httpserver/middleware/wellknown/wellknown.go

package wellknown

import (
	"net/url"

	"github.com/gin-gonic/gin"
	"github.com/go-ap/jsonld"
	"github.com/rs/zerolog/log"
	"go.sebtobie.de/httpserver"
	"go.sebtobie.de/httpserver/middleware"
)

var _ middleware.Middleware = &Middleware{}
var _ middleware.PreSetupMiddleware = &Middleware{}
var _ httpserver.Site = &Middleware{}

type (

	// Link is the reference where the application can find the object
	Link struct {
		Rel  string
		Type string
		Href *url.URL
	}

	// Middleware is an middleware for sites to register themselfs to provide wellknown urls
	Middleware struct {
		// webfinger is an map consisting of protocol as key and an array of WebfingerAccount as value
		webfinger map[string][]Webfinger
	}

	// Webfinger is an function that accepts the account part(after ?resource=<protocol>:) and returns the aliases and the links.
	// The bool value if for faster detection if the account was found.
	Webfinger func(resource string) ([]string, []*Link, bool)
)

// New creates a new initialized Middleware
func New() *Middleware {
	return &Middleware{
		webfinger: map[string][]Webfinger{},
	}
}

// Defaults returns nothing
func (*Middleware) Defaults() middleware.Config {
	return nil
}

// Gin does nothing.
func (*Middleware) Gin(c *gin.Context) {
	c.Next()
}

// Setup does nothing
func (*Middleware) Setup(middleware.Config) {}

// Teardown does nothing
func (*Middleware) Teardown() {}

// PreSetup goes through all sites and collects all registrations for wellknown uris
func (m *Middleware) PreSetup(s []any) error {
	for _, site := range s {
		if wfs, ok := site.(FingerSite); ok {
			for _, finger := range wfs.RegisterFingers() {
				if _, ok := m.webfinger[finger.Protocol]; !ok {
					m.webfinger[finger.Protocol] = []Webfinger{}
				}
				m.webfinger[finger.Protocol] = append(m.webfinger[finger.Protocol], finger.Webfinger)
			}
		}
	}
	return nil
}

// Init initializes the routergroup. It must always run on /
func (m *Middleware) Init(rg *gin.RouterGroup) {
	if len(m.webfinger) > 0 {
		rg.GET(".well-known/webfinger", m.webfingerhf)
	}
}

func (m *Middleware) webfingerhf(c *gin.Context) {
	resource := c.Query("resource")
	if resource == "" {
		c.AbortWithStatus(404)
		return
	}
	uri, err := url.Parse(resource)
	if err != nil {
		log.Error().Err(err).Str("uri", resource).Msg("Failed to parse uri")
		c.AbortWithStatus(404)
		return
	}
	var wf []Webfinger
	var found bool
	if wf, found = m.webfinger[uri.Scheme]; !found {
		c.AbortWithStatus(404)
		return
	}
	var output = struct {
		Subject string   `json:"subject,omitempty"`
		Aliases []string `json:"aliases,omitempty"`
		Links   []*Link  `json:"links,omitempty"`
	}{Subject: resource, Aliases: []string{}, Links: []*Link{}}
	var aliases = []string{}
	var links = []*Link{}
	var input = uri.Opaque
	if uri.Opaque == "" {
		input = resource
	}
	outputok := false
	for _, finger := range wf {
		aliases, links, found = finger(input)
		if !found {
			continue
		}
		output.Aliases = append(output.Aliases, aliases...)
		output.Links = append(output.Links, links...)
		outputok = true
	}
	if outputok {
		c.Header("Access-Control-Allow-Origin", "*")
		json, err := jsonld.Marshal(output)
		if err != nil {
			c.AbortWithStatus(500)
			return
		}
		c.Data(200, jsonld.ContentType, json)
	}
	c.AbortWithStatus(404)
}