Add fastify.isUnderPressure() (#199)

Signed-off-by: Matteo Collina <hello@matteocollina.com>

README.md

@@ -12,7 +12,7 @@ external resources.
 <a name="requirements"></a>
 ## Requirements
 
-Fastify ^2.0.0. Please refer to [this branch](https://github.com/fastify/under-pressure/tree/1.x) and related versions for Fastify ^1.1.0 compatibility.
+Fastify ^4.0.0. Please refer to [this branch](https://github.com/fastify/under-pressure/tree/1.x) and related versions for Fastify ^1.1.0 compatibility.
 
 <a name="install"></a>
 ## Install
@@ -35,6 +35,9 @@ fastify.register(require('@fastify/under-pressure'), {
 })
 
 fastify.get('/', (req, reply) => {
+  if (fastify.isUnderPressure()) {
+    // skip complex computation
+  }
   reply.send({ hello: 'world'})
 })
 

index.js

@@ -60,6 +60,7 @@ async function fastifyUnderPressure (fastify, opts) {
   }
 
   fastify.decorate('memoryUsage', memoryUsage)
+  fastify.decorate('isUnderPressure', isUnderPressure)
 
   const timer = setTimeout(beginMemoryUsageUpdate, sampleInterval)
   timer.unref()
@@ -173,6 +174,30 @@ async function fastifyUnderPressure (fastify, opts) {
     updateEventLoopUtilization()
   }
 
+  function isUnderPressure () {
+    if (checkMaxEventLoopDelay && eventLoopDelay > maxEventLoopDelay) {
+      return true
+    }
+
+    if (checkMaxHeapUsedBytes && heapUsed > maxHeapUsedBytes) {
+      return true
+    }
+
+    if (checkMaxRssBytes && rssBytes > maxRssBytes) {
+      return true
+    }
+
+    if (!externalsHealthy) {
+      return true
+    }
+
+    if (checkMaxEventLoopUtilization && eventLoopUtilized > maxEventLoopUtilization) {
+      return true
+    }
+
+    return false
+  }
+
   function onRequest (req, reply, next) {
     if (checkMaxEventLoopDelay && eventLoopDelay > maxEventLoopDelay) {
       handlePressure(req, reply, next, TYPE_EVENT_LOOP_DELAY, eventLoopDelay)

test/test.js

@@ -11,7 +11,7 @@ const { valid, satisfies, coerce } = require('semver')
 const wait = promisify(setTimeout)
 
 test('Should return 503 on maxEventLoopDelay', t => {
-  t.plan(5)
+  t.plan(6)
 
   const fastify = Fastify()
   fastify.register(underPressure, {
@@ -42,6 +42,7 @@ test('Should return 503 on maxEventLoopDelay', t => {
         message: 'Service Unavailable',
         statusCode: 503
       })
+      t.equal(fastify.isUnderPressure(), true)
       fastify.close()
     })
 
@@ -51,7 +52,7 @@ test('Should return 503 on maxEventLoopDelay', t => {
 
 const isSupportedVersion = satisfies(valid(coerce(process.version)), '12.19.0 || >=14.0.0')
 test('Should return 503 on maxEventloopUtilization', { skip: !isSupportedVersion }, t => {
-  t.plan(5)
+  t.plan(6)
   const fastify = Fastify()
   fastify.register(underPressure, {
     maxEventLoopUtilization: 0.60
@@ -75,6 +76,7 @@ test('Should return 503 on maxEventloopUtilization', { skip: !isSupportedVersion
         message: 'Service Unavailable',
         statusCode: 503
       })
+      t.equal(fastify.isUnderPressure(), true)
       fastify.close()
     })
 
@@ -83,7 +85,7 @@ test('Should return 503 on maxEventloopUtilization', { skip: !isSupportedVersion
 })
 
 test('Should return 503 on maxHeapUsedBytes', t => {
-  t.plan(5)
+  t.plan(6)
 
   const fastify = Fastify()
   fastify.register(underPressure, {
@@ -108,6 +110,7 @@ test('Should return 503 on maxHeapUsedBytes', t => {
         message: 'Service Unavailable',
         statusCode: 503
       })
+      t.equal(fastify.isUnderPressure(), true)
       fastify.close()
     })
 
@@ -116,7 +119,7 @@ test('Should return 503 on maxHeapUsedBytes', t => {
 })
 
 test('Should return 503 on maxRssBytes', t => {
-  t.plan(5)
+  t.plan(6)
 
   const fastify = Fastify()
   fastify.register(underPressure, {
@@ -141,6 +144,7 @@ test('Should return 503 on maxRssBytes', t => {
         message: 'Service Unavailable',
         statusCode: 503
       })
+      t.equal(fastify.isUnderPressure(), true)
       fastify.close()
     })
 
@@ -231,7 +235,7 @@ test('Custom error instance', t => {
 })
 
 test('memoryUsage name space', t => {
-  t.plan(9)
+  t.plan(10)
 
   const fastify = Fastify()
   fastify.register(underPressure, {
@@ -264,6 +268,7 @@ test('memoryUsage name space', t => {
       t.error(err)
       t.equal(response.statusCode, 200)
       t.same(JSON.parse(body), { hello: 'world' })
+      t.equal(fastify.isUnderPressure(), true)
       fastify.close()
     })
 
@@ -311,7 +316,7 @@ test('Custom health check', t => {
   t.plan(8)
 
   t.test('should return 503 when custom health check returns false for healthCheck', t => {
-    t.plan(5)
+    t.plan(6)
 
     const fastify = Fastify()
     fastify.register(underPressure, {
@@ -339,6 +344,7 @@ test('Custom health check', t => {
           message: 'Service Unavailable',
           statusCode: 503
         })
+        t.equal(fastify.isUnderPressure(), true)
         fastify.close()
       })
     })

types/index.d.ts

@@ -8,6 +8,7 @@ import {
 declare module "fastify" {
   interface FastifyInstance {
     memoryUsage(): { heapUsed: number; rssBytes: number; eventLoopDelay: number; eventLoopUtilized: number };
+    isUnderPressure(): boolean;
   }
 }
 

types/index.test-d.ts

@@ -14,7 +14,8 @@ const server = fastify();
   server.register(fastifyUnderPressure);
 
   server.get("/", (req, reply) => {
-    reply.send({ hello: "world" });
+
+    reply.send({ hello: "world", underPressure: server.isUnderPressure() });
   });
 
   server.listen({port: 3000}, err => {