Only namespace prefixes bound on the root node are considered by document.xpath(_ xpath: String)

[martin-cowie]

Description:

• Expected behaviour:

XML namespaces can be bound to a prefix at any element in a document. They can be bound within an element that uses that namespace prefix. XPath expressions should be able to use the same prefixes. E.g given the document:

<root>
    <u:BrowseResponse xmlns:u="urn:foo.bar" />
</root>

the XPath expression /root/u:BrowseResponse should resolve to a nodelist of 1 element.

• Actual behaviour:

The XPath expression /root/u:BrowseResponse resolve to a nodelist of 0 elements and the following is printed

XPath error : Undefined namespace prefix
XPath error : Invalid expression

If the document is amended such that the prefix u: is bound at the root element the xpath expression evaluates correctly.

Environment

• Package Manager:
  • CocoaPods, version: 1.2.2
• Fuzi version: 1.0.1
• Xcode version: 8.3.3

How to reproduce:

The following test fails, demonstrating the issue.

    func testNestedNamespacePrefixWithXPath() {
        let docStr = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><root><u:BrowseResponse xmlns:u=\"urn:foo.bar\"/></root>"

        do {
            let document = try Fuzi.XMLDocument(string: docStr)
            let nodes = document.xpath("/root/u:BrowseResponse")
            XCTAssertFalse(nodes.isEmpty)
        } catch let error {
            print(error)
            XCTFail(String(describing:error))
        }
    }

[cezheng]

Seems like a duplicate of #25
This is how libxml2 deals with namespaces, you have to define a prefix yourself before using it with XPath queries

[martin-cowie]

Thanks for coming back to me Cezheng.

I use Document.definePrefix(_ prefix: String, defaultNamespace ns: String) elsewhere in my code to handle a default namespace. Alas, using the same technique here doesn't work, possibly because urn:foo.bar is not bound as a default namespace in the XML:

    func testNestedNamespacePrefixWithXPath() {
        let docStr = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><root><u:BrowseResponse xmlns:u=\"urn:foo.bar\"/></root>"
        do {
            let document = try Fuzi.XMLDocument(string: docStr)
            document.definePrefix("u", defaultNamespace: "urn:foo.bar") // New code
            let nodes = document.xpath("/root/u:BrowseResponse")
            XCTAssertFalse(nodes.isEmpty)
        } catch let error {
            print(error)
            XCTFail(String(describing:error))
        }
    }

[cezheng]

the relevant code is here

Seems if the namespace definition is under root element, the query should work. And it doesn't make sense to traverse the whole doc just looking for namespaces.