Fix one-by-error for run-length encoding (#141555)

Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>

x-pack/plugins/profiling/server/routes/stacktrace.test.ts

@@ -98,7 +98,7 @@ describe('Stack trace operations', () => {
     }
   });
 
-  test('runLengthDecodeReverse with optional parameter', () => {
+  test('runLengthDecode with optional parameter', () => {
     const tests: Array<{
       bytes: Buffer;
       expected: number[];
@@ -118,7 +118,7 @@ describe('Stack trace operations', () => {
     }
   });
 
-  test('runLengthDecodeReverse without optional parameter', () => {
+  test('runLengthDecode without optional parameter', () => {
     const tests: Array<{
       bytes: Buffer;
       expected: number[];
@@ -137,4 +137,44 @@ describe('Stack trace operations', () => {
       expect(runLengthDecode(t.bytes)).toEqual(t.expected);
     }
   });
+
+  test('runLengthDecode works for very long runs', () => {
+    const tests: Array<{
+      bytes: Buffer;
+      expected: number[];
+    }> = [
+      {
+        bytes: Buffer.from([0x5, 0x2, 0xff, 0x0]),
+        expected: [2, 2, 2, 2, 2].concat(Array(255).fill(0)),
+      },
+      {
+        bytes: Buffer.from([0xff, 0x2, 0x1, 0x2]),
+        expected: Array(256).fill(2),
+      },
+    ];
+
+    for (const t of tests) {
+      expect(runLengthDecode(t.bytes)).toEqual(t.expected);
+    }
+  });
+
+  test('runLengthEncode works for very long runs', () => {
+    const tests: Array<{
+      numbers: number[];
+      expected: Buffer;
+    }> = [
+      {
+        numbers: [2, 2, 2, 2, 2].concat(Array(255).fill(0)),
+        expected: Buffer.from([0x5, 0x2, 0xff, 0x0]),
+      },
+      {
+        numbers: Array(256).fill(2),
+        expected: Buffer.from([0xff, 0x2, 0x1, 0x2]),
+      },
+    ];
+
+    for (const t of tests) {
+      expect(runLengthEncode(t.numbers)).toEqual(t.expected);
+    }
+  });
 });

x-pack/plugins/profiling/server/routes/stacktrace.ts

@@ -68,7 +68,7 @@ export function runLengthEncode(input: number[]): Buffer {
     return Buffer.from(output);
   }
 
-  let count = 0;
+  let count = 1;
   let current = input[0];
 
   for (let i = 1; i < input.length; i++) {
@@ -79,13 +79,13 @@ export function runLengthEncode(input: number[]): Buffer {
       continue;
     }
 
-    output.push(count + 1, current);
+    output.push(count, current);
 
-    count = 0;
+    count = 1;
     current = next;
   }
 
-  output.push(count + 1, current);
+  output.push(count, current);
 
   return Buffer.from(output);
 }