Revert unintentional nullability changes and fix inconsistencies in StringContent ctrs

[antonfirsov]

This is a follow-up on #81506 (comment). We introduced some inconsistencies and unintentional nullability changes in StringContent's constructors. Chronologically:

• Add StringContent ctor providing tighter control over charset #17036 proposed new constructors before the introduction of nullable references to C#
• Annotate System.Net.Http for nullable #33268 changed all mediaType args to be nullable
• We approving the new constructors, the comment with the fianal API suggestion did not takke into account the nullability changes implemented in Annotate System.Net.Http for nullable #33268, falsely "recommending" that nullability should be "reverted". It also proposed the argument MediaTypeHeaderValue mediaType to be non-nullable, which is inconsistent with the then-existing API-s.
• First try at implementing newly suggested ctor for providing tighter control over charset #63231 implemented the proposal in this form, and also altered existing mediaType args to be non-nullable
  • On top of that, the new constructors taking MediaTypeHeaderValue mediaType don't do null-check on that arg, simply allowing the property to be set to null
    

    runtime/src/libraries/System.Net.Http/src/System/Net/Http/StringContent.cs

    Line 59 in 58719ec

    Headers.ContentType = mediaType;

#81722 provides a minimal fix, however, since this was an unintentional change, I suggest to revisit it for .NET 8.0, relaxing nullability for all mediaType declarations, explicitly setting text/plain when null is being passed. This should be fairly trivial to implement.

public class StringContent : ByteArrayContent
{
-   public StringContent(string content, MediaTypeHeaderValue  mediaType);
+   public StringContent(string content, MediaTypeHeaderValue? mediaType);
-   public StringContent(string content, Encoding? encoding, string  mediaType);
+   public StringContent(string content, Encoding? encoding, string? mediaType);
-   public StringContent(string content, Encoding? encoding, MediaTypeHeaderValue  mediaType);
+   public StringContent(string content, Encoding? encoding, MediaTypeHeaderValue? mediaType);
}

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Issue Details

---

This is a follow-up on #81506 (comment). We introduced some inconsistencies and unintentional nullability changes in StringContent's constructors. Chronologically:

• Add StringContent ctor providing tighter control over charset #17036 proposed new constructors before the introduction of nullable references
• Annotate System.Net.Http for nullable #33268 changed all mediaType args to be nullable
• We approving the new constructors, the comment with the fianal API suggestion did not takke into account the nullability changes implemented in Annotate System.Net.Http for nullable #33268, falsely "recommending" that nullability should be "reverted". It also proposed the argument MediaTypeHeaderValue mediaType to be non-nullable, which is inconsistent with then-existing API-s.
• First try at implementing newly suggested ctor for providing tighter control over charset #63231 implemented the proposal in this form, and also altered existing mediaType args to be non-nullable
  • On top of that, it doesn't do null-check for the argument MediaTypeHeaderValue mediaType, simply allowing the property to be set to null
    

    runtime/src/libraries/System.Net.Http/src/System/Net/Http/StringContent.cs

    Line 59 in 58719ec

    Headers.ContentType = mediaType;

Since this was an unintentional change, I suggest to revisit it for .NET 8.0, relaxing nullability for all mediaType arguments, explicitly setting text/plain when null is being passed. This should be fairly trivial to implement.

public class StringContent : ByteArrayContent
{
-   public StringContent(string content, MediaTypeHeaderValue  mediaType);
+   public StringContent(string content, MediaTypeHeaderValue? mediaType);
-   public StringContent(string content, Encoding? encoding, string  mediaType);
+   public StringContent(string content, Encoding? encoding, string? mediaType);
-   public StringContent(string content, Encoding? encoding, MediaTypeHeaderValue  mediaType);
+   public StringContent(string content, Encoding? encoding, MediaTypeHeaderValue? mediaType);
}

Author:	antonfirsov
Assignees:	-
Labels:	area-System.Net.Http, untriaged
Milestone:	-

[bartonjs]

Video

The changes look consistent with the code's treatment of those parameters.

public class StringContent : ByteArrayContent
{
-   public StringContent(string content, MediaTypeHeaderValue  mediaType);
+   public StringContent(string content, MediaTypeHeaderValue? mediaType);
-   public StringContent(string content, Encoding? encoding, string  mediaType);
+   public StringContent(string content, Encoding? encoding, string? mediaType);
-   public StringContent(string content, Encoding? encoding, MediaTypeHeaderValue  mediaType);
+   public StringContent(string content, Encoding? encoding, MediaTypeHeaderValue? mediaType);
}