Url::as_str can produce invalid and non-equivalent URLs

[Mrmaxmeier]

The URL crate includes a fuzzer which tests for equivalence of re-serialized URLs. The fuzzer is included in OSS-Fuzz, but running it locally hits assertions instantly. I'm not sure what's going on there -- an inactive email contact or a buggy fuzzing environment maybe?

Here's an example input:

Invalid serialized URL

[fuzz_targets/parse.rs:11] &utf8 = "b:\t/\t../\t/\t.%2\\"
[fuzz_targets/parse.rs:11] &parsed = Url {
    scheme: "b",
    cannot_be_a_base: false,
    username: "",
    password: None,
    host: None,
    port: None,
    path: "//.%2\\",
    query: None,
    fragment: None,
}
[fuzz_targets/parse.rs:11] &as_str = "b://.%2\\"
thread '<unnamed>' panicked at 'called `Result::unwrap()` on an `Err` value: InvalidDomainCharacter', fuzz_targets/parse.rs:12:56

Non-equivalent serialized URL

[fuzz_targets/parse.rs:11] &utf8 = "K:/.//./\0\0777777\0:/.//./\0\07777"
[fuzz_targets/parse.rs:11] &parsed = Url {
    scheme: "k",
    cannot_be_a_base: false,
    username: "",
    password: None,
    host: None,
    port: None,
    path: "//%00%00777777%00://%00%007777",
    query: None,
    fragment: None,
}
[fuzz_targets/parse.rs:11] &as_str = "k://%00%00777777%00://%00%007777"
thread '<unnamed>' panicked at 'assertion failed: `(left == right)`
  left: `Url { scheme: "k", cannot_be_a_base: false, username: "", password: None, host: None, port: None, path: "//%00%00777777%00://%00%007777", query: None, fragment: None }`,
 right: `Url { scheme: "k", cannot_be_a_base: false, username: "", password: None, host: Some(Domain("%00%00777777%00")), port: None, path: "//%00%007777", query: None, fragment: None }`', fuzz_targets/parse.rs:12:13

[Mrmaxmeier]

Whoops, looks like this is already tracked #729