process: respect Float64Array byte offsets

Account for Float64Array byte offsets when writing CPU, thread CPU,
memory, and resource usage values.

Signed-off-by: Archkon <180910180+Archkon@users.noreply.github.com>

Author: Archkon

src/node_process_methods.cc

@@ -40,7 +40,6 @@ typedef int mode_t;
 namespace node {
 
 using v8::Array;
-using v8::ArrayBuffer;
 using v8::CFunction;
 using v8::Context;
 using v8::Float64Array;
@@ -100,14 +99,14 @@ static void Chdir(const FunctionCallbackInfo<Value>& args) {
   }
 }
 
-inline Local<ArrayBuffer> get_fields_array_buffer(
-    const FunctionCallbackInfo<Value>& args,
-    size_t index,
-    size_t array_length) {
+inline double* get_fields_array_data(const FunctionCallbackInfo<Value>& args,
+                                     size_t index,
+                                     size_t array_length) {
   CHECK(args[index]->IsFloat64Array());
   Local<Float64Array> arr = args[index].As<Float64Array>();
   CHECK_EQ(arr->Length(), array_length);
-  return arr->Buffer();
+  uint8_t* data = static_cast<uint8_t*>(arr->Buffer()->Data());
+  return reinterpret_cast<double*>(data + arr->ByteOffset());
 }
 
 // CPUUsage use libuv's uv_getrusage() this-process resource usage accessor,
@@ -125,8 +124,7 @@ static void CPUUsage(const FunctionCallbackInfo<Value>& args) {
     return env->ThrowUVException(err, "uv_getrusage");
 
   // Get the double array pointer from the Float64Array argument.
-  Local<ArrayBuffer> ab = get_fields_array_buffer(args, 0, 2);
-  double* fields = static_cast<double*>(ab->Data());
+  double* fields = get_fields_array_data(args, 0, 2);
 
   // Set the Float64Array elements to be user / system values in microseconds.
   fields[0] = MICROS_PER_SEC * rusage.ru_utime.tv_sec + rusage.ru_utime.tv_usec;
@@ -148,8 +146,7 @@ static void ThreadCPUUsage(const FunctionCallbackInfo<Value>& args) {
   if (err) return env->ThrowUVException(err, "uv_getrusage_thread");
 
   // Get the double array pointer from the Float64Array argument.
-  Local<ArrayBuffer> ab = get_fields_array_buffer(args, 0, 2);
-  double* fields = static_cast<double*>(ab->Data());
+  double* fields = get_fields_array_data(args, 0, 2);
 
   // Set the Float64Array elements to be user / system values in microseconds.
   fields[0] = MICROS_PER_SEC * rusage.ru_utime.tv_sec + rusage.ru_utime.tv_usec;
@@ -230,8 +227,7 @@ static void MemoryUsage(const FunctionCallbackInfo<Value>& args) {
       env->isolate_data()->node_allocator();
 
   // Get the double array pointer from the Float64Array argument.
-  Local<ArrayBuffer> ab = get_fields_array_buffer(args, 0, 5);
-  double* fields = static_cast<double*>(ab->Data());
+  double* fields = get_fields_array_data(args, 0, 5);
 
   size_t rss;
   int err = uv_resident_set_memory(&rss);
@@ -369,8 +365,7 @@ static void ResourceUsage(const FunctionCallbackInfo<Value>& args) {
   if (err)
     return env->ThrowUVException(err, "uv_getrusage");
 
-  Local<ArrayBuffer> ab = get_fields_array_buffer(args, 0, 16);
-  double* fields = static_cast<double*>(ab->Data());
+  double* fields = get_fields_array_data(args, 0, 16);
 
   fields[0] = MICROS_PER_SEC * rusage.ru_utime.tv_sec + rusage.ru_utime.tv_usec;
   fields[1] = MICROS_PER_SEC * rusage.ru_stime.tv_sec + rusage.ru_stime.tv_usec;

test/parallel/test-process-methods-array-buffer-view.js

@@ -0,0 +1,36 @@
+// Flags: --expose-internals
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const { internalBinding } = require('internal/test/binding');
+
+const binding = internalBinding('process_methods');
+const methods = [
+  ['cpuUsage', 2],
+  ['memoryUsage', 5],
+  ['resourceUsage', 16],
+];
+
+if (!common.isSunOS) {
+  methods.push(['threadCpuUsage', 2]);
+}
+
+for (const [method, length] of methods) {
+  const values = new Float64Array(length + 1);
+  values.fill(-1);
+  values[0] = 42;
+
+  const fields = new Float64Array(
+    values.buffer,
+    Float64Array.BYTES_PER_ELEMENT,
+    length,
+  );
+
+  binding[method](fields);
+
+  assert.strictEqual(values[0], 42, `${method} wrote before the target view`);
+  for (const value of fields) {
+    assert(value >= 0, `${method} did not populate the target view`);
+  }
+}