refactor ServerHealthCheckerCallback::ExtraInfo

Summary:
ExtraInfo was a vector of pairs, refactor it to inherit from a vector of pairs (to not break existing use cases), and add new use cases as struct members.

The struct members can be empty just fine, and we can then factor out parsing each struct member. Right now the code depends on some hardcoded strings never changing.

Also did some minor code cleanup

Reviewed By: jerryliu55

Differential Revision: D69268041

fbshipit-source-id: 4c24907e63d6bd424b4b9a650b4cef4a3f4bd6fa

proxygen/lib/healthcheck/ServerHealthCheckerCallback.cpp

@@ -43,4 +43,14 @@ const std::string serverDownInfoStr(ServerDownInfo info) {
   }
 }
 
+// Convert extraInfo to a map, overrides duplicate headers
+folly::F14FastMap<std::string, std::string>
+ServerHealthCheckerCallback::ExtraInfo::toMap() const {
+  folly::F14FastMap<std::string, std::string> mapOut;
+  for (const auto& it : *this) {
+    mapOut.insert(it);
+  }
+  return mapOut;
+}
+
 } // namespace proxygen

proxygen/lib/healthcheck/ServerHealthCheckerCallback.h

@@ -12,6 +12,7 @@
 #include <vector>
 
 #include <folly/SocketAddress.h>
+#include <folly/container/F14Map.h>
 
 #include <proxygen/lib/utils/Time.h>
 
@@ -59,7 +60,28 @@ const std::string serverDownInfoStr(ServerDownInfo info);
 class ServerHealthCheckerCallback {
  public:
   // Additional info received from a successful healthcheck (e.g. HTTP headers)
-  using ExtraInfo = std::vector<std::pair<std::string, std::string>>;
+  // This is a vector of pairs for legacy reasons.
+  // All new usecases should be defined as struct members.
+  struct ExtraInfo : public std::vector<std::pair<std::string, std::string>> {
+    ExtraInfo() = default;
+    ExtraInfo(const ExtraInfo&) = default;
+    ExtraInfo(ExtraInfo&&) = default;
+    explicit ExtraInfo(std::vector<std::pair<std::string, std::string>> v)
+        : std::vector<std::pair<std::string, std::string>>(std::move(v)) {
+    }
+    ExtraInfo& operator=(
+        const std::vector<std::pair<std::string, std::string>>& v) {
+      std::vector<std::pair<std::string, std::string>>::operator=(v);
+      return *this;
+    }
+    ExtraInfo& operator=(const ExtraInfo& other) = default;
+
+    // Converts all fields within the vector of pairs to a map.
+    [[nodiscard]] folly::F14FastMap<std::string, std::string> toMap() const;
+
+    // Custom fields for WWW healthchecks
+    folly::F14FastMap<std::string, std::string> thriftWWWCustomFields;
+  };
 
   virtual void processHealthCheckFailure(
       const TimePoint& startTime,