[GitHub] [nifi-minifi-cpp] fgerlits commented on a change in pull request #1152: MINIFICPP-1593 ProcFsMonitor to monitor /proc pseduo filesystem

[GitBox <gi...@apache.org>]

fgerlits commented on a change in pull request #1152:
URL: https://github.com/apache/nifi-minifi-cpp/pull/1152#discussion_r829878815



##########
File path: extensions/procfs/DiskStat.cpp
##########
@@ -0,0 +1,70 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "DiskStat.h"
+#include <utility>
+#include "utils/gsl.h"
+
+using namespace std::literals::chrono_literals;
+
+namespace org::apache::nifi::minifi::extensions::procfs {
+
+DiskStatData::MonotonicIncreasingMembers DiskStatData::MonotonicIncreasingMembers::operator-(const MonotonicIncreasingMembers& rhs) const {
+  MonotonicIncreasingMembers diff;
+  diff.reads_completed_ = reads_completed_ - rhs.reads_completed_;
+  diff.reads_merged_ = reads_merged_ - rhs.reads_merged_;
+  diff.sectors_read_ = sectors_read_ - rhs.sectors_read_;
+  diff.milliseconds_spent_reading_ = milliseconds_spent_reading_ - rhs.milliseconds_spent_reading_;
+  diff.writes_completed_ = writes_completed_ - rhs.writes_completed_;
+  diff.writes_merges_ = writes_merges_ - rhs.writes_merges_;
+  diff.sectors_written_ = sectors_written_ - rhs.sectors_written_;
+  diff.milliseconds_spent_writing_ = milliseconds_spent_writing_ - rhs.milliseconds_spent_writing_;
+  diff.milliseconds_spent_io_ = milliseconds_spent_io_ - rhs.milliseconds_spent_io_;
+  diff.weighted_milliseconds_spent_io_ = weighted_milliseconds_spent_io_ - rhs.weighted_milliseconds_spent_io_;
+  return diff;
+}
+
+std::optional<std::pair<std::string, DiskStatData>> DiskStatData::parseDiskStatLine(std::istream& iss) {
+  DiskStatData disk_stat_data;
+  std::string disk_name;
+  iss >> disk_stat_data.major_device_number_ >> disk_stat_data.minor_device_number_ >> disk_name >> disk_stat_data.monotonic_increasing_members_.reads_completed_
+      >> disk_stat_data.monotonic_increasing_members_.reads_merged_ >> disk_stat_data.monotonic_increasing_members_.sectors_read_
+      >> disk_stat_data.monotonic_increasing_members_.milliseconds_spent_reading_ >> disk_stat_data.monotonic_increasing_members_.writes_completed_
+      >> disk_stat_data.monotonic_increasing_members_.writes_merges_ >> disk_stat_data.monotonic_increasing_members_.sectors_written_
+      >> disk_stat_data.monotonic_increasing_members_.milliseconds_spent_reading_ >> disk_stat_data.monotonic_increasing_members_.writes_completed_
+      >> disk_stat_data.monotonic_increasing_members_.writes_merges_ >> disk_stat_data.monotonic_increasing_members_.sectors_written_
+      >> disk_stat_data.monotonic_increasing_members_.milliseconds_spent_writing_ >> disk_stat_data.ios_in_progress_ >> disk_stat_data.ios_in_progress_
+      >> disk_stat_data.monotonic_increasing_members_.milliseconds_spent_io_ >> disk_stat_data.monotonic_increasing_members_.weighted_milliseconds_spent_io_;

Review comment:
       This would be easier to read with one variable per line.
   
   That way, it would also be more visible that
   - lines 48-49 are duplicates of lines 46-47 and should be deleted, and
   - `ios_in_progress_` is read twice on line 50.

##########
File path: extensions/procfs/ProcFs.cpp
##########
@@ -0,0 +1,102 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "ProcFs.h"
+#include <istream>
+
+namespace org::apache::nifi::minifi::extensions::procfs {
+
+namespace {
+bool is_number(const std::string& s) {
+  return !s.empty() && std::all_of(s.begin(), s.end(), ::isdigit);
+}
+}  // namespace
+
+std::unordered_map<pid_t, ProcessStat> ProcFs::getProcessStats() const {
+  std::unordered_map<pid_t, ProcessStat> process_stats;
+  for (const auto &entry : std::filesystem::directory_iterator(root_path_)) {
+    if (entry.is_directory() && is_number(entry.path().filename())) {
+      auto stat_file_path = entry.path() / STAT_FILE;
+      std::ifstream stat_file(stat_file_path);
+      if (auto process_stat_data = ProcessStatData::parseProcessStatFile(stat_file)) {
+        process_stats.emplace(process_stat_data->getPid(), ProcessStat(*process_stat_data, page_size_));
+      }
+    }
+  }
+  return process_stats;
+}
+
+std::unordered_map<std::string, CpuStatData> ProcFs::getCpuStats() const {
+  std::unordered_map<std::string, CpuStatData> cpu_stats;
+  auto stat_file_path = root_path_ / STAT_FILE;
+  std::ifstream stat_file;
+  stat_file.open(stat_file_path);
+  std::string line;
+  while (std::getline(stat_file, line)) {
+    std::istringstream iss(line);
+    std::string entry_name;
+    iss >> entry_name;
+    if (entry_name.starts_with("cpu")) {
+      if (auto cpu_stat_data = CpuStatData::parseCpuStatLine(iss))
+        cpu_stats.emplace(entry_name, *cpu_stat_data);
+    }
+  }
+  return cpu_stats;
+}
+
+std::optional<MemInfo> ProcFs::getMemInfo() const {
+  auto mem_info_file_path = root_path_ / MEMINFO_FILE;
+  std::ifstream mem_info_file(mem_info_file_path);
+  return MemInfo::parseMemInfoFile(mem_info_file);
+}
+
+std::unordered_map<std::string, NetDevData> ProcFs::getNetDevs() const {
+  std::unordered_map<std::string, NetDevData>net_devs;
+  auto stat_file_path = root_path_ / NET_DEV_FILE;
+  std::ifstream stat_file;
+  stat_file.open(stat_file_path);
+  std::string line;
+  std::getline(stat_file, line);
+  std::getline(stat_file, line);
+  while (std::getline(stat_file, line)) {
+    std::istringstream iss(line);
+    std::string entry_name;
+    iss >> entry_name;
+    if (iss.fail())
+      continue;
+    entry_name.pop_back();

Review comment:
       a comment would be useful here, eg. `// remove the ':' from the end of 'eth0:' etc`

##########
File path: libminifi/test/SingleProcessorTestController.h
##########
@@ -54,6 +51,12 @@ class SingleInputTestController : public TestController {
     return result;
   }
 
+  auto trigger(const std::string_view input_flow_file_content, std::unordered_map<std::string, std::string> input_flow_file_attributes = {}) {
+    const auto new_flow_file = createFlowFile(input_flow_file_content, std::move(input_flow_file_attributes));
+    input_->put(new_flow_file);
+    return trigger();
+  }

Review comment:
       I think it would be nicer to rename this `enqueueFlowFile()` and remove line 57 (users would call `trigger()` separately after a call to `enqueueFlowFile()`).

##########
File path: extensions/procfs/ProcFsSerialization.h
##########
@@ -0,0 +1,164 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+#include <concepts>
+
+#include "CpuStat.h"
+#include "DiskStat.h"
+#include "MemInfo.h"
+#include "NetDev.h"
+#include "ProcessStat.h"
+#include "utils/gsl.h"
+
+namespace org::apache::nifi::minifi::extensions::procfs {
+
+void SerializeCPUStatData(const CpuStatData& cpu_stat_data,
+                          std::invocable<const char(&)[], const uint64_t> auto serializer) {
+  serializer("user time", cpu_stat_data.getUser().count());
+  serializer("nice time", cpu_stat_data.getNice().count());
+  serializer("system time", cpu_stat_data.getSystem().count());
+  serializer("idle time", cpu_stat_data.getIdle().count());
+  serializer("io wait time", cpu_stat_data.getIoWait().count());
+  serializer("irq time", cpu_stat_data.getIrq().count());
+  serializer("soft irq time", cpu_stat_data.getSoftIrq().count());
+  serializer("steal time", cpu_stat_data.getSteal().count());
+  serializer("guest time", cpu_stat_data.getGuest().count());
+  serializer("guest nice time", cpu_stat_data.getGuestNice().count());
+}
+
+void SerializeNormalizedCPUStat(const CpuStatData& cpu_stat_data,
+                                std::invocable<const char(&)[], const double> auto serializer) {
+  gsl_Expects(cpu_stat_data.getTotal() > 0ms);
+  serializer("user time %", cpu_stat_data.getUser()/cpu_stat_data.getTotal());
+  serializer("nice time %", cpu_stat_data.getNice()/cpu_stat_data.getTotal());
+  serializer("system time %", cpu_stat_data.getSystem()/cpu_stat_data.getTotal());
+  serializer("idle time %", cpu_stat_data.getIdle()/cpu_stat_data.getTotal());
+  serializer("io wait time %", cpu_stat_data.getIoWait()/cpu_stat_data.getTotal());
+  serializer("irq time %", cpu_stat_data.getIrq()/cpu_stat_data.getTotal());
+  serializer("soft irq %", cpu_stat_data.getSoftIrq()/cpu_stat_data.getTotal());
+  serializer("steal time %", cpu_stat_data.getSteal()/cpu_stat_data.getTotal());
+  serializer("guest time %", cpu_stat_data.getGuest()/cpu_stat_data.getTotal());
+  serializer("guest nice time %", cpu_stat_data.getGuestNice()/cpu_stat_data.getTotal());
+}
+
+void SerializeDiskStatData(const DiskStatData& disk_stat_data,
+                           std::invocable<const char(&)[], const uint64_t> auto serializer) {
+  serializer("Major Device Number", disk_stat_data.getMajorDeviceNumber());
+  serializer("Minor Device Number", disk_stat_data.getMinorDeviceNumber());
+  serializer("Reads Completed", disk_stat_data.getReadsCompleted());
+  serializer("Reads Merged", disk_stat_data.getReadsMerged());
+  serializer("Sectors Read", disk_stat_data.getSectorsRead());
+  serializer("Writes Completed", disk_stat_data.getWritesCompleted());
+  serializer("Writes Merged", disk_stat_data.getWritesMerged());
+  serializer("Sectors Written", disk_stat_data.getSectorsWritten());
+  serializer("IO-s in progress", disk_stat_data.getIosInProgress());
+}
+
+void SerializeDiskStatDataPerSec(const DiskStatData& disk_stat_data,
+                                 const std::chrono::duration<double> duration,
+                                 std::invocable<const char(&)[], const double> auto serializer) {
+  gsl_Expects(duration > 0ms);
+  serializer("Major Device Number", disk_stat_data.getMajorDeviceNumber());
+  serializer("Minor Device Number", disk_stat_data.getMinorDeviceNumber());
+  serializer("Reads Completed/sec", disk_stat_data.getReadsCompleted()/duration.count());
+  serializer("Reads Merged/sec", disk_stat_data.getReadsMerged()/duration.count());
+  serializer("Sectors Read/sec", disk_stat_data.getSectorsRead()/duration.count());
+  serializer("Writes Completed/sec", disk_stat_data.getWritesCompleted()/duration.count());
+  serializer("Writes Merged/sec", disk_stat_data.getWritesMerged()/duration.count());
+  serializer("Sectors Written/sec", disk_stat_data.getSectorsWritten()/duration.count());
+  serializer("IO-s in progress", disk_stat_data.getIosInProgress()/duration.count());
+}
+
+void SerializeMemInfo(const MemInfo& mem_info,
+                      std::invocable<const char(&)[], const uint64_t> auto serializer) {
+  serializer("MemTotal", mem_info.getTotalMemory());
+  serializer("MemFree", mem_info.getAvailableMemory());
+  serializer("MemAvailable", mem_info.getFreeMemory());
+  serializer("MemFree", mem_info.getAvailableMemory());
+  serializer("SwapFree", mem_info.getFreeSwap());
+  serializer("SwapTotal", mem_info.getTotalSwap());

Review comment:
       this is all messed up
   ```suggestion
     serializer("MemTotal", mem_info.getTotalMemory());
     serializer("MemFree", mem_info.getFreeMemory());
     serializer("MemAvailable", mem_info.getAvailableMemory());
     serializer("SwapTotal", mem_info.getTotalSwap());
     serializer("SwapFree", mem_info.getFreeSwap());
   ```

##########
File path: extensions/procfs/ProcFs.cpp
##########
@@ -0,0 +1,102 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "ProcFs.h"
+#include <istream>
+
+namespace org::apache::nifi::minifi::extensions::procfs {
+
+namespace {
+bool is_number(const std::string& s) {
+  return !s.empty() && std::all_of(s.begin(), s.end(), ::isdigit);
+}
+}  // namespace
+
+std::unordered_map<pid_t, ProcessStat> ProcFs::getProcessStats() const {
+  std::unordered_map<pid_t, ProcessStat> process_stats;
+  for (const auto &entry : std::filesystem::directory_iterator(root_path_)) {
+    if (entry.is_directory() && is_number(entry.path().filename())) {
+      auto stat_file_path = entry.path() / STAT_FILE;
+      std::ifstream stat_file(stat_file_path);
+      if (auto process_stat_data = ProcessStatData::parseProcessStatFile(stat_file)) {
+        process_stats.emplace(process_stat_data->getPid(), ProcessStat(*process_stat_data, page_size_));
+      }
+    }
+  }
+  return process_stats;
+}
+
+std::unordered_map<std::string, CpuStatData> ProcFs::getCpuStats() const {
+  std::unordered_map<std::string, CpuStatData> cpu_stats;
+  auto stat_file_path = root_path_ / STAT_FILE;
+  std::ifstream stat_file;
+  stat_file.open(stat_file_path);
+  std::string line;
+  while (std::getline(stat_file, line)) {
+    std::istringstream iss(line);
+    std::string entry_name;
+    iss >> entry_name;
+    if (entry_name.starts_with("cpu")) {
+      if (auto cpu_stat_data = CpuStatData::parseCpuStatLine(iss))
+        cpu_stats.emplace(entry_name, *cpu_stat_data);
+    }
+  }
+  return cpu_stats;
+}
+
+std::optional<MemInfo> ProcFs::getMemInfo() const {
+  auto mem_info_file_path = root_path_ / MEMINFO_FILE;
+  std::ifstream mem_info_file(mem_info_file_path);
+  return MemInfo::parseMemInfoFile(mem_info_file);
+}
+
+std::unordered_map<std::string, NetDevData> ProcFs::getNetDevs() const {
+  std::unordered_map<std::string, NetDevData>net_devs;

Review comment:
       missing space before `net_devs` (why doesn't the linter catch this?)

##########
File path: extensions/procfs/MemInfo.h
##########
@@ -0,0 +1,46 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <string>

Review comment:
       `#include <string>` could be moved to the cpp file, and you could add `#include <stdint.h>` for `uint64_t`
   

##########
File path: extensions/procfs/ProcFsSerialization.h
##########
@@ -0,0 +1,164 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+#include <concepts>
+
+#include "CpuStat.h"
+#include "DiskStat.h"
+#include "MemInfo.h"
+#include "NetDev.h"
+#include "ProcessStat.h"
+#include "utils/gsl.h"
+
+namespace org::apache::nifi::minifi::extensions::procfs {
+
+void SerializeCPUStatData(const CpuStatData& cpu_stat_data,
+                          std::invocable<const char(&)[], const uint64_t> auto serializer) {
+  serializer("user time", cpu_stat_data.getUser().count());
+  serializer("nice time", cpu_stat_data.getNice().count());
+  serializer("system time", cpu_stat_data.getSystem().count());
+  serializer("idle time", cpu_stat_data.getIdle().count());
+  serializer("io wait time", cpu_stat_data.getIoWait().count());
+  serializer("irq time", cpu_stat_data.getIrq().count());
+  serializer("soft irq time", cpu_stat_data.getSoftIrq().count());
+  serializer("steal time", cpu_stat_data.getSteal().count());
+  serializer("guest time", cpu_stat_data.getGuest().count());
+  serializer("guest nice time", cpu_stat_data.getGuestNice().count());
+}
+
+void SerializeNormalizedCPUStat(const CpuStatData& cpu_stat_data,
+                                std::invocable<const char(&)[], const double> auto serializer) {
+  gsl_Expects(cpu_stat_data.getTotal() > 0ms);
+  serializer("user time %", cpu_stat_data.getUser()/cpu_stat_data.getTotal());
+  serializer("nice time %", cpu_stat_data.getNice()/cpu_stat_data.getTotal());
+  serializer("system time %", cpu_stat_data.getSystem()/cpu_stat_data.getTotal());
+  serializer("idle time %", cpu_stat_data.getIdle()/cpu_stat_data.getTotal());
+  serializer("io wait time %", cpu_stat_data.getIoWait()/cpu_stat_data.getTotal());
+  serializer("irq time %", cpu_stat_data.getIrq()/cpu_stat_data.getTotal());
+  serializer("soft irq %", cpu_stat_data.getSoftIrq()/cpu_stat_data.getTotal());
+  serializer("steal time %", cpu_stat_data.getSteal()/cpu_stat_data.getTotal());
+  serializer("guest time %", cpu_stat_data.getGuest()/cpu_stat_data.getTotal());
+  serializer("guest nice time %", cpu_stat_data.getGuestNice()/cpu_stat_data.getTotal());
+}
+
+void SerializeDiskStatData(const DiskStatData& disk_stat_data,
+                           std::invocable<const char(&)[], const uint64_t> auto serializer) {
+  serializer("Major Device Number", disk_stat_data.getMajorDeviceNumber());
+  serializer("Minor Device Number", disk_stat_data.getMinorDeviceNumber());
+  serializer("Reads Completed", disk_stat_data.getReadsCompleted());
+  serializer("Reads Merged", disk_stat_data.getReadsMerged());
+  serializer("Sectors Read", disk_stat_data.getSectorsRead());
+  serializer("Writes Completed", disk_stat_data.getWritesCompleted());
+  serializer("Writes Merged", disk_stat_data.getWritesMerged());
+  serializer("Sectors Written", disk_stat_data.getSectorsWritten());
+  serializer("IO-s in progress", disk_stat_data.getIosInProgress());
+}
+
+void SerializeDiskStatDataPerSec(const DiskStatData& disk_stat_data,
+                                 const std::chrono::duration<double> duration,
+                                 std::invocable<const char(&)[], const double> auto serializer) {
+  gsl_Expects(duration > 0ms);
+  serializer("Major Device Number", disk_stat_data.getMajorDeviceNumber());
+  serializer("Minor Device Number", disk_stat_data.getMinorDeviceNumber());
+  serializer("Reads Completed/sec", disk_stat_data.getReadsCompleted()/duration.count());
+  serializer("Reads Merged/sec", disk_stat_data.getReadsMerged()/duration.count());
+  serializer("Sectors Read/sec", disk_stat_data.getSectorsRead()/duration.count());
+  serializer("Writes Completed/sec", disk_stat_data.getWritesCompleted()/duration.count());
+  serializer("Writes Merged/sec", disk_stat_data.getWritesMerged()/duration.count());
+  serializer("Sectors Written/sec", disk_stat_data.getSectorsWritten()/duration.count());
+  serializer("IO-s in progress", disk_stat_data.getIosInProgress()/duration.count());
+}
+
+void SerializeMemInfo(const MemInfo& mem_info,
+                      std::invocable<const char(&)[], const uint64_t> auto serializer) {
+  serializer("MemTotal", mem_info.getTotalMemory());
+  serializer("MemFree", mem_info.getAvailableMemory());
+  serializer("MemAvailable", mem_info.getFreeMemory());
+  serializer("MemFree", mem_info.getAvailableMemory());
+  serializer("SwapFree", mem_info.getFreeSwap());
+  serializer("SwapTotal", mem_info.getTotalSwap());
+}
+
+void SerializeNetDevData(const NetDevData& net_dev_data,
+                         std::invocable<const char(&)[], const uint64_t> auto serializer) {
+  serializer("Bytes Received", net_dev_data.getBytesReceived());
+  serializer("Packets Received", net_dev_data.getPacketsReceived());
+  serializer("Receive Errors", net_dev_data.getReceiveErrors());
+  serializer("Receive Drop Errors", net_dev_data.getReceiveDropErrors());
+  serializer("Receive Fifo Errors", net_dev_data.getReceiveFifoErrors());
+  serializer("Receive Frame Errors", net_dev_data.getReceiveFrameErrors());
+  serializer("Compressed Packets Received", net_dev_data.getCompressedPacketsReceived());
+  serializer("Multicast Frames Received", net_dev_data.getMulticastFramesReceived());
+
+  serializer("Bytes Transmitted", net_dev_data.getBytesTransmitted());
+  serializer("Packets Transmitted", net_dev_data.getPacketsTransmitted());
+  serializer("Transmit errors", net_dev_data.getTransmitErrors());
+  serializer("Transmit drop errors", net_dev_data.getTransmitDropErrors());
+  serializer("Transmit fifo errors", net_dev_data.getTransmitFifoErrors());
+  serializer("Transmit collisions", net_dev_data.getTransmitCollisions());
+  serializer("Transmit carrier losses", net_dev_data.getTransmitCarrierLosses());
+  serializer("Compressed Packets Transmitted", net_dev_data.getCompressedPacketsTransmitted());
+}
+
+void SerializeNetDevDataPerSec(const NetDevData& net_dev_data,
+                               const std::chrono::duration<double> duration,
+                               std::invocable<const char(&)[], const double> auto serializer) {
+  gsl_Expects(duration > 0ms);
+  serializer("Bytes Received/sec", net_dev_data.getBytesReceived()/duration.count());
+  serializer("Packets Received/sec", net_dev_data.getPacketsReceived()/duration.count());
+  serializer("Receive Errors/sec", net_dev_data.getReceiveErrors()/duration.count());
+  serializer("Receive Drop Errors/sec", net_dev_data.getReceiveDropErrors()/duration.count());
+  serializer("Receive Fifo Errors/sec", net_dev_data.getReceiveFifoErrors()/duration.count());
+  serializer("Receive Frame Errors/sec", net_dev_data.getReceiveFrameErrors()/duration.count());
+  serializer("Compressed Packets Received/sec", net_dev_data.getCompressedPacketsReceived()/duration.count());
+  serializer("Multicast Frames Received/sec", net_dev_data.getMulticastFramesReceived()/duration.count());
+
+  serializer("Bytes Transmitted/sec", net_dev_data.getBytesTransmitted()/duration.count());
+  serializer("Packets Transmitted/sec", net_dev_data.getPacketsTransmitted()/duration.count());
+  serializer("Transmit errors/sec", net_dev_data.getTransmitErrors()/duration.count());
+  serializer("Transmit drop errors/sec", net_dev_data.getTransmitDropErrors()/duration.count());
+  serializer("Transmit fifo errors/sec", net_dev_data.getTransmitFifoErrors()/duration.count());
+  serializer("Transmit collisions/sec", net_dev_data.getTransmitCollisions()/duration.count());
+  serializer("Transmit carrier losses/sec", net_dev_data.getTransmitCarrierLosses()/duration.count());
+  serializer("Compressed Packets Transmitted/sec", net_dev_data.getCompressedPacketsTransmitted()/duration.count());
+}
+
+void SerializeProcessStat(const ProcessStat& process_stat,
+                          std::invocable<const char(&)[], const uint64_t> auto uint64_t_serializer,
+                          std::invocable<const char(&)[], const std::string_view&> auto string_serializer) {
+  string_serializer("COMM", process_stat.getComm());

Review comment:
       is "COMM" standard in this context?  if not, I would prefer "command" or "COMMAND", as too many words start with "comm": common, communication, commercial etc

##########
File path: extensions/procfs/ProcFs.cpp
##########
@@ -0,0 +1,102 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "ProcFs.h"
+#include <istream>
+
+namespace org::apache::nifi::minifi::extensions::procfs {
+
+namespace {
+bool is_number(const std::string& s) {
+  return !s.empty() && std::all_of(s.begin(), s.end(), ::isdigit);
+}
+}  // namespace
+
+std::unordered_map<pid_t, ProcessStat> ProcFs::getProcessStats() const {
+  std::unordered_map<pid_t, ProcessStat> process_stats;
+  for (const auto &entry : std::filesystem::directory_iterator(root_path_)) {
+    if (entry.is_directory() && is_number(entry.path().filename())) {
+      auto stat_file_path = entry.path() / STAT_FILE;
+      std::ifstream stat_file(stat_file_path);
+      if (auto process_stat_data = ProcessStatData::parseProcessStatFile(stat_file)) {
+        process_stats.emplace(process_stat_data->getPid(), ProcessStat(*process_stat_data, page_size_));
+      }
+    }
+  }
+  return process_stats;
+}
+
+std::unordered_map<std::string, CpuStatData> ProcFs::getCpuStats() const {
+  std::unordered_map<std::string, CpuStatData> cpu_stats;
+  auto stat_file_path = root_path_ / STAT_FILE;
+  std::ifstream stat_file;
+  stat_file.open(stat_file_path);
+  std::string line;
+  while (std::getline(stat_file, line)) {
+    std::istringstream iss(line);
+    std::string entry_name;
+    iss >> entry_name;
+    if (entry_name.starts_with("cpu")) {
+      if (auto cpu_stat_data = CpuStatData::parseCpuStatLine(iss))
+        cpu_stats.emplace(entry_name, *cpu_stat_data);
+    }
+  }
+  return cpu_stats;
+}
+
+std::optional<MemInfo> ProcFs::getMemInfo() const {
+  auto mem_info_file_path = root_path_ / MEMINFO_FILE;
+  std::ifstream mem_info_file(mem_info_file_path);
+  return MemInfo::parseMemInfoFile(mem_info_file);
+}
+
+std::unordered_map<std::string, NetDevData> ProcFs::getNetDevs() const {
+  std::unordered_map<std::string, NetDevData>net_devs;
+  auto stat_file_path = root_path_ / NET_DEV_FILE;
+  std::ifstream stat_file;
+  stat_file.open(stat_file_path);
+  std::string line;
+  std::getline(stat_file, line);
+  std::getline(stat_file, line);
+  while (std::getline(stat_file, line)) {
+    std::istringstream iss(line);
+    std::string entry_name;
+    iss >> entry_name;
+    if (iss.fail())
+      continue;
+    entry_name.pop_back();
+    if (auto net_dev_data = NetDevData::parseNetDevLine(iss))
+      net_devs.emplace(entry_name, *net_dev_data);

Review comment:
       Here, and everywhere else where parsing can fail, it would be useful to log the line which has failed to parse.  If the line is not available, only the file name, I would still log that, although that is less useful.

##########
File path: extensions/procfs/ProcFsJsonSerialization.h
##########
@@ -0,0 +1,179 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <string>
+#include <string_view>
+
+#include "ProcFsSerialization.h"
+#include "rapidjson/stream.h"
+#include "rapidjson/document.h"
+
+namespace org::apache::nifi::minifi::extensions::procfs {
+
+namespace details {
+class UInt64Serializer {
+ public:
+  UInt64Serializer(rapidjson::Value& json, rapidjson::Document::AllocatorType& alloc) :
+      json_(json), alloc_(alloc) {
+  }
+  void operator()(const char(&key)[], const uint64_t value) {
+    json_.AddMember(rapidjson::StringRef(key), value, alloc_);
+  }
+ private:
+  rapidjson::Value& json_;
+  rapidjson::Document::AllocatorType& alloc_;
+};
+
+class DoubleSerializer {
+ public:
+  DoubleSerializer(rapidjson::Value& json, rapidjson::Document::AllocatorType& alloc) :
+      json_(json), alloc_(alloc) {
+  }
+  void operator()(const char(&key)[], const double value) {
+    json_.AddMember(rapidjson::StringRef(key), value, alloc_);
+  }
+ private:
+  rapidjson::Value& json_;
+  rapidjson::Document::AllocatorType& alloc_;
+};
+
+class StringSerializer {
+ public:
+  StringSerializer(rapidjson::Value& json, rapidjson::Document::AllocatorType& alloc) :
+      json_(json), alloc_(alloc) {
+  }
+  void operator()(const char(&key)[], const std::string_view& value) {
+    rapidjson::Value value_json(value.data(), value.size(), alloc_);
+    json_.AddMember(rapidjson::StringRef(key), value_json, alloc_);
+  }
+ private:
+  rapidjson::Value& json_;
+  rapidjson::Document::AllocatorType& alloc_;
+};
+}  // namespace details
+
+void addCPUStatToJson(const std::string& cpu_name,
+                      const CpuStatData& cpu_stat,
+                      rapidjson::Value& cpu_root,
+                      rapidjson::Document::AllocatorType& alloc) {
+  rapidjson::Value cpu_key(cpu_name.c_str(), cpu_name.length(), alloc);
+  cpu_root.AddMember(cpu_key.Move(), rapidjson::kObjectType, alloc);
+  rapidjson::Value& cpu_stat_json = cpu_root[cpu_name.c_str()];
+  SerializeCPUStatData(cpu_stat,
+                       details::UInt64Serializer(cpu_stat_json, alloc));
+}
+
+void addCPUStatPeriodToJson(const std::string& cpu_name,
+                            const CpuStatData& start,
+                            const CpuStatData& end,
+                            rapidjson::Value& cpu_root,
+                            rapidjson::Document::AllocatorType& alloc) {
+  rapidjson::Value cpu_key(cpu_name.c_str(), cpu_name.length(), alloc);
+  cpu_root.AddMember(cpu_key.Move(), rapidjson::kObjectType, alloc);
+  rapidjson::Value& cpu_stat_json = cpu_root[cpu_name.c_str()];
+  SerializeNormalizedCPUStat(end-start,
+                             details::DoubleSerializer(cpu_stat_json, alloc));
+}
+
+void addDiskStatToJson(const std::string& disk_name,
+                       const DiskStatData& disk_stat,
+                       rapidjson::Value& disk_root,
+                       rapidjson::Document::AllocatorType& alloc) {
+  rapidjson::Value disk_key(disk_name.c_str(), disk_name.length(), alloc);
+  disk_root.AddMember(disk_key.Move(), rapidjson::kObjectType, alloc);
+  rapidjson::Value& disk_json = disk_root[disk_name.c_str()];
+  SerializeDiskStatData(disk_stat,
+                        details::UInt64Serializer(disk_json, alloc));
+}
+
+void addDiskStatPerSecToJson(const std::string& disk_name,
+                             const DiskStatData disk_stat,
+                             const std::chrono::duration<double> duration,
+                             rapidjson::Value& disk_root,
+                             rapidjson::Document::AllocatorType& alloc) {
+  rapidjson::Value disk_key(disk_name.c_str(), disk_name.length(), alloc);
+  disk_root.AddMember(disk_key.Move(), rapidjson::kObjectType, alloc);
+  rapidjson::Value& disk_json = disk_root[disk_name.c_str()];
+  SerializeDiskStatDataPerSec(disk_stat,
+                              duration,
+                              details::DoubleSerializer(disk_json, alloc));
+}
+
+
+void addNetDevToJson(const std::string& net_name,

Review comment:
       very minor, but I would call this `interface_name` (as that's what it is, eg. "eth0")

##########
File path: extensions/procfs/CpuStat.h
##########
@@ -0,0 +1,68 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <istream>
+#include <optional>
+#include <string>
+
+#include "SystemClockDuration.h"
+
+using namespace std::literals::chrono_literals;
+
+namespace org::apache::nifi::minifi::extensions::procfs {
+
+class CpuStatData {
+  CpuStatData() = default;

Review comment:
       minor, but I would prefer to make this explicitly `private`, either by moving it to the `private:` section or by adding `private:` before it
   
   (also in the other info/stat headers)

##########
File path: extensions/procfs/ProcFsSerialization.h
##########
@@ -0,0 +1,164 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+#include <concepts>
+
+#include "CpuStat.h"
+#include "DiskStat.h"
+#include "MemInfo.h"
+#include "NetDev.h"
+#include "ProcessStat.h"
+#include "utils/gsl.h"
+
+namespace org::apache::nifi::minifi::extensions::procfs {
+
+void SerializeCPUStatData(const CpuStatData& cpu_stat_data,
+                          std::invocable<const char(&)[], const uint64_t> auto serializer) {
+  serializer("user time", cpu_stat_data.getUser().count());
+  serializer("nice time", cpu_stat_data.getNice().count());
+  serializer("system time", cpu_stat_data.getSystem().count());
+  serializer("idle time", cpu_stat_data.getIdle().count());
+  serializer("io wait time", cpu_stat_data.getIoWait().count());
+  serializer("irq time", cpu_stat_data.getIrq().count());
+  serializer("soft irq time", cpu_stat_data.getSoftIrq().count());
+  serializer("steal time", cpu_stat_data.getSteal().count());
+  serializer("guest time", cpu_stat_data.getGuest().count());
+  serializer("guest nice time", cpu_stat_data.getGuestNice().count());
+}
+
+void SerializeNormalizedCPUStat(const CpuStatData& cpu_stat_data,
+                                std::invocable<const char(&)[], const double> auto serializer) {
+  gsl_Expects(cpu_stat_data.getTotal() > 0ms);
+  serializer("user time %", cpu_stat_data.getUser()/cpu_stat_data.getTotal());
+  serializer("nice time %", cpu_stat_data.getNice()/cpu_stat_data.getTotal());
+  serializer("system time %", cpu_stat_data.getSystem()/cpu_stat_data.getTotal());
+  serializer("idle time %", cpu_stat_data.getIdle()/cpu_stat_data.getTotal());
+  serializer("io wait time %", cpu_stat_data.getIoWait()/cpu_stat_data.getTotal());
+  serializer("irq time %", cpu_stat_data.getIrq()/cpu_stat_data.getTotal());
+  serializer("soft irq %", cpu_stat_data.getSoftIrq()/cpu_stat_data.getTotal());
+  serializer("steal time %", cpu_stat_data.getSteal()/cpu_stat_data.getTotal());
+  serializer("guest time %", cpu_stat_data.getGuest()/cpu_stat_data.getTotal());
+  serializer("guest nice time %", cpu_stat_data.getGuestNice()/cpu_stat_data.getTotal());
+}
+
+void SerializeDiskStatData(const DiskStatData& disk_stat_data,
+                           std::invocable<const char(&)[], const uint64_t> auto serializer) {
+  serializer("Major Device Number", disk_stat_data.getMajorDeviceNumber());
+  serializer("Minor Device Number", disk_stat_data.getMinorDeviceNumber());
+  serializer("Reads Completed", disk_stat_data.getReadsCompleted());
+  serializer("Reads Merged", disk_stat_data.getReadsMerged());
+  serializer("Sectors Read", disk_stat_data.getSectorsRead());
+  serializer("Writes Completed", disk_stat_data.getWritesCompleted());
+  serializer("Writes Merged", disk_stat_data.getWritesMerged());
+  serializer("Sectors Written", disk_stat_data.getSectorsWritten());
+  serializer("IO-s in progress", disk_stat_data.getIosInProgress());

Review comment:
       "IO-s" looks strange; I would write "IOs" or "IO operations" or possibly "IO's" (in both places)

##########
File path: extensions/procfs/DiskStat.h
##########
@@ -0,0 +1,83 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <chrono>
+#include <istream>
+#include <optional>
+#include <string>
+#include <utility>
+
+using namespace std::literals::chrono_literals;
+
+namespace org::apache::nifi::minifi::extensions::procfs {
+
+class DiskStatData {
+  DiskStatData() = default;
+
+ public:
+  struct MonotonicIncreasingMembers {
+    uint64_t reads_completed_;
+    uint64_t reads_merged_;
+    uint64_t sectors_read_;
+    uint64_t milliseconds_spent_reading_;
+    uint64_t writes_completed_;
+    uint64_t writes_merges_;

Review comment:
       typo:
   ```suggestion
       uint64_t writes_merged_;
   ```

##########
File path: extensions/procfs/NetDev.cpp
##########
@@ -0,0 +1,58 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "NetDev.h"
+
+using namespace std::literals::chrono_literals;
+
+namespace org::apache::nifi::minifi::extensions::procfs {
+
+std::optional<NetDevData> NetDevData::parseNetDevLine(std::istream& iss) {
+  NetDevData net_dev_data;
+  iss >> net_dev_data.bytes_received_ >> net_dev_data.packets_received_ >> net_dev_data.errs_received_ >> net_dev_data.drop_errors_received_
+      >> net_dev_data.fifo_errors_received_ >> net_dev_data.frame_errors_received_ >> net_dev_data.compressed_packets_received_
+      >> net_dev_data.multicast_frames_received_>> net_dev_data.bytes_transmitted_ >> net_dev_data.packets_transmitted_
+      >> net_dev_data.errs_transmitted_ >> net_dev_data.drop_errors_transmitted_ >> net_dev_data.fifo_errors_transmitted_
+      >> net_dev_data.collisions_transmitted_ >> net_dev_data.carrier_losses_transmitted_ >> net_dev_data.compressed_packets_transmitted_;

Review comment:
       one variable per line would be more readable here, too

##########
File path: extensions/procfs/ProcFsJsonSerialization.h
##########
@@ -0,0 +1,179 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <string>
+#include <string_view>
+
+#include "ProcFsSerialization.h"
+#include "rapidjson/stream.h"
+#include "rapidjson/document.h"
+
+namespace org::apache::nifi::minifi::extensions::procfs {
+
+namespace details {
+class UInt64Serializer {
+ public:
+  UInt64Serializer(rapidjson::Value& json, rapidjson::Document::AllocatorType& alloc) :
+      json_(json), alloc_(alloc) {
+  }
+  void operator()(const char(&key)[], const uint64_t value) {

Review comment:
       Is this a new C++20 feature?  Do you have a link to a description of how it works?  It's pretty cool; clang 13.0.1 doesn't support it, yet, but clang trunk does, so I don't mind keeping it as a "temporarily gcc-only feature".  On the other hand, it may be simpler to use `const char* key`.

##########
File path: extensions/procfs/CpuStat.cpp
##########
@@ -0,0 +1,49 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "CpuStat.h"
+
+using namespace std::literals::chrono_literals;
+
+namespace org::apache::nifi::minifi::extensions::procfs {
+
+std::optional<CpuStatData> CpuStatData::parseCpuStatLine(std::istream& iss) {
+  CpuStatData data;
+  iss >> data.user_ >> data.nice_ >> data.system_ >> data.idle_ >> data.io_wait_ >> data.irq_ >> data.soft_irq_ >> data.steal_ >> data.guest_ >> data.guest_nice_;
+  if (iss.fail())
+    return std::nullopt;
+  data.user_ -= data.guest_;  // Guest time is already accounted in usertime
+  data.nice_ -= data.guest_nice_;

Review comment:
       Are you sure we want to do this?  As a user, I would expect the "user time" and "nice time" reported by ProcFsMonitor to be the same as the number in `/proc/stat` (and might subtract the guest time from it again).

##########
File path: extensions/procfs/ProcFsSerialization.h
##########
@@ -0,0 +1,164 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+#include <concepts>
+
+#include "CpuStat.h"
+#include "DiskStat.h"
+#include "MemInfo.h"
+#include "NetDev.h"
+#include "ProcessStat.h"
+#include "utils/gsl.h"
+
+namespace org::apache::nifi::minifi::extensions::procfs {
+
+void SerializeCPUStatData(const CpuStatData& cpu_stat_data,
+                          std::invocable<const char(&)[], const uint64_t> auto serializer) {
+  serializer("user time", cpu_stat_data.getUser().count());
+  serializer("nice time", cpu_stat_data.getNice().count());
+  serializer("system time", cpu_stat_data.getSystem().count());
+  serializer("idle time", cpu_stat_data.getIdle().count());
+  serializer("io wait time", cpu_stat_data.getIoWait().count());
+  serializer("irq time", cpu_stat_data.getIrq().count());
+  serializer("soft irq time", cpu_stat_data.getSoftIrq().count());
+  serializer("steal time", cpu_stat_data.getSteal().count());
+  serializer("guest time", cpu_stat_data.getGuest().count());
+  serializer("guest nice time", cpu_stat_data.getGuestNice().count());
+}
+
+void SerializeNormalizedCPUStat(const CpuStatData& cpu_stat_data,
+                                std::invocable<const char(&)[], const double> auto serializer) {
+  gsl_Expects(cpu_stat_data.getTotal() > 0ms);
+  serializer("user time %", cpu_stat_data.getUser()/cpu_stat_data.getTotal());
+  serializer("nice time %", cpu_stat_data.getNice()/cpu_stat_data.getTotal());
+  serializer("system time %", cpu_stat_data.getSystem()/cpu_stat_data.getTotal());
+  serializer("idle time %", cpu_stat_data.getIdle()/cpu_stat_data.getTotal());
+  serializer("io wait time %", cpu_stat_data.getIoWait()/cpu_stat_data.getTotal());
+  serializer("irq time %", cpu_stat_data.getIrq()/cpu_stat_data.getTotal());
+  serializer("soft irq %", cpu_stat_data.getSoftIrq()/cpu_stat_data.getTotal());
+  serializer("steal time %", cpu_stat_data.getSteal()/cpu_stat_data.getTotal());
+  serializer("guest time %", cpu_stat_data.getGuest()/cpu_stat_data.getTotal());
+  serializer("guest nice time %", cpu_stat_data.getGuestNice()/cpu_stat_data.getTotal());
+}
+
+void SerializeDiskStatData(const DiskStatData& disk_stat_data,
+                           std::invocable<const char(&)[], const uint64_t> auto serializer) {
+  serializer("Major Device Number", disk_stat_data.getMajorDeviceNumber());
+  serializer("Minor Device Number", disk_stat_data.getMinorDeviceNumber());
+  serializer("Reads Completed", disk_stat_data.getReadsCompleted());
+  serializer("Reads Merged", disk_stat_data.getReadsMerged());
+  serializer("Sectors Read", disk_stat_data.getSectorsRead());
+  serializer("Writes Completed", disk_stat_data.getWritesCompleted());
+  serializer("Writes Merged", disk_stat_data.getWritesMerged());
+  serializer("Sectors Written", disk_stat_data.getSectorsWritten());
+  serializer("IO-s in progress", disk_stat_data.getIosInProgress());
+}
+
+void SerializeDiskStatDataPerSec(const DiskStatData& disk_stat_data,
+                                 const std::chrono::duration<double> duration,
+                                 std::invocable<const char(&)[], const double> auto serializer) {
+  gsl_Expects(duration > 0ms);
+  serializer("Major Device Number", disk_stat_data.getMajorDeviceNumber());
+  serializer("Minor Device Number", disk_stat_data.getMinorDeviceNumber());
+  serializer("Reads Completed/sec", disk_stat_data.getReadsCompleted()/duration.count());
+  serializer("Reads Merged/sec", disk_stat_data.getReadsMerged()/duration.count());
+  serializer("Sectors Read/sec", disk_stat_data.getSectorsRead()/duration.count());
+  serializer("Writes Completed/sec", disk_stat_data.getWritesCompleted()/duration.count());
+  serializer("Writes Merged/sec", disk_stat_data.getWritesMerged()/duration.count());
+  serializer("Sectors Written/sec", disk_stat_data.getSectorsWritten()/duration.count());
+  serializer("IO-s in progress", disk_stat_data.getIosInProgress()/duration.count());
+}
+
+void SerializeMemInfo(const MemInfo& mem_info,
+                      std::invocable<const char(&)[], const uint64_t> auto serializer) {
+  serializer("MemTotal", mem_info.getTotalMemory());
+  serializer("MemFree", mem_info.getAvailableMemory());
+  serializer("MemAvailable", mem_info.getFreeMemory());
+  serializer("MemFree", mem_info.getAvailableMemory());
+  serializer("SwapFree", mem_info.getFreeSwap());
+  serializer("SwapTotal", mem_info.getTotalSwap());
+}
+
+void SerializeNetDevData(const NetDevData& net_dev_data,
+                         std::invocable<const char(&)[], const uint64_t> auto serializer) {
+  serializer("Bytes Received", net_dev_data.getBytesReceived());
+  serializer("Packets Received", net_dev_data.getPacketsReceived());
+  serializer("Receive Errors", net_dev_data.getReceiveErrors());
+  serializer("Receive Drop Errors", net_dev_data.getReceiveDropErrors());
+  serializer("Receive Fifo Errors", net_dev_data.getReceiveFifoErrors());
+  serializer("Receive Frame Errors", net_dev_data.getReceiveFrameErrors());
+  serializer("Compressed Packets Received", net_dev_data.getCompressedPacketsReceived());
+  serializer("Multicast Frames Received", net_dev_data.getMulticastFramesReceived());
+
+  serializer("Bytes Transmitted", net_dev_data.getBytesTransmitted());
+  serializer("Packets Transmitted", net_dev_data.getPacketsTransmitted());
+  serializer("Transmit errors", net_dev_data.getTransmitErrors());
+  serializer("Transmit drop errors", net_dev_data.getTransmitDropErrors());
+  serializer("Transmit fifo errors", net_dev_data.getTransmitFifoErrors());
+  serializer("Transmit collisions", net_dev_data.getTransmitCollisions());
+  serializer("Transmit carrier losses", net_dev_data.getTransmitCarrierLosses());
+  serializer("Compressed Packets Transmitted", net_dev_data.getCompressedPacketsTransmitted());
+}
+
+void SerializeNetDevDataPerSec(const NetDevData& net_dev_data,
+                               const std::chrono::duration<double> duration,
+                               std::invocable<const char(&)[], const double> auto serializer) {
+  gsl_Expects(duration > 0ms);
+  serializer("Bytes Received/sec", net_dev_data.getBytesReceived()/duration.count());
+  serializer("Packets Received/sec", net_dev_data.getPacketsReceived()/duration.count());
+  serializer("Receive Errors/sec", net_dev_data.getReceiveErrors()/duration.count());
+  serializer("Receive Drop Errors/sec", net_dev_data.getReceiveDropErrors()/duration.count());
+  serializer("Receive Fifo Errors/sec", net_dev_data.getReceiveFifoErrors()/duration.count());
+  serializer("Receive Frame Errors/sec", net_dev_data.getReceiveFrameErrors()/duration.count());
+  serializer("Compressed Packets Received/sec", net_dev_data.getCompressedPacketsReceived()/duration.count());
+  serializer("Multicast Frames Received/sec", net_dev_data.getMulticastFramesReceived()/duration.count());
+
+  serializer("Bytes Transmitted/sec", net_dev_data.getBytesTransmitted()/duration.count());
+  serializer("Packets Transmitted/sec", net_dev_data.getPacketsTransmitted()/duration.count());
+  serializer("Transmit errors/sec", net_dev_data.getTransmitErrors()/duration.count());
+  serializer("Transmit drop errors/sec", net_dev_data.getTransmitDropErrors()/duration.count());
+  serializer("Transmit fifo errors/sec", net_dev_data.getTransmitFifoErrors()/duration.count());
+  serializer("Transmit collisions/sec", net_dev_data.getTransmitCollisions()/duration.count());
+  serializer("Transmit carrier losses/sec", net_dev_data.getTransmitCarrierLosses()/duration.count());
+  serializer("Compressed Packets Transmitted/sec", net_dev_data.getCompressedPacketsTransmitted()/duration.count());
+}
+
+void SerializeProcessStat(const ProcessStat& process_stat,
+                          std::invocable<const char(&)[], const uint64_t> auto uint64_t_serializer,
+                          std::invocable<const char(&)[], const std::string_view&> auto string_serializer) {
+  string_serializer("COMM", process_stat.getComm());
+  uint64_t_serializer("RES", process_stat.getMemory());
+  uint64_t_serializer("CPUTIME", process_stat.getCpuTime().count());
+}
+
+void SerializeNormalizedProcessStat(const ProcessStat& process_stat_start,
+                                    const ProcessStat& process_stat_end,
+                                    const std::chrono::duration<double> all_cpu_time,
+                                    std::invocable<const char(&)[], const uint64_t> auto uint64_t_serializer,
+                                    std::invocable<const char(&)[], const std::string_view&> auto string_serializer,
+                                    std::invocable<const char(&)[], const double> auto double_serializer) {
+  gsl_Expects(all_cpu_time > 0ms);
+  gsl_Expects(process_stat_start.getComm() == process_stat_end.getComm());
+  gsl_Expects(process_stat_end.getCpuTime() >= process_stat_start.getCpuTime());
+  auto cpu_time_diff = process_stat_end.getCpuTime()-process_stat_end.getCpuTime();
+  string_serializer("COMM", process_stat_start.getComm());
+  uint64_t_serializer("RES", process_stat_start.getMemory());

Review comment:
       I think
   ```suggestion
     uint64_t_serializer("RES", process_stat_end.getMemory());
   ```
   would be more natural




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