Expose estimatedServerTime as a configurable parameter (#19)

README.md

@@ -50,6 +50,7 @@ new SpeedTest({ configOptions })
 | <b>measureUploadLoadedLatency</b>: <i>boolean</i> | Whether to perform additional latency measurements simultaneously with upload requests, to measure loaded latency (during upload). | `true` |
 | <b>loadedLatencyThrottle</b>: <i>number</i> | Time interval to wait in between loaded latency requests (in milliseconds). | 400 |
 | <b>bandwidthFinishRequestDuration</b>: <i>number</i> | The minimum duration (in milliseconds) to reach in download/upload measurement sets for halting further measurements with larger file sizes in the same direction. | 1000 |
+| <b>estimatedServerTime</b>: <i>number</i> | If the download/upload APIs do not return a server-timing response header containing the time spent in the server, this fixed value (in milliseconds) will be subtracted from all time-to-first-byte calculations. | 10 |
 | <b>latencyPercentile</b>: <i>number</i> | The percentile (between 0 and 1) used to calculate latency from a set of measurements. | 0.5 |
 | <b>bandwidthPercentile</b>: <i>number</i> | The percentile (between 0 and 1) used to calculate bandwidth from a set of measurements. | 0.9 |
 | <b>bandwidthMinRequestDuration</b>: <i>number</i> | The minimum duration (in milliseconds) of a request to consider a measurement good enough to use in the bandwidth calculation. | 10 |

src/config/defaultConfig.js

@@ -45,6 +45,7 @@ export default {
   measureUploadLoadedLatency: true,
   loadedLatencyThrottle: 400, // ms in between loaded latency requests
   bandwidthFinishRequestDuration: 1000, // download/upload duration (ms) to reach for stopping further measurements
+  estimatedServerTime: 10, // ms to discount from latency calculation (if not present in response headers)
 
   // Result interpretation
   latencyPercentile: 0.5, // Percentile used to calculate latency from a set of measurements

src/engines/BandwidthEngine/BandwidthEngine.js

@@ -5,7 +5,6 @@ import memoize from 'lodash.memoize';
 const MAX_RETRIES = 20;
 
 const ESTIMATED_HEADER_FRACTION = 0.005; // ~.5% of packet header / payload size. used when transferSize is not available.
-const ESTIMATED_SERVER_TIME = 15; // ms to discount from latency calculation (if not present in response headers)
 
 const cfGetServerTime = r => {
   // extract server-timing from headers: server-timing: cfRequestDuration;dur=15.999794
@@ -48,7 +47,12 @@ const genContent = memoize(numBytes => '0'.repeat(numBytes));
 class BandwidthMeasurementEngine {
   constructor(
     measurements,
-    { downloadApiUrl, uploadApiUrl, throttleMs = 0 } = {}
+    {
+      downloadApiUrl,
+      uploadApiUrl,
+      throttleMs = 0,
+      estimatedServerTime = 0
+    } = {}
   ) {
     if (!measurements) throw new Error('Missing measurements argument');
     if (!downloadApiUrl) throw new Error('Missing downloadApiUrl argument');
@@ -58,6 +62,7 @@ class BandwidthMeasurementEngine {
     this.#downloadApi = downloadApiUrl;
     this.#uploadApi = uploadApiUrl;
     this.#throttleMs = throttleMs;
+    this.#estimatedServerTime = Math.max(0, estimatedServerTime);
   }
 
   // Public attributes
@@ -138,6 +143,7 @@ class BandwidthMeasurementEngine {
   #retries = 0;
   #minDuration = -Infinity; // of current measurement
   #throttleMs = 0;
+  #estimatedServerTime = 0;
   #currentFetchPromise = undefined;
   #currentNextMsmTimeoutId = undefined;
 
@@ -299,7 +305,7 @@ class BandwidthMeasurementEngine {
         };
         timing.ping = Math.max(
           1e-2,
-          timing.ttfb - (serverTime || ESTIMATED_SERVER_TIME)
+          timing.ttfb - (serverTime || this.#estimatedServerTime)
         ); // ttfb = network latency + server time
 
         timing.duration = (isDown ? calcDownloadDuration : calcUploadDuration)(

src/engines/BandwidthEngine/ParallelLatency.js

@@ -8,12 +8,14 @@ class BandwidthWithParallelLatencyEngine extends BandwidthEngine {
       parallelLatencyThrottleMs = 100,
       downloadApiUrl,
       uploadApiUrl,
+      estimatedServerTime = 0,
       ...ptProps
     } = {}
   ) {
     super(measurements, {
       downloadApiUrl,
       uploadApiUrl,
+      estimatedServerTime,
       ...ptProps
     });
 
@@ -27,7 +29,12 @@ class BandwidthWithParallelLatencyEngine extends BandwidthEngine {
             bypassMinDuration: true
           }
         ],
-        { downloadApiUrl, uploadApiUrl, throttleMs: parallelLatencyThrottleMs }
+        {
+          downloadApiUrl,
+          uploadApiUrl,
+          estimatedServerTime,
+          throttleMs: parallelLatencyThrottleMs
+        }
       );
       this.#latencyEngine.qsParams = {
         during: `${measurements[0].dir}load`

src/index.d.ts

@@ -32,6 +32,7 @@ export interface ConfigOptions {
   measureUploadLoadedLatency?: boolean,
   loadedLatencyThrottle?: number,
   bandwidthFinishRequestDuration?: number,
+  estimatedServerTime?: number;
 
   // Result interpretation
   latencyPercentile?: number,

src/index.js

@@ -154,7 +154,7 @@ class MeasurementEngine {
     const { type, ...msmConfig } = this.#config.measurements[this.#curMsmIdx];
     const msmResults = this.#curTypeResults();
 
-    const { downloadApiUrl, uploadApiUrl } = this.#config;
+    const { downloadApiUrl, uploadApiUrl, estimatedServerTime } = this.#config;
 
     let engine;
     switch (type) {
@@ -292,6 +292,7 @@ class MeasurementEngine {
           {
             downloadApiUrl,
             uploadApiUrl,
+            estimatedServerTime,
             logApiUrl: this.#config.logMeasurementApiUrl,
             measurementId: this.#measurementId,
 
@@ -347,6 +348,7 @@ class MeasurementEngine {
             {
               downloadApiUrl,
               uploadApiUrl,
+              estimatedServerTime,
               logApiUrl: this.#config.logMeasurementApiUrl,
               measurementId: this.#measurementId,
               measureParallelLatency,