SERVER-41495 HostAndPort streaming refactor

2 files changed, 57 insertions, 51 deletions

diff --git a/src/mongo/util/net/hostandport.cpp b/src/mongo/util/net/hostandport.cpp
index 927754c4421..ed74befa3a7 100644
--- a/src/mongo/util/net/hostandport.cpp
+++ b/src/mongo/util/net/hostandport.cpp
@@ -102,40 +102,25 @@ bool HostAndPort::isDefaultRoute() const {
 
 std::string HostAndPort::toString() const {
     StringBuilder ss;
-    append(ss);
+    ss << *this;
     return ss.str();
 }
 
-template <typename SinkFunc>
-static void appendGeneric(const HostAndPort& hp, const SinkFunc& write) {
+void HostAndPort::_appendToVisitor(AppendVisitor& write) const {
     // wrap ipv6 addresses in []s for roundtrip-ability
-    if (hp.host().find(':') != std::string::npos) {
+    if (host().find(':') != std::string::npos) {
         write("[");
-        write(hp.host());
+        write(host());
         write("]");
     } else {
-        write(hp.host());
+        write(host());
     }
-    if (hp.host().find('/') == std::string::npos) {
+    if (host().find('/') == std::string::npos) {
         write(":");
-        write(hp.port());
+        write(port());
     }
 }
 
-template <typename Stream>
-static Stream& appendToStream(const HostAndPort& hp, Stream& sink) {
-    appendGeneric(hp, [&sink](const auto& v) { sink << v; });
-    return sink;
-}
-
-void HostAndPort::append(StringBuilder& sink) const {
-    appendToStream(*this, sink);
-}
-
-void HostAndPort::append(fmt::writer& sink) const {
-    appendGeneric(*this, [&sink](const auto& v) { sink.write(v); });
-}
-
 bool HostAndPort::empty() const {
     return _host.empty() && _port < 0;
 }
@@ -214,16 +199,4 @@ Status HostAndPort::initialize(StringData s) {
     return Status::OK();
 }
 
-std::ostream& operator<<(std::ostream& os, const HostAndPort& hp) {
-    return appendToStream(hp, os);
-}
-
-StringBuilder& operator<<(StringBuilder& os, const HostAndPort& hp) {
-    return appendToStream(hp, os);
-}
-
-StackStringBuilder& operator<<(StackStringBuilder& os, const HostAndPort& hp) {
-    return appendToStream(hp, os);
-}
-
 }  // namespace mongo
diff --git a/src/mongo/util/net/hostandport.h b/src/mongo/util/net/hostandport.h
index 87b8a6c528b..055c09634f5 100644
--- a/src/mongo/util/net/hostandport.h
+++ b/src/mongo/util/net/hostandport.h
@@ -116,12 +116,6 @@ struct HostAndPort {
     std::string toString() const;
 
     /**
-     * Like toString(), but writes to various `sink` instead.
-     */
-    void append(StringBuilder& sink) const;
-    void append(fmt::writer& sink) const;
-
-    /**
      * Returns true if this object represents no valid HostAndPort.
      */
     bool empty() const;
@@ -141,29 +135,68 @@ struct HostAndPort {
     }
 
 private:
+    friend struct fmt::formatter<HostAndPort>;
+
+    struct AppendVisitor {
+        virtual void operator()(StringData v) = 0;
+        virtual void operator()(std::uint16_t v) = 0;
+        virtual ~AppendVisitor() = default;
+    };
+
+    void _appendToVisitor(AppendVisitor& sink) const;
+
+    template <typename F>
+    void _appendToPolymorphicFunc(F f) const;
+
+    template <typename Stream>
+    Stream& _appendToStream(Stream& os) const {
+        _appendToPolymorphicFunc([&](const auto& v) { os << v; });
+        return os;
+    }
+
+    friend std::ostream& operator<<(std::ostream& os, const HostAndPort& hp) {
+        return hp._appendToStream(os);
+    }
+    friend StringBuilder& operator<<(StringBuilder& os, const HostAndPort& hp) {
+        return hp._appendToStream(os);
+    }
+    friend StackStringBuilder& operator<<(StackStringBuilder& os, const HostAndPort& hp) {
+        return hp._appendToStream(os);
+    }
+
     std::string _host;
     int _port;  // -1 indicates unspecified
 };
 
-std::ostream& operator<<(std::ostream& os, const HostAndPort& hp);
-
-StringBuilder& operator<<(StringBuilder& os, const HostAndPort& hp);
-
-StackStringBuilder& operator<<(StackStringBuilder& os, const HostAndPort& hp);
+template <typename F>
+void HostAndPort::_appendToPolymorphicFunc(F f) const {
+    struct Vis : AppendVisitor {
+        explicit Vis(F f) : _f{std::move(f)} {}
+        void operator()(StringData v) override {
+            _f(v);
+        }
+        void operator()(std::uint16_t v) override {
+            _f(v);
+        }
+        F _f;
+    };
+    Vis visitor(std::move(f));
+    _appendToVisitor(visitor);
+}
 
 }  // namespace mongo
 
+namespace fmt {
 template <>
-struct fmt::formatter<mongo::HostAndPort> {
+struct formatter<mongo::HostAndPort> {
     template <typename ParseContext>
-    auto parse(ParseContext& ctx) -> decltype(ctx.begin()) {
+    constexpr auto parse(ParseContext& ctx) {
         return ctx.begin();
     }
-
     template <typename FormatContext>
-    auto format(const mongo::HostAndPort& hp, FormatContext& ctx) -> decltype(ctx.out()) {
-        fmt::writer w(ctx.out());
-        hp.append(w);
+    auto format(const mongo::HostAndPort& hp, FormatContext& ctx) {
+        hp._appendToPolymorphicFunc([&](const auto& v) { fmt::format_to(ctx.out(), "{}", v); });
         return ctx.out();
     }
 };
+}  // namespace fmt