Emitters

Tracker instances must be initialized with an emitter. This section will go into more depth about the Emitter and how it works under the hood.

The simplest Emitter setup requires only the collector URI to be passed to it:

emitter := sp.InitEmitter(RequireCollectorUri("com.acme"), sp.RequireStorage(*storagememory.Init()))

There are other optional builder functions:

Function Name	Description	Required?	Default
RequireCollectorUri	The URI to send events to	Yes	nil
RequireStorage	The storage integration to use	Yes	nil
OptionRequestType	The request type to use (GET or POST)	No	POST
OptionProtocol	The protocol to use (http or https)	No	http
OptionSendLimit	The maximum amount of events to send at a time	No	500
OptionByteLimitGet	The byte limit when sending a GET request	No	40000
OptionByteLimitPost	The byte limit when sending a POST request	No	40000
OptionCallback	Defines a custom callback function	No	nil
OptionHttpClient	A custom HTTP client	No	&Client{}

A more complete example:

emitter := sp.InitEmitter(
  sp.RequireCollectorUri("com.acme"),
  sp.RequireStorage(*storagememory.Init()),
  sp.OptionRequestType("GET"),
  sp.OptionProtocol("https"),
  sp.OptionSendLimit(50),
  sp.OptionByteLimitGet(52000),
  sp.OptionByteLimitPost(52000),
  sp.OptionCallback(func(g []CallbackResult, b []CallbackResult) {
    log.Println("Successes: " + IntToString(len(g)))
    log.Println("Failures: " + IntToString(len(b)))
  }),
)

As of Version 3 of the Tracker you must pass RequireStorage to set the Storage option for the Emitter. Out of the box we support the following:

• StorageMemory: A fully in-memory implementation utilising go-memdb
• StorageSQLite3: A local disk implementation leveraging go-sqlite3

You can also define your own Storage system by implementing the Storage interface found in pkg/storage/storageiface:

type Storage interface {
  AddEventRow(payload Payload) bool
  DeleteAllEventRows() int64
  DeleteEventRows(ids []int) int64
  GetAllEventRows() []EventRow
  GetEventRowsWithinRange(eventRange int) []EventRow
}

To use StorageMemory the constructor looks like so:

import storagememory "github.com/snowplow/snowplow-golang-tracker/v3/pkg/storage/memory"

emitter := sp.InitEmitter(
  sp.RequireCollectorUri("com.acme"),
  sp.RequireStorage(*storagememory.Init()),
  sp.OptionRequestType("GET"),
  sp.OptionProtocol("https"),
  sp.OptionSendLimit(50),
  sp.OptionByteLimitGet(52000),
  sp.OptionByteLimitPost(52000),
  sp.OptionCallback(func(g []CallbackResult, b []CallbackResult) {
    log.Println("Successes: " + IntToString(len(g)))
    log.Println("Failures: " + IntToString(len(b)))
  }),
)

To leverage StorageSQLite3:

import storagesqlite3 "github.com/snowplow/snowplow-golang-tracker/v3/pkg/storage/sqlite3"

emitter := sp.InitEmitter(
  sp.RequireCollectorUri("com.acme"),
  sp.RequireStorage(*storagesqlite3.Init("dbname_path.db")),
  sp.OptionRequestType("GET"),
  sp.OptionProtocol("https"),
  sp.OptionSendLimit(50),
  sp.OptionByteLimitGet(52000),
  sp.OptionByteLimitPost(52000),
  sp.OptionCallback(func(g []CallbackResult, b []CallbackResult) {
    log.Println("Successes: " + IntToString(len(g)))
    log.Println("Failures: " + IntToString(len(b)))
  }),
)

Under the hood

Once the emitter receives an event from the Tracker a few things start to happen:

• The event is added to the storage implementation (either memory or sqlite3)
• A long running go routine is started which will continue to send events as long as they can be found in the database (asynchronous)
• The emitter loop will grab a range of events from the database up until the SendLimit as noted _above
• The emitter will send all of these events as determined by the Request, Protocol and ByteLimits
  • Each request is sent in its own go routine.
• Once sent it will process the results of all the requests sent and will remove all successfully sent events from the database

IF all of the requests failed this loop is terminated eagerly; this is seen as a network failure so attempting to send is a waste of resources. IF there are no more events in the database the loop is terminated.

Builder methods

OptionHttpClient

An HTTP client can be set with custom settings appropriate for the use-case, such as timeouts and other connection settings.

This method accepts a reference to http.Client.