From 79e0296bed62dad1399e888112ea5c6bd1d8c6bd Mon Sep 17 00:00:00 2001
From: Adnan Maolood <me@adnano.co>
Date: Tue, 9 Feb 2021 15:59:45 -0500
Subject: [PATCH] client: Support IDNs

Convert IDNs to punycode before performing DNS lookups.
---
 client.go   | 37 ++++++++++++++++++-------------------
 go.mod      |  2 ++
 go.sum      |  7 +++++++
 punycode.go | 27 +++++++++++++++++++++++++++
 4 files changed, 54 insertions(+), 19 deletions(-)
 create mode 100644 go.sum
 create mode 100644 punycode.go

diff --git a/client.go b/client.go
index 0c92e1d..820e4c3 100644
--- a/client.go
+++ b/client.go
@@ -8,7 +8,6 @@ import (
 	"errors"
 	"fmt"
 	"net"
-	"strings"
 	"time"
 )
 
@@ -44,11 +43,14 @@ func (c *Client) Get(url string) (*Response, error) {
 // Do performs a Gemini request and returns a Gemini response.
 func (c *Client) Do(req *Request) (*Response, error) {
 	// Extract hostname
-	colonPos := strings.LastIndex(req.Host, ":")
-	if colonPos == -1 {
-		colonPos = len(req.Host)
+	hostname, port, err := net.SplitHostPort(req.Host)
+	if err != nil {
+		return nil, err
+	}
+	punycode, err := punycodeHostname(hostname)
+	if err != nil {
+		return nil, err
 	}
-	hostname := req.Host[:colonPos]
 
 	// Connect to the host
 	config := &tls.Config{
@@ -61,11 +63,11 @@ func (c *Client) Do(req *Request) (*Response, error) {
 			return &tls.Certificate{}, nil
 		},
 		VerifyConnection: func(cs tls.ConnectionState) error {
-			return c.verifyConnection(req, cs)
+			return c.verifyConnection(hostname, punycode, cs)
 		},
-		ServerName: hostname,
+		ServerName: punycode,
 	}
-	// Set connection context
+
 	ctx := req.Context
 	if ctx == nil {
 		ctx = context.Background()
@@ -76,7 +78,8 @@ func (c *Client) Do(req *Request) (*Response, error) {
 		Timeout: c.Timeout,
 	}
 
-	netConn, err := dialer.DialContext(ctx, "tcp", req.Host)
+	address := net.JoinHostPort(punycode, port)
+	netConn, err := dialer.DialContext(ctx, "tcp", address)
 	if err != nil {
 		return nil, err
 	}
@@ -129,17 +132,13 @@ func (c *Client) do(conn *tls.Conn, req *Request) (*Response, error) {
 	return resp, nil
 }
 
-func (c *Client) verifyConnection(req *Request, cs tls.ConnectionState) error {
-	// Verify the hostname
-	var hostname string
-	if host, _, err := net.SplitHostPort(req.Host); err == nil {
-		hostname = host
-	} else {
-		hostname = req.Host
-	}
+func (c *Client) verifyConnection(hostname, punycode string, cs tls.ConnectionState) error {
 	cert := cs.PeerCertificates[0]
-	if err := verifyHostname(cert, hostname); err != nil {
-		return err
+	// Try punycode and then hostname
+	if err := verifyHostname(cert, punycode); err != nil {
+		if err := verifyHostname(cert, hostname); err != nil {
+			return err
+		}
 	}
 	// Check expiration date
 	if !time.Now().Before(cert.NotAfter) {
diff --git a/go.mod b/go.mod
index f850117..2eb6847 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,5 @@
 module git.sr.ht/~adnano/go-gemini
 
 go 1.15
+
+require golang.org/x/net v0.0.0-20210119194325-5f4716e94777
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..c512294
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,7 @@
+golang.org/x/net v0.0.0-20210119194325-5f4716e94777 h1:003p0dJM77cxMSyCPFphvZf/Y5/NXf5fzg6ufd1/Oew=
+golang.org/x/net v0.0.0-20210119194325-5f4716e94777/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
+golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
+golang.org/x/text v0.3.3 h1:cokOdA+Jmi5PJGXLlLllQSgYigAEfHXJAERHVMaCc2k=
+golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
+golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
diff --git a/punycode.go b/punycode.go
new file mode 100644
index 0000000..565790c
--- /dev/null
+++ b/punycode.go
@@ -0,0 +1,27 @@
+package gemini
+
+import (
+	"net"
+	"unicode/utf8"
+
+	"golang.org/x/net/idna"
+)
+
+func isASCII(s string) bool {
+	for i := 0; i < len(s); i++ {
+		if s[i] >= utf8.RuneSelf {
+			return false
+		}
+	}
+	return true
+}
+
+func punycodeHostname(hostname string) (string, error) {
+	if net.ParseIP(hostname) != nil {
+		return hostname, nil
+	}
+	if isASCII(hostname) {
+		return hostname, nil
+	}
+	return idna.Lookup.ToASCII(hostname)
+}