System.Xml.XmlResolver

The XmlResolver class resolves external XML resources named by a Uniform Resource Identifier (URI). It is used by the XML parser to access external DTDs, schemas, and other resources.

On this page

Syntax
Inheritance
Properties
Methods
Remarks
Examples

Syntax

public abstract class XmlResolver

Inheritance

Object → XmlResolver

Properties

Name	Type	Description
`Credentials`	`ICredentials`	Gets or sets the credentials used to authenticate Web requests.
`Resolver`	`XmlResolver`	Gets the current resolver (used in advanced scenarios).

Methods

Name Signature Description

Name	Signature	Description
`GetEntity`	public abstract object GetEntity(Uri absoluteUri, string role, Type ofObjectToReturn)	Returns the resource identified by the specified `Uri`.
`ResolveUri`	public virtual Uri ResolveUri(Uri baseUri, string relativeUri)	Combines a base URI and a relative URI into a new absolute URI.
`GetEntityAsync`	public virtual Task<object> GetEntityAsync(Uri absoluteUri, string role, Type ofObjectToReturn, CancellationToken cancellationToken)	Asynchronously returns the resource identified by the specified `Uri`.

GetEntity

public abstract object GetEntity(Uri absoluteUri, string role, Type ofObjectToReturn)

Returns the resource identified by the specified Uri.

ResolveUri

public virtual Uri ResolveUri(Uri baseUri, string relativeUri)

Combines a base URI and a relative URI into a new absolute URI.

GetEntityAsync

public virtual Task<object> GetEntityAsync(Uri absoluteUri, string role, Type ofObjectToReturn, CancellationToken cancellationToken)

Asynchronously returns the resource identified by the specified Uri.

Remarks

The XmlResolver class is an extensibility point. By default, XmlUrlResolver is used, which supports HTTP, HTTPS, FILE, and other schemes. For secure environments, consider using a custom resolver that restricts the set of permissible URIs.

Examples

Creating a custom resolver that only allows local files:

using System;
using System.IO;
using System.Net;
using System.Xml;

public class LocalFileResolver : XmlResolver
{
    public override ICredentials Credentials { set { } }

    public override object GetEntity(Uri absoluteUri, string role, Type ofObjectToReturn)
    {
        if (absoluteUri.IsFile)
        {
            return File.OpenRead(absoluteUri.LocalPath);
        }
        throw new NotSupportedException("Only local file URIs are allowed.");
    }
}

// Usage
var settings = new XmlReaderSettings
{
    XmlResolver = new LocalFileResolver()
};

using var reader = XmlReader.Create("example.xml", settings);

For async resolution:

public class AsyncWebResolver : XmlResolver
{
    public override ICredentials Credentials { get; set; }

    public override async Task<object> GetEntityAsync(Uri absoluteUri, string role, Type ofObjectToReturn, CancellationToken cancellationToken)
    {
        using var client = new HttpClient();
        var stream = await client.GetStreamAsync(absoluteUri, cancellationToken);
        return stream;
    }
}