Replace fire-and-forget PDF trigger with bounded queue#48
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The POST /pdf/v1/ trigger previously used Task.Run with no backpressure, risking unbounded memory and giving dishonest 202 responses when capacity was exceeded. Replaced with a bounded Channel<string> drained by a BackgroundService, with a SemaphoreSlim capping concurrency. * PdfGenerationService extracts shared lock + generate logic * PdfGenerationQueue (IPdfGenerationQueue) owns the bounded channel; TryEnqueue returns false when full (BoundedChannelFullMode.Wait) * PdfGenerationBackgroundService drains the queue; SemaphoreSlim bounds concurrent in-flight MemoryStream allocations * PdfTriggerResult enum replaces bool return; 503 + Retry-After when queue full, fixes latent NotFound -> 200 bug on disabled services * New PdfTriggerQueueCapacity (50) and PdfTriggerMaxConcurrency (2) config keys under TextServices: * Unit tests for PdfHandler trigger result codes and queue capacity Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Summary
The
POST /pdf/v1/{**id}trigger endpoint previously used a bareTask.Runwith no backpressure:MemoryStreamallocations under load202responses: if a trigger was silently dropped, the caller would wait then hit the slow synchronous GET path anywayChanges
New types:
PdfGenerationService/IPdfGenerationService— extracts shared lock + generate logic fromPdfHandler; used by both the GET and background pathsPdfGenerationQueue/IPdfGenerationQueue— boundedChannel<string>wrapper;TryEnqueuereturnsfalsewhen full (BoundedChannelFullMode.Wait)PdfGenerationBackgroundService—BackgroundServicedraining the queue;SemaphoreSlimcaps concurrent in-flight generations (and therefore peakMemoryStreammemory)Updated types:
PdfTriggerResultenum replaces theboolreturn fromPdfTriggerRequest, enabling honest HTTP mapping:202when queued,503 + Retry-Afterwhen queue full,404when no artefact (fixes a latent bug where disabled-service/no-artefact was returning200)SearchApiOptionsgainsPdfTriggerQueueCapacity(default50) andPdfTriggerMaxConcurrency(default2)ServiceCollectionExtensions.AddPdfServices()consolidates PDF DI registrationTests:
PdfHandlerTests(10 tests covering allPdfTriggerResultandPdfRequestpaths) andPdfGenerationQueueTests(2 capacity tests).Test plan
dotnet test src/TextServices.Tests— all 477 tests passPOST /pdf/v1/{id}on a valid ID → 202 withLocationheaderPOST /pdf/v1/{id}when PDF already exists → 200 withlocationbodyPOST /pdf/v1/missing-id→ 404PdfTriggerQueueCapacityto1andPdfTriggerMaxConcurrencyto1in dev config; fire two simultaneous POSTs to different IDs → second returns 503🤖 Generated with Claude Code