Add caching to PdfRenderController

Implemented caching in the PdfRenderController using IMemoryCache to improve performance by avoiding redundant PDF rendering. Added a new constructor parameter for IMemoryCache and a static TimeSpan field for cache duration. Introduced a private method, BuildCacheKey, to generate unique cache keys based on the SHA256 hash of PDF bytes. Updated the RenderPages method to check for cached pages before rendering and store results in the cache.

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Controllers/PdfRenderController.cs

@@ -4,13 +4,17 @@ using EnvelopeGenerator.Application.Common.Interfaces.Doc;
 using EnvelopeGenerator.Domain.Constants;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
+using Microsoft.Extensions.Caching.Memory;
+using System.Security.Cryptography;
 
 namespace EnvelopeGenerator.Server.Controllers;
 
 [ApiController]
 [Route("api/[controller]")]
-public class PdfRenderController(IPdfPageImageRenderer renderer) : ControllerBase
+public class PdfRenderController(IPdfPageImageRenderer renderer, IMemoryCache memoryCache) : ControllerBase
 {
+    private static readonly TimeSpan RenderCacheDuration = TimeSpan.FromMinutes(5);
+
     // TODO(perf): Replace JSON/base64 transport for PdfBytes with application/octet-stream (or multipart) and stream-based request parsing to reduce payload size and allocation pressure for large PDFs.
     [HttpPost("pages")]
     [Authorize(AuthenticationSchemes = AuthScheme.Sender)]
@@ -19,7 +23,19 @@ public class PdfRenderController(IPdfPageImageRenderer renderer) : ControllerBas
         if (request?.PdfBytes is not { Length: > 0 } bytes)
             return BadRequest("Missing PDF bytes.");
 
+        var cacheKey = BuildCacheKey(bytes);
+        if (memoryCache.TryGetValue(cacheKey, out IReadOnlyList<PdfPageImageDto>? cachedPages) && cachedPages is not null)
+            return Ok(cachedPages);
+
         IReadOnlyList<PdfPageImageDto> pages = await renderer.RenderPagesAsImagesAsync(bytes, cancel);
+        memoryCache.Set(cacheKey, pages, RenderCacheDuration);
+
         return Ok(pages);
     }
+
+    private static string BuildCacheKey(byte[] pdfBytes)
+    {
+        var hash = Convert.ToHexString(SHA256.HashData(pdfBytes));
+        return $"pdf-render:pages:v1:dpi110:{hash}";
+    }
 }