Function json_response 

pub fn json_response(
    json_str: &str,
    status_code: Option<&StatusCode>,
    custom_headers: Option<&HashMap<String, Option<String>>>,
    request_headers: &HeaderMap,
    source: Option<&str>,
    cors_allow_credentials_origins: &[String],
) -> Result<Response<BoxBody>, Error>

JSON response — used both for respond.json (RFC 065, source is None) and for a file_path pointing at a .json/.json5 file or a CSV converted to JSON (source names the file, for the server log only — see below).

Parses with the same JSON5 parser Respond::validate already checked this content against at load time (apimock_routing’s own json5 dependency), so the _ => branch below is unreachable for respond.json and for a .json/.json5 file_path in ordinary operation — both are now validated before the server ever starts (RFC 065 D3). It stays reachable for CSV→JSON conversion (not content-validated at load, since the source is CSV, not JSON) and as a defensive fallback if a file changes on disk after startup.

Why source never reaches the response body (RFC 065 D4)

This used to build the client-facing message as "{file_path}: invalid json content", putting the server’s own filesystem path in front of every client that hit this branch. The path is still useful — to whoever runs the server, not to whoever’s making the request — so it goes to the server log via log::error! instead; the client gets a message that names the problem, not the server’s directory layout.