HttpResponseMessageExtensions.cs

using System.Net;
using System.Net.Http;

namespace ModelContextProtocol;

/// <summary>
/// Extension methods for <see cref="HttpResponseMessage"/>.
/// </summary>
internal static class HttpResponseMessageExtensions
{
    private const int MaxResponseBodyLength = 1024;

    /// <summary>
    /// Throws an <see cref="HttpRequestException"/> if the <see cref="HttpResponseMessage.IsSuccessStatusCode"/> property is <see langword="false"/>.
    /// Unlike <see cref="HttpResponseMessage.EnsureSuccessStatusCode"/>, this method includes the response body in the exception message
    /// to help diagnose issues when the server returns error details in the response body.
    /// </summary>
    /// <param name="response">The HTTP response message to check.</param>
    /// <param name="cancellationToken">The token to monitor for cancellation requests.</param>
    /// <returns>A task that represents the asynchronous operation.</returns>
    /// <exception cref="HttpRequestException">The response status code does not indicate success.</exception>
    public static async Task EnsureSuccessStatusCodeWithResponseBodyAsync(this HttpResponseMessage response, CancellationToken cancellationToken = default)
    {
        if (!response.IsSuccessStatusCode)
        {
            string? responseBody = null;
            try
            {
                using var cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
                cts.CancelAfter(TimeSpan.FromSeconds(5));
                responseBody = await response.Content.ReadAsStringAsync(cts.Token).ConfigureAwait(false);

                if (responseBody.Length > MaxResponseBodyLength)
                {
                    responseBody = responseBody.Substring(0, MaxResponseBodyLength) + "...";
                }
            }
            catch
            {
                // Ignore all errors reading the response body (e.g., stream closed, timeout, cancellation) - we'll throw without it.
            }

            throw CreateHttpRequestException(response, responseBody);
        }
    }

    /// <summary>
    /// Creates an <see cref="HttpRequestException"/> for a non-success response, including the response body in the message.
    /// </summary>
    /// <param name="response">The HTTP response message.</param>
    /// <param name="responseBody">The response body content, if available.</param>
    /// <returns>An <see cref="HttpRequestException"/> with the response details.</returns>
    public static HttpRequestException CreateHttpRequestException(HttpResponseMessage response, string? responseBody)
    {
        int statusCodeInt = (int)response.StatusCode;
        string message = string.IsNullOrEmpty(responseBody)
            ? $"Response status code does not indicate success: {statusCodeInt} ({response.ReasonPhrase})."
            : $"Response status code does not indicate success: {statusCodeInt} ({response.ReasonPhrase}). Response body: {responseBody}";

#if NET
        return new HttpRequestException(message, inner: null, response.StatusCode);
#else
        return new HttpRequestException(message);
#endif
    }
}