go-gemini/client.go
2020-09-26 13:29:29 -04:00

241 lines
5.8 KiB
Go

// Package gemini implements the Gemini protocol.
package gemini
import (
"bufio"
"crypto/tls"
"crypto/x509"
"errors"
"io/ioutil"
"net"
"net/url"
"strconv"
"strings"
)
// Client errors.
var (
ErrProtocol = errors.New("gemini: protocol error")
ErrInvalidURL = errors.New("gemini: requested URL is invalid")
ErrCertificateNotValid = errors.New("gemini: certificate is invalid")
ErrCertificateNotTrusted = errors.New("gemini: certificate is not trusted")
ErrCertificateUnknown = errors.New("gemini: certificate is unknown")
)
// Request represents a Gemini request.
type Request struct {
// URL specifies the URL being requested.
URL *url.URL
// For client requests, Host specifies the host on which the URL is sought.
// This field is ignored by the server.
Host string
// Certificate specifies the TLS certificate to use for the request.
Certificate tls.Certificate
// RemoteAddr allows servers and other software to record the network
// address that sent the request.
// This field is ignored by the client.
RemoteAddr net.Addr
// TLS allows servers and other software to record information about the TLS
// connection on which the request was recieved.
// This field is ignored by the client.
TLS tls.ConnectionState
}
// NewRequest returns a new request. The host is inferred from the provided url.
func NewRequest(rawurl string) (*Request, error) {
u, err := url.Parse(rawurl)
if err != nil {
return nil, err
}
host := u.Host
// If there is no port, use the default port of 1965
if u.Port() == "" {
host += ":1965"
}
return &Request{
Host: host,
URL: u,
}, nil
}
// NewProxyRequest returns a new request using the provided host.
// The provided host must contain a port.
func NewProxyRequest(host, rawurl string) (*Request, error) {
u, err := url.Parse(rawurl)
if err != nil {
return nil, err
}
return &Request{
Host: host,
URL: u,
}, nil
}
// write writes the Gemini request to the provided buffered writer.
func (r *Request) write(w *bufio.Writer) error {
url := r.URL.String()
// User is invalid
if r.URL.User != nil || len(url) > 1024 {
return ErrInvalidURL
}
if _, err := w.WriteString(url); err != nil {
return err
}
if _, err := w.Write(crlf); err != nil {
return err
}
return nil
}
// Response is a Gemini response.
type Response struct {
// Status represents the response status.
Status int
// Meta contains more information related to the response status.
// For successful responses, Meta should contain the mimetype of the response.
// For failure responses, Meta should contain a short description of the failure.
// Meta should not be longer than 1024 bytes.
Meta string
// Body contains the response body.
Body []byte
// TLS contains information about the TLS connection on which the response
// was received.
TLS tls.ConnectionState
}
// read reads a Gemini response from the provided buffered reader.
func (resp *Response) read(r *bufio.Reader) error {
// Read the status
statusB := make([]byte, 2)
if _, err := r.Read(statusB); err != nil {
return err
}
status, err := strconv.Atoi(string(statusB))
if err != nil {
return err
}
resp.Status = status
// Read one space
if b, err := r.ReadByte(); err != nil {
return err
} else if b != ' ' {
return ErrProtocol
}
// Read the meta
meta, err := r.ReadString('\r')
if err != nil {
return err
}
// Trim carriage return
meta = meta[:len(meta)-1]
// Ensure meta is less than or equal to 1024 bytes
if len(meta) > 1024 {
return ErrProtocol
}
resp.Meta = meta
// Read terminating newline
if b, err := r.ReadByte(); err != nil {
return err
} else if b != '\n' {
return ErrProtocol
}
// Read response body
if status/10 == StatusClassSuccess {
var err error
resp.Body, err = ioutil.ReadAll(r)
if err != nil {
return err
}
}
return nil
}
// Client represents a Gemini client.
type Client struct {
// KnownHosts is a list of known hosts that the client trusts.
KnownHosts *KnownHosts
// TrustCertificate, if not nil, will be called to determine whether the
// client should trust the given certificate.
// If error is not nil, the connection will be aborted.
TrustCertificate func(cert *x509.Certificate, knownHosts *KnownHosts) error
}
// Send sends a Gemini request and returns a Gemini response.
func (c *Client) Send(req *Request) (*Response, error) {
// Connect to the host
config := &tls.Config{
InsecureSkipVerify: true,
MinVersion: tls.VersionTLS12,
Certificates: []tls.Certificate{req.Certificate},
VerifyPeerCertificate: func(rawCerts [][]byte, _ [][]*x509.Certificate) error {
// Parse the certificate
cert, err := x509.ParseCertificate(rawCerts[0])
if err != nil {
return err
}
// Check that the certificate is valid for the hostname
if cert.Subject.CommonName != hostname(req.Host) {
return ErrCertificateNotValid
}
// Check that the client trusts the certificate
if c.TrustCertificate == nil {
if c.KnownHosts == nil {
return ErrCertificateNotTrusted
} else if err := c.KnownHosts.Lookup(cert); err != nil {
return err
}
} else if err := c.TrustCertificate(cert, c.KnownHosts); err != nil {
return err
}
return nil
},
}
conn, err := tls.Dial("tcp", req.Host, config)
if err != nil {
return nil, err
}
defer conn.Close()
// Write the request
w := bufio.NewWriter(conn)
req.write(w)
if err := w.Flush(); err != nil {
return nil, err
}
// Read the response
resp := &Response{}
r := bufio.NewReader(conn)
// Store connection information
resp.TLS = conn.ConnectionState()
if err := resp.read(r); err != nil {
return nil, err
}
return resp, nil
}
// hostname extracts the host name from a valid host or host:port
func hostname(host string) string {
i := strings.LastIndexByte(host, ':')
if i != -1 {
return host[:i]
}
return host
}