rspec/rules/S2479/csharp/rule.adoc

== Why is this an issue?

Non-encoded https://en.wikipedia.org/wiki/Control_character[control characters] and whitespace characters are often injected in the source code because of a bad manipulation. They are either invisible or difficult to recognize, which can result in bugs when the string is not what the developer expects. If you actually need to use a control character use their encoded version:

* https://en.wikipedia.org/wiki/ASCII[ASCII], for example `\n` and `\t`
* https://en.wikipedia.org/wiki/Unicode[Unicode], for example `U+000D` and `U+0009`

This rule raises an issue when the following characters are seen in a https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/strings/[string literal]:

* https://en.wikipedia.org/wiki/ASCII#Control_characters[ASCII control character]. (character index < 32 or ++=++ 127)
* Unicode https://en.wikipedia.org/wiki/Unicode_character_property#Whitespace[whitespace characters].
* Unicode https://en.wikipedia.org/wiki/C0_and_C1_control_codes[C0 control characters]
* Unicode characters ``++U+200B, U+200C, U+200D, U+2060, U+FEFF, U+2028, U+2029++``

=== Exceptions

* https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/strings/#verbatim-string-literals[Verbatim string literals] and https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/strings/#raw-string-literals[raw string literals], since they have no escape mechanism
* The simple space character: Unicode `U+0020`, ASCII 32

== How to fix it

=== Code examples

==== Noncompliant code example

[source,csharp,diff-id=1,diff-type=noncompliant]
----
string tabInside = "A	B";                 // Noncompliant: contains a tabulation
string zeroWidthSpaceInside = "foo​bar";     // Noncompliant: contains a U+200B character inside
Console.WriteLine(zeroWidthSpaceInside);    // Prints "foo?bar"
----

==== Compliant solution

[source,csharp,diff-id=1,diff-type=compliant]
----
string tabInside = "A\tB";                      // Compliant: escaped value
string zeroWidthSpaceInside = "foo\u200Bbar";   // Compliant: escaped value
Console.WriteLine(zeroWidthSpaceInside);        // Prints "foo?bar"
----

== Resources

=== Documentation

* https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/strings/[Strings and string literals]
* https://en.wikipedia.org/wiki/Control_character[Control character]

ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

Replace the control character at position XX by its escape sequence 'XX'.

'''
== Comments And Links
(visible only on this page)

include::../comments-and-links.adoc[]

endif::env-github,rspecator-view[]