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Source file src/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	}
    63	

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