Fix compilation for old versions of go

.travis.yml

@@ -2,13 +2,14 @@ language: go
 
 go:
   - 1.3
+  - 1.5
   - tip
 
 before_install:
   - go get -t -v ./...
 
 script:
-  - go test -coverprofile=coverage.txt -covermode=atomic
+  - go test -v -coverprofile=coverage.txt -covermode=atomic
 
 after_success:
   - bash <(curl -s https://codecov.io/bash)

compilation_test.go

@@ -0,0 +1,80 @@
+package daemon
+
+import (
+	"os"
+	"os/exec"
+	"runtime"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+func TestCompilation(t *testing.T) {
+	if testing.Short() {
+		t.Skip("short mode")
+	}
+	if !requireMinor(5) {
+		t.Skip(runtime.Version(), "cross-compilation requires compiler bootstrapping")
+	}
+
+	pairs := []string{
+		"darwin/386",
+		"darwin/amd64",
+		"dragonfly/amd64",
+		"freebsd/386",
+		"freebsd/amd64",
+		"freebsd/arm",
+		"linux/386",
+		"linux/amd64",
+		"linux/arm",
+		"linux/arm64",
+		"netbsd/386",
+		"netbsd/amd64",
+		"netbsd/arm",
+		"openbsd/386",
+		"openbsd/amd64",
+		"openbsd/arm",
+		"solaris/amd64",
+		"windows/386",
+		"windows/amd64",
+
+		// TODO(yar): support plan9
+		//"plan9/386",
+		//"plan9/amd64",
+		//"plan9/arm",
+	}
+
+	env := os.Environ()
+	for i := range pairs {
+		p := pairs[i]
+		pair := strings.Split(p, "/")
+		goos, goarch := pair[0], pair[1]
+		if goos == "solaris" && !requireMinor(7) {
+			t.Log("skip, solaris requires at least go1.7")
+			continue
+		}
+		cmd := exec.Command("go", "build", "./")
+		env := append([]string(nil), env...)
+		cmd.Env = append(env, "GOOS="+goos, "GOARCH="+goarch)
+		out, err := cmd.CombinedOutput()
+		if len(out) > 0 {
+			t.Log(p, "\n", string(out))
+		}
+		if err != nil {
+			t.Error(p, err)
+		}
+	}
+}
+
+func requireMinor(minor int) bool {
+	str := runtime.Version()
+	if !strings.HasPrefix(str, "go1.") {
+		return true
+	}
+	str = strings.TrimPrefix(str, "go1.")
+	ver, err := strconv.Atoi(str)
+	if err != nil {
+		return false
+	}
+	return ver >= minor
+}

syscall_dup.go

@@ -1,5 +1,6 @@
 // +build !linux !arm64
 // +build !windows
+// +build go1.7
 
 package daemon
 

syscall_dup_pre17.go

@@ -0,0 +1,13 @@
+// +build !linux !arm64
+// +build !windows
+// +build !go1.7
+
+package daemon
+
+import (
+	"syscall"
+)
+
+func syscallDup(oldfd int, newfd int) (err error) {
+	return syscall.Dup2(oldfd, newfd)
+}