feat: stale-while-revalidate (#416)

Author: fenos

.env.sample

@@ -9,6 +9,15 @@ SERVER_HEADERS_TIMEOUT=65
 SERVER_REGION=region-of-where-your-service-is-running
 
 
+#######################################
+# Request / Response
+#######################################
+REQUEST_URL_LENGTH_LIMIT=7500
+REQUEST_TRACE_HEADER=trace-id
+REQUEST_ETAG_HEADERS=if-none-match
+RESPONSE_S_MAXAGE=0
+
+
 #######################################
 # Auth
 #######################################

src/config.ts

@@ -37,6 +37,8 @@ type StorageConfigType = {
   databaseConnectionTimeout: number
   region: string
   requestTraceHeader?: string
+  requestEtagHeaders: string[]
+  responseSMaxAge: number
   serviceKey: string
   storageBackendType: StorageBackendType
   tenantId: string
@@ -153,6 +155,10 @@ export function getConfig(options?: { reload?: boolean }): StorageConfigType {
     requestUrlLengthLimit:
       Number(getOptionalConfigFromEnv('REQUEST_URL_LENGTH_LIMIT', 'URL_LENGTH_LIMIT')) || 7_500,
     requestTraceHeader: getOptionalConfigFromEnv('REQUEST_TRACE_HEADER', 'REQUEST_ID_HEADER'),
+    requestEtagHeaders: getOptionalConfigFromEnv('REQUEST_ETAG_HEADERS')?.trim().split(',') || [
+      'if-none-match',
+    ],
+    responseSMaxAge: parseInt(getOptionalConfigFromEnv('RESPONSE_S_MAXAGE') || '0', 10),
 
     // Admin
     adminApiKeys: getOptionalConfigFromEnv('SERVER_ADMIN_API_KEYS', 'ADMIN_API_KEYS') || '',

src/storage/renderer/head.ts

@@ -1,6 +1,6 @@
 import { AssetResponse, Renderer, RenderOptions } from './renderer'
-import { FastifyRequest } from 'fastify'
-import { StorageBackendAdapter } from '../backend'
+import { FastifyReply, FastifyRequest } from 'fastify'
+import { ObjectMetadata, StorageBackendAdapter } from '../backend'
 import { ImageRenderer, TransformOptions } from './image'
 
 /**
@@ -20,4 +20,27 @@ export class HeadRenderer extends Renderer {
       transformations: ImageRenderer.applyTransformation(request.query as TransformOptions),
     }
   }
+
+  protected handleCacheControl(
+    request: FastifyRequest<any>,
+    response: FastifyReply<any>,
+    metadata: ObjectMetadata
+  ) {
+    const etag = this.findEtagHeader(request)
+
+    const cacheControl = [metadata.cacheControl]
+
+    if (!etag) {
+      response.header('Cache-Control', cacheControl.join(', '))
+      return
+    }
+
+    if (etag !== metadata.eTag) {
+      cacheControl.push('must-revalidate')
+    } else if (this.sMaxAge > 0) {
+      cacheControl.push(`s-maxage=${this.sMaxAge}`)
+    }
+
+    response.header('Cache-Control', cacheControl.join(', '))
+  }
 }

src/storage/renderer/renderer.ts

@@ -1,6 +1,7 @@
 import { FastifyReply, FastifyRequest } from 'fastify'
 import { ObjectMetadata } from '../backend'
 import { Readable } from 'stream'
+import { getConfig } from '../../config'
 
 export interface RenderOptions {
   bucket: string
@@ -16,12 +17,16 @@ export interface AssetResponse {
   transformations?: string[]
 }
 
+const { requestEtagHeaders, responseSMaxAge } = getConfig()
+
 /**
  * Renderer
  * a generic renderer that respond to a request with an asset content
  * and all the important headers
  */
 export abstract class Renderer {
+  protected sMaxAge = responseSMaxAge
+
   abstract getAsset(request: FastifyRequest, options: RenderOptions): Promise<AssetResponse>
 
   /**
@@ -34,7 +39,7 @@ export abstract class Renderer {
     try {
       const data = await this.getAsset(request, options)
 
-      await this.setHeaders(response, data, options)
+      this.setHeaders(request, response, data, options)
 
       return response.send(data.body)
     } catch (err: any) {
@@ -55,7 +60,12 @@ export abstract class Renderer {
     }
   }
 
-  protected setHeaders(response: FastifyReply<any>, data: AssetResponse, options: RenderOptions) {
+  protected setHeaders(
+    request: FastifyRequest<any>,
+    response: FastifyReply<any>,
+    data: AssetResponse,
+    options: RenderOptions
+  ) {
     response
       .status(data.metadata.httpStatusCode ?? 200)
       .header('Accept-Ranges', 'bytes')
@@ -67,7 +77,7 @@ export abstract class Renderer {
     if (options.expires) {
       response.header('Expires', options.expires)
     } else {
-      response.header('Cache-Control', data.metadata.cacheControl)
+      this.handleCacheControl(request, response, data.metadata)
     }
 
     if (data.metadata.contentRange) {
@@ -95,6 +105,40 @@ export abstract class Renderer {
       }
     }
   }
+
+  protected handleCacheControl(
+    request: FastifyRequest<any>,
+    response: FastifyReply<any>,
+    metadata: ObjectMetadata
+  ) {
+    const etag = this.findEtagHeader(request)
+
+    const cacheControl = [metadata.cacheControl]
+
+    if (!etag) {
+      response.header('Cache-Control', cacheControl.join(', '))
+      return
+    }
+
+    if (this.sMaxAge > 0) {
+      cacheControl.push(`s-maxage=${this.sMaxAge}`)
+    }
+
+    if (etag !== metadata.eTag) {
+      cacheControl.push('stale-while-revalidate=30')
+    }
+
+    response.header('Cache-Control', cacheControl.join(', '))
+  }
+
+  protected findEtagHeader(request: FastifyRequest<any>) {
+    for (const header of requestEtagHeaders) {
+      const etag = request.headers[header]
+      if (etag) {
+        return etag
+      }
+    }
+  }
 }
 
 function normalizeContentType(contentType: string | undefined): string | undefined {