Hi, a user pointed out that a rewrite rule which adds quotes around a variable
causes the variable substution not to happen, e.g.
{
"query": { "key": "\":arg\"" }
}
I had to stare a long time at couch_httpd_rewrite to see why that was the case.
I found the replace_var/3 function to be awesomely gnarly:
https://github.com/apache/couchdb/blob/trunk/src/couchdb/couch_httpd_rewrite.erl#L256
There are so many bad things going on in this function:
1) I'm pretty sure the final clause of the case statement can never be reached.
Calls to replace_var/3 are guarded by is_list/1 and is_binary/1 guards on the
Value, so we're always going to hit one of the previous clauses.
2) Putting that aside for a moment, what was the point of the inner case
statement? Are we writing code that distinguishes between
lists:flatten(?JSON_ENCODE(Value)) and iolist_to_binary(?JSON_ENCODE(Value)) ?
I hope not.
3) I found the is_list(Value) clause to be almost a copy of the outer clause,
but not quite. It looks to me like that clause is being used to handle the
situation like "query":{"key": [":a",":b"]}, but I believe there are better
ways to do that.
4) Sure enough, the rewriter requires an exact match on <<":", Var/binary>> in
order to do the substitution, and it does not JSON encode the result, even if
the query key is something that requires a JSON-encoded value. In effect, I
see no way to use the rewriter to set the value of key to a string.
I started to refactor this function a bit and ended up with
http://friendpaste.com/ZzyuR2gM0JVdDmgGhjXbI. It still doesn't address the
root problem of the JSON-encoding requirement for key/startkey/endkey/etc., but
it's a start. I've never had occasion to look closely at the rewriter before,
so someone else should check to make sure I'm not way out in left field here.
Adam
