Crate safelog

source ·
Expand description


Mark data as sensitive for logging purposes.

Some information is too sensitive to routinely write to system logs, but must nonetheless sometimes be displayed. This crate provides a way to mark such information, and log it conditionally, but not by default.


There are two main ways to mark a piece of data as sensitive: by storing it within a Sensitive object long-term, or by wrapping it in a Sensitive object right before passing it to a formatter:

use safelog::{Sensitive, sensitive};

// With this declaration, a student's name and gpa will be suppressed by default
// when passing the student to Debug.
struct Student {
   name: Sensitive<String>,
   grade: u8,
   homeroom: String,
   gpa: Sensitive<f32>,

// In this function, a user's IP will not be printed by default.
fn record_login(username: &str, ip: &std::net::IpAddr) {
    println!("Login from {} at {}", username, sensitive(ip));

You can disable safe-logging globally (across all threads) or locally (across a single thread).

use safelog::{disable_safe_logging, with_safe_logging_suppressed};

// If we're running in debug mode, turn off safe logging
// globally.  Safe logging will remain disabled until the
// guard object is dropped.
let guard = if debug_mode {
   // This call can fail if safe logging has already been enforced.
} else {

// If we know that it's safe to record sensitive data with a given API,
// we can disable safe logging temporarily. This affects only the current thread.
with_safe_logging_suppressed(|| log_encrypted_data(big_secret));

§An example deployment

This crate was originally created for use in the arti project, which tries to implements the Tor anonymity protocol in Rust. In arti, we want to avoid logging information by default if it could compromise users’ anonymity, or create an incentive for attacking users and relays in order to access their logs.

In general, Arti treats the following information as Sensitive:

  • Client addresses.
  • The destinations (target addresses) of client requests.

Arti does not label all private information as Sensitive: when information isn’t ever suitable for logging, we omit it entirely.

License: MIT OR Apache-2.0


  • A wrapper suitable for logging and including in errors
  • A guard object used to enforce safe logging, or turn it off.
  • An object that may or may not be redacted.
  • A wrapper around a Redactable that displays it in redacted format.
  • A wrapper type for a sensitive value.


  • An error returned when attempting to enforce or disable safe logging.


  • A redactable object is one where we know a way to display part of it when we are running with safe logging enabled.


Type Aliases§

  • A Result returned by the flag-manipulation functions in safelog.