refactor:

- merge xmldsig and xmlenc into a single package
- implement thread-safe error capture
- implement encryption using libxmlsec, discarding the go implementation

error.go

@@ -0,0 +1,76 @@
+package xmlsec
+
+import (
+	"fmt"
+	"runtime"
+	"unsafe"
+
+	"github.com/crewjam/errset"
+)
+
+// #include <pthread.h>
+import "C"
+
+var globalErrors = map[uintptr]errset.ErrSet{}
+
+type Error struct {
+	FileName string
+	Line     int
+	FuncName string
+	Object   string
+	Subject  string
+	Reason   int
+	Message  string
+}
+
+func (e Error) Error() string {
+	return fmt.Sprintf(
+		"func=%s:file=%s:line=%d:obj=%s:subj=%s:error=%d:%s",
+		e.FuncName,
+		e.FileName,
+		e.Line,
+		e.Object,
+		e.Subject,
+		e.Reason,
+		e.Message)
+}
+
+//export onError
+func onError(file *C.char, line C.int, funcName *C.char, errorObject *C.char, errorSubject *C.char, reason C.int, msg *C.char) {
+	err := Error{
+		FuncName: C.GoString(funcName),
+		FileName: C.GoString(file),
+		Line:     int(line),
+		Object:   C.GoString(errorObject),
+		Subject:  C.GoString(errorSubject),
+		Reason:   int(reason),
+		Message:  C.GoString(msg)}
+	threadID := uintptr(unsafe.Pointer(C.pthread_self()))
+	globalErrors[threadID] = append(globalErrors[threadID], err)
+}
+
+// startProcessingXML is called whenever we enter a function exported by this package.
+// It locks the current goroutine to the current thread and establishes a thread-local
+// error object.
+func startProcessingXML() {
+	runtime.LockOSThread()
+	threadID := uintptr(unsafe.Pointer(C.pthread_self()))
+	globalErrors[threadID] = errset.ErrSet{}
+}
+
+// stopProcessingXML unlocks the goroutine-thread lock and deletes the current
+// error stack.
+func stopProcessingXML() {
+	runtime.UnlockOSThread()
+	threadID := uintptr(unsafe.Pointer(C.pthread_self()))
+	delete(globalErrors, threadID)
+}
+
+// popError returns the global error for the current thread and resets it to
+// an empty error. Returns nil if no errors have occurred.
+func popError() error {
+	threadID := uintptr(unsafe.Pointer(C.pthread_self()))
+	rv := globalErrors[threadID].ReturnValue()
+	globalErrors[threadID] = errset.ErrSet{}
+	return rv
+}