add function for tags endpoint

loader/src/server/Server.cpp

@@ -415,3 +415,42 @@ ServerPromise<ByteVector> server::getModLogo(std::string const& id) {
             return parseServerProgress(prog, "Downloading logo for " + id);
         });
 }
+
+ServerPromise<std::unordered_set<std::string>> server::getTags(std::monostate) {
+    auto req = web::WebRequest();
+    req.userAgent(getServerUserAgent());
+    return req.get(getServerAPIBaseURL() + "/tags")
+        .then<std::unordered_set<std::string>, ServerError>([](auto response) -> Result<std::unordered_set<std::string>, ServerError> {
+            if (response) {
+                auto value = response.unwrap();
+
+                // Store the code, since the value is moved afterwards
+                auto code = value.code();
+                
+                // Parse payload
+                auto payload = parseServerPayload(std::move(value));
+                if (!payload) {
+                    return Err(payload.unwrapErr());
+                }
+                matjson::Value json = payload.unwrap();
+                if (!json.is_array()) {
+                    return Err(ServerError(code, "Expected a string array"));
+                }
+
+                std::unordered_set<std::string> tags;
+                for (auto item : json.as_array()) {
+                    if (!item.is_string()) {
+                        return Err(ServerError(code, "Expected a string array"));
+                    }
+                    tags.insert(item.as_string());
+                }
+                return Ok(tags);
+            }
+            else {
+                return Err(parseServerError(response.unwrapErr()));
+            }
+        })
+        .progress<ServerProgress>([](auto prog) {
+            return parseServerProgress(prog, "Downloading valid tags");
+        });
+}

loader/src/server/Server.hpp

@@ -101,6 +101,9 @@ namespace server {
     ServerPromise<ServerModsList> getMods(ModsQuery const& query);
     ServerPromise<ServerModMetadata> getMod(std::string const& id);
     ServerPromise<ByteVector> getModLogo(std::string const& id);
+    ServerPromise<std::unordered_set<std::string>> getTags(std::monostate = std::monostate());
+
+    // ^^ Note: Any funcs with `std::monostate` parameter is because ServerResultCache expects a single query arg
 
     // Caching for server endpoints
     namespace detail {
@@ -108,6 +111,7 @@ namespace server {
         struct ExtractServerReqParams {
             using Result = R;
             using Query  = Q;
+            ExtractServerReqParams(ServerPromise<R>(*)(Q)) {}
             ExtractServerReqParams(ServerPromise<R>(*)(Q const&)) {}
         };
     }
@@ -209,7 +213,10 @@ namespace server {
             return inst;
         }
         
-        ServerPromise<Result> get(Query const& query) {
+        ServerPromise<Result> get() requires std::is_same_v<Query, std::monostate> {
+            return m_cache.get(Query());
+        }
+        ServerPromise<Result> get(Query const& query) requires (!std::is_same_v<Query, std::monostate>) {
             return m_cache.get(query);
         }
         ServerPromise<Result> refetch(Query const& query) {