Added wrapper around goselect library.

This simplifies handling of select syscall.

unixutils/select.go

@@ -0,0 +1,101 @@
+//
+// Copyright 2014-2016 Cristian Maglie. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+//
+
+// +build linux darwin freebsd
+
+package unixutils // "go.bug.st/serial.v1/unixutils"
+
+import (
+	"time"
+
+	"github.com/creack/goselect"
+)
+
+// FDSet is a set of file descriptors suitable for a select call
+type FDSet struct {
+	set goselect.FDSet
+	max uintptr
+}
+
+// NewFDSet creates a set of file descriptors suitable for a Select call.
+func NewFDSet(fds ...int) *FDSet {
+	s := &FDSet{}
+	s.Add(fds...)
+	return s
+}
+
+// Add adds the file descriptors passed as parameter to the FDSet.
+func (s *FDSet) Add(fds ...int) {
+	for _, fd := range fds {
+		f := uintptr(fd)
+		s.set.Set(f)
+		if f > s.max {
+			s.max = f
+		}
+	}
+}
+
+// FDResultSets contains the result of a Select operation.
+type FDResultSets struct {
+	readable  *goselect.FDSet
+	writeable *goselect.FDSet
+	errors    *goselect.FDSet
+}
+
+// IsReadable test if a file descriptor is ready to be read.
+func (r *FDResultSets) IsReadable(fd int) bool {
+	return r.readable.IsSet(uintptr(fd))
+}
+
+// IsWritable test if a file descriptor is ready to be written.
+func (r *FDResultSets) IsWritable(fd int) bool {
+	return r.writeable.IsSet(uintptr(fd))
+}
+
+// IsError test if a file descriptor is in error state.
+func (r *FDResultSets) IsError(fd int) bool {
+	return r.errors.IsSet(uintptr(fd))
+}
+
+// Select performs a select system call,
+// file descriptors in the rd set are tested for read-events,
+// file descriptors in the wd set are tested for write-events and
+// file descriptors in the er set are tested for error-events.
+// The function will block until an event happens or the timeout expires.
+// The function return an FDResultSets that contains all the file descriptor
+// that have a pending read/write/error event.
+func Select(rd, wr, er *FDSet, timeout time.Duration) (*FDResultSets, error) {
+	max := uintptr(0)
+	res := &FDResultSets{}
+	if rd != nil {
+		// fdsets are copied so the parameters are left untouched
+		copyOfRd := rd.set
+		res.readable = &copyOfRd
+		// Determine max fd.
+		max = rd.max
+	}
+	if wr != nil {
+		// fdsets are copied so the parameters are left untouched
+		copyOfWr := wr.set
+		res.writeable = &copyOfWr
+		// Determine max fd.
+		if wr.max > max {
+			max = wr.max
+		}
+	}
+	if er != nil {
+		// fdsets are copied so the parameters are left untouched
+		copyOfEr := er.set
+		res.errors = &copyOfEr
+		// Determine max fd.
+		if er.max > max {
+			max = er.max
+		}
+	}
+
+	err := goselect.Select(int(max+1), res.readable, res.writeable, res.errors, timeout)
+	return res, err
+}