feat(#48): Added support for negative indexing when using rsq (#49)

* feat(#48): Added support for negative indexing when using rsq

* fix: removed console.log and fixed wrong example url in readme

* chore: added info about the use of negative rsq values to README

* fix: removed console.log left over from testing

README.md

@@ -95,13 +95,13 @@ Currently, the Chaos Stream Proxy supports 4 types of corruptions for HLS and MP
 
 To specify the configurations for a particular corruption, you will need to add a stringified JSON object as a query parameter to the proxied URL.
 Each corruption has a unique configuration JSON object template. Each object can be used to target one specific segment for corruption.
-e.i. `https://<chaos-proxy>/api/v2/manifests/hls/proxy-master.m3u8?url=<some_url>?some_corruption=[{i:0},{i:1},{i:2}, ... ,{i:N}]`
+e.i. `https://<chaos-proxy>/api/v2/manifests/hls/proxy-master.m3u8?url=<some_url>&some_corruption=[{i:0},{i:1},{i:2}, ... ,{i:N}]`
 
 Across all corruptions, there are 3 ways to target a segment in a playlist for corruption.
 
 1. `i`: The segment's list index in any Media Playlist, with HLS segments starting at 0 and MPEG-DASH segments starting at 1. For a Media Playlist with 12 segments, `i`=11, would target the last segment for HLS and `i`=12, would target the last segment for MPEG-DASH.
 2. `sq`: The segment's Media Sequence Number for HLS, or the "$Number$" or "$Time$" part of a segment URL for DASH. For an HLS Media Playlist with 12 segments, and where `#EXT-X-MEDIA-SEQUENCE` is 100, `sq`=111 would target the last segment. When corrupting a live HLS stream it is recommended to target with `rsq`.
-3. `rsq`: A relative sequence number, counted from where the live stream is currently at when requesting manifest. (**HLS SUPPORTED ONLY IN STATEFUL MODE**)
+3. `rsq`: A relative sequence number, counted from where the live stream is currently at when requesting manifest. Can also use a negative integer, which enables counting backwards from the end of the manifest instead. (**HLS SUPPORTED ONLY IN STATEFUL MODE**)
 
 Below are configuration JSON object templates for the currently supported corruptions. A query should have its value be an array consisting of any one of these 3 types of items:
 

src/manifests/handlers/hls/media.ts

@@ -78,12 +78,12 @@ export default async function hlsMediaHandler(
         }
       }
     }
-
     const [error, allMutations, levelMutations] =
       configUtils.getAllManifestConfigs(
         mediaSequence,
         false,
-        mediaSequenceOffset
+        mediaSequenceOffset,
+        mediaM3U.items.PlaylistItem.length
       );
     if (error) {
       return generateErrorResponse(error);

src/manifests/utils/configs.test.ts

@@ -193,7 +193,44 @@ describe('configs', () => {
         // Act
 
         const [err, actual] = configs.getAllManifestConfigs(0, false, 100);
+        // Assert
+        expect(err).toBeNull();
+        expect(actual.get(115)).toEqual(
+          new Map([
+            [
+              'statusCode',
+              {
+                fields: { code: 400 },
+                sq: 115
+              }
+            ]
+          ])
+        );
+        expect(actual.get(15)).toEqual(
+          new Map([
+            [
+              'throttle',
+              {
+                fields: { rate: 1000 },
+                sq: 15
+              }
+            ]
+          ])
+        );
+      });
+      it('should handle media sequence offsets with negative rsq value', () => {
+        // Arrange
+        const configs = statefulConfig.corruptorConfigUtils(
+          new URLSearchParams(
+            'statusCode=[{rsq:-1,code:400}]&throttle=[{sq:15,rate:1000}]'
+          )
+        );
+
+        configs.register(statusCodeConfig).register(throttleConfig);
+
+        // Act
 
+        const [err, actual] = configs.getAllManifestConfigs(0, false, 100, 15);
         // Assert
         expect(err).toBeNull();
         expect(actual.get(115)).toEqual(

src/manifests/utils/configs.ts

@@ -54,7 +54,8 @@ export interface CorruptorConfigUtils {
   getAllManifestConfigs: (
     mseq?: number,
     isDash?: boolean,
-    mseqOffset?: number
+    mseqOffset?: number,
+    playlistSize?: number
   ) => [
     ServiceError | null,
     IndexedCorruptorConfigMap | null,
@@ -131,7 +132,12 @@ export const corruptorConfigUtils = function (
       }
       return this;
     },
-    getAllManifestConfigs(mseq = 0, isDash = false, mseqOffset = 0) {
+    getAllManifestConfigs(
+      mseq = 0,
+      isDash = false,
+      mseqOffset = 0,
+      playlistSize = 0
+    ) {
       const outputMap = new CorruptorIndexMap();
       const levelMap = new CorruptorLevelMap();
       const configs = (
@@ -171,7 +177,11 @@ export const corruptorConfigUtils = function (
           // Replace relative sequence numbers with absolute ones
           params = params.map((param) => {
             if (param.rsq) {
-              param.sq = Number(param.rsq) + mseqOffset;
+              const rsq = Number(param.rsq);
+              param['sq'] =
+                rsq < 0 && playlistSize > 0
+                  ? mseqOffset + playlistSize + rsq + 1
+                  : Number(param.rsq) + mseqOffset;
               delete param.rsq;
             }
             return param;
@@ -182,6 +192,7 @@ export const corruptorConfigUtils = function (
         if (error) {
           return [error, null];
         }
+
         configList.forEach((item) => {
           if (item.i != undefined) {
             outputMap.deepSet(item.i, config.name, item, false);

src/manifests/utils/hlsManifestUtils.ts

@@ -1,9 +1,5 @@
 import { M3U, Manifest } from '../../shared/types';
-import {
-  newState,
-  proxyPathBuilder,
-  segmentUrlParamString
-} from '../../shared/utils';
+import { proxyPathBuilder, segmentUrlParamString } from '../../shared/utils';
 import { CorruptorConfigMap, IndexedCorruptorConfigMap } from './configs';
 import clone from 'clone';
 
@@ -143,15 +139,13 @@ export default function (): HLSManifestTools {
       configsMap: IndexedCorruptorConfigMap
     ) {
       const m3u: M3U = clone(originalM3U);
+      const playlistSize = m3u.items.PlaylistItem.length;
 
       // configs for each index
-      const corruptions = this.utils.mergeMap(
-        m3u.items.PlaylistItem.length,
-        configsMap
-      );
+      const corruptions = this.utils.mergeMap(playlistSize, configsMap);
 
       // Attach corruptions to manifest
-      for (let i = 0; i < m3u.items.PlaylistItem.length; i++) {
+      for (let i = 0; i < playlistSize; i++) {
         const item = m3u.items.PlaylistItem[i];
         const corruption = corruptions[i];
         let sourceSegURL: string = item.get('uri');