1 files changed, 123 insertions, 0 deletions
diff --git a/src/mongo/idl/feature_flag.cpp b/src/mongo/idl/feature_flag.cpp
new file mode 100644
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+++ b/src/mongo/idl/feature_flag.cpp
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+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/idl/feature_flag.h"
+#include "mongo/db/commands/feature_compatibility_version_parser.h"
+#include "mongo/util/debug_util.h"
+
+namespace mongo {
+
+// (Generic FCV reference): feature flag support
+FeatureFlag::FeatureFlag(bool enabled, StringData versionString)
+    : _enabled(enabled), _version(ServerGlobalParams::FeatureCompatibility::kLatest) {
+
+    // Verify the feature flag invariants. IDL binder verifies these hold but we add these checks to
+    // prevent incorrect direct instantiation.
+    //
+    // If default is true, then version should be present.
+    // If default is false, then no version is allowed.
+    if (kDebugBuild) {
+        if (enabled) {
+            dassert(!versionString.empty());
+        } else {
+            dassert(versionString.empty());
+        }
+    }
+
+    if (!versionString.empty()) {
+        _version = FeatureCompatibilityVersionParser::parseVersion(versionString);
+    }
+}
+
+bool FeatureFlag::isEnabled(const ServerGlobalParams::FeatureCompatibility& fcv) const {
+    if (!_enabled) {
+        return false;
+    }
+
+    return fcv.isGreaterThanOrEqualTo(_version);
+}
+
+bool FeatureFlag::isEnabledAndIgnoreFCV() const {
+    return _enabled;
+}
+
+ServerGlobalParams::FeatureCompatibility::Version FeatureFlag::getVersion() const {
+    uassert(5111001, "Feature Flag is not enabled, cannot retrieve version", _enabled);
+
+    return _version;
+}
+
+void FeatureFlag::set(bool enabled) {
+    _enabled = enabled;
+}
+
+FeatureFlagServerParameter::FeatureFlagServerParameter(StringData name, FeatureFlag& storage)
+    : ServerParameter(ServerParameterSet::getGlobal(), name, true, false), _storage(storage) {}
+
+void FeatureFlagServerParameter::append(OperationContext* opCtx,
+                                        BSONObjBuilder& b,
+                                        const std::string& name) {
+    bool enabled = _storage.isEnabledAndIgnoreFCV();
+
+    {
+        auto sub = BSONObjBuilder(b.subobjStart(name));
+        sub.append("value"_sd, enabled);
+
+        if (enabled) {
+            sub.append("version",
+                       FeatureCompatibilityVersionParser::serializeVersion(_storage.getVersion()));
+        }
+    }
+}
+
+Status FeatureFlagServerParameter::set(const BSONElement& newValueElement) {
+    bool newValue;
+
+    if (auto status = newValueElement.tryCoerce(&newValue); !status.isOK()) {
+        return {status.code(),
+                str::stream() << "Failed setting " << name() << ": " << status.reason()};
+    }
+
+    _storage.set(newValue);
+
+    return Status::OK();
+}
+
+Status FeatureFlagServerParameter::setFromString(const std::string& str) {
+    auto swNewValue = idl_server_parameter_detail::coerceFromString<bool>(str);
+    if (!swNewValue.isOK()) {
+        return swNewValue.getStatus();
+    }
+
+    _storage.set(swNewValue.getValue());
+
+    return Status::OK();
+}
+
+}  // namespace mongo