Refactor client.TrustCertificate workflow

cert.go

@@ -16,7 +16,7 @@ import (
 	"time"
 )
 
-// CertificateStore maps hostnames to certificates.
+// CertificateStore maps certificate scopes to certificates.
 // The zero value of CertificateStore is an empty store ready to use.
 type CertificateStore struct {
 	store map[string]tls.Certificate

client.go

@@ -43,12 +43,10 @@ type Client struct {
 	// the request will not be sent again and the response will be returned.
 	CreateCertificate func(hostname, path string) (tls.Certificate, error)
 
-	// TrustCertificate determines whether the client should trust
+	// TrustCertificate is called to determine whether the client
-	// the provided certificate.
+	// should trust a certificate it has not seen before.
-	// If the returned error is not nil, the connection will be aborted.
+	// If TrustCertificate is nil, the certificate will not be trusted.
-	// If TrustCertificate is nil, the client will check KnownHosts
+	TrustCertificate func(hostname string, cert *x509.Certificate) Trust
-	// for the certificate.
-	TrustCertificate func(hostname string, cert *x509.Certificate, knownHosts *KnownHosts) error
 }
 
 // Get performs a Gemini request for the given url.
@@ -198,10 +196,25 @@ func (c *Client) verifyConnection(req *Request, cs tls.ConnectionState) error {
 	if err := verifyHostname(cert, hostname); err != nil {
 		return err
 	}
-	// Check that the client trusts the certificate
+	// Check the known hosts
-	var err error
+	err := c.KnownHosts.Lookup(hostname, cert)
+	switch err {
+	case ErrCertificateExpired, ErrCertificateNotFound:
+	default:
+		return err
+	}
+	// See if the client trusts the certificate
 	if c.TrustCertificate != nil {
-		return c.TrustCertificate(hostname, cert, &c.KnownHosts)
+		switch c.TrustCertificate(hostname, cert) {
+		case TrustOnce:
+			c.KnownHosts.AddTemporary(hostname, cert)
+			return nil
+		case TrustAlways:
+			c.KnownHosts.Add(hostname, cert)
+			return nil
+		default:
+			return ErrCertificateNotTrusted
+		}
 	} else {
 		err = c.KnownHosts.Lookup(hostname, cert)
 	}

examples/client.go

@@ -8,12 +8,22 @@ import (
 	"crypto/x509"
 	"fmt"
 	"io/ioutil"
+	"log"
 	"os"
 	"time"
 
 	"git.sr.ht/~adnano/go-gemini"
 )
 
+const trustPrompt = `The certificate offered by %s is of unknown trust. Its fingerprint is:
+%s
+
+If you knew the fingerprint to expect in advance, verify that this matches.
+Otherwise, this should be safe to trust.
+
+[t]rust always; trust [o]nce; [a]bort
+=> `
+
 var (
 	scanner = bufio.NewScanner(os.Stdin)
 	client  = &gemini.Client{}