libgo/go/net/port.go

   1 // Copyright 2016 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 package net
   6
   7 // parsePort parses service as a decimal interger and returns the
   8 // corresponding value as port. It is the caller's responsibility to
   9 // parse service as a non-decimal integer when needsLookup is true.
  10 //
  11 // Some system resolvers will return a valid port number when given a number
  12 // over 65536 (see https://github.com/golang/go/issues/11715). Alas, the parser
  13 // can't bail early on numbers > 65536. Therefore reasonably large/small
  14 // numbers are parsed in full and rejected if invalid.
  15 func parsePort(service string) (port int, needsLookup bool) {
  16         if service == "" {
  17                 // Lock in the legacy behavior that an empty string
  18                 // means port 0. See golang.org/issue/13610.
  19                 return 0, false
  20         }
  21         const (
  22                 max    = uint32(1<<32 - 1)
  23                 cutoff = uint32(1 << 30)
  24         )
  25         neg := false
  26         if service[0] == '+' {
  27                 service = service[1:]
  28         } else if service[0] == '-' {
  29                 neg = true
  30                 service = service[1:]
  31         }
  32         var n uint32
  33         for _, d := range service {
  34                 if '0' <= d && d <= '9' {
  35                         d -= '0'
  36                 } else {
  37                         return 0, true
  38                 }
  39                 if n >= cutoff {
  40                         n = max
  41                         break
  42                 }
  43                 n *= 10
  44                 nn := n + uint32(d)
  45                 if nn < n || nn > max {
  46                         n = max
  47                         break
  48                 }
  49                 n = nn
  50         }
  51         if !neg && n >= cutoff {
  52                 port = int(cutoff - 1)
  53         } else if neg && n > cutoff {
  54                 port = int(cutoff)
  55         } else {
  56                 port = int(n)
  57         }
  58         if neg {
  59                 port = -port
  60         }
  61         return port, false
  62 }