go-gemini/tofu.go
2020-10-31 22:34:51 -04:00

205 lines
5.2 KiB
Go

package gemini
import (
"bufio"
"crypto/sha512"
"crypto/x509"
"fmt"
"io"
"os"
"path/filepath"
"strconv"
"strings"
"time"
)
// Trust represents the trustworthiness of a certificate.
type Trust int
const (
TrustNone Trust = iota // The certificate is not trusted.
TrustOnce // The certificate is trusted once.
TrustAlways // The certificate is trusted always.
)
// KnownHosts represents a list of known hosts.
// The zero value for KnownHosts is an empty list ready to use.
type KnownHosts struct {
hosts map[string]certInfo
file *os.File
}
// LoadDefault loads the known hosts from the default known hosts path, which is
// $XDG_DATA_HOME/gemini/known_hosts.
// It creates the path and any of its parent directories if they do not exist.
// KnownHosts will append to the file whenever a certificate is added.
func (k *KnownHosts) LoadDefault() error {
path, err := defaultKnownHostsPath()
if err != nil {
return err
}
return k.Load(path)
}
// Load loads the known hosts from the provided path.
// It creates the path and any of its parent directories if they do not exist.
// KnownHosts will append to the file whenever a certificate is added.
func (k *KnownHosts) Load(path string) error {
if dir := filepath.Dir(path); dir != "." {
err := os.MkdirAll(dir, 0755)
if err != nil {
return err
}
}
f, err := os.OpenFile(path, os.O_CREATE|os.O_RDONLY, 0644)
if err != nil {
return err
}
k.Parse(f)
f.Close()
// Open the file for append-only use
f, err = os.OpenFile(path, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0644)
if err != nil {
return err
}
k.file = f
return nil
}
// Add adds a certificate to the list of known hosts.
// If KnownHosts was loaded from a file, Add will append to the file.
func (k *KnownHosts) Add(hostname string, cert *x509.Certificate) {
k.add(hostname, cert, true)
}
// AddTemporary adds a certificate to the list of known hosts
// without writing it to the known hosts file.
func (k *KnownHosts) AddTemporary(hostname string, cert *x509.Certificate) {
k.add(hostname, cert, false)
}
func (k *KnownHosts) add(hostname string, cert *x509.Certificate, write bool) {
if k.hosts == nil {
k.hosts = map[string]certInfo{}
}
info := certInfo{
Algorithm: "SHA-512",
Fingerprint: Fingerprint(cert),
Expires: cert.NotAfter.Unix(),
}
k.hosts[hostname] = info
// Append to the file
if write && k.file != nil {
appendKnownHost(k.file, hostname, info)
}
}
// Lookup looks for the provided certificate in the list of known hosts.
// If the hostname is not in the list, Lookup returns ErrCertificateNotFound.
// If the fingerprint doesn't match, Lookup returns ErrCertificateNotTrusted.
// Otherwise, Lookup returns nil.
func (k *KnownHosts) Lookup(hostname string, cert *x509.Certificate) error {
now := time.Now().Unix()
fingerprint := Fingerprint(cert)
if c, ok := k.hosts[hostname]; ok {
if c.Expires <= now {
// Certificate is expired
return ErrCertificateExpired
}
if c.Fingerprint != fingerprint {
// Fingerprint does not match
return ErrCertificateNotTrusted
}
// Certificate is found
return nil
}
return ErrCertificateNotFound
}
// Parse parses the provided reader and adds the parsed known hosts to the list.
// Invalid lines are ignored.
func (k *KnownHosts) Parse(r io.Reader) {
if k.hosts == nil {
k.hosts = map[string]certInfo{}
}
scanner := bufio.NewScanner(r)
for scanner.Scan() {
text := scanner.Text()
parts := strings.Split(text, " ")
if len(parts) < 4 {
continue
}
hostname := parts[0]
algorithm := parts[1]
if algorithm != "SHA-512" {
continue
}
fingerprint := parts[2]
expires, err := strconv.ParseInt(parts[3], 10, 0)
if err != nil {
continue
}
k.hosts[hostname] = certInfo{
Algorithm: algorithm,
Fingerprint: fingerprint,
Expires: expires,
}
}
}
// Write writes the known hosts to the provided io.Writer.
func (k *KnownHosts) Write(w io.Writer) {
for h, c := range k.hosts {
appendKnownHost(w, h, c)
}
}
type certInfo struct {
Algorithm string // fingerprint algorithm e.g. SHA-512
Fingerprint string // fingerprint in hexadecimal, with ':' between each octet
Expires int64 // unix time of certificate notAfter date
}
func appendKnownHost(w io.Writer, hostname string, c certInfo) (int, error) {
return fmt.Fprintf(w, "%s %s %s %d\n", hostname, c.Algorithm, c.Fingerprint, c.Expires)
}
// Fingerprint returns the SHA-512 fingerprint of the provided certificate.
func Fingerprint(cert *x509.Certificate) string {
sum512 := sha512.Sum512(cert.Raw)
var b strings.Builder
for i, f := range sum512 {
if i > 0 {
b.WriteByte(':')
}
fmt.Fprintf(&b, "%02X", f)
}
return b.String()
}
// defaultKnownHostsPath returns the default known_hosts path.
// The default path is $XDG_DATA_HOME/gemini/known_hosts
func defaultKnownHostsPath() (string, error) {
dataDir, err := userDataDir()
if err != nil {
return "", err
}
return filepath.Join(dataDir, "gemini", "known_hosts"), nil
}
// userDataDir returns the user data directory.
func userDataDir() (string, error) {
dataDir, ok := os.LookupEnv("XDG_DATA_HOME")
if ok {
return dataDir, nil
}
home, err := os.UserHomeDir()
if err != nil {
return "", err
}
return filepath.Join(home, ".local", "share"), nil
}