How can I add a query string into HttpClient.BaseAdress in c#?

Question

I'm trying to pass a query string into a BaseAddress but it doesn't recognize the quotation mark "?".

The quotation breaks the URI

First I create my BaseAddress

httpClient.BaseAddress = new Uri($"https://api.openweathermap.org/data/2.5/weather?appid={Key}/");

Then I call the GetAsync method, trying to add another parameter

using (var response = await ApiHelper.httpClient.GetAsync("&q=mexico"))....

This is the URI the code is calling

https://api.openweathermap.org/data/2.5/&q=mexico

Possible duplicate of [Build query string for System.Net.HttpClient get](https://stackoverflow.com/questions/17096201/build-query-string-for-system-net-httpclient-get) — Carl Pease, Jun 07 '19 at 00:51
I think if you want to use that `BaseAddress` property effectively you need to use the `GetAsync` methods that take `System.Uri` as a parameter. It will parse your partial url and append it to the base. your querystring should start with a question mark `?q=mexico&other=2' — Glenn Ferrie, Jun 07 '19 at 00:55
I'd be tempted to create a [`DelegatingHandler`](https://learn.microsoft.com/en-us/previous-versions/visualstudio/hh193679(v%3Dvs.118)) since I don't think this is possible without a handler or manually appending it to the URL in every request. — ProgrammingLlama, Jun 07 '19 at 01:04
Hi, is there anything you're still unsure about with this question? — ProgrammingLlama, Jul 02 '19 at 10:43

ProgrammingLlama · Accepted Answer · 2019-06-07T01:35:54.613

I'd be tempted to use a DelegatingHandler if you need to apply an API key to every single request:

private class KeyHandler : DelegatingHandler
{
    private readonly string _escapedKey;

    public KeyHandler(string key)  : this(new HttpClientHandler(), key)
    {
    }

    public KeyHandler(HttpMessageHandler innerHandler, string key) : base(innerHandler)
    {
        // escape the key since it might contain invalid characters
        _escapedKey = Uri.EscapeDataString(key);
    }

    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        // we'll use the UriBuilder to parse and modify the url
        var uriBuilder = new UriBuilder(request.RequestUri);

        // when the query string is empty, we simply want to set the appid query parameter
        if (string.IsNullOrEmpty(uriBuilder.Query))
        {
            uriBuilder.Query = $"appid={_escapedKey}";
        }
        // otherwise we want to append it
        else
        {
            uriBuilder.Query = $"{uriBuilder.Query}&appid={_escapedKey}";
        }
        // replace the uri in the request object
        request.RequestUri = uriBuilder.Uri;
        // make the request as normal
        return base.SendAsync(request, cancellationToken);
    }
}

Usage:

httpClient = new HttpClient(new KeyHandler(Key));
httpClient.BaseAddress = new Uri($"https://api.openweathermap.org/data/2.5/weather"); 

// since the logic of adding/appending the appid is done based on what's in
// the query string, you can simply write `?q=mexico` here, instead of `&q=mexico`
using (var response = await ApiHelper.httpClient.GetAsync("?q=mexico"))

** Note: If you're using ASP.NET Core, you should call services.AddHttpClient() and then use IHttpHandlerFactory to generate the inner handler for KeyHandler.

can you recommend any examples of doing this in .net core. Are you simply referring to calling .AddHttpMessageHandler() — tappetyclick, Jul 15 '22 at 10:29
Also wondering the same thing, could you expand the last part of your answer? — silkfire, Feb 15 '23 at 11:29

score 0 · Answer 2 · answered Nov 19 '19 at 10:19

This is how I work around it:

Http client impl:

namespace StocksApi2.httpClients
{
    public interface IAlphavantageClient
    {
        Task<string> GetSymboleDetailes(string queryToAppend);
    }

    public class AlphavantageClient : IAlphavantageClient
    {
        private readonly HttpClient _client;

        public AlphavantageClient(HttpClient httpClient)
        {
            httpClient.BaseAddress = new Uri("https://www.alphavantage.co/query?apikey=<REPLACE WITH YOUR TOKEN>&");
            httpClient.DefaultRequestHeaders.Add("Accept", "application/json; charset=utf-8");
            httpClient.DefaultRequestHeaders.Add("User-Agent", "HttpClientFactory-Sample");

            _client = httpClient;
        }

        public async Task<string> GetSymboleDetailes(string queryToAppend)
        {
            _client.BaseAddress = new Uri(_client.BaseAddress + queryToAppend);
            return await _client.GetStringAsync("");
        }
    }
}

Controller:

namespace StocksApi2.Controllers
{
    [ApiController]
    [Route("api/[controller]")]
    public class SymbolDetailsController : ControllerBase
    {
        private readonly IAlphavantageClient _client;

        public SymbolDetailsController(IAlphavantageClient client)
        {
            _client = client;
        }


        [HttpGet]
        public async Task<ActionResult> Get([FromQuery]string function = "TIME_SERIES_INTRADAY",
            [FromQuery]string symbol = "MSFT", [FromQuery]string interval = "5min")
        {

            try {
                string query = $"function={function}&symbol={symbol}&interval={interval}";
                string result = await _client.GetSymboleDetailes(query);
                return Ok(result);
            }catch(Exception e)
            {
                return NotFound("Error: " + e);
            }

        }
    }
}

And in Startup.cs inside ConfigureServices:

  services.AddHttpClient();
  services.AddHttpClient<IAlphavantageClient, AlphavantageClient>();

How can I add a query string into HttpClient.BaseAdress in c#?

2 Answers2