tsp, TCGC adoption, Handle optional content-type

[haolingdong-msft]

Will need to modify codegen to support adding the javadoc to let user input content-type.
Link #2861 (comment)

Depends on TCGC issue: Azure/typespec-azure#1259

Currently in codegen we get content types from requests.protocol.http.mediaTypes. Not from the values of contentType constant.
We need to pay attention to is single optional content type and multiple optional content types cases.

model ImageRequest {
  @body body?: bytes;
  @header contentType?: "image/png";
}
  @post
  op upload(...ImageRequest): void;

model ImageRequest {
  @body body?: bytes;
  @header contentType?: "image/png" | "image/jpeg";
}
  @post
  op upload(...ImageRequest): void;

Tasks

• Add optional content type to code-model
• Support optional content type in codegen

TCGC dependency

• [TCGC][Bug] TCGC added content-type header should be optional if request body is optional typespec-azure#1259

[weidongxu-microsoft]

In swagger, if body is optional, it can still specify the media type via produces keyword (not content-type header parameter).

Not sure how typespec does this, e.g.

model ImageRequest {
  @body body?: bytes;
  @header contentType?: "image/png" | "image/jpeg";
}

@post
op upload(...ImageRequest): void;

and what TCGC should give.

[haolingdong-msft]

In swagger, if body is optional, it can still specify the media type via produces keyword (not content-type header parameter).

Not sure how typespec does this, e.g.

model ImageRequest {
  @body body?: bytes;
  @header contentType?: "image/png" | "image/jpeg";
}

@post
op upload(...ImageRequest): void;

and what TCGC should give.

codegen should return optional content type whose value is ["image/png", "image/jpeg"]

Current behavior for optional content type:

1. content type is single

model ImageRequest {
  @body body?: bytes;
  @header contentType?: "image/png";
}

@post
op upload(...ImageRequest): void;

output code looks good:

2. content type is multiple

model ImageRequest {
  @body body?: bytes;
  @header contentType?: "image/png" | "image/jpeg";
}

@post
op upload(...ImageRequest): void;

output code does not suggested allowed values for content-type

So the current handling for multiple content type will need enhancement.