errutil: common error handling functions

Signed-off-by: John Mulligan <jmulligan@redhat.com>

errutil/strerror.go

@@ -0,0 +1,41 @@
+package errutil
+
+/* force XSI-complaint strerror_r() */
+
+// #define _POSIX_C_SOURCE 200112L
+// #undef _GNU_SOURCE
+// #include <stdlib.h>
+// #include <errno.h>
+// #include <string.h>
+import "C"
+
+import (
+	"unsafe"
+)
+
+// FormatErrno returns the absolute value of the errno as well as a string
+// describing the errno. The string will be empty is the errno is not known.
+func FormatErrno(errno int) (int, string) {
+	buf := make([]byte, 1024)
+	// strerror expects errno >= 0
+	if errno < 0 {
+		errno = -errno
+	}
+
+	ret := C.strerror_r(
+		C.int(errno),
+		(*C.char)(unsafe.Pointer(&buf[0])),
+		C.size_t(len(buf)))
+	if ret != 0 {
+		return errno, ""
+	}
+
+	return errno, C.GoString((*C.char)(unsafe.Pointer(&buf[0])))
+}
+
+// StrError returns a string describing the errno. The string will be empty if
+// the errno is not known.
+func StrError(errno int) string {
+	_, s := FormatErrno(errno)
+	return s
+}

errutil/strerror_test.go

@@ -0,0 +1,32 @@
+package errutil
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFormatError(t *testing.T) {
+	e, msg := FormatErrno(39)
+	assert.Equal(t, 39, e)
+	assert.Equal(t, msg, "Directory not empty")
+
+	e, msg = FormatErrno(-5)
+	assert.Equal(t, 5, e)
+	assert.Equal(t, msg, "Input/output error")
+
+	e, msg = FormatErrno(345)
+	assert.Equal(t, 345, e)
+	assert.Equal(t, msg, "")
+}
+
+func TestStrError(t *testing.T) {
+	msg := StrError(39)
+	assert.Equal(t, msg, "Directory not empty")
+
+	msg = StrError(-5)
+	assert.Equal(t, msg, "Input/output error")
+
+	msg = StrError(345)
+	assert.Equal(t, msg, "")
+}