[GitHub] [trafficserver] SolidWallOfCode commented on a diff in pull request #9485: Unit parser

["SolidWallOfCode (via GitHub)" <gi...@apache.org>]

SolidWallOfCode commented on code in PR #9485:
URL: https://github.com/apache/trafficserver/pull/9485#discussion_r1124670916


##########
src/tscpp/util/ts_unit_parser.cc:
##########
@@ -0,0 +1,78 @@
+/** @file Support for common diagnostics between core, plugins, and libswoc.
+
+  This enables specifying the set of methods usable by a user agent based on the remove IP address
+  for a user agent connection.
+
+  @section license License
+
+  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 <chrono>
+
+#include "tscpp/util/ts_unit_parser.h"
+
+namespace ts
+{
+
+auto
+UnitParser::operator()(swoc::TextView const &src) const noexcept -> Rv<value_type>
+{
+  value_type zret = 0;
+  TextView text   = src; // Keep @a src around to report error offsets.
+
+  while (text.ltrim_if(&isspace)) {
+    TextView parsed;
+    auto n = swoc::svtou(text, &parsed);
+    if (parsed.empty()) {
+      return Errata("Required count not found at offset {}", text.data() - src.data());
+    } else if (n == std::numeric_limits<decltype(n)>::max()) {
+      return Errata("Count at offset {} was out of bounds", text.data() - src.data());
+    }
+    text.remove_prefix(parsed.size());
+    auto ptr = text.ltrim_if(&isspace).data(); // save for error reporting.
+    // Everything up to the next digit or whitespace.
+    auto unit = text.clip_prefix_of([](char c) { return !(isspace(c) || isdigit(c)); });
+    if (unit.empty()) {
+      if (_unit_required_p) {
+        return Errata("Required unit not found at offset {}", ptr - src.data());
+      }
+    } else {
+      auto mult = _units[unit]; // What's the multiplier?
+      if (mult == 0) {
+        return Errata("Unknown unit \"{}\" at offset {}", unit, ptr - src.data());
+      }
+      n *= mult;
+    }
+    zret += n;
+  }
+  return zret;
+}
+
+// Concrete unit parsers.
+
+using namespace std::chrono;
+UnitParser const time_parser{UnitParser::Units{{{nanoseconds{1}.count(), {"ns", "nanosec", "nanoseconds"}},
+                                                {nanoseconds{microseconds{1}}.count(), {"us", "microsec", "microseconds"}},
+                                                {nanoseconds{milliseconds{1}}.count(), {"ms", "millisec", "milliseconds"}},
+                                                {nanoseconds{seconds{1}}.count(), {"s", "sec", "seconds"}},
+                                                {nanoseconds{minutes{1}}.count(), {"m", "min", "minutes"}},
+                                                {nanoseconds{hours{1}}.count(), {"h", "hour", "hours"}},
+                                                {nanoseconds{hours{24}}.count(), {"d", "day", "days"}},
+                                                {nanoseconds{hours{168}}.count(), {"w", "week", "weeks"}}}}};
+
+} // namespace ts

Review Comment:
   No, there's still computation that occurs to initialize the parser data structure. I'm not sure what you mean by "static initializer" other than the parser being a static data structure which is constructed at process start time. That is,
   ```
   UnitParser const time_parser{ ... };
   ```
   which declares a static instance of `UnitParser`.



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