validhostname.go

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// This file contains code adapted from golang's crypto/x509/verify.go

package tlscommon

import (
	"strings"
	"unicode/utf8"
)

func matchHostnames(pattern, host string) bool {
	pattern = toLowerCaseASCII(pattern)
	host = toLowerCaseASCII(strings.TrimSuffix(host, "."))

	if len(pattern) == 0 || len(host) == 0 {
		return false
	}

	patternParts := strings.Split(pattern, ".")
	hostParts := strings.Split(host, ".")

	if len(patternParts) != len(hostParts) {
		return false
	}

	for i, patternPart := range patternParts {
		if i == 0 && patternPart == "*" {
			continue
		}
		if patternPart != hostParts[i] {
			return false
		}
	}

	return true
}

// toLowerCaseASCII returns a lower-case version of in. See RFC 6125 6.4.1. We use
// an explicitly ASCII function to avoid any sharp corners resulting from
// performing Unicode operations on DNS labels.
func toLowerCaseASCII(in string) string {
	// If the string is already lower-case then there's nothing to do.
	isAlreadyLowerCase := true
	for _, c := range in {
		if c == utf8.RuneError {
			// If we get a UTF-8 error then there might be
			// upper-case ASCII bytes in the invalid sequence.
			isAlreadyLowerCase = false
			break
		}
		if 'A' <= c && c <= 'Z' {
			isAlreadyLowerCase = false
			break
		}
	}

	if isAlreadyLowerCase {
		return in
	}

	out := []byte(in)
	for i, c := range out {
		if 'A' <= c && c <= 'Z' {
			out[i] += 'a' - 'A'
		}
	}
	return string(out)
}

// validHostname reports whether host is a valid hostname that can be matched or
// matched against according to RFC 6125 2.2, with some leniency to accommodate
// legacy values.
func validHostname(host string, isPattern bool) bool {
	if !isPattern {
		host = strings.TrimSuffix(host, ".")
	}
	if len(host) == 0 {
		return false
	}

	for i, part := range strings.Split(host, ".") {
		if part == "" {
			// Empty label.
			return false
		}
		if isPattern && i == 0 && part == "*" {
			// Only allow full left-most wildcards, as those are the only ones
			// we match, and matching literal '*' characters is probably never
			// the expected behavior.
			continue
		}
		for j, c := range part {
			if 'a' <= c && c <= 'z' {
				continue
			}
			if '0' <= c && c <= '9' {
				continue
			}
			if 'A' <= c && c <= 'Z' {
				continue
			}
			if c == '-' && j != 0 {
				continue
			}
			if c == '_' {
				// Not a valid character in hostnames, but commonly
				// found in deployments outside the WebPKI.
				continue
			}
			return false
		}
	}

	return true
}