Why is HttpClient BaseAddress not working

Question

Consider the following code  where the BaseAddress defines a partial URI path   using  var handler   new HttpClientHandler    using  var client   new HttpClient handler         client BaseAddress   new Uri  http   something com api        var response   await client GetAsync   resource 7        I expect this to perform a GET request to http   something com api resource 7  But it doesn t   After some searching  I find this question and answer  HttpClient with BaseAddress  The suggestion is to place   on the end of the BaseAddress   using  var handler   new HttpClientHandler    using  var client   new HttpClient handler         client BaseAddress   new Uri  http   something com api         var response   await client GetAsync   resource 7        It still doesn t work  Here s the documentation  HttpClient BaseAddress What s going on here

User · Answer

Reference Resolution is described by RFC 3986 Uniform Resource Identifier (URI): Generic Syntax. And that is exactly how it supposed to work. To preserve base URI path you need to add slash at the end of the base URI and remove slash at the beginning of relative URI.

If base URI contains non-empty path, merge procedure discards it's last part (after last /). Relevant section:

5.2.3. Merge Paths

The pseudocode above refers to a "merge" routine for merging a relative-path reference with the path of the base URI. This is accomplished as follows:

If the base URI has a defined authority component and an empty path, then return a string consisting of "/" concatenated with the reference's path; otherwise

return a string consisting of the reference's path component appended to all but the last segment of the base URI's path (i.e., excluding any characters after the right-most "/" in the base URI path, or excluding the entire base URI path if it does not contain any "/" characters).

If relative URI starts with a slash, it is called a absolute-path relative URI. In this case merge procedure ignore all base URI path. For more information check 5.2.2. Transform References section.

User · Answer

Ran into a issue with the HTTPClient  even with the suggestions still could not get it to authenticate  Turns out I needed a trailing     in my relative path   i e   var result   await  client GetStringAsync  awxUrl    api v2 inventories  name     inventoryName     var result   await  client PostAsJsonAsync  awxUrl    api v2 job templates     templateId   launch     new                   inventory   inventoryId

User · Answer

It turns out that  out of the four possible permutations of including or excluding trailing or leading forward slashes on the BaseAddress and the relative URI passed to the GetAsync method -- or whichever other method of HttpClient -- only one permutation works   You must place a slash at the end of the BaseAddress  and you must not place a slash at the beginning of your relative URI  as in the following example   using  var handler   new HttpClientHandler    using  var client   new HttpClient handler         client BaseAddress   new Uri  http   something com api         var response   await client GetAsync  resource 7        Even though I answered my own question  I figured I d contribute the solution here since  again  this unfriendly behavior is undocumented  My colleague and I spent most of the day trying to fix a problem that was ultimately caused by this oddity of HttpClient

[c#] Why is HttpClient BaseAddress not working?

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