Remove more unsafe code from IPAddress parsing

[EgorBo]

let's see what benchmarks think...

[EgorBo]

@MihuBot

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[EgorBo]

@EgorBot -amd -arm -windows_intel

using System;
using System.Net;
using BenchmarkDotNet.Attributes;

public class IPv4_u16_Benchmarks
{
    public IEnumerable<string> Data() => [
        "127.0.0.1",
        "192.168.0.1",
        "8.8.8.8",
        "255.255.255.255"];

    [Benchmark, ArgumentsSource(nameof(Data))]
    public IPAddress Parse_IPv4_u16(string ip) => IPAddress.Parse(ip);
}

public class IPv4_u8_Benchmarks
{
    public IEnumerable<byte[]> Data() => [
        "127.0.0.1"u8.ToArray(),
        "192.168.0.1"u8.ToArray(),
        "8.8.8.8"u8.ToArray(),
        "255.255.255.255"u8.ToArray()];

    [Benchmark, ArgumentsSource(nameof(Data))]
    public IPAddress Parse_IPv4_u8(byte[] ip) => IPAddress.Parse(ip);
}

public class IPv6_u16_Benchmarks
{
    public IEnumerable<string> Data() => [
        "::1",
        "2001:db8::1",
        "fe80::1ff:fe23:4567:890a",
        "2001:4860:4860::8888"];

    [Benchmark, ArgumentsSource(nameof(Data))]
    public IPAddress Parse_IPv6_u16(string ip) => IPAddress.Parse(ip);
}

public class IPv6_u8_Benchmarks
{
    public IEnumerable<byte[]> Data() => [
        "::1"u8.ToArray(),
        "2001:db8::1"u8.ToArray(),
        "fe80::1ff:fe23:4567:890a"u8.ToArray(),
        "2001:4860:4860::8888"u8.ToArray()];

    [Benchmark, ArgumentsSource(nameof(Data))]
    public IPAddress Parse_IPv6_u8(byte[] ip) => IPAddress.Parse(ip);
}

[Copilot]

Pull Request Overview

This PR refactors the IPv4 and IPv6 address validation methods across the Uri and networking libraries to eliminate unsafe code and use ReadOnlySpan<T> instead of pointer-based operations. The key changes include:

• Converting pointer-based (char*) validation methods to span-based implementations
• Changing ref int end parameters to out int end parameters with 0-based indexing
• Removing unsafe blocks and fixed statements throughout the codebase

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/libraries/System.Private.Uri/src/System/Uri.cs	Updated CheckHostName and CheckAuthorityHelper to use span-based IPv4/IPv6 helpers with adjusted index calculations
src/libraries/System.Private.Uri/src/System/IPv6AddressHelper.cs	Converted InternalIsValid and IsValid from unsafe pointer methods to span-based methods
src/libraries/System.Private.Uri/src/System/IPv4AddressHelper.cs	Simplified ParseCanonicalName by removing unsafe code and using span slicing
src/libraries/System.Net.Primitives/src/System/Net/IPAddressParser.cs	Removed unsafe blocks from IsValid, TryParseIpv4, and TryParseIPv6 methods
src/libraries/Common/src/System/Net/IPv6AddressHelper.Common.cs	Converted IsValidStrict from pointer-based to span-based with adjusted indexing and removed sequenceLength = 0 assignment
src/libraries/Common/src/System/Net/IPv4AddressHelper.Common.cs	Refactored IsValid, IsValidCanonical, and ParseNonCanonical to use spans with 0-based indexing

[EgorBo]

PTAL @stephentoub @MihaZupan

It seems to slightly improve the performance a bit (see EgorBot/runtime-utils#534) due to a bit of tweaking, but mostly because of ref end argument that was used directly instead of a local. And, obviously, we no longer need pinning. Also, had to use [0, 0, 0], see #121248

It seems like this code has a good test coverage, all off-by-one mistakes led to test failures.
I also encountered a small out-of-bounds load in IPv6AddressHelper.InternalIsValid that was accessing string's null terminator most likely unintentionally. It can be reproduced via calling Uri.TryCreate("http://[", UriKind.Absolute, out Uri uri);. Since we can't get there with anything other than a string object, it's not a security issue, but I had to add an extra bound check and return false there.

[MihaZupan]

Thanks

I also encountered a small out-of-bounds load in IPv6AddressHelper.InternalIsValid that was accessing string's null terminator most likely unintentionally

Nice catch

[MihaZupan]

@MihuBot fuzz IPAddress

[EgorBo]

/ba-g deadletter