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dotnet/samples/AzureFunctions/08_ReliableStreaming/FunctionTriggers.cs

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+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Text;
+using Microsoft.Agents.AI;
+using Microsoft.Agents.AI.DurableTask;
+using Microsoft.Agents.AI.Hosting.AzureFunctions;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Features;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.Azure.Functions.Worker;
+using Microsoft.DurableTask.Client;
+using Microsoft.Extensions.Logging;
+
+namespace ReliableStreaming;
+
+/// <summary>
+/// HTTP trigger functions for reliable streaming of durable agent responses.
+/// </summary>
+/// <remarks>
+/// This class exposes two endpoints:
+/// <list type="bullet">
+/// <item>
+/// <term>Create</term>
+/// <description>Starts an agent run and streams responses. The response format depends on the
+/// <c>Accept</c> header: <c>text/plain</c> returns raw text (ideal for terminals), while
+/// <c>text/event-stream</c> or any other value returns Server-Sent Events (SSE).</description>
+/// </item>
+/// <item>
+/// <term>Stream</term>
+/// <description>Resumes a stream from a cursor position, enabling reliable message delivery</description>
+/// </item>
+/// </list>
+/// </remarks>
+public sealed class FunctionTriggers
+{
+    private readonly RedisStreamResponseHandler _streamHandler;
+    private readonly ILogger<FunctionTriggers> _logger;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="FunctionTriggers"/> class.
+    /// </summary>
+    /// <param name="streamHandler">The Redis stream handler for reading/writing agent responses.</param>
+    /// <param name="logger">The logger instance.</param>
+    public FunctionTriggers(RedisStreamResponseHandler streamHandler, ILogger<FunctionTriggers> logger)
+    {
+        this._streamHandler = streamHandler;
+        this._logger = logger;
+    }
+
+    /// <summary>
+    /// Creates a new agent session, starts an agent run with the provided prompt,
+    /// and streams the response back to the client.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// The response format depends on the <c>Accept</c> header:
+    /// <list type="bullet">
+    /// <item><c>text/plain</c>: Returns raw text output, ideal for terminal display with curl</item>
+    /// <item><c>text/event-stream</c> or other: Returns Server-Sent Events (SSE) with cursor support</item>
+    /// </list>
+    /// </para>
+    /// <para>
+    /// The response includes an <c>x-conversation-id</c> header containing the conversation ID.
+    /// For SSE responses, clients can use this conversation ID to resume the stream if disconnected
+    /// by calling the <see cref="StreamAsync"/> endpoint with the conversation ID and the last received cursor.
+    /// </para>
+    /// <para>
+    /// Each SSE event contains the following fields:
+    /// <list type="bullet">
+    /// <item><c>id</c>: The Redis stream entry ID (use as cursor for resumption)</item>
+    /// <item><c>event</c>: Either "message" for content or "done" for stream completion</item>
+    /// <item><c>data</c>: The text content of the response chunk</item>
+    /// </list>
+    /// </para>
+    /// </remarks>
+    /// <param name="request">The HTTP request containing the prompt in the body.</param>
+    /// <param name="durableClient">The Durable Task client for signaling agents.</param>
+    /// <param name="context">The function invocation context.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A streaming response in the format specified by the Accept header.</returns>
+    [Function(nameof(CreateAsync))]
+    public async Task<IActionResult> CreateAsync(
+        [HttpTrigger(AuthorizationLevel.Anonymous, "post", Route = "agent/create")] HttpRequest request,
+        [DurableClient] DurableTaskClient durableClient,
+        FunctionContext context,
+        CancellationToken cancellationToken)
+    {
+        // Read the prompt from the request body
+        string prompt = await new StreamReader(request.Body).ReadToEndAsync(cancellationToken);
+        if (string.IsNullOrWhiteSpace(prompt))
+        {
+            return new BadRequestObjectResult("Request body must contain a prompt.");
+        }
+
+        AIAgent agentProxy = durableClient.AsDurableAgentProxy(context, "TravelPlanner");
+
+        // Create a new agent thread
+        AgentThread thread = await agentProxy.GetNewThreadAsync(cancellationToken);
+        string agentSessionId = thread.GetService<AgentSessionId>().ToString();
+
+        this._logger.LogInformation("Creating new agent session: {AgentSessionId}", agentSessionId);
+
+        // Run the agent in the background (fire-and-forget)
+        DurableAgentRunOptions options = new() { IsFireAndForget = true };
+        await agentProxy.RunAsync(prompt, thread, options, cancellationToken);
+
+        this._logger.LogInformation("Agent run started for session: {AgentSessionId}", agentSessionId);
+
+        // Check Accept header to determine response format
+        // text/plain = raw text output (ideal for terminals)
+        // text/event-stream or other = SSE format (supports resumption)
+        string? acceptHeader = request.Headers.Accept.FirstOrDefault();
+        bool useSseFormat = acceptHeader?.Contains("text/plain", StringComparison.OrdinalIgnoreCase) != true;
+
+        return await this.StreamToClientAsync(
+            conversationId: agentSessionId, cursor: null, useSseFormat, request.HttpContext, cancellationToken);
+    }
+
+    /// <summary>
+    /// Resumes streaming from a specific cursor position for an existing session.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// Use this endpoint to resume a stream after disconnection. Pass the conversation ID
+    /// (from the <c>x-conversation-id</c> response header) and the last received cursor
+    /// (Redis stream entry ID) to continue from where you left off.
+    /// </para>
+    /// <para>
+    /// If no cursor is provided, streaming starts from the beginning of the stream.
+    /// This allows clients to replay the entire response if needed.
+    /// </para>
+    /// <para>
+    /// The response format depends on the <c>Accept</c> header:
+    /// <list type="bullet">
+    /// <item><c>text/plain</c>: Returns raw text output, ideal for terminal display with curl</item>
+    /// <item><c>text/event-stream</c> or other: Returns Server-Sent Events (SSE) with cursor support</item>
+    /// </list>
+    /// </para>
+    /// </remarks>
+    /// <param name="request">The HTTP request. Use the <c>cursor</c> query parameter to specify the cursor position.</param>
+    /// <param name="conversationId">The conversation ID to stream from.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A streaming response in the format specified by the Accept header.</returns>
+    [Function(nameof(StreamAsync))]
+    public async Task<IActionResult> StreamAsync(
+        [HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = "agent/stream/{conversationId}")] HttpRequest request,
+        string conversationId,
+        CancellationToken cancellationToken)
+    {
+        if (string.IsNullOrWhiteSpace(conversationId))
+        {
+            return new BadRequestObjectResult("Conversation ID is required.");
+        }
+
+        // Get the cursor from query string (optional)
+        string? cursor = request.Query["cursor"].FirstOrDefault();
+
+        this._logger.LogInformation(
+            "Resuming stream for conversation {ConversationId} from cursor: {Cursor}",
+            conversationId,
+            cursor ?? "(beginning)");
+
+        // Check Accept header to determine response format
+        // text/plain = raw text output (ideal for terminals)
+        // text/event-stream or other = SSE format (supports cursor-based resumption)
+        string? acceptHeader = request.Headers.Accept.FirstOrDefault();
+        bool useSseFormat = acceptHeader?.Contains("text/plain", StringComparison.OrdinalIgnoreCase) != true;
+
+        return await this.StreamToClientAsync(conversationId, cursor, useSseFormat, request.HttpContext, cancellationToken);
+    }
+
+    /// <summary>
+    /// Streams chunks from the Redis stream to the HTTP response.
+    /// </summary>
+    /// <param name="conversationId">The conversation ID to stream from.</param>
+    /// <param name="cursor">Optional cursor to resume from. If null, streams from the beginning.</param>
+    /// <param name="useSseFormat">True to use SSE format, false for plain text.</param>
+    /// <param name="httpContext">The HTTP context for writing the response.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>An empty result after streaming completes.</returns>
+    private async Task<IActionResult> StreamToClientAsync(
+        string conversationId,
+        string? cursor,
+        bool useSseFormat,
+        HttpContext httpContext,
+        CancellationToken cancellationToken)
+    {
+        // Set response headers based on format
+        httpContext.Response.Headers.ContentType = useSseFormat
+            ? "text/event-stream"
+            : "text/plain; charset=utf-8";
+        httpContext.Response.Headers.CacheControl = "no-cache";
+        httpContext.Response.Headers.Connection = "keep-alive";
+        httpContext.Response.Headers["x-conversation-id"] = conversationId;
+
+        // Disable response buffering if supported
+        httpContext.Features.Get<IHttpResponseBodyFeature>()?.DisableBuffering();
+
+        try
+        {
+            await foreach (StreamChunk chunk in this._streamHandler.ReadStreamAsync(
+                conversationId,
+                cursor,
+                cancellationToken))
+            {
+                if (chunk.Error != null)
+                {
+                    this._logger.LogWarning("Stream error for conversation {ConversationId}: {Error}", conversationId, chunk.Error);
+                    await WriteErrorAsync(httpContext.Response, chunk.Error, useSseFormat, cancellationToken);
+                    break;
+                }
+
+                if (chunk.IsDone)
+                {
+                    await WriteEndOfStreamAsync(httpContext.Response, chunk.EntryId, useSseFormat, cancellationToken);
+                    break;
+                }
+
+                if (chunk.Text != null)
+                {
+                    await WriteChunkAsync(httpContext.Response, chunk, useSseFormat, cancellationToken);
+                }
+            }
+        }
+        catch (OperationCanceledException)
+        {
+            this._logger.LogInformation("Client disconnected from stream {ConversationId}", conversationId);
+        }
+
+        return new EmptyResult();
+    }
+
+    /// <summary>
+    /// Writes a text chunk to the response.
+    /// </summary>
+    private static async Task WriteChunkAsync(
+        HttpResponse response,
+        StreamChunk chunk,
+        bool useSseFormat,
+        CancellationToken cancellationToken)
+    {
+        if (useSseFormat)
+        {
+            await WriteSSEEventAsync(response, "message", chunk.Text!, chunk.EntryId);
+        }
+        else
+        {
+            await response.WriteAsync(chunk.Text!, cancellationToken);
+        }
+
+        await response.Body.FlushAsync(cancellationToken);
+    }
+
+    /// <summary>
+    /// Writes an end-of-stream marker to the response.
+    /// </summary>
+    private static async Task WriteEndOfStreamAsync(
+        HttpResponse response,
+        string entryId,
+        bool useSseFormat,
+        CancellationToken cancellationToken)
+    {
+        if (useSseFormat)
+        {
+            await WriteSSEEventAsync(response, "done", "[DONE]", entryId);
+        }
+        else
+        {
+            await response.WriteAsync("\n", cancellationToken);
+        }
+
+        await response.Body.FlushAsync(cancellationToken);
+    }
+
+    /// <summary>
+    /// Writes an error message to the response.
+    /// </summary>
+    private static async Task WriteErrorAsync(
+        HttpResponse response,
+        string error,
+        bool useSseFormat,
+        CancellationToken cancellationToken)
+    {
+        if (useSseFormat)
+        {
+            await WriteSSEEventAsync(response, "error", error, null);
+        }
+        else
+        {
+            await response.WriteAsync($"\n[Error: {error}]\n", cancellationToken);
+        }
+
+        await response.Body.FlushAsync(cancellationToken);
+    }
+
+    /// <summary>
+    /// Writes a Server-Sent Event to the response stream.
+    /// </summary>
+    private static async Task WriteSSEEventAsync(
+        HttpResponse response,
+        string eventType,
+        string data,
+        string? id)
+    {
+        StringBuilder sb = new();
+
+        // Include the ID if provided (used as cursor for resumption)
+        if (!string.IsNullOrEmpty(id))
+        {
+            sb.AppendLine($"id: {id}");
+        }
+
+        sb.AppendLine($"event: {eventType}");
+        sb.AppendLine($"data: {data}");
+        sb.AppendLine(); // Empty line marks end of event
+
+        await response.WriteAsync(sb.ToString());
+    }
+}