Content Type of POST request payload - json

Question

I am sending a JSON body in my POST Request, but http.DetectContentType is identifying it as a text/plain type.
I want to have flexibility to process request payload based on their content type - if XML {} if JSON {} else {NO Processing}
To achieve this conditional processing, I am using http.DetectContentType to return the content type o the request but it is returning text/plain is every scenario.
func Test(w http.ResponseWriter, r *http.Request) *ErrorObject {
reqBuffer := make([]byte, 512)
_, err := r.Body.Read(reqBuffer)
if err != nil {
return ErrorObject{}.New(1, err, nil)
}
contentType := GetContentType(reqBuffer)
fmt.Printf(contentType)
if contentType == "application/xml" || contentType == "text/xml" {
w.Header().Set("Content-Type", "application/xml; charset=UTF-8") ...}
if contentType == "application/json" || contentType == "text/json" {
w.Header().Set("Content-Type", "application/json; charset=UTF-8") ... }
else return Invalid Request Type error
}
func GetContentType(buffer []byte) string {
fmt.Println(string(buffer))
contentType := http.DetectContentType(buffer)
fmt.Printf(contentType)
return contentType
}
Expect to return the function - Content Type as application/json but getting text/plain
Using POSTMAN to send request to server with Body as raw and JSON
{
"data": [
{
"group": "TEST",
"name": "TEST",
"released": true,
"version": 1,
"teststeps": [
{
"bin": 32,
"comment": "PAA",
"dataType": "J",
"format": "R6.2",
"id": "PAA3",
"osg": 8,
"usg": 0
}
],
"parameters": [
{
"comment": "test",
"description": "test",
"format": "R7.0",
"id": 1,
"teststepId": "PAA",
"value": 30,
"type": "teststep"
}
]
}
]
}

Answer 1

I am using http.DetectContentType to return the content type o the request but it is returning text/plain is every scenario.
According to the documentation DetectContentType "... implements the algorithm described at https://mimesniff.spec.whatwg.org/ to determine the Content-Type of the given data". The algorithm there is primarily for handling content types which the browser can handle by itself.
And if you look at the actual code you'll see that it does not care about application/json or similar at all and that it returns text/plain for anything which looks non-binary (and was not matched before as with text/html).
In other words: this is the wrong tool for the job. The proper way would be for the client to specify what kind of content is sent using the Content-Type header and not to let the server guess the kind of content.