Holster

A place to holster mailgun's golang libraries and tools

Installation

To use, run the following command:

go get github.com/mailgun/holster/v4

Clock

A drop in (almost) replacement for the system time package to make scheduled events deterministic in tests. See the clock readme for details

HttpSign

HttpSign is a library for signing and authenticating HTTP requests between web services. See the httpsign readme for details

Distributed Election

A distributed election implementation using etcd to coordinate elections See the etcd v3 readme for details

Errors

Errors is a fork of https://github.com/pkg/errors with additional functions for improving the relationship between structured logging and error handling in go See the errors readme for details

WaitGroup

Waitgroup is a simplification of sync.Waitgroup with item and error collection included.

Running many short term routines over a collection with .Run()

import "github.com/mailgun/holster/v4/syncutil"
var wg syncutil.WaitGroup
for _, item := range items {
    wg.Run(func(item interface{}) error {
        // Do some long running thing with the item
        fmt.Printf("Item: %+v\n", item.(MyItem))
        return nil
    }, item)
}
errs := wg.Wait()
if errs != nil {
    fmt.Printf("Errs: %+v\n", errs)
}

Clean up long running routines easily with .Loop()

import "github.com/mailgun/holster/v4/syncutil"
pipe := make(chan int32, 0)
var wg syncutil.WaitGroup
var count int32

wg.Loop(func() bool {
    select {
    case inc, ok := <-pipe:
        // If the pipe was closed, return false
        if !ok {
            return false
        }
        atomic.AddInt32(&count, inc)
    }
    return true
})

// Feed the loop some numbers and close the pipe
pipe <- 1
pipe <- 5
pipe <- 10
close(pipe)

// Wait for the loop to exit
wg.Wait()

Loop .Until() .Stop() is called

import "github.com/mailgun/holster/v4/syncutil"
var wg syncutil.WaitGroup

wg.Until(func(done chan struct{}) bool {
    select {
    case <- time.Tick(time.Second):
        // Do some periodic thing
    case <- done:
        return false
    }
    return true
})

// Close the done channel and wait for the routine to exit
wg.Stop()

FanOut

FanOut spawns a new go-routine each time .Run() is called until size is reached, subsequent calls to .Run() will block until previously .Run() routines have completed. Allowing the user to control how many routines will run simultaneously. .Wait() then collects any errors from the routines once they have all completed. FanOut allows you to control how many goroutines spawn at a time while WaitGroup will not.

import "github.com/mailgun/holster/v4/syncutil"
// Insert records into the database 10 at a time
fanOut := syncutil.NewFanOut(10)
for _, item := range items {
    fanOut.Run(func(cast interface{}) error {
        item := cast.(Item)
        return db.ExecuteQuery("insert into tbl (id, field) values (?, ?)",
            item.Id, item.Field)
    }, item)
}

// Collect errors
errs := fanOut.Wait()
if errs != nil {
    // do something with errs
}

LRUCache

Implements a Least Recently Used Cache with optional TTL and stats collection

This is a LRU cache based off github.com/golang/groupcache/lru expanded with the following

• Peek() - Get the value without updating the expiration or last used or stats
• Keys() - Get a list of keys at this point in time
• Stats() - Returns stats about the current state of the cache
• AddWithTTL() - Adds a value to the cache with a expiration time
• Each() - Concurrent non blocking access to each item in the cache
• Map() - Efficient blocking modification to each item in the cache

TTL is evaluated during calls to .Get() if the entry is past the requested TTL .Get() removes the entry from the cache counts a miss and returns not ok

import "github.com/mailgun/holster/v4/collections"
cache := collections.NewLRUCache(5000)
go func() {
    for {
        select {
        // Send cache stats every 5 seconds
        case <-time.Tick(time.Second * 5):
            stats := cache.GetStats()
            metrics.Gauge(metrics.Metric("demo", "cache", "size"), int64(stats.Size), 1)
            metrics.Gauge(metrics.Metric("demo", "cache", "hit"), stats.Hit, 1)
            metrics.Gauge(metrics.Metric("demo", "cache", "miss"), stats.Miss, 1)
        }
    }
}()

cache.Add("key", "value")
value, ok := cache.Get("key")

for _, key := range cache.Keys() {
    value, ok := cache.Get(key)
    if ok {
        fmt.Printf("Key: %+v Value %+v\n", key, value)
    }
}

ExpireCache

ExpireCache is a cache which expires entries only after 2 conditions are met

1. The Specified TTL has expired
2. The item has been processed with ExpireCache.Each()

This is an unbounded cache which guaranties each item in the cache has been processed before removal. This cache is useful if you need an unbounded queue, that can also act like an LRU cache.

Every time an item is touched by .Get() or .Set() the duration is updated which ensures items in frequent use stay in the cache. Processing the cache with .Each() can modify the item in the cache without updating the expiration time by using the .Update() method.

The cache can also return statistics which can be used to graph cache usage and size.

NOTE: Because this is an unbounded cache, the user MUST process the cache with .Each() regularly! Else the cache items will never expire and the cache will eventually eat all the memory on the system

import "github.com/mailgun/holster/v4/collections"
// How often the cache is processed
syncInterval := time.Second * 10

// In this example the cache TTL is slightly less than the sync interval
// such that before the first sync; items that where only accessed once
// between sync intervals should expire. This technique is useful if you
// have a long syncInterval and are only interested in keeping items
// that where accessed during the sync cycle
cache := collections.NewExpireCache((syncInterval / 5) * 4)

go func() {
    for {
        select {
        // Sync the cache with the database every 10 seconds
        // Items in the cache will not be expired until this completes without error
        case <-time.Tick(syncInterval):
            // Each() uses FanOut() to run several of these concurrently, in this
            // example we are capped at running 10 concurrently, Use 0 or 1 if you
            // don't need concurrent FanOut
            cache.Each(10, func(key interface{}, value interface{}) error {
                item := value.(Item)
                return db.ExecuteQuery("insert into tbl (id, field) values (?, ?)",
                    item.Id, item.Field)
            })
        // Periodically send stats about the cache
        case <-time.Tick(time.Second * 5):
            stats := cache.GetStats()
            metrics.Gauge(metrics.Metric("demo", "cache", "size"), int64(stats.Size), 1)
            metrics.Gauge(metrics.Metric("demo", "cache", "hit"), stats.Hit, 1)
            metrics.Gauge(metrics.Metric("demo", "cache", "miss"), stats.Miss, 1)
        }
    }
}()

cache.Add("domain-id", Item{Id: 1, Field: "value"},
item, ok := cache.Get("domain-id")
if ok {
    fmt.Printf("%+v\n", item.(Item))
}

TTLMap

Provides a threadsafe time to live map useful for holding a bounded set of key'd values that can expire before being accessed. The expiration of values is calculated when the value is accessed or the map capacity has been reached.

import "github.com/mailgun/holster/v4/collections"
ttlMap := collections.NewTTLMap(10)
clock.Freeze(time.Now())

// Set a value that expires in 5 seconds
ttlMap.Set("one", "one", 5)

// Set a value that expires in 10 seconds
ttlMap.Set("two", "twp", 10)

// Simulate sleeping for 6 seconds
clock.Sleep(time.Second * 6)

// Retrieve the expired value and un-expired value
_, ok1 := ttlMap.Get("one")
_, ok2 := ttlMap.Get("two")

fmt.Printf("value one exists: %t\n", ok1)
fmt.Printf("value two exists: %t\n", ok2)

// Output: value one exists: false
// value two exists: true

Default values

These functions assist in determining if values are the golang default and if so, set a value

import "github.com/mailgun/holster/v4/setter"
var value string

// Returns true if 'value' is zero (the default golang value)
setter.IsZero(value)

// Returns true if 'value' is zero (the default golang value)
setter.IsZeroValue(reflect.ValueOf(value))

// If 'dest' is empty or of zero value, assign the default value.
// This panics if the value is not a pointer or if value and
// default value are not of the same type.
var config struct {
    Foo string
    Bar int
}
setter.SetDefault(&config.Foo, "default")
setter.SetDefault(&config.Bar, 200)

// Supply additional default values and SetDefault will
// choose the first default that is not of zero value
setter.SetDefault(&config.Foo, os.Getenv("FOO"), "default")

// Use 'SetOverride() to assign the first value that is not empty or of zero
// value.  The following will override the config file if 'foo' is provided via
// the cli or defined in the environment.

loadFromFile(&config)
argFoo = flag.String("foo", "", "foo via cli arg")

setter.SetOverride(&config.Foo, *argFoo, os.Env("FOO"))

Check for Nil interface

func NewImplementation() MyInterface {
    // Type and Value are not nil
    var p *MyImplementation = nil
    return p
}

thing := NewImplementation()
assert.False(t, thing == nil)
assert.True(t, setter.IsNil(thing))
assert.False(t, setter.IsNil(&MyImplementation{}))

GetEnv

Get a val