Added readOptionalUDataDTagElement
diff --git a/ndn-cpp/c/encoding/binary-xml-decoder.c b/ndn-cpp/c/encoding/binary-xml-decoder.c
index fd9ed4c..243835a 100644
--- a/ndn-cpp/c/encoding/binary-xml-decoder.c
+++ b/ndn-cpp/c/encoding/binary-xml-decoder.c
@@ -211,6 +211,25 @@
return NDN_ERROR_success;
}
+ndn_Error ndn_BinaryXmlDecoder_readOptionalUDataDTagElement
+ (struct ndn_BinaryXmlDecoder *self, unsigned int expectedTag, unsigned char **value, unsigned int *valueLength)
+{
+ ndn_Error error;
+ int gotExpectedTag;
+ if ((error = ndn_BinaryXmlDecoder_peekDTag(self, expectedTag, &gotExpectedTag)))
+ return error;
+ if (gotExpectedTag) {
+ if ((error = ndn_BinaryXmlDecoder_readUDataDTagElement(self, expectedTag, value, valueLength)))
+ return error;
+ }
+ else {
+ *value = 0;
+ *valueLength = 0;
+ }
+
+ return NDN_ERROR_success;
+}
+
ndn_Error ndn_BinaryXmlDecoder_readUnsignedIntegerDTagElement
(struct ndn_BinaryXmlDecoder *self, unsigned int expectedTag, unsigned int *value)
{
diff --git a/ndn-cpp/c/encoding/binary-xml-decoder.h b/ndn-cpp/c/encoding/binary-xml-decoder.h
index bd1197b..31a17fe 100644
--- a/ndn-cpp/c/encoding/binary-xml-decoder.h
+++ b/ndn-cpp/c/encoding/binary-xml-decoder.h
@@ -107,6 +107,20 @@
(struct ndn_BinaryXmlDecoder *self, unsigned int expectedTag, unsigned char **value, unsigned int *valueLength);
/**
+ * Peek at the next element and if it is the expectedTag, call ndn_BinaryXmlDecoder_readUDataDTagElement.
+ * Otherwise, set value and valueLength to 0.
+ * @param self pointer to the ndn_BinaryXmlDecoder struct
+ * @param expectedTag the expected value for DTAG
+ * @param value output a pointer to the binary data inside self's input buffer. However, if allowNull is 1 and the
+ * binary data item is absent, then return 0.
+ * @param valueLength output the length of the binary data. However, if allowNull is 1 and the
+ * binary data item is absent, then return 0.
+ * @return 0 for success, else an error code.
+ */
+ndn_Error ndn_BinaryXmlDecoder_readOptionalUDataDTagElement
+ (struct ndn_BinaryXmlDecoder *self, unsigned int expectedTag, unsigned char **value, unsigned int *valueLength);
+
+/**
* Decode the header from self's input starting at offset, expecting the type to be DTAG and the value to be expectedTag.
* Then read one item expecting it to be type UDATA, parse it as an unsigned decimal integer and return the integer.
* Finally, read the element close. Update offset.