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CA1055: URI return values should not be strings

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Property Value
Rule ID CA1055
Title URI return values should not be strings
Category Design
Fix is breaking or non-breaking Breaking
Enabled by default in .NET 9 No

Cause

The name of a method contains "uri", "Uri", "urn", "Urn", "url", or "Url", and the method returns a string.

By default, this rule only looks at externally visible methods, but this is configurable.

Rule description

This rule splits the method name into tokens based on the Pascal casing convention and checks whether each token equals "uri", "Uri", "urn", "Urn", "url", or "Url". If there's a match, the rule assumes that the method returns a uniform resource identifier (URI). A string representation of a URI is prone to parsing and encoding errors, and can lead to security vulnerabilities. The System.Uri class provides these services in a safe and secure manner.

How to fix violations

To fix a violation of this rule, change the return type to a Uri.

When to suppress warnings

It's safe to suppress a warning from this rule if the return value does not represent a URI.

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable CA1055
// The code that's violating the rule is on this line.
#pragma warning restore CA1055

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.CA1055.severity = none

For more information, see How to suppress code analysis warnings.

Configure code to analyze

Use the following options to configure which parts of your codebase to run this rule on.

You can configure these options for just this rule, for all rules it applies to, or for all rules in this category (Design) that it applies to. For more information, see Code quality rule configuration options.

Include specific API surfaces

You can configure which parts of your codebase to run this rule on, based on their accessibility. For example, to specify that the rule should run only against the non-public API surface, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CAXXXX.api_surface = private, internal

Exclude specific symbols

You can exclude specific symbols, such as types and methods, from analysis. For example, to specify that the rule should not run on any code within types named MyType, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CAXXXX.excluded_symbol_names = MyType

Allowed symbol name formats in the option value (separated by |):

  • Symbol name only (includes all symbols with the name, regardless of the containing type or namespace).
  • Fully qualified names in the symbol's documentation ID format. Each symbol name requires a symbol-kind prefix, such as M: for methods, T: for types, and N: for namespaces.
  • .ctor for constructors and .cctor for static constructors.

Examples:

Option Value Summary
dotnet_code_quality.CAXXXX.excluded_symbol_names = MyType Matches all symbols named MyType.
dotnet_code_quality.CAXXXX.excluded_symbol_names = MyType1|MyType2 Matches all symbols named either MyType1 or MyType2.
dotnet_code_quality.CAXXXX.excluded_symbol_names = M:NS.MyType.MyMethod(ParamType) Matches specific method MyMethod with the specified fully qualified signature.
dotnet_code_quality.CAXXXX.excluded_symbol_names = M:NS1.MyType1.MyMethod1(ParamType)|M:NS2.MyType2.MyMethod2(ParamType) Matches specific methods MyMethod1 and MyMethod2 with the respective fully qualified signatures.

Exclude specific types and their derived types

You can exclude specific types and their derived types from analysis. For example, to specify that the rule should not run on any methods within types named MyType and their derived types, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CAXXXX.excluded_type_names_with_derived_types = MyType

Allowed symbol name formats in the option value (separated by |):

  • Type name only (includes all types with the name, regardless of the containing type or namespace).
  • Fully qualified names in the symbol's documentation ID format, with an optional T: prefix.

Examples:

Option Value Summary
dotnet_code_quality.CAXXXX.excluded_type_names_with_derived_types = MyType Matches all types named MyType and all of their derived types.
dotnet_code_quality.CAXXXX.excluded_type_names_with_derived_types = MyType1|MyType2 Matches all types named either MyType1 or MyType2 and all of their derived types.
dotnet_code_quality.CAXXXX.excluded_type_names_with_derived_types = M:NS.MyType Matches specific type MyType with given fully qualified name and all of its derived types.
dotnet_code_quality.CAXXXX.excluded_type_names_with_derived_types = M:NS1.MyType1|M:NS2.MyType2 Matches specific types MyType1 and MyType2 with the respective fully qualified names, and all of their derived types.

Example

The following example shows a type, ErrorProne, that violates this rule, and a type, SaferWay, that satisfies the rule.

public class ErrorProne
{
    // Violates rule UriPropertiesShouldNotBeStrings.
    public string? SomeUri { get; set; }

    // Violates rule UriParametersShouldNotBeStrings.
    public void AddToHistory(string uriString) { }

    // Violates rule UriReturnValuesShouldNotBeStrings.
    public string GetReferrerUri(string httpHeader)
    {
        return "http://www.adventure-works.com";
    }
}

public class SaferWay
{
    // To retrieve a string, call SomeUri.ToString().
    // To set using a string, call SomeUri = new Uri(string).
    public Uri? SomeUri { get; set; }

    public void AddToHistory(string uriString)
    {
        // Check for UriFormatException.
        AddToHistory(new Uri(uriString));
    }

    public void AddToHistory(Uri uriType) { }

    public Uri GetReferrerUri(string httpHeader)
    {
        return new Uri("http://www.adventure-works.com");
    }
}

Imports System

Namespace ca1055

    Public Class ErrorProne

        ' Violates rule UriPropertiesShouldNotBeStrings.
        Property SomeUri As String

        ' Violates rule UriParametersShouldNotBeStrings.
        Sub AddToHistory(uriString As String)
        End Sub

        ' Violates rule UriReturnValuesShouldNotBeStrings.
        Function GetRefererUri(httpHeader As String) As String
            Return "http://www.adventure-works.com"
        End Function

    End Class

    Public Class SaferWay

        ' To retrieve a string, call SomeUri.ToString().
        ' To set using a string, call SomeUri = New Uri(string).
        Property SomeUri As Uri

        Sub AddToHistory(uriString As String)
            ' Check for UriFormatException.
            AddToHistory(New Uri(uriString))
        End Sub

        Sub AddToHistory(uriString As Uri)
        End Sub

        Function GetRefererUri(httpHeader As String) As Uri
            Return New Uri("http://www.adventure-works.com")
        End Function

    End Class

End Namespace