No, it’s not mandatory.
Per the HTTP 1.1 specification: Any HTTP/1.1 message containing an entity-body SHOULD include a Content-Type header field defining the media type of that body.
If the media type remains unknown, the recipient SHOULD treat it as type “application/octet-stream”.
What is the use of content type?
A content type is a reusable collection of metadata (columns), workflow, behavior, and other settings for a category of items or documents in a Microsoft SharePoint Foundation 2010 list or document library. Content types enable you to manage the settings for a category of information in a centralized, reusable way.
What is Content Type in post request?
To specify the content types of the request body and output, use the Content-Type and Accept headers. Indicates that the request body format is JSON. Indicates that the request body format is XML. Indicates that the request body is URL encoded.
What is rest content type?
The entity header Content-Type is used to indicate the media type of the resource. In responses, a Content-Type header tells the client what the content type of the returned content actually is. In requests, such as POST or PUT, the client tells the server what type of data is actually sent.
What is content length?
The Content-Length header is a number denoting an the exact byte length of the HTTP body. Generally the Content-Length header is used for HTTP 1.1 so that the receiving party knows when the current response* has finished, so the connection can be reused for another request.