JSON pointer query, trailing slashes and empty keys

[mfriedemann]

Hey,

I found an inconsistency, or potentially a bug, with the handling of JSON pointers in JSONObject.query().

Specifically, the handling of trailing slashes differs between the root element and elements further down.

From reading the RFC and a discussion about it, I got the impression that a trailing slash is supposed to refer to an empty key, but this only works with the root element.
For elements further down, a trailing slash will not select the empty key below the element, but the element itself instead.

example code

public void testPointerQuery() {
	JSONObject none = new JSONObject();
	JSONObject emptyKeyRoot = new JSONObject("{'':'empty key at root'}");
	JSONObject emptyKeyBelow = new JSONObject("{'foo':{'':'empty key below foo'}}");
	
	System.out.println("json=" + none + " ptr='' query -> " + none.query(""));
	System.out.println("json=" + none + " ptr='/' query -> " + none.query("/"));
	
	System.out.println("json=" + emptyKeyRoot + " ptr='' query -> " + emptyKeyRoot.query(""));
	System.out.println("json=" + emptyKeyRoot + " ptr='/' query -> " + emptyKeyRoot.query("/"));
	
	System.out.println("json=" + emptyKeyBelow + " ptr='' query -> " + emptyKeyBelow.query(""));
	System.out.println("json=" + emptyKeyBelow + " ptr='/' query -> " + emptyKeyBelow.query("/"));
	System.out.println("json=" + emptyKeyBelow + " ptr='/foo' query -> " + emptyKeyBelow.query("/foo"));
	System.out.println("json=" + emptyKeyBelow + " ptr='/foo/' query -> " + emptyKeyBelow.query("/foo/"));
}

output for example code above

json={} ptr='' query -> {}
json={} ptr='/' query -> null
json={"":"empty key at root"} ptr='' query -> {"":"empty key at root"}
json={"":"empty key at root"} ptr='/' query -> empty key at root
json={"foo":{"":"empty key below foo"}} ptr='' query -> {"foo":{"":"empty key below foo"}}
json={"foo":{"":"empty key below foo"}} ptr='/' query -> null
json={"foo":{"":"empty key below foo"}} ptr='/foo' query -> {"":"empty key below foo"}
json={"foo":{"":"empty key below foo"}} ptr='/foo/' query -> {"":"empty key below foo"}

expected output (last line)

json={"foo":{"":"empty key below foo"}} ptr='/foo/' query -> empty key below foo

This happens with both the string and URI fragment representations, using the 20180130 maven artifact.

Thanks,
M.

[stleary]

Investigating...

[stleary]

Please reference the RFC you read?
Are you asserting that JSONPointer strings ending with '/' are valid?
Given your test case, what, in your opinion, would correct output look like?
Nice work, by the way.

[mfriedemann]

I am referring to RFC 6901, and a discussion I found about implementation details.
Specifically, RFC 6901, Section 3 states:

A JSON Pointer is a Unicode string (see [RFC4627], Section 3)
containing a sequence of zero or more reference tokens, each prefixed
by a '/' (%x2F) character.

Additionally, the list of examples contains the mapping of pointer (left) to evaluation result (right)

"/" 0

for an example document

{
"" : 0
}

Unfortunately, the RFC does not specify this in greater depth, but given the wording cited above ("prefixed by'/'), I would assert that trailing slashes should be valid and that they should reference empty keys (or fail, if none exists at that level).

I won't be able to check the proposed fix today, will try and look at it tomorrow.

Thanks,
M.

[mfriedemann]

As per the comment to #411, I can confirm that it fixes #410.

Thanks,
M.