LibIPC: Replace Encoder::encode methods with IPC::encode specializations

Currently, the stream operator overload hides most encoding errors. In
an effort to make IPC encoding fallible, this first replaces the Encoder
overloads with IPC::encode specializations. The return type is still a
boolean, a future commit will change it to ErrorOr.

Note that just like in the analogous decoder commit (9b48362), these
specializations must be defined at the namespace scope. Further, all
arithmetic specializations are now in one method.

Userland/Libraries/LibIPC/Encoder.h

@@ -11,6 +11,7 @@
 #include <AK/StdLibExtras.h>
 #include <AK/Variant.h>
 #include <LibCore/SharedCircularQueue.h>
+#include <LibIPC/Concepts.h>
 #include <LibIPC/Forward.h>
 #include <LibIPC/Message.h>
 
@@ -30,80 +31,6 @@ public:
     {
     }
 
-    Encoder& operator<<(bool);
-    Encoder& operator<<(u8);
-    Encoder& operator<<(u16);
-    Encoder& operator<<(unsigned);
-    Encoder& operator<<(unsigned long);
-    Encoder& operator<<(unsigned long long);
-    Encoder& operator<<(i8);
-    Encoder& operator<<(i16);
-    Encoder& operator<<(i32);
-    Encoder& operator<<(i64);
-    Encoder& operator<<(float);
-    Encoder& operator<<(double);
-    Encoder& operator<<(char const*);
-    Encoder& operator<<(StringView);
-    Encoder& operator<<(DeprecatedString const&);
-    Encoder& operator<<(ByteBuffer const&);
-    Encoder& operator<<(JsonValue const&);
-    Encoder& operator<<(URL const&);
-    Encoder& operator<<(Dictionary const&);
-    Encoder& operator<<(File const&);
-    Encoder& operator<<(AK::Empty const&);
-    template<typename K, typename V>
-    Encoder& operator<<(HashMap<K, V> const& hashmap)
-    {
-        *this << (u32)hashmap.size();
-        for (auto it : hashmap) {
-            *this << it.key;
-            *this << it.value;
-        }
-        return *this;
-    }
-
-    template<typename K, typename V>
-    Encoder& operator<<(OrderedHashMap<K, V> const& hashmap)
-    {
-        *this << (u32)hashmap.size();
-        for (auto it : hashmap) {
-            *this << it.key;
-            *this << it.value;
-        }
-        return *this;
-    }
-
-    template<typename T>
-    Encoder& operator<<(Vector<T> const& vector)
-    {
-        *this << (u64)vector.size();
-        for (auto& value : vector)
-            *this << value;
-        return *this;
-    }
-
-    template<typename T, size_t Size>
-    Encoder& operator<<(Core::SharedSingleProducerCircularQueue<T, Size> const& queue)
-    {
-        *this << IPC::File(queue.fd());
-        return *this;
-    }
-
-    template<typename... VariantTypes>
-    Encoder& operator<<(AK::Variant<VariantTypes...> const& variant)
-    {
-        *this << variant.index();
-        variant.visit([this](auto const& underlying_value) { *this << underlying_value; });
-        return *this;
-    }
-
-    template<Enum T>
-    Encoder& operator<<(T const& enum_value)
-    {
-        *this << AK::to_underlying(enum_value);
-        return *this;
-    }
-
     template<typename T>
     Encoder& operator<<(T const& value)
     {
@@ -112,18 +39,29 @@ public:
     }
 
     template<typename T>
-    Encoder& operator<<(Optional<T> const& optional)
+    bool encode(T const& value);
+
+    ErrorOr<void> extend_capacity(size_t capacity)
     {
-        *this << optional.has_value();
-        if (optional.has_value())
-            *this << optional.value();
-        return *this;
+        return m_buffer.data.try_ensure_capacity(m_buffer.data.size() + capacity);
     }
 
-    template<typename T>
-    void encode(T const& value)
+    void append(u8 value)
     {
-        IPC::encode(*this, value);
+        m_buffer.data.unchecked_append(value);
+    }
+
+    ErrorOr<void> append(u8 const* values, size_t count)
+    {
+        TRY(extend_capacity(count));
+        m_buffer.data.unchecked_append(values, count);
+        return {};
+    }
+
+    ErrorOr<void> append_file_descriptor(int fd)
+    {
+        auto auto_fd = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) AutoCloseFileDescriptor(fd)));
+        return m_buffer.fds.try_append(move(auto_fd));
     }
 
 private:
@@ -133,4 +71,137 @@ private:
     MessageBuffer& m_buffer;
 };
 
+template<Arithmetic T>
+bool encode(Encoder& encoder, T const& value)
+{
+    if (encoder.extend_capacity(sizeof(T)).is_error())
+        return false;
+
+    if constexpr (sizeof(T) == 1) {
+        encoder.append(static_cast<u8>(value));
+    } else if constexpr (sizeof(T) == 2) {
+        encoder.append(static_cast<u8>(value));
+        encoder.append(static_cast<u8>(value >> 8));
+    } else if constexpr (sizeof(T) == 4) {
+        encoder.append(static_cast<u8>(value));
+        encoder.append(static_cast<u8>(value >> 8));
+        encoder.append(static_cast<u8>(value >> 16));
+        encoder.append(static_cast<u8>(value >> 24));
+    } else if constexpr (sizeof(T) == 8) {
+        encoder.append(static_cast<u8>(value));
+        encoder.append(static_cast<u8>(value >> 8));
+        encoder.append(static_cast<u8>(value >> 16));
+        encoder.append(static_cast<u8>(value >> 24));
+        encoder.append(static_cast<u8>(value >> 32));
+        encoder.append(static_cast<u8>(value >> 40));
+        encoder.append(static_cast<u8>(value >> 48));
+        encoder.append(static_cast<u8>(value >> 56));
+    } else {
+        static_assert(DependentFalse<T>);
+    }
+
+    return true;
+}
+
+template<Enum T>
+bool encode(Encoder& encoder, T const& value)
+{
+    return encoder.encode(to_underlying(value));
+}
+
+template<>
+bool encode(Encoder&, float const&);
+
+template<>
+bool encode(Encoder&, double const&);
+
+template<>
+bool encode(Encoder&, StringView const&);
+
+template<>
+bool encode(Encoder&, DeprecatedString const&);
+
+template<>
+bool encode(Encoder&, ByteBuffer const&);
+
+template<>
+bool encode(Encoder&, JsonValue const&);
+
+template<>
+bool encode(Encoder&, URL const&);
+
+template<>
+bool encode(Encoder&, Dictionary const&);
+
+template<>
+bool encode(Encoder&, File const&);
+
+template<>
+bool encode(Encoder&, Empty const&);
+
+template<Concepts::Vector T>
+bool encode(Encoder& encoder, T const& vector)
+{
+    if (!encoder.encode(static_cast<u64>(vector.size())))
+        return false;
+
+    for (auto const& value : vector) {
+        if (!encoder.encode(value))
+            return false;
+    }
+
+    return true;
+}
+
+template<Concepts::HashMap T>
+bool encode(Encoder& encoder, T const& hashmap)
+{
+    if (!encoder.encode(static_cast<u32>(hashmap.size())))
+        return false;
+
+    for (auto it : hashmap) {
+        if (!encoder.encode(it.key))
+            return false;
+        if (!encoder.encode(it.value))
+            return false;
+    }
+
+    return true;
+}
+
+template<Concepts::SharedSingleProducerCircularQueue T>
+bool encode(Encoder& encoder, T const& queue)
+{
+    return encoder.encode(IPC::File { queue.fd() });
+}
+
+template<Concepts::Optional T>
+bool encode(Encoder& encoder, T const& optional)
+{
+    if (!encoder.encode(optional.has_value()))
+        return false;
+
+    if (optional.has_value())
+        return encoder.encode(optional.value());
+    return true;
+}
+
+template<Concepts::Variant T>
+bool encode(Encoder& encoder, T const& variant)
+{
+    if (!encoder.encode(variant.index()))
+        return false;
+
+    return variant.visit([&](auto const& value) {
+        return encoder.encode(value);
+    });
+}
+
+// This must be last so that it knows about the above specializations.
+template<typename T>
+bool Encoder::encode(T const& value)
+{
+    return IPC::encode(*this, value);
+}
+
 }