Cannot use nil for CFType (Go 1.10+)

fixes #40

Cannot use nil for CFType (Go 1.10+), round 2

reducing code changes between Go versions

conversions can occur in older Go versions too

extract eventIDSinceNow constant to other files

Go-version specific files.

reworks #34 which resolves int overflow #31

minimize code differences between Go versions

Work around bizarre bugs in 1.10.3 (not 1.10.4)

golang/go#24161

use C.kCFAllocatorDefault instead of C.CFAllocatorRef(0)

thanks to @havoc-io for the tip

reduce duplication between go 1.10 before/after

thanks to C.kCFAllocatorDefault change

.travis.yml

@@ -4,6 +4,7 @@ os: osx
 go:
   - "stable"
   - "1.10.4"
+  - "1.10.3" # 1.10.3 (and earlier 1.10.x) have unique bugs to work around.
   - "1.9.7"
   - "1.8.7"
 

go_1_10_after.go

@@ -0,0 +1,27 @@
+// +build darwin,go1.10
+
+package fsevents
+
+/*
+#include <CoreServices/CoreServices.h>
+*/
+import "C"
+
+const (
+	nullCFStringRef = C.CFStringRef(0)
+	nullCFUUIDRef   = C.CFUUIDRef(0)
+)
+
+// NOTE: The following code is identical between go_1_10_after and go_1_10_before,
+// however versions of Go 1.10.x prior to 1.10.4 fail to compile when the code utilizing
+// the above constants is in a different file (wrap.go).
+
+// GetDeviceUUID retrieves the UUID required to identify an EventID
+// in the FSEvents database
+func GetDeviceUUID(deviceID int32) string {
+	uuid := C.FSEventsCopyUUIDForDevice(C.dev_t(deviceID))
+	if uuid == nullCFUUIDRef {
+		return ""
+	}
+	return cfStringToGoString(C.CFUUIDCreateString(C.kCFAllocatorDefault, uuid))
+}

go_1_10_before.go

@@ -0,0 +1,25 @@
+// +build darwin,!go1.10
+
+package fsevents
+
+/*
+#include <CoreServices/CoreServices.h>
+*/
+import "C"
+
+var (
+	nullCFStringRef = C.CFStringRef(nil)
+	nullCFUUIDRef   = C.CFUUIDRef(nil)
+)
+
+// NOTE: The following code is identical between go_1_10_after and go_1_10_before.
+
+// GetDeviceUUID retrieves the UUID required to identify an EventID
+// in the FSEvents database
+func GetDeviceUUID(deviceID int32) string {
+	uuid := C.FSEventsCopyUUIDForDevice(C.dev_t(deviceID))
+	if uuid == nullCFUUIDRef {
+		return ""
+	}
+	return cfStringToGoString(C.CFUUIDCreateString(C.kCFAllocatorDefault, uuid))
+}

go_1_9_2_after.go

@@ -0,0 +1,11 @@
+// +build darwin,go1.9.2
+
+package fsevents
+
+/*
+#include <CoreServices/CoreServices.h>
+*/
+import "C"
+
+// eventIDSinceNow is a sentinel to begin watching events "since now".
+const eventIDSinceNow = uint64(C.kFSEventStreamEventIdSinceNow)

go_1_9_2_before.go

@@ -0,0 +1,13 @@
+// +build darwin,!go1.9.2
+
+package fsevents
+
+// Prior to Go 1.9.2, converting C.kFSEventStreamEventIdSinceNow to a uint64
+// results in the error: "constant -1 overflows uint64".
+// Related Go issue: https://github.com/golang/go/issues/21708
+
+// Hardcoding the value here from FSEvents.h:
+//   kFSEventStreamEventIdSinceNow = 0xFFFFFFFFFFFFFFFFULL
+
+// eventIDSinceNow is a sentinel to begin watching events "since now".
+const eventIDSinceNow = uint64(0xFFFFFFFFFFFFFFFF)

wrap.go

@@ -1,4 +1,4 @@
-// +build darwin,go1.10
+// +build darwin
 
 package fsevents
 
@@ -34,9 +34,6 @@ import (
 	"unsafe"
 )
 
-// eventIDSinceNow is a sentinel to begin watching events "since now".
-const eventIDSinceNow = uint64(C.kFSEventStreamEventIdSinceNow)
-
 // LatestEventID returns the most recently generated event ID, system-wide.
 func LatestEventID() uint64 {
 	return uint64(C.FSEventsGetCurrentEventId())
@@ -105,21 +102,11 @@ func GetStreamRefPaths(f FSEventStreamRef) []string {
 	return ss
 }
 
-// GetDeviceUUID retrieves the UUID required to identify an EventID
-// in the FSEvents database
-func GetDeviceUUID(deviceID int32) string {
-	uuid := C.FSEventsCopyUUIDForDevice(C.dev_t(deviceID))
-	if uuid == C.CFUUIDRef(0) {
-		return ""
-	}
-	return cfStringToGoString(C.CFUUIDCreateString(nil, uuid))
-}
-
 func cfStringToGoString(cfs C.CFStringRef) string {
-	if cfs == 0 {
+	if cfs == nullCFStringRef {
 		return ""
 	}
-	cfStr := C.CFStringCreateCopy(nil, cfs)
+	cfStr := copyCFString(cfs)
 	length := C.CFStringGetLength(cfStr)
 	if length == 0 {
 		// short-cut for empty strings
@@ -148,6 +135,11 @@ func cfStringToGoString(cfs C.CFStringRef) string {
 	return *(*string)(unsafe.Pointer(strHeader))
 }
 
+// copyCFString makes an immutable copy of a string with CFStringCreateCopy.
+func copyCFString(cfs C.CFStringRef) C.CFStringRef {
+	return C.CFStringCreateCopy(C.kCFAllocatorDefault, cfs)
+}
+
 // CFRunLoopRef wraps C.CFRunLoopRef
 type CFRunLoopRef C.CFRunLoopRef
 
@@ -169,10 +161,7 @@ func createPaths(paths []string) (C.CFArrayRef, error) {
 			// because of them
 			errs = append(errs, err)
 		}
-		cpath := C.CString(p)
-		defer C.free(unsafe.Pointer(cpath))
-
-		str := C.CFStringCreateWithCString(nil, cpath, C.kCFStringEncodingUTF8)
+		str := makeCFString(p)
 		C.CFArrayAppendValue(C.CFMutableArrayRef(cPaths), unsafe.Pointer(str))
 	}
 	var err error
@@ -182,6 +171,13 @@ func createPaths(paths []string) (C.CFArrayRef, error) {
 	return cPaths, err
 }
 
+// makeCFString makes an immutable string with CFStringCreateWithCString.
+func makeCFString(str string) C.CFStringRef {
+	s := C.CString(str)
+	defer C.free(unsafe.Pointer(s))
+	return C.CFStringCreateWithCString(C.kCFAllocatorDefault, s, C.kCFStringEncodingUTF8)
+}
+
 // CFArrayLen retrieves the length of CFArray type
 // See https://developer.apple.com/library/mac/documentation/CoreFoundation/Reference/CFArrayRef/#//apple_ref/c/func/CFArrayGetCount
 func cfArrayLen(ref C.CFArrayRef) int {