Function IPv6ToString

src/netaddress.cpp:514–567

Return an IPv6 address text representation with zero compression as described in RFC 5952 ("A Recommendation for IPv6 Address Text Representation").

// Return an IPv6 address text representation with zero compression as described in RFC 5952
// ("A Recommendation for IPv6 Address Text Representation").
static std::string IPv6ToString(std::span<const uint8_t> a, uint32_t scope_id)
{
    assert(a.size() == ADDR_IPV6_SIZE);
    const std::array groups{
        ReadBE16(&a[0]),
        ReadBE16(&a[2]),
        ReadBE16(&a[4]),
        ReadBE16(&a[6]),
        ReadBE16(&a[8]),
        ReadBE16(&a[10]),
        ReadBE16(&a[12]),
        ReadBE16(&a[14]),
    };

    // The zero compression implementation is inspired by Rust's std::net::Ipv6Addr, see
    // https://github.com/rust-lang/rust/blob/cc4103089f40a163f6d143f06359cba7043da29b/library/std/src/net/ip.rs#L1635-L1683
    struct ZeroSpan {
        size_t start_index{0};
        size_t len{0};
    };

    // Find longest sequence of consecutive all-zero fields. Use first zero sequence if two or more
    // zero sequences of equal length are found.
    ZeroSpan longest, current;
    for (size_t i{0}; i < groups.size(); ++i) {
        if (groups[i] != 0) {
            current = {i + 1, 0};
            continue;
        }
        current.len += 1;
        if (current.len > longest.len) {
            longest = current;
        }
    }

    std::string r;
    r.reserve(39);
    for (size_t i{0}; i < groups.size(); ++i) {
        // Replace the longest sequence of consecutive all-zero fields with two colons ("::").
        if (longest.len >= 2 && i >= longest.start_index && i < longest.start_index + longest.len) {
            if (i == longest.start_index) {
                r += "::";
            }
            continue;
        }
        r += strprintf("%s%x", ((!r.empty() && r.back() != ':') ? ":" : ""), groups[i]);
    }

    if (scope_id != 0) {
        r += strprintf("%%%u", scope_id);
    }

    return r;
}

std::string OnionToString(std::span<const uint8_t> addr)
{