port.go

Documentation: net

		 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 integer 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://golang.org/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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