BWF: Add UnHex (hexadecimal encoding to raw bytes).

Author: SolidWallOfCode

code/include/swoc/bwf_ex.h

@@ -206,6 +206,23 @@ SubText<ARG>
 Optional(TextView fmt, ARG &&arg) {
   return detail::Optional(meta::CaseArg, fmt, std::forward<ARG>(arg));
 }
+
+/** Convert from ASCII hexadecimal to raw bytes.
+ *
+ * E.g. if the source span contains "4576696c20446176652052756c7a" then "Evil Dave Rulz" is the output.
+ * For format specifier support, on lhe max width is used. Any @c MemSpan compatible class can be used
+ * as the target, including @c std::string and @c std::string_view.
+ *
+ * @code
+ *   void f(std::string const& str) {
+ *     w.print("{}", bwf::UnHex(str));
+ *     // ...
+ * @endcode
+ */
+struct UnHex {
+  UnHex(MemSpan<void const> const& span) : _span(span) {}
+  MemSpan<void const> _span; ///< Source span.
+};
 } // namespace bwf
 
 /** Repeatedly output a pattern.
@@ -237,6 +254,8 @@ BufferWriter &bwformat(BufferWriter &w, bwf::Spec const &spec, bwf::Errno const
  */
 BufferWriter &bwformat(BufferWriter &w, bwf::Spec const &spec, bwf::Date const &date);
 
+BufferWriter &bwformat(BufferWriter &w, bwf::Spec const& spec, bwf::UnHex const& obj);
+
 /** Output a nested formatted string.
  *
  * @tparam Args Argument pack for @a subtext.

code/src/bw_format.cc

@@ -960,8 +960,8 @@ bwformat(BufferWriter &w, bwf::Spec const &spec, bwf::Pattern const &pattern) {
   return w;
 }
 
-swoc::BufferWriter &
-bwformat(swoc::BufferWriter &w, swoc::bwf::Spec const &spec, std::error_code const &ec) {
+BufferWriter &
+bwformat(BufferWriter &w, bwf::Spec const &spec, std::error_code const &ec) {
   static const auto G_CAT = &std::generic_category();
   static const auto S_CAT  = &std::system_category();
 
@@ -984,6 +984,17 @@ bwformat(swoc::BufferWriter &w, swoc::bwf::Spec const &spec, std::error_code con
   return w;
 }
 
+BufferWriter&
+bwformat(BufferWriter &w, bwf::Spec const& spec, bwf::UnHex const& obj) {
+  auto span { obj._span };
+  size_t limit = spec._max;
+  while (span.size() >= 2 && limit--) {
+    auto b = svto_radix<16>(span.clip_prefix(2).rebind<char const>());
+    w.write(b);
+  }
+  return w;
+}
+
 }} // namespace swoc::SWOC_VERSION_NS
 
 namespace std {

unit_tests/test_bw_format.cc

@@ -231,6 +231,26 @@ TEST_CASE("BWFormat numerics", "[bwprint][bwformat]") {
   REQUIRE(bw.view() == "Char 'a'");
   bw.clear().print("Byte '{}'", uint8_t{'a'});
   REQUIRE(bw.view() == "Byte '97'");
+
+  SECTION("Hexadecimal buffers") {
+    swoc::MemSpan<void const> cvs{"Evil Dave Rulz"_tv}; // TextView intermediate keeps nul byte out.
+    TextView const edr_in_hex{"4576696c20446176652052756c7a"};
+    bw.clear().format(swoc::bwf::Spec(":x"), cvs);
+    REQUIRE(bw.view() == edr_in_hex);
+    bw.clear().format(swoc::bwf::Spec::DEFAULT, swoc::bwf::UnHex(edr_in_hex));
+    REQUIRE(bw.view() == "Evil Dave Rulz");
+    bw.clear().format(swoc::bwf::Spec::DEFAULT, swoc::bwf::UnHex("112233445566778800"));
+    REQUIRE(memcmp(bw.view(), "\x11\x22\x33\x44\x55\x66\x77\x88\x00"_tv) == 0);
+    // Check if max width in the spec works - should leave bytes from the previous.
+    bw.clear().format(swoc::bwf::Spec{":,2"}, swoc::bwf::UnHex("deadbeef"));
+    REQUIRE(memcmp(TextView(bw.data(), 4), "\xde\xad\x33\x44"_tv) == 0);
+    std::string text, hex;
+    bwprint(hex, "{:x}", cvs);
+    bwprint(text, "{}", swoc::bwf::UnHex(edr_in_hex));
+    REQUIRE(hex == edr_in_hex);
+    REQUIRE(text == TextView(cvs.rebind<char const>()));
+  }
+
 }
 
 TEST_CASE("bwstring", "[bwprint][bwappend][bwstring]") {