core(network-analyzer): move throughput to NetworkAnalyzer (#5900)

lighthouse-core/audits/byte-efficiency/byte-efficiency-audit.js

@@ -56,16 +56,6 @@ class UnusedBytes extends Audit {
     }
   }
 
-  /**
-   * @param {number} bytes
-   * @param {number} networkThroughput measured in bytes/second
-   * @return {number}
-   */
-  static bytesToMs(bytes, networkThroughput) {
-    const milliseconds = bytes / networkThroughput * 1000;
-    return milliseconds;
-  }
-
   /**
    * Estimates the number of bytes this network record would have consumed on the network based on the
    * uncompressed size (totalBytes). Uses the actual transfer size from the network record if applicable.

lighthouse-core/audits/byte-efficiency/total-byte-weight.js

@@ -57,24 +57,20 @@ class TotalByteWeight extends ByteEfficiencyAudit {
    * @return {Promise<LH.Audit.Product>}
    */
   static async audit(artifacts, context) {
-    const devtoolsLogs = artifacts.devtoolsLogs[ByteEfficiencyAudit.DEFAULT_PASS];
-    const [networkRecords, networkThroughput] = await Promise.all([
-      artifacts.requestNetworkRecords(devtoolsLogs),
-      artifacts.requestNetworkThroughput(devtoolsLogs),
-    ]);
+    const devtoolsLog = artifacts.devtoolsLogs[ByteEfficiencyAudit.DEFAULT_PASS];
+    const records = await artifacts.requestNetworkRecords(devtoolsLog);
 
     let totalBytes = 0;
-    /** @type {Array<{url: string, totalBytes: number, totalMs: number}>} */
+    /** @type {Array<{url: string, totalBytes: number}>} */
     let results = [];
-    networkRecords.forEach(record => {
+    records.forEach(record => {
       // exclude data URIs since their size is reflected in other resources
       // exclude unfinished requests since they won't have transfer size information
       if (record.parsedURL.scheme === 'data' || !record.finished) return;
 
       const result = {
         url: record.url,
         totalBytes: record.transferSize,
-        totalMs: ByteEfficiencyAudit.bytesToMs(record.transferSize, networkThroughput),
       };
 
       totalBytes += result.totalBytes;

lighthouse-core/gather/computed/network-analysis.js

@@ -15,7 +15,7 @@ class NetworkAnalysis extends ComputedArtifact {
 
   /**
    * @param {Array<LH.Artifacts.NetworkRequest>} records
-   * @return {LH.Artifacts.NetworkAnalysis}
+   * @return {Omit<LH.Artifacts.NetworkAnalysis, 'throughput'|'records'>}
    */
   static computeRTTAndServerResponseTime(records) {
     // First pass compute the estimated observed RTT to each origin's servers.
@@ -45,7 +45,11 @@ class NetworkAnalysis extends ComputedArtifact {
       serverResponseTimeByOrigin.set(origin, summary.median);
     }
 
-    return {rtt: minimumRtt, additionalRttByOrigin, serverResponseTimeByOrigin, throughput: 0};
+    return {
+      rtt: minimumRtt,
+      additionalRttByOrigin,
+      serverResponseTimeByOrigin,
+    };
   }
 
   /**
@@ -55,10 +59,9 @@ class NetworkAnalysis extends ComputedArtifact {
    */
   async compute_(devtoolsLog, computedArtifacts) {
     const records = await computedArtifacts.requestNetworkRecords(devtoolsLog);
-    const throughput = await computedArtifacts.requestNetworkThroughput(devtoolsLog);
+    const throughput = NetworkAnalyzer.estimateThroughput(records);
     const rttAndServerResponseTime = NetworkAnalysis.computeRTTAndServerResponseTime(records);
-    rttAndServerResponseTime.throughput = throughput * 8; // convert from KBps to Kbps
-    return rttAndServerResponseTime;
+    return {records, throughput, ...rttAndServerResponseTime};
   }
 }
 

lighthouse-core/lib/dependency-graph/simulator/network-analyzer.js

@@ -385,6 +385,64 @@ class NetworkAnalyzer {
     return NetworkAnalyzer.summarize(estimatesByOrigin);
   }
 
+
+  /**
+   * Computes the average throughput for the given records in bits/second.
+   * Excludes data URI, failed or otherwise incomplete, and cached requests.
+   * Returns Infinity if there were no analyzable network records.
+   *
+   * @param {Array<LH.Artifacts.NetworkRequest>} networkRecords
+   * @return {number}
+   */
+  static estimateThroughput(networkRecords) {
+    let totalBytes = 0;
+
+    // We will measure throughput by summing the total bytes downloaded by the total time spent
+    // downloading those bytes. We slice up all the network records into start/end boundaries, so
+    // it's easier to deal with the gaps in downloading.
+    const timeBoundaries = networkRecords.reduce((boundaries, record) => {
+      const scheme = record.parsedURL && record.parsedURL.scheme;
+      // Requests whose bodies didn't come over the network or didn't completely finish will mess
+      // with the computation, just skip over them.
+      if (scheme === 'data' || record.failed || !record.finished ||
+          record.statusCode > 300 || !record.transferSize) {
+        return boundaries;
+      }
+
+      // If we've made it this far, all the times we need should be valid (i.e. not undefined/-1).
+      totalBytes += record.transferSize;
+      boundaries.push({time: record.responseReceivedTime, isStart: true});
+      boundaries.push({time: record.endTime, isStart: false});
+      return boundaries;
+    }, /** @type {Array<{time: number, isStart: boolean}>} */([])).sort((a, b) => a.time - b.time);
+
+    if (!timeBoundaries.length) {
+      return Infinity;
+    }
+
+    let inflight = 0;
+    let currentStart = 0;
+    let totalDuration = 0;
+
+    timeBoundaries.forEach(boundary => {
+      if (boundary.isStart) {
+        if (inflight === 0) {
+          // We just ended a quiet period, keep track of when the download period started
+          currentStart = boundary.time;
+        }
+        inflight++;
+      } else {
+        inflight--;
+        if (inflight === 0) {
+          // We just entered a quiet period, update our duration with the time we spent downloading
+          totalDuration += boundary.time - currentStart;
+        }
+      }
+    });
+
+    return totalBytes * 8 / totalDuration;
+  }
+
   /**
    * @param {Array<LH.Artifacts.NetworkRequest>} records
    * @return {LH.Artifacts.NetworkRequest}

lighthouse-core/test/audits/byte-efficiency/total-byte-weight-test.js

@@ -35,7 +35,6 @@ function generateArtifacts(records) {
   return {
     devtoolsLogs: {defaultPass: []},
     requestNetworkRecords: () => Promise.resolve(records),
-    requestNetworkThroughput: () => Promise.resolve(1024),
   };
 }