gitea.tea/modules/utils/ssh_host.go

// Copyright 2026 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package utils

import (
	"fmt"
	"net"
	"net/url"
	"strconv"
	"strings"
)

// NormalizeSSHHost validates an SSH host setting and returns it trimmed.
// The accepted format is host or host:port. IPv6 addresses must be bracketed.
func NormalizeSSHHost(raw string) (string, error) {
	sshHost := strings.TrimSpace(raw)
	if sshHost == "" {
		return "", nil
	}

	if strings.ContainsAny(sshHost, "/\\") {
		return "", fmt.Errorf("invalid SSH host %q: use host or host:port, not a URL or path", raw)
	}
	if strings.ContainsAny(sshHost, " \t\r\n") {
		return "", fmt.Errorf("invalid SSH host %q: whitespace is not allowed", raw)
	}
	if strings.Contains(sshHost, "@") {
		return "", fmt.Errorf("invalid SSH host %q: use host or host:port without a user", raw)
	}

	host := sshHost
	port := ""
	colonCount := strings.Count(sshHost, ":")
	portSpecified := false

	switch {
	case strings.HasPrefix(sshHost, "["):
		if strings.Contains(sshHost, "]:") {
			portSpecified = true
			var err error
			host, port, err = net.SplitHostPort(sshHost)
			if err != nil {
				return "", fmt.Errorf("invalid SSH host %q: %w", raw, err)
			}
		} else if strings.HasSuffix(sshHost, "]") {
			host = strings.TrimSuffix(strings.TrimPrefix(sshHost, "["), "]")
		} else {
			return "", fmt.Errorf("invalid SSH host %q: malformed IPv6 address", raw)
		}
	case colonCount == 1:
		portSpecified = true
		parts := strings.SplitN(sshHost, ":", 2)
		host = parts[0]
		port = parts[1]
	case colonCount > 1:
		return "", fmt.Errorf("invalid SSH host %q: IPv6 addresses must be bracketed", raw)
	}

	if host == "" {
		return "", fmt.Errorf("invalid SSH host %q: host is required", raw)
	}
	if portSpecified {
		if port == "" {
			return "", fmt.Errorf("invalid SSH host %q: port is required", raw)
		}
		portNumber, err := strconv.Atoi(port)
		if err != nil || portNumber < 1 || portNumber > 65535 {
			return "", fmt.Errorf("invalid SSH host %q: port must be between 1 and 65535", raw)
		}
	}

	return sshHost, nil
}

// ResolveSSHHost returns the explicit SSH host when provided, otherwise the
// hostname from the Gitea server URL.
func ResolveSSHHost(serverURL *url.URL, explicitSSHHost string) (string, error) {
	sshHost, err := NormalizeSSHHost(explicitSSHHost)
	if err != nil {
		return "", err
	}
	if sshHost != "" {
		return sshHost, nil
	}
	if serverURL == nil {
		return "", nil
	}
	return serverURL.Hostname(), nil
}