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