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The opinionated, production-grade server framework for Go

Vektor's goal is to help you develop web services faster. Vektor handles much of the boilerplate needed to start building a Go server, so you can serve a request in less than 10 lines of code:

import ""

server := vk.New(vk.UseAppName("Vektor API Server"), vk.UseDomain(""))

server.GET("/ping", HandlePing)

if err := server.Start(); err != nil {

func HandlePing(r *http.Request, ctx *vk.Ctx) (interface{}, error) {
return "pong", nil

Those are the basics, but Vektor is capable of scaling up to serve powerful production workloads, using its full suite of API-oriented features.

Set up vk

The server object

The vk.Server type contains everything needed to build a web service. It includes the router, a middleware system, customizable plug-in points, and handy built-in components like LetsEncrypt support and CORS handlers.

Creating a server object is done with vk.New() and accepts an optional list of OptionModifiers which allow customization of the server:

server := vk.New(
vk.UseAppName("Vektor API Server"),

To create a server object without TLS support, omit the vk.UseDomain() modifier and specify an HTTP port to listen on.

server := vk.New(
vk.UseAppName("Vektor API HTTP-only"),

The included OptionsModifiers are:

OptionDescriptionENV key
UseDomain(domain string)Enable LetsEncrypt support with the provided domain name (will serve on :80 and :443 for challenge server and API server). LetsEncrypt is disabled by default.VK_DOMAIN
UseTLSConfig(config *tls.Config)Enable TLS and use the provided TLS config to serve HTTPS. This will override the domain option.N/A
UseTLSPort(port int)Choose an HTTPS port on which to serve requests.VK_TLS_PORT
UseHTTPPort(port int)Choose an HTTP port on which to serve requests. When using TLS, the LetsEncrypt challenge server will run on the configured HTTP port.VK_HTTP_PORT
UseAppName(name string)When the application starts, name will be logged. Empty by default.VK_APP_NAME
UseEnvPrefix(prefix string)Use prefix instead of VK for environment variables, for example APP_HTTP_PORT instead of VK_HTTP_PORT.N/A
UseLogger(logger *vlog.Logger)Set the logger object to be used. The logger is used internally by vk and is available to all handler functions via the ctx object. If this option is not passed, vlog.Default is used, and its environment variable prefix set to the same as vk's. (VK by default).N/A

Each of the options can be set using the modifier function, or by setting the associated environment variable. The environment variable will override the modifier function.

Note the use of UseEnvPrefix if you would prefer to use something other than VK for your environment variables!

Handler functions

vk's handler function definition is:

func HandlePing(r *http.Request, ctx *vk.Ctx) (interface{}, error)

Here's a breakdown of each part:

r *http.Request: The request object for the request being handled.

ctx *vk.Ctx: A context object containing more options for interacting with the request. See more below.

(interface{}, error): The return types of the handler allow you to respond to HTTP requests by simply returning values. If an error is returned, vk will interpret it as a failed request and respond with an error code, if error is nil, then the interface{} value is used to respond based on the response handling rules. Responding to requests is handled in depth below in Responding to requests


Similar to handlers for HTTP requests, here is the function definition for WebSocket connections:

func(r *http.Request, ctx *Ctx, conn *websocket.Conn) error

Each of the arguments are equivalent to the arguments passed to HTTP handlers, with one additonal argument:

conn is a *websocket.Conn from the Gorilla library.

View the Gorilla documentation for more information on reading and writing to the connection.

Mounting routes

To define routes for your vk server, use the HTTP method functions on the server object:

server := vk.New(
vk.UseAppName("Vektor API Server"),

server.GET("/users", HandleGetUsers)
server.POST("/groups", HandleCreateGroup)

If you prefer to pass the HTTP method as an argument, use server.Handle() instead.

Note that attempting to add new handlers after calling server.Start() is a no-op

Route groups

vk allows grouping routes by a common path prefix. For example, if you want a group of routes to begin with the /api/ path, you can create an API route group and then mount all of your handlers to that group.

apiGroup := vk.Group("/api")
apiGroup.GET("/events", HandleGetEvents)


Calling AddGroup will calculate the full paths for all routes and mount them to the server. In the example above, the handler would be mounted at /api/events.

Groups can even be added to groups!

v1 := vk.Group("/v1")
v1.GET("/events", HandleEventsV1)

v2 := vk.Group("/v2")
v2.GET("/events", HandleEventsV2)

apiGroup := vk.Group("/api")


This will create a natural grouping of your routes, with the above example creating the /api/v1/events and /api/v2/events routes.

Middleware and Afterware

Groups become even more powerful when combined with Middleware and Afterware. Middleware are pseudo request handlers that run in sequence before the mounted vk.HandlerFunc is run. Middleware functions can modify a request and its context, or they can return an error, which causes the request handling to be terminated immediately. Two examples:

func headerMiddleware(r *http.Request, ctx *vk.Ctx) error {
ctx.Headers.Set("X-Vektor-Test", "foobar")

return nil

func denyMiddleware(r *http.Request, ctx *vk.Ctx) error {
if strings.Contains(r.URL.Path, "hack") {

return vk.E(403, "begone, hacker")

return nil

Middleware have a similar function signature to vk.HandlerFunc, but only return an error. The first example modifies the request context to add a response header. The second example detects a hacker and returns an error, which is handled exactly like any other error response (see below). Returning an error from a Middleware prevents the request from ever reaching the registered handler.

Middleware are applied to route groups with the Before method:

v1 := vk.Group("/v1").Before(vk.ContentTypeMiddleware("application/json"), denyMiddleware, headerMiddleware)
v1.GET("/events", HandleEventsV1)

This example shows a group created with three middleware. The first adds the Content-Type response header (and is included with vk), the second and third are the examples from above. When the group is mounted to the server, the chain of middleware are put in place, and are run before the registered handler. When groups are nested, the middleware from the parent group are run before the middleware of any child groups. In the example of nested groups above, any middleware set on the apiGroup groups would run before any middleware set on the v1 or v2 groups.

Afterware is similar, but is run after the request handler. Who knew! Afterware cannot modify response body or status code, but can modify response headers using the ctx object. Afterware will always run, even if something earlier in the request chain fails. Here's an example:

func logAfter(r *http.Request, ctx *vk.Ctx) {
ctx.Log.Info("request completed")

v2 := vk.Group("/v2").Before(vk.ContentTypeMiddleware("application/json")).After(logAfter)
v2.GET("/events", HandleEventsV2)

Middleware and Afterware in vk is designed to be easily composable, creating chains of behaviour easily grouped to sets of routes. Middleware can also help increase security of applications, allowing authentication, request throttling, active defence, etc, to run before the registered handler and keeping sensitive code from even being reached in the case of an unauthorized request.

Responding to requests

Response types

vk includes two types, Response and Error (with helper functions vk.Respond(...) and vk.Err(...)) that can be used to gain extra control over the response code and contents that you want to return:

type createdResponse struct {
Name string `json:"name"`
UUID string `json:"uuid"`

func HandleCreate(r *http.Request, ctx *vk.Ctx) (interface{}, error) {
// Do some work

resp := createdResponse {
Name: "Wendy",
UUID: "jfioqerjhp98qergnjw98h23"

// Return 201 (Created) and JSON
return vk.Respond(http.StatusCreated, resp), nil

func HandleDelete(r *http.Request, ctx *vk.Ctx) (interface{}, error) {
// Oops, something went wrong

return nil, vk.Err(http.StatusConflict, "the user is already deleted") // responds with HTTP status 409 and body {"status": 409, "message": "the user is already deleted"}

vk.Respond and vk.Err can be used with their shortcuts vk.R and vk.E if you like your code to be terse.

Response handling rules

vk processes the (interface{}, error) returned by handler functions in a spcific way to ensure you always know how it will behave while still being able to use simple types in your code.

Successful responses (i.e. the interface{} returned by handler functions):

vk.Response is an (optional) type that can be used to control the behaviour of the response, if desired. vk.Respond(...) returns a vk.Response.

  1. If the type is vk.Response, set the HTTP status code provided and process Response.body as follows. (If the type is NOT vk.Response, the status code is set to 200 OK)
  2. If the type is string, write the string (as UTF-8 bytes) to the response body.
  3. If the type is bytes, write them directly to the response body.
  4. If the type is a struct, attempt to marshal to JSON and write JSON bytes to the response body.

If a Content-Type is not explicitly set by your code in the middleware chain or HandlerFunc, the value will be inferred from the type returned from the HandlerFunc.


Handler returns...Status CodeResponse bodyContent-Type
return "Hello, World", nil200 OK"Hello World" (as UTF-8 bytes)text/plain
return jsonBytesFromJSONMarshal, nil200 OK[JSON bytes as generated by json.Marshal]application/octet-stream
return someStructInstance, nil200 OK[JSON respresentation of struct automatically marshalled by vk]application/json
return vk.R(http.StatusCreated, "created"), nil201 Created"created" (as UTF-8 bytes)text/plain
return vk.R(http.StatusCreated, someStructInstance), nil201 Created[JSON respresentation of struct automatically marshalled by vk]application/json

Failure responses (i.e. the error returned by middleware or handler functions):

vk.Error is an interface that can be used to control the behaviour of error responses. vk.ErrorResponse is a concrete type that implements vk.Error. Any errors that do NOT implement vk.Error will be treated as potentially unsafe, and their contents will be logged but not returned to the caller. Use vk.Wrap(...) if you'd like to wrap an error in vk.ErrorResponse. vk.Err returns a vk.Error.

vk.Error looks like this:

type Error interface {
Error() string // this ensures all Errors will also conform to the normal error interface

Message() string
Status() int

Errors returned from middleware or HandlerFuncs are handled as follows:

  1. If the type is vk.Error, set the HTTP status code provided and respond with JSON as follows: {"status": err.Status(), "message": err.Message()}

  2. If the type is NOT vk.Error, log the potentially unsafe error contents, set the HTTP status code to 500, and respond with "Internal Server Error"


Handler returns...Status CodeResponse bodyContent-Type
return nil, errors.New("failed to add user")500 Internal Server Error"Internal Server Error" (as UTF-8 bytes)text/plain
return nil, vk.E(http.StatusForbidden, "not permitted to do this thing")403 Forbidden{"status": 403, "message": "not permitted to do this thing"}application/json
return nil, vk.Wrap(http.StatusApplicationError, err)434 Application Error{"status": 434, "message": err.Error()}application/json

Standard http.HandlerFunc

vk can use standard http.HandlerFunc handlers by mounting them with server.HandleHTTP. This is useful for mounting handler functions provided by third party libraries (such as Prometheus), but they are not able to take advantage of many vk features such as middleware or route groups currently.

The Ctx Object

Each request handler is passed a vk.Ctx object, which is a context object for the request. It is similar to the context.Context type (and uses one under the hood), but Ctx has been augmented for use in web service development.

Ctx includes a standard Go context.Context which can be used as a pseudo key/value store using ctx.Set() and ctx.Get(). This allows passing things into request handlers such as database connections or other persistent objects. Middleware and Afterware can access the Ctx to modify it, or access data from it.

The server's configured vlog.Logger object is included (ctx.Log) for logging within request handlers, and a shortcut for setting the logger's scope for the current request exists with ctx.UseScope(...). You can learn about scope in the vlog docs. A default scope will always be set with the request ID included.

Accessing the URL params for the request (such as /users/:uuid) is done with ctx.Params, and ctx.RespHeaders can be used to set response headers if needed.

Ctx can also be used to easily get a request ID, with ctx.RequestID(). The Request ID is generated and cached on the object, and so calling it multiple times will return the same value. If you prefer to set your own Request ID, ctx.UseRequestID() will do the trick. However it will mean the first log message for the request will have a different ID as it uses the default ID generated for the ctx.