1 files changed, 62 insertions, 0 deletions
diff --git a/src/net/port.go b/src/net/port.go
new file mode 100644
index 0000000..32e7628
--- /dev/null
+++ b/src/net/port.go
@@ -0,0 +1,62 @@
+// 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
+}