fn try_from()

in cert/aziot-certd-config/src/lib.rs [228:274]
26 lines of code
4 McCabe index (conditional complexity)

    fn try_from(
        subject: &CertSubject,
    ) -> Result<openssl::x509::X509Name, openssl::error::ErrorStack> {
        // NOTE: X.509 requires CNs to be at most 64 characters.
        //
        // Ref: https://www.rfc-editor.org/rfc/rfc5280 PAGE 124
        const CN_MAX_LENGTH: usize = 64;

        #[inline]
        fn truncate_cn_length(cn: &str) -> String {
            // NOTE: An option that would allow returning a string reference is
            // ```
            // let mut it = cn.chars();
            // let _ = it.by_ref().take(CN_MAX_LENGTH).last();
            // &cn[..usize::try_from(unsafe { it.as_str().as_ptr().offset(cn.as_str().as_ptr()) }).unwrap()]
            // ```
            cn.chars().take(CN_MAX_LENGTH).collect()
        }

        let mut builder = openssl::x509::X509Name::builder()?;

        match subject {
            CertSubject::CommonName(cn) => {
                builder
                    .append_entry_by_nid(openssl::nid::Nid::COMMONNAME, &truncate_cn_length(cn))?;
            }
            CertSubject::Subject(fields) => {
                for (name, value) in fields {
                    // NOTE: Size limits exist for other X509Name fields as
                    // well [RFC5280].  We only truncate the Common Name since
                    // we have only encountered customer issues with Common Name
                    // length so far [1, 2].
                    //
                    // Ref[RFC5280]: https://www.rfc-editor.org/rfc/rfc5280
                    // Ref[1]: https://github.com/Azure/iotedge/issues/6288
                    // Ref[2]: https://github.com/Azure/iot-identity-service/pull/411#discussion_r871640144
                    if name.eq_ignore_ascii_case("cn") {
                        builder.append_entry_by_text(name, &truncate_cn_length(value))?;
                    } else {
                        builder.append_entry_by_text(name, value)?;
                    }
                }
            }
        }

        Ok(builder.build())
    }