Aug 19, 2017

[Golang] Introducing go-sarah: simple yet highly customizable bot framework

As mentioned in the latest blog post, I created a new bot framework: go-sarah. This article introduces its notable features and overall architecture along with some sample codes. Upcoming articles should focus on details about each specific aspect.

Notable features

User's Conversational Context

In this project, user's conversational context is referred to as "user context," which stores previous user states and defines what function should be executed on following input. While typical bot implementation is somewhat "stateless" and hence user-and-bot interaction does not consider previous state, Sarah natively supports the idea of this conversational context. Its aim is to let user provide information as they send messages, and finally build up complex arguments to be passed.

For example, instead of obligating user to input long confusing text such as ".todo Fix Sarah's issue #123 by 2017-04-15 12:00:00" at once, let user build up arguments in a conversational manner as below image:

Live Configuration Update

When configuration file for a command is updated, Sarah automatically detects the event and re-builds the command or scheduled task in thread-safe manner so the next execution of that command/task appropriately reflects the new configuration values.

See the usage of CommandPropsBuilder and ScheduledTaskPropsBuilder for detail.

Concurrent Execution by Default

Developers may implement their own bot by a) implementing sarah.Bot interface or b) implementing sarah.Adapter and pass it to sarah.NewBot() to get instance of default Bot implementation.

Either way, a component called sarah.Runner takes care of Commmand execution against given user input. This sarah.Runner dispatches tasks to its internal workers, which means developers do not have to make extra effort to handle flooding incoming messages.

Alerting Mechanism

When a bot confronts critical situation and can not continue its operation or recover, Sarah's alerting mechanism sends alert to administrator. Zero or more sarah.Alerter implementations can be registered to send alert to desired destinations.

Higher Customizability

To have higher customizability, Sarah is composed of fine grained components that each has one domain to serve; sarah.Alerter is responsible for sending bot's critical state to administrator, workers.Worker is responsible for executing given job in a panic-proof manner, etc... Each component comes with an interface and default implementation, so developers may change Sarah's behavior by implementing corresponding component's interface and replacing default implementation.

Overall Architecture

Below illustrates some major components.


Runner is the core of Sarah; It manages other components' lifecycles, handles concurrent job execution with internal workers, watches configuration file changes, re-configures commands/tasks on file changes, executes scheduled tasks, and most importantly makes Sarah comes alive.

Runner may take multiple Bot implementations to run multiple Bots in single process, so resources such as workers and memory space can be shared.

Bot / Adapter

Bot interface is responsible for actual interaction with chat services such as Slack, LINE, gitter, etc...

Bot receives messages from chat services, sees if the sending user is in the middle of user context, searches for corresponding Command, executes Command, and sends response back to chat service.

Important thing to be aware of is that, once Bot receives message from chat service, it sends the input to Runner via a designated channel. Runner then dispatches a job to internal worker, which calls Bot.Respond and sends response via Bot.SendMessage. In other words, after sending input via the channel, things are done in concurrent manner without any additional work. Change worker configuration to throttle the number of concurrent execution -- this may also impact the number of concurrent HTTP requests against chat service provider.


Technically Bot is just an interface. So, if desired, developers can create their own Bot implementations to interact with preferred chat services. However most Bots have similar functionalities, and it is truly cumbersome to implement one for every chat service of choice.

Therefore defaultBot is already predefined. This can be initialized via sarah.NewBot.


sarah.NewBot takes multiple arguments: Adapter implementation and arbitrary number ofsarah.DefaultBotOptions as functional options. This Adapter thing becomes a bridge between defaultBot and chat service. DefaultBot takes care of finding corresponding Command against given input, handling stored user context, and other miscellaneous tasks; Adapter takes care of connecting/requesting to and messaging with chat service.

package main

import (

func main() {
        // Setup slack bot.
        // Any Bot implementation can be fed to Runner.RegisterBot(), but for convenience slack and gitter adapters are predefined.
        // sarah.NewBot takes adapter and returns defaultBot instance, which satisfies Bot interface.
        configBuf, _ := ioutil.ReadFile("/path/to/adapter/config.yaml")
        slackConfig := slack.NewConfig() // config struct is returned with default settings.
        yaml.Unmarshal(configBuf, slackConfig)
        slackAdapter, _ := slack.NewAdapter(slackConfig)


Command interface represents a plugin that receives user input and return response. Command.Match is called against user input in Bot.Respond. If it returns true, then the command is considered "corresponds to user input," and hence its Execute method is called.

Any struct that satisfies Command interface can be fed to Bot.AppendCommand as a command. CommandPropsBuilder is provided to easily implement Command interface on the fly:

Simple Command

There are several ways to setup Commands:
  • Define a struct that implements Command interface. Pass its instance to Bot.ApendCommand.
  • Use CommandPropsBuilder to construct a non-contradicting set of arguments, and pass this to Runner.Runner internally builds a command, and re-built it when configuration struct is present and corresponding configuration file is updated.
Below are several ways to setup CommandProps with CommandPropsBuilder for different customization.
// In separate plugin file such as echo/command.go
// Export some pre-build command props
package echo

import (

// CommandProps is a set of configuration options that can be and should be treated as one in logical perspective.
// This can be fed to Runner to build Command on the fly.
// CommandProps is re-used when command is re-built due to configuration file update.
var matchPattern = regexp.MustCompile(`^\.echo`)
var SlackProps = sarah.NewCommandPropsBuilder().
        Func(func(_ context.Context, input sarah.Input) (*sarah.CommandResponse, error) {
                // ".echo foo" to "foo"
                return slack.NewStringResponse(sarah.StripMessage(matchPattern, input.Message())), nil
        InputExample(".echo knock knock").

// To have complex checking logic, MatchFunc can be used instead of MatchPattern.
var CustomizedProps = sarah.NewCommandPropsBuilder().
        MatchFunc(func(input sarah.Input) bool {
                // Check against input.Message(), input.SenderKey(), and input.SentAt()
                // to see if particular user is sending particular message in particular time range
                return false
        // Call some other setter methods to do the rest.

// Configurable is a helper function that returns CommandProps built with given CommandConfig.
// CommandConfig can be first configured manually or from YAML/JSON file, and then fed to this function.
// Returned CommandProps can be fed to Runner and when configuration file is updated,
// Runner detects the change and re-build the Command with updated configuration struct.
func Configurable(config sarah.CommandConfig) *sarah.CommandProps {
        return sarah.NewCommandPropsBuilder().
                ConfigurableFunc(config, func(_ context.Context, input sarah.Input, conf sarah.CommandConfig) (*sarah.CommandResponse, error) {
                        return nil, nil
                // Call some other setter methods to do the rest.

Reconfigurable Command

With CommandPropsBuilder.ConfigurableFunc, a desired configuration struct may be added. This configuration struct is passed on command execution as 3rd argument. Runner is watching the changes on configuration files' directory and if configuration file is updated, then the corresponding command is built, again.

To let Runner supervise file change event, set sarah.Config.PluginConfigRoot. Internal directory watcher supervises sarah.Config.PluginConfigRoot + "/" + BotType + "/" as Bot's configuration directory. When any file under that directory is updated, Runner searches for corresponding CommandProps based on the assumption that the file name is equivalent to CommandProps.identifier + ".(yaml|yml|json)". If a corresponding CommandProps exists, Runner rebuild Command with latest configuration values and replaces with the old one.

Scheduled Task

While commands are set of functions that respond to user input, scheduled tasks are those that run in scheduled manner. e.g. Say "Good morning, sir!" every 7:00 a.m., search on database and send "today's chores list" to each specific room, etc...

ScheduledTask implementation can be fed to Runner.RegisterScheduledTask. When Runner.Run is called, clock starts to tick and scheduled task becomes active; Tasks will be executed as scheduled, and results are sent to chat service via Bot.SendMessage.

Simple Scheduled Task

Technically any struct that satisfies ScheduledTask interface can be treated as scheduled task, but a builder is provided to construct a ScheduledTask on the fly.
package foo

import (

// TaskProps is a set of configuration options that can be and should be treated as one in logical perspective.
// This can be fed to Runner to build ScheduledTask on the fly.
// ScheduledTaskProps is re-used when command is re-built due to configuration file update.
var TaskProps = sarah.NewScheduledTaskPropsBuilder().
        Func(func(_ context.Context) ([]*sarah.ScheduledTaskResult, error) {
                return []*sarah.ScheduledTaskResult{
                                Content:     "Howdy!!",
                                Destination: slackobject.ChannelID("XXX"),
                }, nil

Reconfigurable Scheduled Task

With ScheduledTaskPropsBuilder.ConfigurableFunc, a desired configuration struct may be added. This configuration struct is passed on task execution as 2nd argument. Runner is watching the changes on configuration files' directory and if configuration file is updated, then the corresponding task is built/scheduled, again.

To let Runner supervise file change event, set sarah.Config.PluginConfigRoot. Internal directory watcher supervises sarah.Config.PluginConfigRoot + "/" + BotType + "/" as Bot's configuration directory. When any file under that directory is updated, Runner searches for corresponding ScheduledTaskProps based on the assumption that the file name is equivalent to ScheduledTaskProps.identifier + ".(yaml|yml|json)". If a corresponding ScheduledTaskProps exists, Runner rebuild ScheduledTask with latest configuration values and replaces with the old one.


As described in "Notable Features," Sarah stores user's current state when Command's response expects user to send series of messages with extra supplemental information. UserContextStorage is where the state is stored. Developers may store state into desired storage by implementing UserContextStorage interface. Two implementations are currently provided by author:

Store in Process Memory Space

defaultUserContextStorage is a UserContextStorage implementation that stores ContextualFunc, a function to be executed on next user input, in the exact same memory space that process is currently running. Under the hood this storage is simply a map where key is user identifier and value is ContextualFunc. This ContextFunc can be any function including instance method and anonymous function that satisfies ContextFunc type. However it is recommended to use anonymous function since some variable declared on last method call can be casually referenced in this scope.

Store in External KVS

go-sarah-rediscontext stores combination of function identifier and serializable arguments in Redis. This is extremely effective when multiple Bot processes run and user context must be shared among them.
e.g. Chat platform such as LINE sends HTTP requests to Bot on every user input, where Bot may consist of multiple servers/processes to balance those requests.


When registered Bot encounters critical situation and requires administrator's direct attention, Runner sends alert message as configured with Alerter. LINE alerter is provided by default, but anything that satisfies Alerter interface can be registered as Alerter. Developer may add multiple Alerter implementations via Runner.RegisterAlerter so it is recommended to register multiple Alerters to avoid Alerting channel's malfunction and make sure administrator notices critical state.

Bot/Adapter may send BotNonContinurableError via error channel to notify critical state to Runner. e.g. Adapter can not connect to chat service provider after reasonable number of retrials.

Getting Started

That is pretty much everything developers should know before getting started. To see working example code, visit Fore more details, make sure to follow upcoming blog posts.

Aug 6, 2017

Parenting software engineer

It was a cold day for spring that my wife gave birth to a beautiful baby girl, Sarah. Despite the snowy weather, Sarah was sleeping peacefully in her mother's arm. Being overwhelmed with grateful feeling after watching the faces of a newborn and her mother, I realized a passion to give birth to something was evolving in me. Giving birth is the most beautiful and creative act only allowed for females that weaves a rich tapestry of life, so I as a male software engineer wanted closer experience to this. That was the moment I decided to start a new project.

I named this project Sarah. This project would not only be a good memento of my daughter's birth, but also be a good memory of our growth. Once a software engineer stops growing as one, he can easily be left behind from this rapidly growing industry. This fact frightened me all the time. I needed to grow as much as my daughter did. However many parents complained that having kids gave them less time to work on what they want to and there was nothing they could do about. This was a reasonable complaint I was not going to agree. Having a daughter must be something enriches my life; not something burdens me. If there is someone to blame, that should be me. Not my daughter. Working on a new project that focuses on a new area of interest should help me grow as a software engineer.

For this project, I chose customizable chatbot framework as a theme. It was 2015 and creating chatbot was becoming a new trend. In technical perspective, creating chatbot framework involves skills such as follows:
  1. having better design to clearly separate abstraction from implementation layer
  2. having better understanding about multiple communication protocols depending on what chat service to adapt.
They captured me as promising challenges that bring me to the next higher level.

I started implementing Sarah with Python 3.5. At that time, the official announcement of PEP 484 release was around the corner and PyCharm was working on adapting this type hinting feature. While learning Python, I found a package named abc that could be used to define abstract base class. I thought a combination of type hinting and abc could provide well structured architecture. Decorator was also a good solution to minimize plugins function's specification by wrapping its core logic with actual messaging logic. However it became obvious that I took type hinting too serious. Instead of passing around arbitrary dictionary as function argument, I preferred to define designated class that represents particular object and pass its instance. I even implemented a base class called ValueObject to provide immutable objects. Passing those objects among public interfaces could be a good idea in terms of unambiguity, but I did the same to private methods. At this time Python's flexibility was lost and my code became an inferior Java.

A few months later I redesigned this project and started implementing with Golang. I found learning Golang was a joyful experience. The previous Python codebase not only gave me a better understanding of the whole picture, it also presented some hidden requirements that I missed last time. To fulfill the requirements, I added another layer called Runner at the bottom. Adapter focuses on connecting to designated chat service; Runner focuses on coordinating and supervising other components. Thanks to this newly added component, the other components' implementations became simpler and more focused. As described on its repository, Sarah is now composed of fine grained components and interfaces, which make it is easier to replace pre-defined default behavior with customized implementation.

As of July 4th, 2017, Sarah is no longer pre-alpha and is now listed on awesome-go. While I am proud of what I have achieved, I must admit that this is not the end of our journey. Throughout all time, working on Sarah was not just coding. As a matter of fact coding on private time was the last thing I could do as a parent. That frustrated me from time to time. But I also knew we were going to have less and less time to spend together as my daughter grew up; She would make friends in school, spend time with them, make a boyfriend, go to college, and eventually leave home. Having this project told me an important lesson that our time is always limited and we need to have a continuing effort to spend it wisely. I will continue to work on Sarah, but I am sure the actual Sarah, my daughter, always has higher priority. I am her father. I always am.

[EDIT] FYI, this project's design philosophy, detailed specs, and my learned knowledge will be introduced on following blog posts. Until then its github repository should help.