// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package net
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// parsePort parses service as a decimal integer and returns the
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// corresponding value as port. It is the caller's responsibility to
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// parse service as a non-decimal integer when needsLookup is true.
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//
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// Some system resolvers will return a valid port number when given a number
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// over 65536 (see https://golang.org/issues/11715). Alas, the parser
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// can't bail early on numbers > 65536. Therefore reasonably large/small
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// numbers are parsed in full and rejected if invalid.
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func parsePort(service string) (port int, needsLookup bool) {
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if service == "" {
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// Lock in the legacy behavior that an empty string
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// means port 0. See golang.org/issue/13610.
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return 0, false
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}
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const (
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max = uint32(1<<32 - 1)
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cutoff = uint32(1 << 30)
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)
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neg := false
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if service[0] == '+' {
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service = service[1:]
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} else if service[0] == '-' {
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neg = true
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service = service[1:]
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}
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var n uint32
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for _, d := range service {
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if '0' <= d && d <= '9' {
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d -= '0'
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} else {
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return 0, true
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}
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if n >= cutoff {
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n = max
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break
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}
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n *= 10
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nn := n + uint32(d)
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if nn < n || nn > max {
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n = max
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break
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}
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n = nn
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}
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if !neg && n >= cutoff {
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port = int(cutoff - 1)
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} else if neg && n > cutoff {
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port = int(cutoff)
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} else {
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port = int(n)
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}
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if neg {
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port = -port
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}
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return port, false
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}
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