snarkvm_circuit_environment::prelude::string_parser

Function is_char_supported

Source 
pub fn is_char_supported(c: char) -> bool
Expand description

Checks for supported code points.

We regard the following characters as safe:

  • Horizontal tab (code 9).
  • Line feed (code 10).
  • Carriage return (code 13).
  • Space (code 32).
  • Visible ASCII (codes 33-126).
  • Non-ASCII Unicode scalar values (codes 128+) except
    • bidi embeddings, overrides and their termination (codes U+202A-U+202E)
    • isolates (codes U+2066-U+2069)

The Unicode bidi characters are well-known for presenting Trojan Source dangers. The ASCII backspace (code 8) can be also used to make text look different from what it is, and a similar danger may apply to delete (126). Other ASCII control characters (except for horizontal tab, space, line feed, and carriage return, which are allowed) may or may not present dangers, but we see no good reason for allowing them. At some point we may want disallow additional non-ASCII characters, if we see no good reason to allow them.

Note that we say ‘Unicode scalar values’ above, because we read UTF-8-decoded characters, and thus we will never encounter surrogate code points, and we do not need to explicitly exclude them in this function.