, or click on Search to highlight statements that match a string.

I'd love to get some feedback from other Salesforce developers. Try out Apex Flame, and let me know what you think.

As for the debugging issue that initially inspired the creation of Apex Flame, it turned out to be the combination of a trigger that wasn't checking whether the old and new values of a field were different, causing it to run code unnecessarily, combined with a workflow rule that was causing the trigger to be called multiple times.

Another recent case in which it turned out to be helpful was in troubleshooting a process builder flow that was failing to update child records as expected. The flow assumed that if the parent record is new (ISNEW()) that it didn't have child records. It turns out this isn't necessarily true because a trigger on the parent object can create child records, and the flow runs after the after insert trigger. The order of execution is documented, but visualizing the execution order made it clear what was causing the unexpected behavior.

tech » salesforce | Permanent Link

Tue, 11 Nov 2014

Net Neutrality

Thinking past hop 1

I had a great idea a few days ago, to start a website streaming cat videos called Petflix. I rented a server for $10/month that gave me 1Mbps of outbound bandwidth.

Growth has been exponential. I now have 20 customers that now pay me $1/month for streaming cat videos. Unfortunately, during peak cat video viewing hours, I've started getting complaints that the video streams are choppy.

Each stream uses 100kbps. So when I get more than 10 concurrent viewers, I max out my bandwidth, and packets start getting dropped.

I could buy another 1Mbps of bandwidth for $10/month, but that would make my website unprofitable. So I came up with a brilliant idea that would keep this operation going.

I have an old computer in my basement that I'm not using. I called up Comcast and offered to send them my computer, preloaded with all of my cat videos. They could install it in their data center, and I would configure my DNS servers to send all of my traffic originating from Comcast customers to the computer in their data center. Since 90% of my customers are on the Comcast network, I can grow my website without incurring any additional bandwidth costs.

Obama on net neutrality

The recent statement by Barack Obama on net neutrality suffers from the same error that most proponents make in arguing for net neutrality. It assumes away the problem of how the internet actually works.

Packets don't magically appear on an ISPs network, ready for the ISP to either send on to a customer, or throttle or block for some nefarious reason.

The Internet is a big interconnected network with lots of different agreements for connecting two networks together. As the owner of Petflix, I pay Tektonic for connecting my virtual server (which I also pay them for) with their network. Tektonic pays to connect their network with TierPoint (and for power and space in a data center). TierPoint pays to connect their network with Level 3. Level 3 and Comcast connect their networks, but the terms are contentious. And as a customer of an ISP, I pay for connecting my home network with Comcast.

Traditionally, large networks like Comcast and Level 3 would form settlement-free peering agreements. Both parties get about equal value out of connecting their networks, and it was deemed mutually beneficial to connect their networks without one party paying the other. Netflix started sending lots of traffic over the connection between Level 3 and Comcast, and Comcast no longer thinks they are getting equal value from peering, and wants to renegotiate so Level 3 pays them.

To be fair, Obama sort of recognizes that the problem isn't just between the ISP and their customers. One of his bullet points argues that net neutrality should apply between an ISP and other networks.

But if we apply the other rules of No Blocking, No Throttling, and No Paid Prioritization to the connections between ISPs and other networks, it's unclear what kind of arrangements would be legal. Would the government have to mandate the amount of bandwidth at these interconnects?

What We Talk About When We Talk About Bandwidth

Getting back to my parable, when a customer of Comcast pays for 20Mbps of bandwidth, and they can't even get 100kbps of throughput to Petflix, whose fault is it?

Is it Comcast's responsibility to ensure that there is enough bandwidth through Level 3, TierPoint, Tektonic, and Petflix?

Is it Petflix's responsibility?

Fortunately, we have a pretty good way of sorting it out: markets. If Petflix is so important to Comcast customers that Comcast will lose customers to competitors by not providing a satisfying cat video viewing experience, Comcast will likely work to ensure sufficient bandwidth is available, unless the cost to do so makes those customers unprofitable.

If Petflix customers start cancelling their subscriptions because they can't enjoy my videos, I will probably pay to ensure sufficient bandwidth is available, unless doing so makes the operation no longer profitable.

Net Competition

I'm sure readers will object that Comcast is nearly a monopoly in most markets, and therefore markets won't solve the problem. And I agree. So instead of championing net neutrality, I encourage readers to champion net competition.

Instead of adding federal regulation on top of local regulation which grants ISPs like Comcast monopolies, deregulate the market in ISPs. In Portland, there could be three high-speed ISPs competing for consumers' business soon.

Nobody knows what amount of bandwidth should exist between the millions of connections between networks, and who should pay how much to whom for these connections. Only the market can sort it out.

Obamacare for the Internet?

Senator Ted Cruz referred to net neutrality as Obamacare for the internet. Is that a valid analogy?

"Net Neutrality" is Obamacare for the Internet; the Internet should not operate at the speed of government.

— Senator Ted Cruz (@SenTedCruz) November 10, 2014

I would consider these the primary characteristics of Obamacare:

Obamacare doesn't seem like a great analogy for net neutrality. Both do add federal regulation on top of local/state regulation. And it's not inconceivable that if the FCC were to start regulating ISPs in the way that Obama suggests, that problems caused would lead to suggestions for more government "solutions" like government-run markets for network connectivity, but that's a bit of a stretch.

With a little research, Cruz probably could have come up with an act of Congress that would make a better analogy than the ACA.

tech | Permanent Link

Fri, 31 Oct 2014

Promises are Useful

Henrik Joretag tweeted that he doesn't like promises in javascript.

I’m just gonna say it: I really don’t like promises in JS. It’s a clever pattern, but I just don’t see the upside, sorry.

— Henrik Joreteg (@HenrikJoreteg) October 26, 2014

I've been working on a large javascript application for the past two years, and I've found promises to be invaluable in expressing the dependencies between functions.

But Henrik's a smart guy, having authored Human Javascript and written lots of Ampersand.js, so I decided to look at a recent case where I found the use of promises helpful, and try to come up with the best alternative solution.

The Backstory

I recently discovered a bug in our app initialization. It's an offline-first mobile app. We have a function that looks like this:

App.init = function() {
   return Session.initialize()
      .then(_.noop, handleError);

When the app starts up, it needs to:

  1. Load some user info from the local datastore, if possible; otherwise, from the network
  2. Load metadata about the models used in the app and initialize controllers
  3. Set up polling for application cache updates and event handles to appcache events, to prompt the user to restart when a new version of the app is available, for example
  4. Show the initial application screen
  5. Schedule a sync of metadata and data
  6. and if an error occurs during any of these steps, handle it gracefully

The chaining of promise-returning functions in App.init nicely expresses the dependencies between these steps.
We need valid session info for the user before we can initialize the models, which may require fetching data over the network.
We can't show the initial home screen until the controllers have been initialized to bind to DOM events and display information from the models.
If there's a new version of the app available, we want to prompt the user to restart before they start using the app, and we don't want to schedule a sync until the app is being used.

Unfortunately, during a recent upgrade some users ran into a bug in some code I wrote to upgrade the local database, called from App.initializeModelsAndControllers. The result was an uncaught javascript error, Uncaught RangeError: Maximum call stack size exceeded, on the initialization screen which is displayed before App.init is called.

I fixed the bug which broke upgrading some databases, but I also realized that the dependency between App.initializeModelsAndControllers and App.manageAppCache should be reversed. If there's an upgrade available, we want users to be able to restart into it before initializing the app further (and running more code with a larger surface area for possible bugs).

The diff to make this change with our promise-returning functions is nice and simple:

--- a/app.js
+++ b/app.js
@@ -1,7 +1,7 @@
 App.init = function() {
   return Session.initialize()
-     .then(App.initializeModelsAndControllers)
+     .then(App.initializeModelsAndControllers)
      .then(_.identity, handleError);

(The careful reader will notice that stuck users need a way of upgrading the broken app stored in the app cache. The cache manifest gets fetched automatically to check for and trigger an app update each time the page is loaded, so even though we haven't set up an event handler to prompt the user to restart after the update has been downloaded, if the user waits a few minutes to ensure that the app update is complete, then kills and restarts the app, the new version will be loaded.
The careful reader who happens to be a coworker or affected customer will note that this didn't actually work because our cache manifest requires a valid session and our app starts up without refreshing the OAuth session to speed up start-up time. An upcoming release of GreatVines app to the iOS app store will contain a new setting to trigger the session refresh at app initialization. Affected customers have been given a work-around that requires tethering the device to a computer via USB. Developers using the Salesforce Mobile SDK are welcome to email me for more info.)

Recapping the Question

App.init = function() {
   return Session.initialize()
      .then(_.noop, handleError);

Now, back to the issue at hand. What would this function look like using an alternative to promises. Ignoring the possible use of a preprocessor that changes the semantics of javascript, the two likely candidates are callback passing and event emitter models.

The typical callback hell approach looks something like this:

App.init = function(success, error) {
   Session.initialize(function() {
      App.manageAppCache(function() {
         App.initializeModelsAndControllers(function() {
            App.showHomeScreen(function() {
               App.scheduleSync(success, error);
            }, error);
         }, error);
      }, error);
   }, error);

For simplicity, I've ignored the fact that the original version both had some error-handling and returns the error to the caller through a rejected promise, but I'm pretty sure this is not what Henrik had in mind. So what might an improved callback-passing approach look like?

App.init = function(success, error) {
   var scheduleSync = App.scheduleSync.bind(App, success, error);
   var showHomeScreen = App.showHomeScreen.bind(App, scheduleSync, error);
   var initializeModelsAndControllers = App.initializeModelsAndControllers.bind(App, showHomeScreen, error);
   var manageAppCache = App.manageAppCache.bind(App, initializeModelsAndControllers, error);
   Session.initialize(manageAppCache, error);

By pre-binding the callbacks, we avoid the nested indentations, but we've reversed the order of the dependencies, so that's not a great improvement.

I've failed to come up with a good callback-passing alternative to promises, so let's look at what event emitter approach would look like.

App.init = function() {
   App.once('sessionInitialized', App.manageAppCache);
   App.once('appCacheManaged', App.initializeModelsAndControllers);
   App.once('modelsAndControllersInitialized', App.showHomeScreen);
   App.once('homeScreenShown', App.scheduleSync);
   var initialized = App.trigger.bind(App, 'initialized');
   App.once('syncScheduled', initialied);
   App.once('sessionInitializationError appCacheManagementError modelsAndControllersInitializationError homeScreenError syncSchedulingError', function(error) {'sessionInitialized', App.manageAppCache);'appCacheManaged', App.initializeModelsAndControllers);'modelsAndControllersInitialized', App.showHomeScreen);'homeScreenShown', App.scheduleSync);'syncScheduled', initialied);
      App.trigger('initializationError', error);

This approach does allow us to list dependencies from top to bottom, and doesn't take us into calllback hell, but it has some problems as well.
With the promise-returning and callback-passing approaches, each function was loosly coupled to the caller, returning a promise or accepting success and error callbacks. With this event emitter approach, we need to make sure both the caller and called agree upon the names of events. Admittedly, most functions are going to be more tightly coupled than these, regardless of the approach, having to agree upon parameters to the called function and parameters to the resolved promise or callback, but they don't need to share any special information like the event name to determine when the called function is done.

This event emitter example also requires more work to clean up when an error occurs.

Perhaps instead of using a single event bus, we could listen for events on multiple objects and standardize on event names. Events could be triggered on each function.

App.init = function() {
   var initialized = App.init.trigger.bind(App.init, 'initialized');
   var error = function(error) {
      App.init.trigger('error', error);'done', App.manageAppCache);'error', error);'done', App.initializeModelsAndControllers);'error', error);'done', App.showHomeScreen);'error', error);'done', App.scheduleSync);'error', error);'done', initialized);'error', error);
   // Assume every function mixes in BackboneEvents
   Session.initialize.once('done', App.manageAppCache);
   Session.initialize.once('error', error);

   App.manageAppCache.once('done', App.initializeModelsAndControllers);
   App.manageAppCache.once('error', error);

   App.initializeModelsAndControllers.once('done', App.showHomeScreen);
   App.initializeModelsAndControllers.once('error', error);

   App.homeScreenShown.once('done', App.scheduleSync);
   App.homeScreenShown.once('error', error);

   App.scheduleSync.once('done', initialized);
   App.scheduleSync.once('error', error);


This is very verbose, containing a lot of boilerplate. We could create a function to create these bindings, e.g.

var when = function(fn, next, error) {
   fn.once('done', next);
   fn.once('error', error);
when(Session.initialize, App.manageAppCache, error);

But it doesn't feel like we're on the right path. We'd still have to handle unbinding all of the error handlers when an error occurs in one of the functions.

It's also worth pointing out that using an event emitter isn't really appropriate in a case like this where you want to get an async response to a specific function call. If the called function can be called multiple times, you don't know that the event that was triggered was in response to your call without passing additional information back with the event, and then filtering.

There's Got To Be A Better Way

Unsatisfied with any of the alternatives to promises I came up with, I replied to Henrik's tweet, and he said that he uses Async.js and Node's error-first convention. So let's look at what using async.series would look like.

App.init = function(callback) {
   ], callback);

Finally, we've come to an alternative solution that feels equivalent to the promise one. The async.series solution has at least one benefit over the promise-chaining one: the Async library has a separate function, async.waterfall, to use when the return value from one function should be passed as a parameter to the next function in the series. In my original solution, it's not clear without looking at the function definitions whether the return value from each function is used by the next function.

Given the simple error handling in App.init, in which an error anywhere in the chain aborts the flow, and a single error handler function is responsible for handling the error from any of the functions, Async.js would be a decent replacement.

But for a more complicated flow, a promise-based approach would probably come out on top. For example, here's what App.initializeModelsAndControllers looks like:

App.initializeModelsAndControllers = function() {
   return Base.init()
      .then(App.handleUpgrades, App.remoteInit)

This function introduces a fork in the chain of serialized functions:

  1. Initialize the models
  2. Check whether the app is ready to start up offline
  3. Initialize the controllers

It looks like this could be done with, but it would probably start getting messy.

tech | Permanent Link

The state is that great fiction by which everyone tries to live at the expense of everyone else. - Frederic Bastiat