go-gemini/tofu.go

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package gemini
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import (
"bufio"
"crypto/sha512"
"crypto/x509"
"fmt"
"io"
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"os"
"path/filepath"
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"strings"
)
// 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.
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type KnownHosts struct {
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hosts map[string]Fingerprint
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file *os.File
}
// LoadDefault loads the known hosts from the default known hosts path, which is
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// $XDG_DATA_HOME/gemini/known_hosts.
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// 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 {
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path, err := defaultKnownHostsPath()
if err != nil {
return err
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}
return k.Load(path)
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}
// Load loads the known hosts from the provided path.
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// 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 {
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if dir := filepath.Dir(path); dir != "." {
err := os.MkdirAll(dir, 0755)
if err != nil {
return err
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}
}
f, err := os.OpenFile(path, os.O_CREATE|os.O_RDONLY, 0644)
if err != nil {
return err
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}
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
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}
k.file = f
return nil
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}
// Add adds a certificate to the list of known hosts.
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// 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)
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}
// AddTemporary adds a certificate to the list of known hosts
// without writing it to the known hosts file.
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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 {
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k.hosts = map[string]Fingerprint{}
}
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fingerprint := NewFingerprint(cert)
k.hosts[hostname] = fingerprint
// Append to the file
if write && k.file != nil {
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appendKnownHost(k.file, hostname, fingerprint)
}
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}
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// Lookup returns the fingerprint of the certificate corresponding to
// the given hostname.
func (k *KnownHosts) Lookup(hostname string) (Fingerprint, bool) {
c, ok := k.hosts[hostname]
return c, ok
}
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// Parse parses the provided reader and adds the parsed known hosts to the list.
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// Invalid lines are ignored.
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func (k *KnownHosts) Parse(r io.Reader) {
if k.hosts == nil {
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k.hosts = map[string]Fingerprint{}
}
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scanner := bufio.NewScanner(r)
for scanner.Scan() {
text := scanner.Text()
parts := strings.Split(text, " ")
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if len(parts) < 3 {
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continue
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}
hostname := parts[0]
algorithm := parts[1]
if algorithm != "SHA-512" {
continue
}
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fingerprint := parts[2]
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k.hosts[hostname] = Fingerprint{
Algorithm: algorithm,
Hex: fingerprint,
}
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}
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}
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// 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)
}
}
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func appendKnownHost(w io.Writer, hostname string, f Fingerprint) (int, error) {
return fmt.Fprintf(w, "%s %s %s\n", hostname, f.Algorithm, f.Hex)
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}
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// Fingerprint represents a fingerprint using a certain algorithm.
type Fingerprint struct {
Algorithm string // fingerprint algorithm e.g. SHA-512
Hex string // fingerprint in hexadecimal, with ':' between each octet
}
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// NewFingerprint returns the SHA-512 fingerprint of the provided certificate.
func NewFingerprint(cert *x509.Certificate) Fingerprint {
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sum512 := sha512.Sum512(cert.Raw)
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var b strings.Builder
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for i, f := range sum512 {
if i > 0 {
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b.WriteByte(':')
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}
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fmt.Fprintf(&b, "%02X", f)
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}
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return Fingerprint{
Algorithm: "SHA-512",
Hex: b.String(),
}
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}
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// 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
}