#mail #quoted #mime #string

archived quoted-string

Specification independent utilities to handle quoted strings (in Mail, MIME types, ..)

5 releases

Uses old Rust 2015

0.6.1 Oct 11, 2019
0.6.0 Jun 11, 2018
0.3.0 Nov 27, 2017
0.2.2 Nov 13, 2017

#489 in Encoding

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Used in 24 crates (6 directly)


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quoted-string Crates.io quoted-string License License Build Status

This crate provides utilities to handle quoted strings like such appearing in Media Types (both MIME (i.e. Mail) and HTTP). As there are many small but significant differences in different specifications this crate does not provide a specific implementation. Instead a QuotedStringSpec trait is exposed. Implementing it (on zero-sized types) should allow the usage with any quoted-string specification.

Available functionality contains

  • quote_if_needed (&quote): quotes content (if needed), the UnquotedValidator part of QuotedStringSpec can be used to specify which values are valid without needing to be represented as a quoted string. E.g. in a Media Type a parameter value of abc can and should be directly represented on benefit quoted_if_needed is that it returns a Cow so the string is only copied if it actually needs to be represented as quoted string.

  • to_content: retrieve the content of a quoted string which means that the surrounding '"' quotes will be removed and any quoted-pair (e.g. "\\\""/r#"\""#) will be replaced with it's value. This function returns Cow::Borrowed if there are no quoted-pairs preventing needless allocations.

  • ContentChars: an iterator over the chars of the content of a quoted-string, i.e. it will strip the surrounding DQUOTEs and will ()on the fly) unquote quoted-pairs not needing any extra memory allocations. This can be used to semantically compare two quoted strings regardless of how they used quoted-pairs, it implements Eq.

  • parse (&validate): parses a quoted-string positioned at the start of the input. It is written to be easily integrateable with nom (through does not require nom in any way, using it standalone is as easy)


extern crate quoted_string;

// we use a QuotedStringSpec provided for testing here,
// not that it's made to hit some edge cases in a simple way
// so it does not correspond to any used real Spec
use quoted_string::test_utils::{TestSpec as Spec};
use quoted_string::spec::AsciiWordValidator;
use quoted_string::{parse, quote, quote_if_needed, to_content};

fn main() {
    let res = parse::<Spec>("\"quoted\\\"st\\ring\"; tail=x").unwrap();
    let qs = res.quoted_string;
    assert_eq!(qs, "\"quoted\\\"st\\ring\"");
    assert_eq!(res.tail, "; tail=x");
    let content = to_content::<Spec>(qs)
        .expect("[BUG] to_content is guaranteed to succeed if input is a valid quoted string");
    assert_eq!(content, "quoted\"string");
    let re_quoted = quote::<Spec>(&*content)
        .expect("[BUG] quote is guaranteed to succeed if the input is representable in a quoted string");
    assert_eq!(re_quoted, "\"quoted\\\"string\"");

    // TestSpec specifies us-ascii words with 6 letters need no quoting
    let mut without_quoting = AsciiWordValidator;
    let out = quote_if_needed::<Spec, _>("simple", &mut without_quoting).unwrap();
    assert_eq!(&*out, "simple");


Licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

Change Log

  • 0.3.0: Made the crate independent of any specific quoted-string specification by introducing QuotedStringSpec as there are to many differences between quoted-string's in Media Type occurring in HTTP and thus occurring in MIME (Mail)

  • 0.3.1: Noticed that ValidationResult was not exposed, but also didn't got a private type in public interface warning... fixed that

  • 0.4.0:

    • Removed Escape from ValidationResult
    • Renamed NotSemanticWs to NotSemantic
    • Renamed Quotable to NeedsQuotedPair
    • Removed unnecessary Err Associated Type from UnquotedValidator
    • added default impl for end_validation of UnquotedValidator andQuotedValidator
  • 0.5.0:

    • Changed Spec to use a automaton internally
    • renamed strip_quotes to strip_dquotes
    • default impl for WithoutQuotingValidator::end
  • 0.6.0:

    • min rust version is now rustc v1.24
    • added AsciiWordValidator
    • fixed example in README

No runtime deps