When no recording matches

HttpRecordingOptions.MissBehavior decides what happens to a request that matches no recording:

When it is not set, the default depends on the mode: Passthrough in Auto mode, so that the missing recording is created, and Throw in Replay mode. The option is not used in Record mode, where every request is sent.

Fail on any request that is not recorded

Setting the option also applies to Auto mode. Auto with Throw replays what was recorded and fails on anything else, without ever sending a request:

var options = new HttpRecordingOptions
{
    Mode = HttpRecordingMode.Auto,
    MissBehavior = HttpRecordingMissBehavior.Throw,
};

HttpRecordingMissException derives from InvalidOperationException. Its message is safe to log: it contains no credentials from the URI and masks every query string value. Method and RequestUri give the request as it was sent:

var exception = await Assert.ThrowsAsync<HttpRecordingMissException>(
    () => httpClient.GetAsync(new Uri("https://example.com/api/items?token=secret")));

// The message is safe to log: query values are masked
Assert.Equal("No recorded response found for GET https://example.com/api/items?token=***.", exception.Message);

// The properties hold the request as it was sent
Assert.Equal("GET", exception.Method);
Assert.Equal("https://example.com/api/items?token=secret", exception.RequestUri);

Return an error response

ReturnDefault lets the code under test handle the miss like a server error. The body of the response gives the request, with the same redaction as the exception message:

var options = new HttpRecordingOptions
{
    Mode = HttpRecordingMode.Replay,
    MissBehavior = HttpRecordingMissBehavior.ReturnDefault,
};
using var recordingHandler = new HttpRecordingHandler(new JsonHttpRecordingStore(recordingPath), options);
using var httpClient = new HttpClient(recordingHandler);

using var response = await httpClient.GetAsync(new Uri("https://example.com/api/items/1"));
Assert.Equal(HttpStatusCode.InternalServerError, response.StatusCode);
Assert.Equal("No recorded response found for GET https://example.com/api/items/1.", await response.Content.ReadAsStringAsync());

Call the real service

Passthrough needs an inner handler. In Replay mode, it sends the requests that have no recording to the service without recording them, so the store stays as it is.