連絡先を携帯電話と同期するにはどうすればよいですか? Go に CardDAV を実装する!

package main

import (
    "context"
    "net/http"

    "github.com/emersion/go-webdav/carddav"
)

type (
    ctxKey   struct{}
    ctxValue struct {
        username string
    }
)

func NewCardDAVHandler() http.Handler {
    actualHandler := carddav.Handler{
        Backend: &ownBackend{},
    }

    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        username, password, ok := r.BasicAuth()
        // check username and password: adjust the logic to your system (do NOT store passwords in plaintext)
        if !ok || username != "admin" || password != "s3cr3t" {
            // abort the request handling on failure
            w.Header().Add("WWW-Authenticate", `Basic realm="Please authenticate", charset="UTF-8"`)
            http.Error(w, "HTTP Basic auth is required", http.StatusUnauthorized)
            return
        }

        // user is authenticated: store this info in the context
        ctx := context.WithValue(r.Context(), ctxKey{}, ctxValue{username})
        // delegate the work to the CardDAV handle
        actualHandler.ServeHTTP(w, r.WithContext(ctx))
    })
}

func currentUsername(ctx context.Context) (string, error) {
    if v, ok := ctx.Value(ctxKey{}).(ctxValue); ok {
        return v.username, nil
    }
    return "", errors.New("not authenticated")
}

type ownBackend struct{}

// must begin and end with a slash
func (b *ownBackend) CurrentUserPrincipal(ctx context.Context) (string, error) {
    username, err := currentUsername(ctx)
    return "/" + url.PathEscape(username) + "/", err
}

// must begin and end with a slash as well
func (b *ownBackend) AddressBookHomeSetPath(ctx context.Context) (string, error) {
    principal, err := b.CurrentUserPrincipal(ctx)
    return principal + "contacts/", err
}

func utf8Field(v string) *vcard.Field {
    return &vcard.Field{
        Value: v,
        Params: vcard.Params{
            "CHARSET": []string{"UTF-8"},
        },
    }
}

func vcardFromUser(u graphqlient.User) vcard.Card {
    c := vcard.Card{}

    c.Set(vcard.FieldFormattedName, utf8Field(u.Firstname+" "+u.Lastname))
    c.SetName(&vcard.Name{
        Field:      utf8Field(""),
        FamilyName: u.Lastname,
        GivenName:  u.Firstname,
    })
    c.SetRevision(u.UpdatedAt)
    c.SetValue(vcard.FieldUID, u.Extid)

    c.Set(vcard.FieldOrganization, utf8Field(u.Unit))

    // addFields sorts the key to ensure a stable order
    addFields := func(fieldName string, values map[string]string) {
        for _, k := range slices.Sorted(maps.Keys(values)) {
            v := values[k]
            c.Add(fieldName, &vcard.Field{
                Value: v,
                Params: vcard.Params{
                    vcard.ParamType: []string{k + ";CHARSET=UTF-8"}, // hacky but prevent maps ordering issues
                    // "CHARSET":       []string{"UTF-8"},
                },
            })
        }
    }

    addFields(vcard.FieldEmail, u.Emails)
    addFields(vcard.FieldTelephone, u.Phones)

    vcard.ToV4(c)
    return c
}

openssl req -new -subj "/C=US/ST=Utah/CN=192.168.XXX.XXX" -newkey rsa:2048 -nodes -keyout localhost.key -out localhost.csr
openssl x509 -req -days 365 -in localhost.csr -signkey localhost.key -out localhost.crt