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|
package safehttp
import (
"context"
"crypto/tls"
"fmt"
"net"
"net/http"
"strings"
"time"
)
var (
privateIPBlocks []*net.IPNet
AllowLocal bool // For testing
)
func init() {
for _, cidr := range []string{
"127.0.0.0/8", // IPv4 loopback
"10.0.0.0/8", // RFC1918
"172.16.0.0/12", // RFC1918
"192.168.0.0/16", // RFC1918
"169.254.0.0/16", // IPv4 link-local
"::1/128", // IPv6 loopback
"fe80::/10", // IPv6 link-local
"fc00::/7", // IPv6 unique local addr
} {
_, block, _ := net.ParseCIDR(cidr)
privateIPBlocks = append(privateIPBlocks, block)
}
}
func isPrivateIP(ip net.IP) bool {
if AllowLocal {
return false
}
if ip.IsLoopback() || ip.IsLinkLocalUnicast() || ip.IsLinkLocalMulticast() {
return true
}
for _, block := range privateIPBlocks {
if block.Contains(ip) {
return true
}
}
return false
}
func SafeDialer(dialer *net.Dialer) func(context.Context, string, string) (net.Conn, error) {
return func(ctx context.Context, network, address string) (net.Conn, error) {
host, _, err := net.SplitHostPort(address)
if err != nil {
host = address
}
if ip := net.ParseIP(host); ip != nil {
if isPrivateIP(ip) {
return nil, fmt.Errorf("connection to private IP %s is not allowed", ip)
}
} else {
ips, err := net.DefaultResolver.LookupIP(ctx, "ip", host)
if err != nil {
return nil, err
}
for _, ip := range ips {
if isPrivateIP(ip) {
return nil, fmt.Errorf("connection to private IP %s is not allowed", ip)
}
}
}
return dialer.DialContext(ctx, network, address)
}
}
func NewSafeClient(timeout time.Duration) *http.Client {
dialer := &net.Dialer{
Timeout: 30 * time.Second,
KeepAlive: 30 * time.Second,
}
transport := http.DefaultTransport.(*http.Transport).Clone()
transport.DialContext = SafeDialer(dialer)
transport.Proxy = nil // Disable proxy to ensure SSRF checks are not bypassed
return &http.Client{
Timeout: timeout,
Transport: &H2FallbackTransport{Transport: transport},
CheckRedirect: func(req *http.Request, via []*http.Request) error {
if len(via) >= 10 {
return fmt.Errorf("too many redirects")
}
host, _, err := net.SplitHostPort(req.URL.Host)
if err != nil {
host = req.URL.Host
}
if ip := net.ParseIP(host); ip != nil {
if isPrivateIP(ip) {
return fmt.Errorf("redirect to private IP %s is not allowed", ip)
}
} else {
ips, err := net.DefaultResolver.LookupIP(req.Context(), "ip", host)
if err != nil {
return err
}
for _, ip := range ips {
if isPrivateIP(ip) {
return fmt.Errorf("redirect to private IP %s is not allowed", ip)
}
}
}
return nil
},
}
}
// H2FallbackTransport wraps an *http.Transport and retries failed requests with HTTP/1.1
// if an HTTP/2 protocol error is detected. This is useful for crawling external feeds
// where some servers may have buggy HTTP/2 implementations.
type H2FallbackTransport struct {
Transport *http.Transport
}
func (t *H2FallbackTransport) RoundTrip(req *http.Request) (*http.Response, error) {
resp, err := t.Transport.RoundTrip(req)
if err != nil && isHTTP2Error(err) && (req.Method == "GET" || req.Method == "HEAD" || req.Body == nil) {
// Clone the transport and disable HTTP/2 for the retry
h1Transport := t.Transport.Clone()
h1Transport.TLSNextProto = make(map[string]func(string, *tls.Conn) http.RoundTripper)
h1Transport.ForceAttemptHTTP2 = false
return h1Transport.RoundTrip(req)
}
return resp, err
}
func isHTTP2Error(err error) bool {
if err == nil {
return false
}
msg := strings.ToLower(err.Error())
return strings.Contains(msg, "http2") ||
strings.Contains(msg, "stream error") ||
strings.Contains(msg, "goaway") ||
strings.Contains(msg, "protocol")
}
|
