yihui504 opened a new issue, #6087:
URL: https://github.com/apache/couchdb/issues/6087
### Version
3.5.1
### Describe the problem you're encountering
`GET /testdb/_changes?limit=abc` returns HTTP **500** with an unhandled
Erlang `badarg`:
```json
{"error":"unknown_error","reason":"badarg","ref":3761585293}
```
The same invalid input on `_all_docs` returns a clean HTTP **400**:
```json
{"error":"query_parse_error","reason":"Invalid value for integer: \"abc\""}
```
So `_changes` leaks an unhandled server exception (plus a stack-hash `ref`)
for what `_all_docs` handles as a normal client error. `limit=1.5` (float)
produces the same 500 `badarg`.
### Expected Behaviour
Return HTTP 400 `query_parse_error` for non-numeric `limit`, consistent with
`_all_docs`.
### Steps to Reproduce
```bash
docker run -d -p 5984:5984 -e COUCHDB_USER=admin -e COUCHDB_PASSWORD=admin
--name couchdb-t couchdb:3.5
curl -s -X POST http://admin:admin@localhost:5984/_cluster_setup -H
"Content-Type: application/json" \
-d
'{"action":"enable_single_node","bind_address":"0.0.0.0","port":5984,"singlenode":true}'
curl -s -X PUT http://admin:admin@localhost:5984/testdb
curl -s -X POST http://admin:admin@localhost:5984/testdb/_bulk_docs -H
"Content-Type: application/json" \
-d '{"docs":[{"_id":"d1","v":1}]}'
# _changes: 500 (bug)
curl -i "http://admin:admin@localhost:5984/testdb/_changes?limit=abc";
# HTTP/1.1 500 Internal Server Error
# {"error":"unknown_error","reason":"badarg","ref":...}
curl -i "http://admin:admin@localhost:5984/testdb/_changes?limit=1.5";
# HTTP/1.1 500 Internal Server Error (same badarg)
# _all_docs: 400 (expected)
curl -i "http://admin:admin@localhost:5984/testdb/_all_docs?limit=abc";
# HTTP/1.1 400 Bad Request
# {"error":"query_parse_error","reason":"Invalid value for integer: \"abc\""}
```
### Your Environment
- CouchDB 3.4.3 and 3.5.1/3.5.2 (official Docker images `couchdb:3.4` and
`couchdb:3.5`)
- Single-node setup (`_cluster_setup enable_single_node`)
- OS: Windows 11 host, Docker Desktop
### Additional Context
## Root cause (source)
`src/chttpd/src/chttpd_db.erl`, `parse_changes_query/1`
([3.5.0](https://github.com/apache/couchdb/blob/3.5.0/src/chttpd/src/chttpd_db.erl),
line 2098):
```erlang
{"limit", _} ->
Args#changes_args{limit = list_to_integer(Value)}; %% bare call, NO
try/catch
```
The very next parameter, `timeout` (line 2104), wraps the same call:
```erlang
{"timeout", _} ->
try list_to_integer(Value) of ... %% has try/catch
```
So `limit` is the only integer parameter in `parse_changes_query` parsed
without a `try` guard, which is why `list_to_integer("abc")` raises uncaught
`badarg` → HTTP 500. The fix is to wrap `limit` in the same `try` block used
for `timeout`.
`list_to_integer/1` is an Erlang BIF; its `"abc" -> badarg` behaviour is
OTP-version-independent. `diff` of `parse_changes_query` between the 3.4.3 and
3.5.0 tags exits 0 (byte-identical).
## Related prior fix
[COUCHDB-2375](https://issues.apache.org/jira/browse/COUCHDB-2375) — same
class of "invalid query parameter → HTTP 500 instead of 400" bug, for the `rev`
parameter on PUT. Resolved as **Fixed**. This is the same pattern on
`_changes?limit=`.
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