change implementation of log callbacks to work in go 1.6

Change-Id: I443f01419608e9b1dd88bc0593855ed1d812f148
Reviewed-on: http://review.couchbase.org/60992
Reviewed-by: Steve Yen <steve.yen@gmail.com>
Tested-by: Marty Schoch <marty.schoch@gmail.com>

forestdb.go

@@ -11,6 +11,7 @@ package forestdb
 
 //#include <stdlib.h>
 //#include <libforestdb/forestdb.h>
+//#include "log.h"
 //extern void LogCallbackInternal(int, char*, char*);
 //void log_callback(int errcode, char *msg, void *ctx) {
 //    LogCallbackInternal(errcode, msg, ctx);
@@ -169,12 +170,20 @@ type logContext struct {
 	userCtx  interface{}
 }
 
+// Hold references to log callbacks and contexts.
+var logCallbacks []LogCallback
+var logContexts []interface{}
+
+func registerLogCallback(cb LogCallback, ctx interface{}) int {
+	logCallbacks = append(logCallbacks, cb)
+	logContexts = append(logContexts, ctx)
+	return len(logCallbacks) - 1
+}
+
 func (k *KVStore) SetLogCallback(l LogCallback, userCtx interface{}) {
-	ctx := logContext{
-		callback: &l,
-		name:     k.name,
-		userCtx:  userCtx,
-	}
+	var ctx C.log_context
+	ctx.offset = C.int(registerLogCallback(l, userCtx))
+	ctx.name = C.CString(k.name)
 	C.fdb_set_log_callback(k.db, C.fdb_log_callback(C.log_callback), unsafe.Pointer(&ctx))
 }
 

log.go

@@ -1,5 +1,6 @@
 package forestdb
 
+//#include "log.h"
 import "C"
 import (
 	"log"
@@ -8,8 +9,10 @@ import (
 
 //export LogCallbackInternal
 func LogCallbackInternal(errCode C.int, msg *C.char, ctx *C.char) {
-	context := (*logContext)(unsafe.Pointer(ctx))
-	(*context.callback)(context.name, int(errCode), C.GoString(msg), context.userCtx)
+	context := (*C.log_context)(unsafe.Pointer(ctx))
+	cb := logCallbacks[context.offset]
+	userCtx := logContexts[context.offset]
+	cb(C.GoString(context.name), int(errCode), C.GoString(msg), userCtx)
 }
 
 //export FatalErrorCallbackInternal

log.h

@@ -0,0 +1,5 @@
+struct log_context {
+   int offset;
+   char *name;
+};
+typedef struct log_context log_context;

log_test.go

@@ -57,8 +57,15 @@ func TestLogCallback(t *testing.T) {
 		if errCode != -10 {
 			t.Errorf("expected error code -10, got %d", errCode)
 		}
+		if ctx, ok := ctx.(map[string]interface{}); ok {
+			if ctx["customKey"] != "customVal" {
+				t.Errorf("expected to see my custom context")
+			}
+		} else {
+			t.Errorf("expected custom context to be the type i passed in")
+		}
 		// don't check the message as it could change
-	}, nil)
+	}, map[string]interface{}{"customKey": "customVal"})
 	err = kvstore.SetKV([]byte("key"), []byte("value"))
 	if err == nil {
 		t.Fatalf("expected error, got nil")