Implement MessageMutator and FamilyTracker

Bug: 173729274
Test: Reboot TCU *after* HU and verify Wi-Fi STA gets SSID list
Change-Id: Ie7b0e264a73bd4597470fab8a9bcbfd03e82e9b3

automotive/can/1.0/default/libnl++/Android.bp

@@ -22,6 +22,7 @@ cc_library_static {
         "protocols/common/Empty.cpp",
         "protocols/common/Error.cpp",
         "protocols/generic/Ctrl.cpp",
+        "protocols/generic/FamilyTracker.cpp",
         "protocols/generic/Generic.cpp",
         "protocols/generic/GenericMessageBase.cpp",
         "protocols/generic/Unknown.cpp",
@@ -34,6 +35,7 @@ cc_library_static {
         "protocols/all.cpp",
         "Attributes.cpp",
         "MessageFactory.cpp",
+        "MessageMutator.cpp",
         "Socket.cpp",
         "common.cpp",
         "printer.cpp",

automotive/can/1.0/default/libnl++/MessageMutator.cpp

@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <libnl++/MessageMutator.h>
+
+namespace android::nl {
+
+MessageMutator::MessageMutator(nlmsghdr* buffer, size_t totalLen)
+    : mConstBuffer(buffer, totalLen), mMutableBuffer(buffer) {
+    CHECK(totalLen >= sizeof(nlmsghdr));
+}
+
+nlmsghdr* MessageMutator::operator->() const {
+    return mMutableBuffer;
+}
+
+MessageMutator::operator Buffer<nlmsghdr>() const {
+    return mConstBuffer;
+}
+
+uint64_t MessageMutator::read(Buffer<nlattr> attr) const {
+    return attr.data<uint64_t>().copyFirst();
+}
+
+void MessageMutator::write(Buffer<nlattr> attr, uint64_t val) const {
+    const auto attrData = attr.data<uint64_t>();
+    const auto offset = mConstBuffer.getOffset(attrData);
+    CHECK(offset.has_value()) << "Trying to write attribute that's not a member of this message";
+
+    const auto writeableBuffer = reinterpret_cast<uint8_t*>(mMutableBuffer) + *offset;
+    const auto attrSize = attrData.getRaw().len();
+
+    if (attrSize > sizeof(val)) memset(writeableBuffer, 0, attrSize);
+    memcpy(writeableBuffer, &val, std::min(sizeof(val), attrSize));
+}
+
+}  // namespace android::nl

automotive/can/1.0/default/libnl++/include/libnl++/Attributes.h

@@ -93,14 +93,29 @@ class Attributes : private Buffer<nlattr> {
      */
     template <typename T>
     T get(nlattrtype_t attrtype) const {
-        const auto& ind = index();
-        const auto it = ind.find(attrtype);
-        if (it == ind.end()) {
+        const auto buffer = getBuffer(attrtype);
+        if (!buffer.has_value()) {
             LOG(WARNING) << "Netlink attribute is missing: " << attrtype;
             return T{};
         }
 
-        return parse<T>(it->second);
+        return parse<T>(*buffer);
+    }
+
+    /**
+     * Fetches underlying buffer of a given attribute.
+     *
+     * This is a low-level access method unlikely to be useful in most cases. Please consider
+     * using #get instead.
+     *
+     * \param attrtype Attribute to fetch
+     * \return Attribute buffer.
+     */
+    std::optional<Buffer<nlattr>> getBuffer(nlattrtype_t attrtype) const {
+        const auto& ind = index();
+        const auto it = ind.find(attrtype);
+        if (it == ind.end()) return std::nullopt;
+        return it->second;
     }
 
     /**

automotive/can/1.0/default/libnl++/include/libnl++/Buffer.h

@@ -91,6 +91,18 @@ class Buffer {
         return {impl::data<const T, const D>(mData, offset), dataEnd()};
     }
 
+    template <typename B>
+    std::optional<uintptr_t> getOffset(Buffer<B> inner) const {
+        const auto selfStart = uintptr_t(mData);
+        const auto selfEnd = uintptr_t(mBufferEnd);
+        const auto innerStart = uintptr_t(inner.mData);
+        const auto innerEnd = uintptr_t(inner.mBufferEnd);
+
+        if (innerStart < selfStart || innerEnd > selfEnd) return std::nullopt;
+
+        return innerStart - selfStart;
+    }
+
     class iterator {
       public:
         iterator() : mCurrent(nullptr, size_t(0)) {

automotive/can/1.0/default/libnl++/include/libnl++/MessageMutator.h

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <libnl++/Message.h>
+
+namespace android::nl {
+
+/**
+ * In-place message mutator.
+ *
+ * Useful for making small changes (such as adjusting const-sized attributes or struct fields)
+ * efficiently and in-place. However, if you need to rebuild the message (e.g. to modify variable
+ * sized attributes or add/remove them), you need to use MessageFactory instead.
+ */
+class MessageMutator {
+  public:
+    /**
+     * Construct message mutator object from editable buffer.
+     */
+    MessageMutator(nlmsghdr* buffer, size_t totalLen);
+
+    nlmsghdr* operator->() const;
+    operator Buffer<nlmsghdr>() const;
+
+    /**
+     * Read current attribute value.
+     *
+     * \param Read-only attribute buffer.
+     * \returns Attribute value.
+     */
+    uint64_t read(Buffer<nlattr> attr) const;
+
+    /**
+     * Write new attribute value.
+     *
+     * \param Read-only attribute buffer.
+     * \param val New value to set.
+     */
+    void write(Buffer<nlattr> attr, uint64_t val) const;
+
+  private:
+    const Buffer<nlmsghdr> mConstBuffer;
+    nlmsghdr* mMutableBuffer;
+};
+
+}  // namespace android::nl

automotive/can/1.0/default/libnl++/include/libnl++/generic/FamilyTracker.h

@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <libnl++/Buffer.h>
+#include <libnl++/Message.h>
+
+#include <linux/genetlink.h>
+
+#include <optional>
+
+namespace android::nl::generic {
+
+/**
+ * Tracker of Netlink family ID registrations.
+ */
+class FamilyTracker {
+  public:
+    /**
+     * Try parsing NL80211 message.
+     *
+     * Proper parsing of NL80211 nessages requires prior parsing of control message for Generic
+     * Netlink protocol.
+     *
+     * \param msg Message to parse
+     * \returns Parsed NL80211 message or std::nullopt if it wasn't one
+     */
+    std::optional<Message<genlmsghdr>> parseNl80211(Buffer<nlmsghdr> msg);
+
+  private:
+    /* For efficiency, we use a single hardcoded family ID. However, if we supported multiple family
+     * types, this should probably be a map.
+     */
+    std::optional<uint16_t> mNl80211FamilyId;
+
+    /**
+     * Track Generic protocol messages.
+     *
+     * This method is looking for family registration messages.
+     *
+     * \param msg Message to track
+     * \returns True, if the message was a control message (regardless of carrying
+     *          family info or not)
+     */
+    bool track(const Buffer<nlmsghdr>& msg);
+};
+
+}  // namespace android::nl::generic

automotive/can/1.0/default/libnl++/protocols/generic/FamilyTracker.cpp

@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <libnl++/generic/FamilyTracker.h>
+
+#include <android-base/logging.h>
+
+namespace android::nl::generic {
+
+bool FamilyTracker::track(const Buffer<nlmsghdr>& buffer) {
+    const auto msgMaybe = nl::Message<genlmsghdr>::parse(buffer, {GENL_ID_CTRL});
+    if (!msgMaybe.has_value()) return false;
+
+    const auto msg = *msgMaybe;
+    if (msg->cmd != CTRL_CMD_NEWFAMILY) return true;
+
+    const auto familyName = msg.attributes.get<std::string>(CTRL_ATTR_FAMILY_NAME);
+    const auto familyId = msg.attributes.get<uint16_t>(CTRL_ATTR_FAMILY_ID);
+
+    if (familyId < GENL_START_ALLOC) {
+        LOG(WARNING) << "Invalid family ID: " << familyId;
+        return true;
+    }
+
+    if (familyName == "nl80211") mNl80211FamilyId = familyId;
+
+    return true;
+}
+
+std::optional<Message<genlmsghdr>> FamilyTracker::parseNl80211(Buffer<nlmsghdr> msg) {
+    if (track(msg)) return std::nullopt;
+    if (!mNl80211FamilyId.has_value()) return std::nullopt;
+
+    return nl::Message<genlmsghdr>::parse(msg, {*mNl80211FamilyId});
+}
+
+}  // namespace android::nl::generic