Getting a Request Headers value

Question

Very simple I m sure  but driving me up the wall  There is a component that I use in my web application that identifies itself during a web request by adding the header  XYZComponent true  - the problem I m having is  how do you check for this in your view   The following wont work   if  Request Headers  XYZComponent   Count    gt  0    Nor this   if  Request Headers AllKeys Where k   gt  k     XYZComponent   Count    gt  0    Both throw exceptions if the header variable has not been set  Any help would be most appreciated

User · Answer

Header exists   if  Request Headers  XYZComponent      null    or even better   string xyzHeader   Request Headers  XYZComponent    bool isXYZ   if  bool TryParse xyzHeader  out isXYZ   amp  amp  isXYZ    which will check whether it is set to true  This should be fool-proof because it does not care on leading trailing whitespace and is case-insensitive  bool TryParse does work on null   Addon  You could make this more simple with this extension method which returns a nullable boolean  It should work on both invalid input and null   public static bool  ToBoolean this string s        bool result       if  bool TryParse s  out result           return result      else         return null      Usage  because this is an extension method and not instance method this will not throw an exception on null - it may be confusing  though    if  Request Headers  XYZComponent   ToBoolean      true

User · Answer

In dotnet core  Request Headers  X-MyCustomHeader   returns StringValues which will not be null  You can check the count though to make sure it found your header as follows   var myHeaderValue   Request Headers  X-MyCustomHeader    if myHeaderValue Count    0  return Unauthorized    string myHeader   myHeaderValue ToString      For illustration purposes

User · Answer

if   Request Headers  XYZComponent              true            header is present and set to  true

User · Answer

The following code should allow you to check for the existance of the header you re after in Request Headers   if  Request Headers AllKeys Contains  XYZComponent             Can now check if the value is true      var value   Convert ToBoolean Request Headers  XYZComponent

User · Answer

if  Request Headers  XYZComponent   Count    gt  0        will attempted to count the number of characters in the returned string  but if the header doesn t exist it will return NULL  hence why it s throwing an exception  Your second example effectively does the same thing  it will search through the collection of Headers and return NULL if it doesn t exist  which you then attempt to count the number of characters on   Use this instead   if Request Headers  XYZComponent      null    Or if you want to treat blank or empty strings as not set then use   if  Request Headers  XYZComponent          Trim   Length  gt  0    The Null Coalesce operator    will return a blank string if the header is null  stopping it throwing a NullReferenceException   A variation of your second attempt will also work   if  Request Headers AllKeys Any k   gt  string Equals k   XYZComponent         Edit  Sorry didn t realise you were explicitly checking for the value true   bool isSet   Boolean TryParse Request Headers  XYZComponent    out isSet   amp  amp  isSet    Will return false if Header value is false  or if Header has not been set or if Header is any other value other than true or false  Will return true is the Header value is the string  true

User · Answer

string strHeader   Request Headers  XYZComponent   bool bHeader   Boolean TryParse strHeader  out bHeader    amp  amp  bHeader   if  true  than true if  false  or anything else   fooBar   than false   or  string strHeader   Request Headers  XYZComponent   bool b  bool  bHeader   Boolean TryParse strHeader  out b    b   default bool     if  true  than true if  false  than false else   fooBar   than null

User · Answer

Firstly you don t do this in your view  You do it in the controller and return a view model to the view so that the view doesn t need to care about custom HTTP headers but just displaying data on the view model   public ActionResult Index         var xyzComponent   Request Headers  xyzComponent        var model   new MyModel                IsCustomHeaderSet    xyzComponent    null            return View model

[c#] Getting a Request.Headers value

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