Function escape_controls 

pub fn escape_controls(body: &str, max: usize) -> String

Truncates a backend response body and escapes its control characters so it is safe to show in a diagnostic.

The function keeps the first max characters of body. It replaces each control character among them, including newlines and carriage returns, with its escaped form, such as \n or \u{1b}. Escaping can make the result longer than max characters. An empty body returns the fixed marker (empty body).

The escaping stops a backend body from forging log lines or slipping terminal control sequences into a diagnostic.

A transport passes the error body of a response with a failure status through this function before it hands the body to classify_http_failure. Every transport therefore truncates and escapes a backend body by the same rule.