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client.go
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client.go
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package profilefed
import (
"bytes"
"crypto/ed25519"
"encoding/base64"
"encoding/json"
"errors"
"fmt"
"io"
"net/http"
"net/url"
"sync"
"queerdevs.org/profilefed/webfinger"
)
const responseSizeLimit = 32_000_000
var (
// ErrPubkeyNotFound signifies that the server public key is not found.
ErrPubkeyNotFound = errors.New("server pubkey not found")
// ErrNoSignature signifies that the response contains no signature.
ErrNoSignature = errors.New("response contains no signature")
// ErrSignatureMismatch signifies that the message does not match the server signature.
ErrSignatureMismatch = errors.New("message does not match server signature")
)
// DefaultClient returns a default client for ProfileFed.
//
// It uses an in-memory synchronized map to store public keys.
// For production, it's highly recommended to implement a custom
// client that persists the keys to a database or similar, so that
// restarting your app doesn't provide opportunities for malicious servers.
func DefaultClient() Client {
defaultMap := sync.Map{}
return Client{
SavePubkey: func(serverName string, previousNames []string, pubkey ed25519.PublicKey) error {
defaultMap.Store(serverName, pubkey)
for _, name := range previousNames {
defaultMap.Delete(name)
}
return nil
},
GetPubkey: func(serverName string) (ed25519.PublicKey, error) {
pubkey, ok := defaultMap.Load(serverName)
if !ok {
return nil, ErrPubkeyNotFound
}
return pubkey.(ed25519.PublicKey), nil
},
}
}
// Client represents a ProfileFed client
type Client struct {
// SavePubkey saves the public key for a given server.
SavePubkey func(serverName string, previousNames []string, pubkey ed25519.PublicKey) error
// GetPubkey retrieves the public key for a given server.
// If the key isn't found, GetPubkey should return [ErrPubkeyNotFound]
GetPubkey func(serverName string) (ed25519.PublicKey, error)
}
// Lookup looks up the profile descriptor for the given resource.
func (c Client) Lookup(resource string) (*Descriptor, error) {
wfdesc, err := webfinger.LookupAcct(resource)
if err != nil {
return nil, err
}
out := &Descriptor{}
return out, c.lookup(wfdesc, "", false, out)
}
// LookupID looks up the profile descriptor that matches the given ID
// for the given resource.
func (c Client) LookupID(resource, id string) (*Descriptor, error) {
wfdesc, err := webfinger.LookupAcct(resource)
if err != nil {
return nil, err
}
out := &Descriptor{}
return out, c.lookup(wfdesc, id, false, out)
}
// Lookup looks up all the available profile descriptors for the given resource.
func (c Client) LookupAll(resource string) (map[string]*Descriptor, error) {
wfdesc, err := webfinger.LookupAcct(resource)
if err != nil {
return nil, err
}
out := map[string]*Descriptor{}
return out, c.lookup(wfdesc, "", true, &out)
}
// LookupWebFinger is the same as [Client.Lookup], but it accepts an existing WebFinger
// descriptor rather than looking one up.
func (c Client) LookupWebFinger(wfdesc *webfinger.Descriptor) (*Descriptor, error) {
out := &Descriptor{}
return out, c.lookup(wfdesc, "", false, out)
}
// LookupWebFingerID is the same as [Client.LookupID], but it accepts an existing WebFinger
// descriptor rather than looking one up.
func (c Client) LookupWebFingerID(wfdesc *webfinger.Descriptor, id string) (*Descriptor, error) {
out := &Descriptor{}
return out, c.lookup(wfdesc, id, false, out)
}
// LookupAllWebFinger is the same as [Client.LookupAll], but it accepts an existing WebFinger
// descriptor rather than looking one up.
func (c Client) LookupAllWebFinger(wfdesc *webfinger.Descriptor) (map[string]*Descriptor, error) {
out := map[string]*Descriptor{}
return out, c.lookup(wfdesc, "", true, &out)
}
func (c Client) lookup(wfdesc *webfinger.Descriptor, id string, all bool, dest any) error {
pfdLink, ok := wfdesc.LinkByType("application/x-pfd+json")
if !ok {
return errors.New("server does not support the profilefed protocol")
}
pfdURL, err := url.Parse(pfdLink.Href)
if err != nil {
return err
}
pubkeySaved := false
pubkey, err := c.GetPubkey(pfdURL.Host)
if errors.Is(err, ErrPubkeyNotFound) {
data, sig, prevSigs, err := getServerInfo(pfdURL.Scheme, pfdURL.Host)
if err != nil {
return err
}
var info serverInfoData
err = json.Unmarshal(data, &info)
if err != nil {
return err
}
// If this server is advertising previous names, make sure
// we verify that it's telling the truth by checking the whether
// any of its signatures match using the pubkeys of the previous names.
if len(info.PreviousNames) > 0 {
for _, prevName := range info.PreviousNames {
pubkey, err = c.GetPubkey(prevName)
if errors.Is(err, ErrPubkeyNotFound) {
continue
} else if err != nil {
return err
}
if ed25519.Verify(pubkey, data, sig) {
break
}
for _, prevSig := range prevSigs {
if ed25519.Verify(pubkey, data, prevSig) {
break
}
}
// If we haven't broken out of the loop by now, this
// name could not be verified, so return an error.
return ErrSignatureMismatch
}
}
pubkey, err = base64.StdEncoding.DecodeString(info.PublicKey)
if err != nil {
return err
}
err = c.SavePubkey(pfdURL.Host, info.PreviousNames, pubkey)
if err != nil {
return err
}
pubkeySaved = true
} else if err != nil {
return err
}
q := pfdURL.Query()
if all {
q.Set("all", "1")
} else if id != "" {
q.Set("id", id)
}
pfdURL.RawQuery = q.Encode()
res, err := http.Get(pfdURL.String())
if err != nil {
return err
}
defer res.Body.Close()
if err := checkResp(res, "getProfileDescriptor"); err != nil {
return err
}
data, err := io.ReadAll(io.LimitReader(res.Body, responseSizeLimit))
if err != nil {
return err
}
if err := res.Body.Close(); err != nil {
return err
}
sig, err := getSignature(res)
if err != nil {
return err
}
if !ed25519.Verify(pubkey, data, sig) {
// If the pubkey was just saved in the current request, we probably
// already have the newest one, so just return a mismatch error.
if pubkeySaved {
return ErrSignatureMismatch
}
serverData, infoSig, sigs, err := getServerInfo(pfdURL.Scheme, pfdURL.Host)
if err != nil {
return err
}
var info serverInfoData
err = json.Unmarshal(serverData, &info)
if err != nil {
return err
}
newPubkey, err := base64.StdEncoding.DecodeString(info.PublicKey)
if err != nil {
return err
}
// If the pubkey hasn't changed but we couldn't
// verify the signature, return an error immediately.
if bytes.Equal(pubkey, newPubkey) {
return ErrSignatureMismatch
}
verified := false
for _, sig := range sigs {
if ed25519.Verify(pubkey, serverData, sig) {
verified = true
break
}
}
if !verified {
return ErrSignatureMismatch
}
if !ed25519.Verify(newPubkey, infoSig, serverData) {
return ErrSignatureMismatch
}
err = c.SavePubkey(pfdURL.Host, info.PreviousNames, newPubkey)
if err != nil {
return err
}
if !ed25519.Verify(newPubkey, data, sig) {
return ErrSignatureMismatch
}
}
return json.Unmarshal(data, dest)
}
// getServerInfo retrieves server information.
func getServerInfo(scheme, host string) (data, sig []byte, prevSigs [][]byte, err error) {
serverInfoURL := url.URL{
Scheme: scheme,
Host: host,
Path: "/_profilefed/server",
}
res, err := http.Get(serverInfoURL.String())
if err != nil {
return nil, nil, nil, err
}
defer res.Body.Close()
if err := checkResp(res, "getServerInfo"); err != nil {
return nil, nil, nil, err
}
sig, err = getSignature(res)
if err != nil {
return nil, nil, nil, err
}
data, err = io.ReadAll(io.LimitReader(res.Body, responseSizeLimit))
return data, sig, getPrevSignatures(res), err
}
// getPrevSignatures extracts previous signatures from a response.
func getPrevSignatures(res *http.Response) [][]byte {
var sigs [][]byte
sigStrs := res.Header[http.CanonicalHeaderKey("X-ProfileFed-Previous")]
for _, sigStr := range sigStrs {
sig, err := base64.StdEncoding.DecodeString(sigStr)
if err != nil {
continue // Skip invalid signatures
}
sigs = append(sigs, sig)
}
return sigs
}
// getSignature extracts the signature from a response.
func getSignature(res *http.Response) ([]byte, error) {
sigStr := res.Header.Get("X-ProfileFed-Sig")
if sigStr == "" {
return nil, ErrNoSignature
}
return base64.StdEncoding.DecodeString(sigStr)
}
// checkResp returns an error if the response is not 200 OK.
func checkResp(res *http.Response, opName string) error {
if res.StatusCode != 200 {
return fmt.Errorf("%s: %s", opName, res.Status)
}
return nil
}