Add ObisId::from_string

Author: PolarGoose

src/dlms_parser/obis_id.h

@@ -4,6 +4,7 @@
 #include <compare>
 #include <cstdio>
 #include <cstdint>
+#include <optional>
 #include <span>
 #include <string_view>
 #include <algorithm>
@@ -21,6 +22,40 @@ struct ObisId final {
 
   [[nodiscard]] bool empty() const { return v == std::array<uint8_t, 6>{}; }
 
+  [[nodiscard]] static std::optional<ObisId> from_string(const std::string_view str) noexcept {
+    std::array<uint8_t, 6> values{};
+    size_t count = 0;
+    size_t pos = 0;
+
+    while (pos < str.size()) {
+      if (count == values.size()) return std::nullopt;
+      if (str[pos] < '0' || str[pos] > '9') return std::nullopt;
+
+      unsigned value = 0;
+      while (pos < str.size() && str[pos] >= '0' && str[pos] <= '9') {
+        value = value * 10U + static_cast<unsigned>(str[pos] - '0');
+        if (value > 255U) return std::nullopt;
+        ++pos;
+      }
+
+      values[count++] = static_cast<uint8_t>(value);
+
+      if (pos == str.size()) break;
+      if (str[pos] != '.' && str[pos] != '-') return std::nullopt;
+
+      ++pos;
+      if (pos == str.size()) return std::nullopt;
+    }
+
+    if (count == 5) {
+      values[5] = 255;
+    } else if (count != values.size()) {
+      return std::nullopt;
+    }
+
+    return ObisId(values[0], values[1], values[2], values[3], values[4], values[5]);
+  }
+
   [[nodiscard]] std::string_view to_string(std::span<char> buffer) const {
     if (buffer.empty()) return {};
     const int len = snprintf(buffer.data(), buffer.size(), "%u.%u.%u.%u.%u.%u", v[0], v[1], v[2], v[3], v[4], v[5]);

tests/test_obis_id.cpp

@@ -0,0 +1,33 @@
+#include <doctest.h>
+
+#include "tests/log_fixture.h"
+#include "dlms_parser/obis_id.h"
+
+using namespace dlms_parser;
+
+TEST_CASE_FIXTURE(LogFixture, "OBIS ID parsing") {
+  SUBCASE("dot-separated six-byte form") {
+    const auto parsed = ObisId::from_string("0.0.96.1.0.255");
+
+    REQUIRE(parsed.has_value());
+    CHECK(*parsed == ObisId(0, 0, 96, 1, 0, 255));
+  }
+
+  SUBCASE("five-byte form defaults F to 255") {
+    const auto parsed = ObisId::from_string("0-0.96.1.0");
+
+    REQUIRE(parsed.has_value());
+    CHECK(*parsed == ObisId(0, 0, 96, 1, 0, 255));
+  }
+
+  SUBCASE("rejects malformed strings") {
+    CHECK_FALSE(ObisId::from_string("").has_value());
+    CHECK_FALSE(ObisId::from_string(".0.96.1.0.255").has_value());
+    CHECK_FALSE(ObisId::from_string("0..96.1.0.255").has_value());
+    CHECK_FALSE(ObisId::from_string("0.0.96.1.0.").has_value());
+    CHECK_FALSE(ObisId::from_string("0.0.96.1").has_value());
+    CHECK_FALSE(ObisId::from_string("0.0.96.1.0.255.1").has_value());
+    CHECK_FALSE(ObisId::from_string("0.0.256.1.0.255").has_value());
+    CHECK_FALSE(ObisId::from_string("0.0.96.1.0x255").has_value());
+  }
+}