Server generation and customization

What are the dependencies required by the generated server?

The code generation process ends with a message indicating package dependencies for your generated code.

Basically, here are the required packages:

And depending on your generation options, a command line flags handling package:

This dependency used to be necessary up to release 0.14:

These packages may of course be vendored with your own source.

Originally from issue #1085.

How to add custom flags?

go-swagger ships with an option to select a flag management package: swagger generate server --flag-strategy=[go-flags|pflag|flag]

You may of course customize your server to accept arbitrary flags the way you prefer. This should be normally done with the generated main.go. For customization, you may either skip the generation of the main package (--skip-main) and provide your own, or customize template generation to generate a custom main.

Here's an example: kv store example

Originally from issue #1036.

How do you integrate the flag sets of go-swagger and other packages, in particular, glog?

Use-case: logger

I am trying to integrate a package into a go-swagger generated API that is using the logger. When I initialize the glog logger it appears to shield the flags defined in the go-swagger runtime.

Answer: the generated API has a Logger property that is a function with signature: func(string, ...interface{})

You can configure it with any logger that exposes the signature.


Use-case: logger flags

Still having a problem with how and where to initialize glog so that both sets of flags are honored: the runtime flags, such as --tls-certificate and the glog flags like -log_dir and -stderrthreshold.

If I initialize glog in the config_xxx.go I don't get the go-swagger runtime flags, and if I initialize glog in the engine, I get the error: logging before flag.Parse. I realize that this question is not so much about logging per se, but more about how to merge the flag sets defined by different packages.

Answer: you can generate a server with --flag-strategy pflag

After that you can use its integration to add goflags. You would do this in the main file. Subsequently it's probably a good idea to generate code with --exclude-main so the update is preserved.

See also:


import (
    goflag "flag"
    flag ""

var ip *int = flag.Int("flagname", 1234, "help message for flagname")

func main() {

Originally from issue #762.

How to serve two or more swagger specs from one server?

Use-case: I want a go-swagger generated server to serve 2 swagger specs that have no overlap on paths. One is a generic metadata api that is implemented by many services and the other is a service-specific api. The built-in server.go template Server struct, by having exactly one API & handler, appears to prevent this.


  1. Use go-swagger mixin command to merge specs into a single one
  2. Create yourself a top-level swagger file that just includes the two lower-level ones (using $ref). You may use go-swagger flatten to flatten the resulting spec
  3. You can also make your own main function and use the code from the generation of both spec (with --skip-main). This allows for customization like using a different middleware stack, which in turn gives you the ability to serve 2 swagger specs at different paths.

Originally from issue #1005. (comes with a sample main.go for spec composition).

How to access access API struct inside operator handler?

Use-Case: my question is how can I access the generated API interface from within an operation handler function ? Can i pass it somehow via context or any other way to do that?

Answer: No. It's not reachable from within the handler anywhere.

I created a module like apache access module ACL based on IP address for different URLs. Instead of URL for lookup key I decided to use Operation.ID. Lookup would be faster in that way because each operation has a unique id according to swagger specification. The problem comes when I want to check against that ACL of mine...

Suggestions: This is possible in 2 ways.

  • first way is by using an authenticator,
  • the second way is making a middleware (not global)

Example with Authenticator:

// Authenticator represents an authentication strategy
// implementations of Authenticator know how to authenticate the
// request data and translate that into a valid principal object or an error
type Authenticator interface {
    Authenticate(interface{}) (bool, interface{}, error)

You may see the schemes currently supported here:

Example with Middleware:

// The middleware configuration is for the handler executors. These do not apply to the swagger.json document.
// The middleware executes after routing but before authentication, binding and validation.
func setupMiddlewares(handler http.Handler) http.Handler {
    return handler

to get to the matched route in one of those you can:

import ""
context.Get(3, request)

That gets you a matched route.

Note: it might be worth it to expose Context as an exported method on the API builder. That would be a simple PR to add the following code in go-swagger

func (o *LifecycleManagerAPI) Context() *middleware.Context {
    if o.context == nil {
        o.context = middleware.NewRoutableContext(o.spec, o, nil)
    return o.context

then your middleware could take a context in and use RouteInfo(request) like this one:

Similar use-case: I have some domain objects I need access to in the handlers (db connection, telemetry client, etc).

What is the recommended way/place to define these and access them in the handlers?

Would I define them in configure_xxx() and make wrapper functions for the handlers to make them accessible? Or is there a nice way to add them to the context? I was looking for some examples of this but couldn't find anything.

Hint: look at this one:

The important takeaway is that main and the handlers have to be pulled outside of the generated code since only configure_xxx() is protected. And main() doesn't call configureAPI() ... that was a little confusing looking through the other examples and not seeing any changes to the vanilla config code.

Similar use-case: dependency injection

Wouldn't it be better to have all the handlers automatically be part of a default struct that simply has a Context member variable or empty interface?

That would save everyone a lot of copy/paste when we need to inject some info. I mean, a different context than the one available on params.HTTPRequest.Context(), more like an application level context, e.g. something I can stuff a database reference or other business state into.

Hint: remember that the generated packages are made of a series of files that you can extend and tailor to your own needs by adding more files.

For instance, a new (non generated) file in the operations package could bring to life the applicative context/dependencies injection and be called from the configure_xxx. You may alternatively modify the generation by providing your own templates, and possibly extend the interface of the Server struct.

Originally from issue #661.

Use go-swagger to generate different client or servers

Use-Case: I am using go-swagger to generate some part of a server application automatically and I would love to reuse our code by transforming the code in go templates.

It would be enough to export the appGenerator type and have a function that returns it (maybe generator.GenerateServer itself?). I would then use appGenerator to execute the templates. How could I realize this? Is it possible with go-swagger?

Answer: you can provide your own templates for go-swagger.

The client and server generators allow you to specify a directory on disk to add custom templates.

Here are some docs:

In VIC they do this:

Hint: you can also override templates by using the same names:

Wouldn't this generate roughly the same structure of the server?

I don't want to change minor details, I want to have code that looks totally different (but only for the server part, models and clients are more than okay) while using code the parsing and validation from go-swagger. This means different number of files and different functionalities.

Answer: yes, it would generate a similar structure.

Note: customizing templates already brings many options to the table, including generating artifacts in other languages than go.

There is some documentation on the config file format here:

Also keep in mind that go-openapi and go-swagger constitute a toolkit and provide you the tools to adapt to your own use case. The swagger command line and standard templates only covers general purpose use-cases.

If you think your use-case would benefit to many people, feel free to make the necessary changes for your case to work and submitting a PR.

Example config file for generation:

    - name: configure
      source: asset:serverConfigureapi
      target: "{{ joinFilePath .Target .ServerPackage }}"
      file_name: "{{ .Name }}_client.go"
      skip_exists: true
    - name: main
      source: asset:serverMain
      target: "{{ joinFilePath .Target \"cmd\" (dasherize (pascalize .Name)) }}-server"
      file_name: "main.go"
    - name: embedded_spec
      source: asset:swaggerJsonEmbed
      target: "{{ joinFilePath .Target .ServerPackage }}"
      file_name: "embedded_spec.go"
    - name: server
      source: asset:serverServer
      target: "{{ joinFilePath .Target .ServerPackage }}"
      file_name: "server.go"
    - name: builder
      source: asset:serverBuilder
      target: "{{ joinFilePath .Target .ServerPackage .Package }}"
      file_name: "{{ snakize (pascalize .Name) }}_api.go"
    - name: doc
      source: asset:serverDoc
      target: "{{ joinFilePath .Target .ServerPackage }}"
      file_name: "doc.go"
   - name: definition
     source: asset:model
     target: "{{ joinFilePath .Target .ModelPackage }}"
     file_name: "{{ (snakize (pascalize .Name)) }}.go"
   - name: parameters
     source: asset:serverParameter
     target: "{{ joinFilePath .Target .ServerPackage .APIPackage .Package }}"
     file_name: "{{ (snakize (pascalize .Name)) }}_parameters.go"
   - name: responses
     source: asset:serverResponses
     target: "{{ joinFilePath .Target .ServerPackage .APIPackage .Package }}"
     file_name: "{{ (snakize (pascalize .Name)) }}_responses.go"
   - name: handler
     source: asset:serverOperation
     target: "{{ joinFilePath .Target .ServerPackage .APIPackage .Package }}"
     file_name: "{{ (snakize (pascalize .Name)) }}.go"

Support streaming responses

Use-Case: Docker client expects a stream of JSON structs from daemon to show a progress bar, as in:

curl -i -X POST http://IP:PORT/images/create?fromImage=alpine&tag=latest

How could I write a server providing a streaming response?

Answer: Operations in the generated server are expected to return a responder.

This interface is defined as:

// Responder is an interface for types to implement
// when they want to be considered for writing HTTP responses
type Responder interface {
    WriteResponse(http.ResponseWriter, httpkit.Producer)

With the middleware.ResponderFunc helper construct, you can just write a func(http.ResponseWriter, httpkit.Producer) where you want a streaming response.

This should be sufficient. However:

I've toyed with a channel based stream where you send struct objects to a channel, which then gets streamed to the browser. I decided against this because it seemed to just add complexity for little benefit. I can be persuaded to implement such a responder though, and should somebody send a PR like that I would not say no to it.

Originally from issue #305.

OAuth authentication does not redirect to the authorization server

Use-Case: oauth2 accessCode flow does not redirect to the authorization server

In my understanding, if the accessCode flow is used for oauth2 securitydefinition, the generated server could redirect the authentication to the oauth2 server, e.g., However, my generated code does not perform the redirection. Could anyone help on this? Thanks.

Like in:

swagger: '2.0'
  title: oauth2 debug
  version: 0.3.0
- application/json
  - http
basePath: /api
    type: oauth2
    flow: accessCode
    authorizationUrl: ''
    tokenUrl: 'h'
      admin: Admin scope
      user: User scope
  - OauthSecurity:
    - user

The generated server does not redirect the browser to the google login page.

Answer: Redirection flow is for UI. The spec has them so your UI can do the redirection.

Swagger 2.0 only defines those properties as hints for a UI to work, this doesn't have to be server side. At the same time the redirection flow is not supported in an API but you can use an OAuth 2.0 middleware from any library to get you that functionality

Originally from issue #1217.

HTTPS TLS Cipher Suites not supported by AWS Elastic LoadBalancer

Use-case: AWS Elastic LoadBalancer forwards https requests to instances, and their security policy is 'ELBSecurityPolicy-2016-08'. However, while running the server on https, the server keeps on logging

http: TLS handshake error from 192.168.X.X:XXXXX: tls: no cipher suite supported by both client and server.

If we remove the cipher suites on the generated code, it resolves the issue -

CipherSuites: []uint16{

The ELB security policy 'ELBSecurityPolicy-2016-08' does include these cipher suites, however all requests sent by the ELB are rejected by the server.

Answer: you can generate the server with a different compatibility mode for the older generation of ciphers

swagger generate server --compatibility-mode=intermediate

Originally from issue #1383.

Which mime types are supported?

Use-Case: I seem to be unable to find supported mime-types that the API's can consume and produce. Any references?

Answer: see the current list of supported media MIMEs here You can add more through the consumer producer mechanism.

Originally from issue #1022.

Is it possible to return error to main function of server?

Use-Case: Is it possible to return error to main function of server?

For example, my server saves some configs in file, and I want that if config file is missing, then server must be stopped with some error code. It is possible to do it with panic(err), but I think it is not good way. So can I return error main function of server ?

Answer: you can make your own main function.

There is an example here:

There is a command line argument to avoid overwriting the main when generating: --exclude-main.

Originally from issue #1060.

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