capture errors from libxml2

fixes #4

decrypt_test.go

@@ -139,7 +139,7 @@ func (testSuite *DecryptTest) TestInvalid(c *C) {
 	c.Assert(err, IsNil)
 
 	_, err = Decrypt(testSuite.Key, []byte("<invalid xml"))
-	c.Assert(err, ErrorMatches, "malformed XML")
+	c.Assert(err, ErrorMatches, ".*Couldn't find end of Start Tag.*")
 
 	_, err = Decrypt(testSuite.Key, []byte("<invalid></invalid>"))
 	c.Assert(err, ErrorMatches, "xmlSecFindNode cannot find EncryptedData node")
@@ -149,7 +149,7 @@ func (testSuite *DecryptTest) TestInvalid(c *C) {
 
 	docStr = []byte(`<?xml version="1.0" encoding="UTF-8"?><saml2p:Response xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol" Destination="https://15661444.ngrok.io/saml2/acs" ID="_59c2431b4916af2018984213940ee675" InResponseTo="id-3d21faf29a101222d740735fa512f161" IssueInstant="2015-11-29T21:29:09.991Z" Version="2.0"><saml2:Issuer xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion" Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity">https://idp.testshib.org/idp/shibboleth</saml2:Issuer><saml2p:Status><saml2p:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/></saml2p:Status><saml2:EncryptedAssertion xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion"><xenc:EncryptedData xmlns:xenc="http://www.w3.org/2001/04/xmlenc#" Id="_62d64ca491a287a346272669fbe93191" Type="http://www.w3.org/2001/04/xmlenc#Element">invalid<`)
 	_, err = Decrypt(testSuite.Key, docStr)
-	c.Assert(err, ErrorMatches, "malformed XML")
+	c.Assert(err, ErrorMatches, ".*Premature end of data in tag.*")
 
 	docStr = []byte(`<?xml version="1.0" encoding="UTF-8"?>
 <X>

encrypt_realworld_test.go

@@ -95,7 +95,7 @@ func (testSuite *XmlencRealWorldTest) TestInvalid(c *C) {
 	c.Assert(err, IsNil)
 
 	_, err = Decrypt(testSuite.Key, []byte("<invalid xml"))
-	c.Assert(err, ErrorMatches, "malformed XML")
+	c.Assert(err, ErrorMatches, ".*Couldn't find end of Start Tag.*")
 
 	_, err = Decrypt(testSuite.Key, []byte("<invalid></invalid>"))
 	c.Assert(err, ErrorMatches, "xmlSecFindNode cannot find EncryptedData node")
@@ -105,7 +105,7 @@ func (testSuite *XmlencRealWorldTest) TestInvalid(c *C) {
 
 	docStr := []byte(`<?xml version="1.0" encoding="UTF-8"?><saml2p:Response xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol" Destination="https://15661444.ngrok.io/saml2/acs" ID="_59c2431b4916af2018984213940ee675" InResponseTo="id-3d21faf29a101222d740735fa512f161" IssueInstant="2015-11-29T21:29:09.991Z" Version="2.0"><saml2:Issuer xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion" Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity">https://idp.testshib.org/idp/shibboleth</saml2:Issuer><saml2p:Status><saml2p:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/></saml2p:Status><saml2:EncryptedAssertion xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion"><xenc:EncryptedData xmlns:xenc="http://www.w3.org/2001/04/xmlenc#" Id="_62d64ca491a287a346272669fbe93191" Type="http://www.w3.org/2001/04/xmlenc#Element">invalid<`)
 	_, err = Decrypt(testSuite.Key, docStr)
-	c.Assert(err, ErrorMatches, "malformed XML")
+	c.Assert(err, ErrorMatches, ".*Premature end of data in tag.*")
 
 	docStr = []byte(`<?xml version="1.0" encoding="UTF-8"?>
 <X>

error.go

@@ -4,6 +4,7 @@ import (
 	"C"
 	"fmt"
 	"runtime"
+	"strings"
 
 	"github.com/crewjam/errset"
 )
@@ -32,8 +33,8 @@ func (e libraryError) Error() string {
 		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) {
+//export onXmlsecError
+func onXmlsecError(file *C.char, line C.int, funcName *C.char, errorObject *C.char, errorSubject *C.char, reason C.int, msg *C.char) {
 	err := libraryError{
 		FuncName: C.GoString(funcName),
 		FileName: C.GoString(file),
@@ -46,6 +47,13 @@ func onError(file *C.char, line C.int, funcName *C.char, errorObject *C.char, er
 	globalErrors[threadID] = append(globalErrors[threadID], err)
 }
 
+//export onXmlError
+func onXmlError(msg *C.char) {
+	threadID := getThreadID()
+	globalErrors[threadID] = append(globalErrors[threadID],
+		fmt.Errorf("%s", strings.TrimSuffix(C.GoString(msg), "\n")))
+}
+
 // 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. If the library later calls onError then the error will be appended

error_thunk.go

@@ -1,13 +1,31 @@
 package xmlsec
 
-// onError_cgo is a C function that can be passed to xmlSecErrorsSetCallback which
-// in turn invokes the go function onError which captures errors generated by
-// libxmlsec.
+// #include <stdio.h>
+// #include <stdarg.h>
+// #include <libxml/parser.h>
+// #include <libxml/parserInternals.h>
+// #include <libxml/xmlmemory.h>
+// #include <xmlsec/xmlsec.h>
+// #include <xmlsec/errors.h>
 //
-// For reasons I do not completely understand, it must be defined in a different
-// file from onError.
-
-// void onError_cgo(char *file, int line, char *funcName, char *errorObject, char *errorSubject, int reason, char *msg) {
-//   onError(file, line, funcName, errorObject, errorSubject, reason, msg);
+// void onXmlError(const char *msg);  // implemented in go
+// void onXmlsecError(const char *file, int line, const char *funcName, const char *errorObject, const char *errorSubject, int reason, const char *msg);  // implemented in go
+//
+// static void onXmlGenericError_cgo(void *ctx, const char *format, ...) {
+// 	char buffer[256];
+// 	va_list args;
+// 	va_start(args, format);
+// 	vsnprintf(buffer, 256, format, args);
+// 	va_end (args);
+//  onXmlError(buffer);
+// }
+//
+// static void onXmlsecError_cgo(const char *file, int line, const char *funcName, const char *errorObject, const char *errorSubject, int reason, const char *msg) {
+// 	onXmlsecError(file, line, funcName, errorObject, errorSubject, reason, msg);
+// }
+//
+// void captureXmlErrors() {
+// 	xmlSecErrorsSetCallback(onXmlsecError_cgo);
+// 	xmlSetGenericErrorFunc(NULL, onXmlGenericError_cgo);
 // }
 import "C"

xmldsig_test.go

@@ -218,7 +218,7 @@ func (testSuite *XMLDSigTest) TestVerifyFailsWhenMessageModified(c *C) {
 
 func (testSuite *XMLDSigTest) TestInvalidXML(c *C) {
 	_, err := Sign(testSuite.Key, []byte("<invalid xml"), SignatureOptions{})
-	c.Assert(err, ErrorMatches, "malformed XML")
+	c.Assert(err, ErrorMatches, ".*Couldn't find end of Start Tag.*")
 
 	_, err = Sign(testSuite.Key, []byte("<invalid></invalid>"), SignatureOptions{})
 	c.Assert(err, ErrorMatches, "cannot find start node")
@@ -227,7 +227,7 @@ func (testSuite *XMLDSigTest) TestInvalidXML(c *C) {
 	c.Assert(err, ErrorMatches, "failed to load pem key")
 
 	err = Verify(testSuite.Cert, []byte("<invalid xml"), SignatureOptions{})
-	c.Assert(err, ErrorMatches, "malformed XML")
+	c.Assert(err, ErrorMatches, ".*Couldn't find end of Start Tag.*")
 
 	err = Verify(testSuite.Cert, []byte("<invalid></invalid>"), SignatureOptions{})
 	c.Assert(err, ErrorMatches, "cannot find start node")

xmlsec.go

@@ -1,9 +1,6 @@
 package xmlsec
 
-import (
-	"errors"
-	"unsafe"
-)
+import "unsafe"
 
 // Note: on mac you need:
 //   brew install libxmlsec1 libxml2
@@ -30,7 +27,7 @@ import "C"
 // }
 import "C"
 
-// void onError_cgo(char *file, int line, char *funcName, char *errorObject, char *errorSubject, int reason, char *msg);
+// void captureXmlErrors();
 import "C"
 
 func init() {
@@ -46,26 +43,26 @@ func init() {
 		panic("xmlsec crypto initialization failed.")
 	}
 
-	C.xmlSecErrorsSetCallback((C.xmlSecErrorsCallback)(unsafe.Pointer(C.onError_cgo)))
+	C.captureXmlErrors()
 }
 
 func newDoc(buf []byte, idattrs []XMLIDOption) (*C.xmlDoc, error) {
 	ctx := C.xmlCreateMemoryParserCtxt((*C.char)(unsafe.Pointer(&buf[0])),
 		C.int(len(buf)))
 	if ctx == nil {
-		return nil, errors.New("error creating parser")
+		return nil, mustPopError()
 	}
 	defer C.xmlFreeParserCtxt(ctx)
 
 	C.xmlParseDocument(ctx)
 
 	if ctx.wellFormed == C.int(0) {
-		return nil, errors.New("malformed XML")
+		return nil, mustPopError()
 	}
 
 	doc := ctx.myDoc
 	if doc == nil {
-		return nil, errors.New("parse failed")
+		return nil, mustPopError()
 	}
 
 	for _, idattr := range idattrs {