hugo-micropub/webmention.go

package main

import (
	"crypto/md5"
	"encoding/json"
	"errors"
	"fmt"
	"log"
	"net/http"
	"net/url"
	"strings"
	"time"
	"willnorris.com/go/webmention"
)

type Mention struct {
	Source string `json:"source"`
	Target string `json:"target"`
	Date   string `json:"date"`
}

func SendWebmentions(url string) {
	client := webmention.New(nil)
	dl, err := client.DiscoverLinks(url, ".h-entry")
	if err != nil {
		return
	}
	// Send Webmentions
	for _, link := range filterLinks(dl) {
		endpoint, err := client.DiscoverEndpoint(link)
		if err != nil || len(endpoint) < 1 {
			continue
		}
		_, err = client.SendWebmention(endpoint, url, link)
		if err != nil {
			log.Println("Sent webmention to " + link + " failed")
			continue
		}
		log.Println("Sent webmention to " + link)
	}
}

func filterLinks(links []string) []string {
	var filteredLinks []string
LINKFILTER:
	for _, link := range links {
		if strings.HasPrefix(link, BlogUrl) {
			continue
		}
		for _, ignoredURL := range IgnoredWebmentionUrls {
			if strings.HasPrefix(link, ignoredURL) {
				continue LINKFILTER
			}
		}
		filteredLinks = append(filteredLinks, link)
	}
	return filteredLinks
}

func HandleWebmention(w http.ResponseWriter, r *http.Request) {
	if r.Method != "POST" {
		w.WriteHeader(http.StatusMethodNotAllowed)
		_, _ = w.Write([]byte("The HTTP method is not allowed, make a POST request"))
		return
	}
	sourceUrl, err := url.Parse(r.FormValue("source"))
	if err != nil || !(sourceUrl.Scheme == "http" || sourceUrl.Scheme == "https") {
		err = errors.New("failed to parse webmention source URL")
		w.WriteHeader(http.StatusBadRequest)
		_, _ = w.Write([]byte(err.Error()))
		return
	}
	targetUrl, err := url.Parse(r.FormValue("target"))
	if err != nil || !(sourceUrl.Scheme == "http" || sourceUrl.Scheme == "https") {
		err = errors.New("failed to parse webmention target URL")
		w.WriteHeader(http.StatusBadRequest)
		_, _ = w.Write([]byte(err.Error()))
		return
	}
	// Check if urls don't equal
	if sourceUrl.String() == targetUrl.String() {
		err = errors.New("source and target equal")
		w.WriteHeader(http.StatusBadRequest)
		_, _ = w.Write([]byte(err.Error()))
		return
	}
	// Check if target is blog
	if !strings.HasPrefix(targetUrl.String(), BlogUrl) {
		err = errors.New("wrong webmention target")
		w.WriteHeader(http.StatusBadRequest)
		_, _ = w.Write([]byte(err.Error()))
		return
	}
	// Check response code for source
	respCode, err := responseCodeForSource(sourceUrl.String())
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		_, _ = w.Write([]byte(err.Error()))
		return
	}
	if respCode < 200 || respCode >= 300 {
		if respCode == 410 {
			// Delete mention, because source is gone
			// TODO: Implement deletion
			returnSuccess(targetUrl.String(), w, r)
			return
		} else {
			err = errors.New("source returned error")
			w.WriteHeader(http.StatusBadRequest)
			_, _ = w.Write([]byte(err.Error()))
			return
		}
	}
	// Check if source mentions target
	if !sourceMentionsTarget(sourceUrl.String(), targetUrl.String()) {
		err = errors.New("source doesn't mention target")
		w.WriteHeader(http.StatusBadRequest)
		_, _ = w.Write([]byte(err.Error()))
		return
	}
	mention := &Mention{
		Source: sourceUrl.String(),
		Target: targetUrl.String(),
		Date:   time.Now().Format(time.RFC3339),
	}
	err = saveWebmention(mention)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		_, _ = w.Write([]byte(err.Error()))
		return
	}
	returnSuccess(targetUrl.String(), w, r)
	return
}

func responseCodeForSource(source string) (int, error) {
	client := &http.Client{}
	resp, err := client.Get(source)
	if err != nil || resp == nil {
		return 0, err
	}
	return resp.StatusCode, nil
}

func sourceMentionsTarget(source string, target string) bool {
	client := webmention.New(nil)
	dl, err := client.DiscoverLinks(source, "")
	if err != nil {
		return false
	}
	for _, link := range dl {
		if link == target {
			return true
		}
	}
	return false
}

func saveWebmention(mention *Mention) (err error) {
	bytesRepresentation, err := json.Marshal(mention)
	if err != nil {
		return errors.New("failed to marshal json before committing")
	}
	filePath := fmt.Sprintf("data/mentions/%x/%x.json", md5.Sum([]byte(strings.ReplaceAll(mention.Target, "/", ""))), md5.Sum([]byte(mention.Source)))
	err = SelectedStorage.UpdateFile(filePath, string(bytesRepresentation), "New webmention from "+mention.Source)
	return
}

func returnSuccess(target string, w http.ResponseWriter, r *http.Request) {
	if strings.Contains(r.Header.Get("Accept"), "text/html") {
		// Redirect browser
		w.Header().Add("Location", target)
		w.WriteHeader(http.StatusSeeOther)
	} else {
		w.WriteHeader(http.StatusOK)
	}
	// Purge CDN in 10 seconds
	go func() {
		if SelectedCdn != nil {
			time.Sleep(10 * time.Second)
			SelectedCdn.Purge(target)
		}
	}()
	return
}