net: defer file.close() + minor style cleanup

Moved the relevant file.close() usages close to after the
file opens and put them in defer statements, so that readers
don't have to think too much as to where the file is
being closed.

Change-Id: Ic4190b02ea2f5ac281b9ba104e0023e9f87ca8c7
Reviewed-on: https://go-review.googlesource.com/41796Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/ipsock_plan9.go

@@ -28,6 +28,7 @@ func probe(filename, query string) bool {
 	if file, err = open(filename); err != nil {
 		return false
 	}
+	defer file.close()
 
 	r := false
 	for line, ok := file.readLine(); ok && !r; line, ok = file.readLine() {
@@ -42,7 +43,6 @@ func probe(filename, query string) bool {
 			}
 		}
 	}
-	file.close()
 	return r
 }
 

src/net/lookup_unix.go

@@ -16,28 +16,31 @@ var onceReadProtocols sync.Once
 // readProtocols loads contents of /etc/protocols into protocols map
 // for quick access.
 func readProtocols() {
-	if file, err := open("/etc/protocols"); err == nil {
-		for line, ok := file.readLine(); ok; line, ok = file.readLine() {
-			// tcp    6   TCP    # transmission control protocol
-			if i := byteIndex(line, '#'); i >= 0 {
-				line = line[0:i]
-			}
-			f := getFields(line)
-			if len(f) < 2 {
-				continue
+	file, err := open("/etc/protocols")
+	if err != nil {
+		return
+	}
+	defer file.close()
+
+	for line, ok := file.readLine(); ok; line, ok = file.readLine() {
+		// tcp    6   TCP    # transmission control protocol
+		if i := byteIndex(line, '#'); i >= 0 {
+			line = line[0:i]
+		}
+		f := getFields(line)
+		if len(f) < 2 {
+			continue
+		}
+		if proto, _, ok := dtoi(f[1]); ok {
+			if _, ok := protocols[f[0]]; !ok {
+				protocols[f[0]] = proto
 			}
-			if proto, _, ok := dtoi(f[1]); ok {
-				if _, ok := protocols[f[0]]; !ok {
-					protocols[f[0]] = proto
-				}
-				for _, alias := range f[2:] {
-					if _, ok := protocols[alias]; !ok {
-						protocols[alias] = proto
-					}
+			for _, alias := range f[2:] {
+				if _, ok := protocols[alias]; !ok {
+					protocols[alias] = proto
 				}
 			}
 		}
-		file.close()
 	}
 }
 

src/net/port_unix.go

@@ -17,6 +17,8 @@ func readServices() {
 	if err != nil {
 		return
 	}
+	defer file.close()
+
 	for line, ok := file.readLine(); ok; line, ok = file.readLine() {
 		// "http 80/tcp www www-http # World Wide Web HTTP"
 		if i := byteIndex(line, '#'); i >= 0 {
@@ -43,7 +45,6 @@ func readServices() {
 			}
 		}
 	}
-	file.close()
 }
 
 // goLookupPort is the native Go implementation of LookupPort.