SERVER-40621 Add fmt::formatter<mongo::HostAndPort>

3 files changed, 57 insertions, 8 deletions

diff --git a/src/mongo/util/net/hostandport.cpp b/src/mongo/util/net/hostandport.cpp
index 5c30ef22aa8..d81a81fab36 100644
--- a/src/mongo/util/net/hostandport.cpp
+++ b/src/mongo/util/net/hostandport.cpp
@@ -110,18 +110,30 @@ std::string HostAndPort::toString() const {
     return ss.str();
 }
 
-void HostAndPort::append(StringBuilder& ss) const {
+template <typename SinkFunc>
+static void appendGeneric(const HostAndPort& hp, const SinkFunc& write) {
     // wrap ipv6 addresses in []s for roundtrip-ability
-    if (host().find(':') != std::string::npos) {
-        ss << '[' << host() << ']';
+    if (hp.host().find(':') != std::string::npos) {
+        write("[");
+        write(hp.host());
+        write("]");
     } else {
-        ss << host();
+        write(hp.host());
     }
-    if (host().find('/') == std::string::npos) {
-        ss << ':' << port();
+    if (hp.host().find('/') == std::string::npos) {
+        write(":");
+        write(hp.port());
     }
 }
 
+void HostAndPort::append(StringBuilder& sink) const {
+    appendGeneric(*this, [&sink](const auto& v) { sink << v; });
+}
+
+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;
 }
diff --git a/src/mongo/util/net/hostandport.h b/src/mongo/util/net/hostandport.h
index fdadf39d9e1..03e3ef2ee5e 100644
--- a/src/mongo/util/net/hostandport.h
+++ b/src/mongo/util/net/hostandport.h
@@ -29,6 +29,7 @@
 
 #pragma once
 
+#include <fmt/format.h>
 #include <iosfwd>
 #include <string>
 
@@ -126,9 +127,10 @@ struct HostAndPort {
     std::string toString() const;
 
     /**
-     * Like toString(), above, but writes to "ss", instead.
+     * Like toString(), but writes to various `sink` instead.
      */
-    void append(StringBuilder& ss) const;
+    void append(StringBuilder& sink) const;
+    void append(fmt::writer& sink) const;
 
     /**
      * Returns true if this object represents no valid HostAndPort.
@@ -169,3 +171,18 @@ template <typename Allocator>
 StringBuilderImpl<Allocator>& operator<<(StringBuilderImpl<Allocator>& os, const HostAndPort& hp);
 
 }  // namespace mongo
+
+template <>
+struct fmt::formatter<mongo::HostAndPort> {
+    template <typename ParseContext>
+    auto parse(ParseContext& ctx) -> decltype(ctx.begin()) {
+        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);
+        return ctx.out();
+    }
+};
diff --git a/src/mongo/util/net/hostandport_test.cpp b/src/mongo/util/net/hostandport_test.cpp
index c70c8e7f4ae..69163791b3a 100644
--- a/src/mongo/util/net/hostandport_test.cpp
+++ b/src/mongo/util/net/hostandport_test.cpp
@@ -29,6 +29,8 @@
 
 #include "mongo/platform/basic.h"
 
+#include <fmt/format.h>
+
 #include "mongo/db/server_options.h"
 #include "mongo/unittest/unittest.h"
 #include "mongo/util/assert_util.h"
@@ -123,5 +125,23 @@ TEST(HostAndPort, CanIdentifyDefaultRoutes) {
     ASSERT_TRUE(HostAndPort("[0:0:0::00:0:0]").isDefaultRoute());
 }
 
+TEST(HostAndPort, Fmt) {
+    const std::string specs[] = {
+        "1.2.3.4",           //
+        "1.2.3.4:123",       //
+        "[1:2:3:4]",         //
+        "[1:2:3:4]:123",     //
+        "/dev/mongod.sock",  //
+    };
+    for (const auto& spec : specs) {
+        const HostAndPort hp(spec);
+        const std::string hps = hp.toString();
+        ASSERT_EQUALS(fmt::format("{}", hp), hps);
+        ASSERT_EQUALS(fmt::format("<{}>", hp), "<" + hps + ">");
+        ASSERT_EQUALS(fmt::format("{}", hp), hps);
+        ASSERT_EQUALS(fmt::format("{1:} says {0:}", "hello", hp), hps + " says hello");
+    }
+}
+
 }  // namespace
 }  // namespace mongo