Add method to check if hostname is found in KnownHosts

README.md

@@ -33,7 +33,8 @@ A quick overview of the Gemini protocol:
 The way this is implemented in this package is like so:
 
 1. Client makes a request with `NewRequest`. The client then sends the request
-	with `Send(*Request) (*Response, error)`.
+	with `Send(*Request) (*Response, error)`. The client can optionally verify
+	the server certificates with `VerifyCertificate(*x509.Certificate, *Request)`
 2. Server recieves the request and constructs a response.
 	The server calls the `Serve(*ResponseWriter, *Request)` method on the
 	`Handler` field. The handler writes the response. The server then closes

client.go

@@ -166,7 +166,7 @@ func (resp *Response) read(r *bufio.Reader) error {
 type Client struct {
 	// VerifyCertificate, if not nil, will be called to verify the server certificate.
 	// If error is not nil, the connection will be aborted.
-	VerifyCertificate func(cert *x509.Certificate) error
+	VerifyCertificate func(cert *x509.Certificate, req *Request) error
 }
 
 // Send sends a Gemini request and returns a Gemini response.
@@ -180,7 +180,7 @@ func (c *Client) Send(req *Request) (*Response, error) {
 			if err != nil {
 				return err
 			}
-			return c.VerifyCertificate(cert)
+			return c.VerifyCertificate(cert, req)
 		},
 	}
 	conn, err := tls.Dial("tcp", req.Host, config)

examples/client/client.go

@@ -15,10 +15,7 @@ import (
 
 var (
 	client = &gemini.Client{
-		VerifyCertificate: func(cert *x509.Certificate) error {
-			// if gemini.Fingerprint(cert) != expected {
-			// 	return errors.New("invalid server certificate")
-			// }
+		VerifyCertificate: func(cert *x509.Certificate, req *gemini.Request) error {
 			return nil
 		},
 	}

tofu.go

@@ -10,6 +10,7 @@ import (
 	"io"
 	"strconv"
 	"strings"
+	"time"
 )
 
 // Errors.
@@ -17,16 +18,31 @@ var (
 	ErrInvalidKnownHosts = errors.New("gemini: invalid known hosts")
 )
 
+// KnownHosts represents a list of known hosts.
+type KnownHosts []KnownHost
+
+// Has reports whether the given hostname and certificate are in the list.
+func (k KnownHosts) Has(hostname string, cert *x509.Certificate) bool {
+	now := time.Now().Unix()
+	fingerprint := Fingerprint(cert)
+	for i := range k {
+		if k[i].Expires < now && k[i].Hostname == hostname && k[i].Fingerprint == fingerprint {
+			return true
+		}
+	}
+	return false
+}
+
 // KnownHost represents a known host.
 type KnownHost struct {
 	Hostname    string // e.g. gemini.circumlunar.space
-	Algorithm   string // fingerprint algorithm
+	Algorithm   string // fingerprint algorithm e.g. SHA-512
 	Fingerprint string // fingerprint in hexadecimal, with ':' between each octet
-	NotAfter    int64  // unix time of certificate notAfter date
+	Expires     int64  // unix time of certificate notAfter date
 }
 
 // ParseKnownHosts parses and returns a list of known hosts from the provided io.Reader.
-func ParseKnownHosts(r io.Reader) ([]KnownHost, error) {
+func ParseKnownHosts(r io.Reader) (KnownHosts, error) {
 	hosts := []KnownHost{}
 
 	scanner := bufio.NewScanner(r)
@@ -41,7 +57,7 @@ func ParseKnownHosts(r io.Reader) ([]KnownHost, error) {
 		hostname := parts[0]
 		algorithm := parts[1]
 		fingerprint := parts[2]
-		notAfter, err := strconv.ParseInt(parts[3], 10, 0)
+		expires, err := strconv.ParseInt(parts[3], 10, 0)
 		if err != nil {
 			return nil, ErrInvalidKnownHosts
 		}
@@ -50,13 +66,18 @@ func ParseKnownHosts(r io.Reader) ([]KnownHost, error) {
 			Hostname:    hostname,
 			Algorithm:   algorithm,
 			Fingerprint: fingerprint,
-			NotAfter:    notAfter,
+			Expires:     expires,
 		})
 	}
 
 	return hosts, nil
 }
 
+// AppendKnownHost appends the host to the provided io.Writer.
+func AppendKnownHost(host KnownHost, w io.Writer) error {
+	return nil
+}
+
 // Fingerprint returns the SHA-512 fingerprint of the provided certificate.
 func Fingerprint(cert *x509.Certificate) string {
 	sum512 := sha512.Sum512(cert.Raw)