LibWasm: Start implementing WASI

This commit starts adding support for WASI, along with the framework to
implement all the functions (though only a couple are currently
implemented).

1 files changed, 943 insertions, 0 deletions

diff --git a/Userland/Libraries/LibWasm/Wasi.h b/Userland/Libraries/LibWasm/Wasi.h
new file mode 100644
index 0000000000..0dedce568d
--- /dev/null
+++ b/Userland/Libraries/LibWasm/Wasi.h
@@ -0,0 +1,943 @@
+/*
+ * Copyright (c) 2023, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/DistinctNumeric.h>
+#include <AK/Endian.h>
+#include <AK/Function.h>
+#include <AK/LexicalPath.h>
+#include <AK/RedBlackTree.h>
+#include <AK/String.h>
+#include <AK/Vector.h>
+#include <LibWasm/AbstractMachine/AbstractMachine.h>
+#include <LibWasm/Forward.h>
+
+namespace Wasm::Wasi::ABI {
+
+// NOTE: The "real" ABI used in the wild is described by [api.h from libc-bottom-half](https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h)
+//       This is *not* the same ABI as the one described in the WASI spec, nor is it the same ABI as api.h on wasi-libc/master.
+// The highlights of the ABI are:
+// - (most) structs are passed as pointers to heap.
+// - arrays are fat pointers splat across two arguments
+// - return object locations are also passed as arguments, the number of arguments depends on the return type itself:
+//    - ArgsSizes / EnvironSizes / the return type of sock_recv use two arguments
+//    - everything else is passed like a normal struct
+
+template<auto impl>
+struct InvocationOf {
+    HostFunction operator()(Implementation&, StringView name);
+};
+
+template<typename T, size_t N>
+void serialize(T const&, Array<Bytes, N>);
+
+template<typename T, size_t N>
+T deserialize(Array<ReadonlyBytes, N> const&);
+
+template<typename T>
+struct ToCompatibleValue {
+    using Type = void;
+};
+
+template<typename T>
+struct CompatibleValue {
+    typename ToCompatibleValue<T>::Type value;
+
+    Wasm::Value to_wasm_value() const;
+};
+
+template<typename T>
+CompatibleValue<T> to_compatible_value(Wasm::Value const&);
+
+template<typename T>
+T deserialize(CompatibleValue<T> const&);
+
+}
+
+namespace Wasm::Wasi {
+
+// NOTE: This is a copy of LittleEndian from Endian.h,
+//       we can't use those because they have a packed attribute, and depend on it;
+//       but we want proper alignment on these types.
+template<typename T>
+class alignas(T) LittleEndian {
+public:
+    constexpr LittleEndian() = default;
+
+    constexpr LittleEndian(T value)
+        : m_value(AK::convert_between_host_and_little_endian(value))
+    {
+    }
+
+    constexpr operator T() const { return AK::convert_between_host_and_little_endian(m_value); }
+    constexpr T value() const { return AK::convert_between_host_and_little_endian(m_value); }
+
+    LittleEndian& operator+=(T other)
+    {
+        m_value = AK::convert_between_host_and_little_endian(AK::convert_between_host_and_little_endian(m_value) + other);
+        return *this;
+    }
+
+    // This returns the internal representation. In this case, that is the value stored in little endian format.
+    constexpr Bytes bytes() { return Bytes { &m_value, sizeof(m_value) }; }
+    constexpr ReadonlyBytes bytes() const { return ReadonlyBytes { &m_value, sizeof(m_value) }; }
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+    static LittleEndian read_from(Array<ReadonlyBytes, 1> const& bytes);
+
+private:
+    T m_value { 0 };
+};
+
+using Size = LittleEndian<u32>;
+using FileSize = LittleEndian<u64>;
+using Timestamp = LittleEndian<u64>;
+
+namespace Detail {
+template<typename>
+struct __Pointer_tag;
+template<typename>
+struct __ConstPointer_tag;
+}
+
+// NOTE: Might need to be updated if WASI ever supports memory64.
+using UnderlyingPointerType = u32;
+
+template<typename T>
+using Pointer = DistinctNumeric<LittleEndian<UnderlyingPointerType>, Detail::__Pointer_tag<T>, AK::DistinctNumericFeature::Comparison>;
+template<typename T>
+using ConstPointer = DistinctNumeric<LittleEndian<UnderlyingPointerType>, Detail::__ConstPointer_tag<T>, AK::DistinctNumericFeature::Comparison>;
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L70
+enum class ClockID : u32 {
+    Realtime,
+    Monotonic,
+    ProcessCPUTimeID,
+    ThreadCPUTimeID,
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L105
+enum class Errno : u16 {
+    Success,
+    TooBig,
+    Access,
+    AddressInUse,
+    AddressNotAvailable,
+    AFNotSupported,
+    Again,
+    Already,
+    BadF,
+    BadMessage,
+    Busy,
+    Canceled,
+    Child,
+    ConnectionAborted,
+    ConnectionRefused,
+    ConnectionReset,
+    Deadlock,
+    DestinationAddressRequired,
+    Domain,
+    DQuot, // Reserved, Unused.
+    Exist,
+    Fault,
+    FBig,
+    HostUnreachable,
+    IdentifierRemoved,
+    IllegalSequence,
+    InProgress,
+    Interrupted,
+    Invalid,
+    IO,
+    IsConnected,
+    IsDirectory,
+    Loop,
+    MFile,
+    MLink,
+    MessageSize,
+    MultiHop, // Reserved, Unused.
+    NameTooLong,
+    NetworkDown,
+    NetworkReset,
+    NetworkUnreachable,
+    NFile,
+    NoBufferSpace,
+    NoDevice,
+    NoEntry,
+    NoExec,
+    NoLock,
+    NoLink,
+    NoMemory,
+    NoMessage,
+    NoProtocolOption,
+    NoSpace,
+    NoSys,
+    NotConnected,
+    NotDirectory,
+    NotEmpty,
+    NotRecoverable,
+    NotSocket,
+    NotSupported,
+    NoTTY,
+    NXIO,
+    Overflow,
+    OwnerDead,
+    Permission,
+    Pipe,
+    Protocol,
+    ProtocolNotSupported,
+    ProtocolType,
+    Range,
+    ReadOnlyFS,
+    SPipe,
+    SRCH,
+    Stale,
+    TimedOut,
+    TextBusy,
+    XDev,
+    NotCapable,
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L498
+struct Rights {
+    using CompatibleType = u64;
+
+    struct Bits {
+        bool fd_datasync : 1;
+        bool fd_read : 1;
+        bool fd_seek : 1;
+        bool fd_fdstat_set_flags : 1;
+        bool fd_sync : 1;
+        bool fd_tell : 1;
+        bool fd_write : 1;
+        bool fd_advise : 1;
+        bool fd_allocate : 1;
+        bool path_create_directory : 1;
+        bool path_create_file : 1;
+        bool path_link_source : 1;
+        bool path_link_target : 1;
+        bool path_open : 1;
+        bool fd_readdir : 1;
+        bool path_readlink : 1;
+        bool path_rename_source : 1;
+        bool path_rename_target : 1;
+        bool path_filestat_get : 1;
+        bool path_filestat_set_size : 1;
+        bool path_filestat_set_times : 1;
+        bool fd_filestat_get : 1;
+        bool fd_filestat_set_size : 1;
+        bool fd_filestat_set_times : 1;
+        bool path_symlink : 1;
+        bool path_remove_directory : 1;
+        bool path_unlink_file : 1;
+        bool poll_fd_readwrite : 1;
+        bool sock_shutdown : 1;
+        bool sock_accept : 1;
+
+        u64 _unused : 34;
+    };
+
+    static_assert(sizeof(Bits) == sizeof(CompatibleType));
+
+    union {
+        Bits bits;
+        LittleEndian<CompatibleType> data;
+    };
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+    static Rights read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L663
+using FD = DistinctNumeric<LittleEndian<u32>, struct __FD_tag, AK::DistinctNumericFeature::Comparison>;
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L671
+struct IOVec {
+    Pointer<u8> buf;
+    Size buf_len;
+
+    static IOVec read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L692
+struct CIOVec {
+    ConstPointer<u8> buf;
+    Size buf_len;
+
+    static CIOVec read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L713
+using FileDelta = LittleEndian<i64>;
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L721
+enum class Whence : u8 {
+    Set,
+    Cur,
+    End,
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L746
+using DirCookie = LittleEndian<u64>;
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L754
+using DirNameLen = LittleEndian<u32>;
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L762
+using INode = LittleEndian<u64>;
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L770
+enum class FileType : u8 {
+    Unknown,
+    BlockDevice,
+    CharacterDevice,
+    Directory,
+    RegularFile,
+    SocketDGram,
+    SocketStream,
+    SymbolicLink,
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L818
+struct DirEnt {
+    DirCookie d_next;
+    INode d_ino;
+    DirNameLen d_namlen;
+    FileType d_type;
+    u8 _padding[3] { 0 }; // Not part of the API, but the struct is required to be 24 bytes - even though it has no explicit padding.
+};
+static_assert(sizeof(DirEnt) == 24);
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L851
+enum class Advice : u8 {
+    Normal,
+    Sequential,
+    Random,
+    WillNeed,
+    DontNeed,
+    NoReuse,
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L889
+struct FDFlags {
+    using CompatibleType = u16;
+
+    struct Bits {
+        bool append : 1;
+        bool dsync : 1;
+        bool nonblock : 1;
+        bool rsync : 1;
+        bool sync : 1;
+        u16 _unused : 11;
+    };
+    static_assert(sizeof(Bits) == sizeof(CompatibleType));
+
+    union {
+        Bits bits;
+        LittleEndian<CompatibleType> data;
+    };
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+    static FDFlags read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L924
+struct FDStat {
+    FileType fs_filetype;
+    FDFlags fs_flags;
+    Rights fs_rights_base;
+    Rights fs_rights_inheriting;
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+};
+static_assert(sizeof(FDStat) == 24);
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L959
+using Device = LittleEndian<u64>;
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L967
+struct FSTFlags {
+    using CompatibleType = u16;
+
+    struct Bits {
+        bool atim : 1;
+        bool atim_now : 1;
+        bool mtim : 1;
+        bool mtim_now : 1;
+        u16 _unused : 12;
+    };
+
+    static_assert(sizeof(Bits) == sizeof(CompatibleType));
+
+    union {
+        Bits bits;
+        LittleEndian<CompatibleType> data;
+    };
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+    static FSTFlags read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+static_assert(sizeof(FSTFlags) == 2);
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L995
+struct LookupFlags {
+    using CompatibleType = u32;
+
+    struct Bits {
+        bool symlink_follow : 1;
+        u32 _unused : 31;
+    };
+
+    static_assert(sizeof(Bits) == sizeof(CompatibleType));
+
+    union {
+        Bits bits;
+        LittleEndian<CompatibleType> data;
+    };
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+    static LookupFlags read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+static_assert(sizeof(LookupFlags) == 4);
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1008
+struct OFlags {
+    using CompatibleType = u16;
+
+    struct Bits {
+        bool creat : 1;
+        bool directory : 1;
+        bool excl : 1;
+        bool trunc : 1;
+
+        u16 _unused : 12;
+    };
+
+    static_assert(sizeof(Bits) == sizeof(CompatibleType));
+
+    union {
+        Bits bits;
+        LittleEndian<CompatibleType> data;
+    };
+
+    static OFlags read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+static_assert(sizeof(OFlags) == 2);
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1036
+using LinkCount = LittleEndian<u64>;
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1044
+struct FileStat {
+    Device dev;
+    INode ino;
+    FileType filetype;
+    LinkCount nlink;
+    FileSize size;
+    Timestamp atim;
+    Timestamp mtim;
+    Timestamp ctim;
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+};
+static_assert(sizeof(FileStat) == 64);
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1102
+using UserData = LittleEndian<u64>;
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1110
+enum class EventType : u8 {
+    Clock,
+    FDRead,
+    FDWrite,
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1137
+struct EventRWFlags {
+    using CompatibleType = u16;
+
+    struct Bits {
+        bool fd_readwrite_hangup : 1;
+
+        u16 _unused : 15;
+    };
+
+    static_assert(sizeof(Bits) == sizeof(CompatibleType));
+
+    union {
+        Bits bits;
+        LittleEndian<CompatibleType> data;
+    };
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+    static EventRWFlags read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1151
+struct EventFDReadWrite {
+    FileSize nbytes;
+    EventRWFlags flags;
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+    static EventFDReadWrite read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1186
+struct Event {
+    UserData userdata;
+    Errno errno_;
+    EventType type;
+    EventFDReadWrite fd_readwrite;
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+    static Event read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1220
+struct SubClockFlags {
+    using CompatibleType = u16;
+
+    struct Bits {
+        bool subscription_clock_abstime : 1;
+
+        u16 _unused : 15;
+    };
+    static_assert(sizeof(Bits) == sizeof(CompatibleType));
+
+    union {
+        Bits bits;
+        LittleEndian<CompatibleType> data;
+    };
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+    static SubClockFlags read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1237
+struct SubscriptionClock {
+    ClockID id;
+    Timestamp timeout;
+    Timestamp precision;
+    SubClockFlags flags;
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+    static SubscriptionClock read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1272
+struct SubscriptionFDReadWrite {
+    FD file_descriptor;
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+    static SubscriptionFDReadWrite read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1287
+struct SubscriptionU {
+    u8 tag;
+    union {
+        SubscriptionClock clock;
+        SubscriptionFDReadWrite fd_read;
+        SubscriptionFDReadWrite fd_write;
+    };
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+    static SubscriptionU read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1306
+struct Subscription {
+    UserData userdata;
+    SubscriptionU u;
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+    static Subscription read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+static_assert(sizeof(Subscription) == 48);
+static_assert(alignof(Subscription) == 8);
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1334
+using ExitCode = LittleEndian<u32>;
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1342
+enum class Signal : u8 {
+    None,
+    HUP,
+    INT,
+    QUIT,
+    ILL,
+    TRAP,
+    ABRT,
+    BUS,
+    FPE,
+    KILL,
+    USR1,
+    SEGV,
+    USR2,
+    PIPE,
+    ALRM,
+    TERM,
+    CHLD,
+    CONT,
+    STOP,
+    TSTP,
+    TTIN,
+    TTOU,
+    URG,
+    XCPU,
+    XFSZ,
+    VTALRM,
+    PROF,
+    WINCH,
+    POLL,
+    PWR,
+    SYS,
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1536
+struct RIFlags {
+    using CompatibleType = u16;
+
+    struct Bits {
+        bool recv_peek : 1;
+        bool recv_waitall : 1;
+
+        u16 _unused : 14;
+    };
+    static_assert(sizeof(Bits) == sizeof(CompatibleType));
+
+    union {
+        Bits bits;
+        LittleEndian<CompatibleType> data;
+    };
+
+    static RIFlags read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1554
+struct ROFlags {
+    using CompatibleType = u16;
+
+    struct Bits {
+        bool recv_data_truncated : 1;
+
+        u16 _unused : 15;
+    };
+    static_assert(sizeof(Bits) == sizeof(CompatibleType));
+
+    union {
+        Bits bits;
+        LittleEndian<CompatibleType> data;
+    };
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1568
+using SIFlags = LittleEndian<u16>;
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1576
+struct SDFlags {
+    using CompatibleType = u8;
+
+    struct Bits {
+        bool rd : 1;
+        bool wr : 1;
+
+        u8 _unused : 6;
+    };
+    static_assert(sizeof(Bits) == sizeof(CompatibleType));
+
+    union {
+        Bits bits;
+        LittleEndian<CompatibleType> data;
+    };
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+    static SDFlags read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1594
+enum class PreOpenType : u8 {
+    Dir,
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1607
+struct PreStatDir {
+    Size pr_name_len;
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+    static PreStatDir read_from(Array<ReadonlyBytes, 1> const& bytes);
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1636
+struct PreStat {
+    u8 tag;
+    union {
+        PreStatDir dir;
+    };
+
+    void serialize_into(Array<Bytes, 1> bytes) const;
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1676
+struct ArgsSizes {
+    Size count;
+    Size size;
+
+    using SerializationComponents = TypeList<Size, Size>;
+
+    void serialize_into(Array<Bytes, 2> bytes) const;
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L1708
+struct EnvironSizes {
+    Size count;
+    Size size;
+
+    using SerializationComponents = TypeList<Size, Size>;
+
+    void serialize_into(Array<Bytes, 2> bytes) const;
+};
+
+// https://github.com/WebAssembly/wasi-libc/blob/2c2fc9a2fddd0927a66f1c142e65c8dab6f5c5d7/libc-bottom-half/headers/public/wasi/api.h#L2664
+struct SockRecvResult {
+    Size size;
+    ROFlags roflags;
+
+    using SerializationComponents = TypeList<Size, ROFlags>;
+
+    void serialize_into(Array<Bytes, 2> bytes) const;
+};
+
+template<typename TResult, typename Tag = u32>
+struct Result {
+    Result(TResult&& result)
+        : bits {}
+        , tag(0)
+    {
+        new (&bits) TResult(move(result));
+    }
+
+    Result(Errno&& error)
+        : bits {}
+        , tag(1)
+    {
+        new (&bits) Errno(error);
+    }
+
+    Optional<TResult&> result() const
+    {
+        if (tag == 0)
+            return *bit_cast<TResult*>(&bits[0]);
+        return {};
+    }
+
+    Optional<Errno&> error() const
+    {
+        if (tag == 1)
+            return *bit_cast<Errno*>(&bits[0]);
+        return {};
+    }
+
+    bool is_error() const { return tag == 1; }
+
+    template<size_t N>
+    Errno serialize_into(Array<Bytes, N>&& spans) const
+    {
+        if (tag == 1)
+            return error().value();
+
+        ABI::serialize(*result(), move(spans));
+        return Errno::Success;
+    }
+
+private:
+    alignas(max(alignof(TResult), alignof(Errno))) u8 bits[max(sizeof(TResult), sizeof(Errno))];
+    LittleEndian<Tag> tag;
+};
+
+template<typename Tag>
+struct Result<void, Tag> {
+    Result()
+        : error_bits {}
+        , tag(0)
+    {
+    }
+
+    Result(Errno&& error)
+        : error_bits {}
+        , tag(1)
+    {
+        new (&error_bits) Errno(error);
+    }
+
+    Optional<Empty> result() const
+    {
+        if (tag == 0)
+            return { Empty {} };
+        return {};
+    }
+    Optional<Errno&> error() const
+    {
+        if (tag == 1)
+            return *bit_cast<Errno*>(&error_bits[0]);
+        return {};
+    }
+    bool is_error() const { return tag == 1; }
+
+private:
+    alignas(Errno) u8 error_bits[sizeof(Errno)];
+    LittleEndian<Tag> tag;
+};
+
+struct Implementation {
+    struct MappedPath {
+        LexicalPath host_path;
+        LexicalPath mapped_path;
+        mutable Optional<int> opened_fd {};
+    };
+
+    struct Details {
+        Function<Vector<AK::String>()> provide_arguments;
+        Function<Vector<AK::String>()> provide_environment;
+        Function<Vector<MappedPath>()> provide_preopened_directories;
+    };
+
+    explicit Implementation(Details&& details)
+        : provide_arguments(move(details.provide_arguments))
+        , provide_environment(move(details.provide_environment))
+        , provide_preopened_directories(move(details.provide_preopened_directories))
+    {
+        // Map all of std{in,out,err} by default.
+        m_fd_map.insert(0, 0);
+        m_fd_map.insert(1, 1);
+        m_fd_map.insert(2, 2);
+    }
+
+    ErrorOr<HostFunction> function_by_name(StringView);
+
+private:
+    template<auto impl>
+    HostFunction invocation_of(StringView name) { return ABI::InvocationOf<impl> {}(*this, name); }
+
+    ErrorOr<Result<void>> impl$args_get(Configuration&, Pointer<Pointer<u8>> argv, Pointer<u8> argv_buf);
+    ErrorOr<Result<ArgsSizes>> impl$args_sizes_get(Configuration&);
+    ErrorOr<Result<void>> impl$environ_get(Configuration&, Pointer<Pointer<u8>> environ, Pointer<u8> environ_buf);
+    ErrorOr<Result<EnvironSizes>> impl$environ_sizes_get(Configuration&);
+    ErrorOr<Result<Timestamp>> impl$clock_res_get(Configuration&, ClockID id);
+    ErrorOr<Result<Timestamp>> impl$clock_time_get(Configuration&, ClockID id, Timestamp precision);
+    ErrorOr<Result<void>> impl$fd_advise(Configuration&, FD, FileSize offset, FileSize len, Advice);
+    ErrorOr<Result<void>> impl$fd_allocate(Configuration&, FD, FileSize offset, FileSize len);
+    ErrorOr<Result<void>> impl$fd_close(Configuration&, FD);
+    ErrorOr<Result<void>> impl$fd_datasync(Configuration&, FD);
+    ErrorOr<Result<FDStat>> impl$fd_fdstat_get(Configuration&, FD);
+    ErrorOr<Result<void>> impl$fd_fdstat_set_flags(Configuration&, FD, FDFlags);
+    ErrorOr<Result<void>> impl$fd_fdstat_set_rights(Configuration&, FD, Rights fs_rights_base, Rights fs_rights_inheriting);
+    ErrorOr<Result<FileStat>> impl$fd_filestat_get(Configuration&, FD);
+    ErrorOr<Result<void>> impl$fd_filestat_set_size(Configuration&, FD, FileSize);
+    ErrorOr<Result<void>> impl$fd_filestat_set_times(Configuration&, FD, Timestamp atim, Timestamp mtim, FSTFlags);
+    ErrorOr<Result<Size>> impl$fd_pread(Configuration&, FD, Pointer<IOVec> iovs, Size iovs_len, FileSize offset);
+    ErrorOr<Result<PreStat>> impl$fd_prestat_get(Configuration&, FD);
+    ErrorOr<Result<void>> impl$fd_prestat_dir_name(Configuration&, FD, Pointer<u8> path, Size path_len);
+    ErrorOr<Result<Size>> impl$fd_pwrite(Configuration&, FD, Pointer<CIOVec> iovs, Size iovs_len, FileSize offset);
+    ErrorOr<Result<Size>> impl$fd_read(Configuration&, FD, Pointer<IOVec> iovs, Size iovs_len);
+    ErrorOr<Result<Size>> impl$fd_readdir(Configuration&, FD, Pointer<u8> buf, Size buf_len, DirCookie cookie);
+    ErrorOr<Result<void>> impl$fd_renumber(Configuration&, FD from, FD to);
+    ErrorOr<Result<FileSize>> impl$fd_seek(Configuration&, FD, FileDelta offset, Whence whence);
+    ErrorOr<Result<void>> impl$fd_sync(Configuration&, FD);
+    ErrorOr<Result<FileSize>> impl$fd_tell(Configuration&, FD);
+    ErrorOr<Result<Size>> impl$fd_write(Configuration&, FD, Pointer<CIOVec> iovs, Size iovs_len);
+    ErrorOr<Result<void>> impl$path_create_directory(Configuration&, FD, Pointer<u8> path, Size path_len);
+    ErrorOr<Result<FileStat>> impl$path_filestat_get(Configuration&, FD, LookupFlags, ConstPointer<u8> path, Size path_len);
+    ErrorOr<Result<void>> impl$path_filestat_set_times(Configuration&, FD, LookupFlags, Pointer<u8> path, Size path_len, Timestamp atim, Timestamp mtim, FSTFlags);
+    ErrorOr<Result<void>> impl$path_link(Configuration&, FD, LookupFlags, Pointer<u8> old_path, Size old_path_len, FD, Pointer<u8> new_path, Size new_path_len);
+    ErrorOr<Result<FD>> impl$path_open(Configuration&, FD, LookupFlags, Pointer<u8> path, Size path_len, OFlags, Rights fs_rights_base, Rights fs_rights_inheriting, FDFlags fd_flags);
+    ErrorOr<Result<Size>> impl$path_readlink(Configuration&, FD, LookupFlags, Pointer<u8> path, Size path_len, Pointer<u8> buf, Size buf_len);
+    ErrorOr<Result<void>> impl$path_remove_directory(Configuration&, FD, Pointer<u8> path, Size path_len);
+    ErrorOr<Result<void>> impl$path_rename(Configuration&, FD, Pointer<u8> old_path, Size old_path_len, FD, Pointer<u8> new_path, Size new_path_len);
+    ErrorOr<Result<void>> impl$path_symlink(Configuration&, Pointer<u8> old_path, Size old_path_len, FD, Pointer<u8> new_path, Size new_path_len);
+    ErrorOr<Result<void>> impl$path_unlink_file(Configuration&, FD, Pointer<u8> path, Size path_len);
+    ErrorOr<Result<Size>> impl$poll_oneoff(Configuration&, ConstPointer<Subscription> in, Pointer<Event> out, Size nsubscriptions);
+    ErrorOr<Result<void>> impl$proc_exit(Configuration&, ExitCode); // Note: noreturn.
+    ErrorOr<Result<void>> impl$proc_raise(Configuration&, Signal);
+    ErrorOr<Result<void>> impl$sched_yield(Configuration&);
+    ErrorOr<Result<void>> impl$random_get(Configuration&, Pointer<u8> buf, Size buf_len);
+    ErrorOr<Result<FD>> impl$sock_accept(Configuration&, FD fd, FDFlags fd_flags);
+    ErrorOr<Result<SockRecvResult>> impl$sock_recv(Configuration&, FD fd, Pointer<IOVec> ri_data, Size ri_data_len, RIFlags ri_flags);
+    ErrorOr<Result<Size>> impl$sock_send(Configuration&, FD fd, Pointer<CIOVec> si_data, Size ri_data_len, SIFlags si_flags);
+    ErrorOr<Result<void>> impl$sock_shutdown(Configuration&, FD fd, SDFlags how);
+
+    Vector<AK::String> const& arguments() const;
+    Vector<AK::String> const& environment() const;
+    Vector<MappedPath> const& preopened_directories() const;
+
+    using PreopenedDirectoryDescriptor = DistinctNumeric<LittleEndian<size_t>, struct PreopenedDirectoryDescriptor_tag, AK::DistinctNumericFeature::Comparison, AK::DistinctNumericFeature::CastToUnderlying, AK::DistinctNumericFeature::Increment>;
+    using UnmappedDescriptor = DistinctNumeric<LittleEndian<size_t>, struct UnmappedDescriptor_tag, AK::DistinctNumericFeature::Comparison, AK::DistinctNumericFeature::CastToUnderlying>;
+    using MappedDescriptor = Variant<u32, PreopenedDirectoryDescriptor>;
+    using Descriptor = Variant<u32, PreopenedDirectoryDescriptor, UnmappedDescriptor>;
+
+    Descriptor map_fd(FD);
+
+public:
+    Function<Vector<AK::String>()> provide_arguments;
+    Function<Vector<AK::String>()> provide_environment;
+    Function<Vector<MappedPath>()> provide_preopened_directories;
+
+private:
+    struct Cache {
+        Optional<Vector<AK::String>> cached_arguments;
+        Optional<Vector<AK::String>> cached_environment;
+        Optional<Vector<MappedPath>> cached_preopened_directories;
+    };
+
+    mutable Cache cache {};
+
+    RedBlackTree<u32, MappedDescriptor> m_fd_map;
+    size_t m_first_unmapped_preopened_directory_index { 0 };
+};
+
+#undef IMPL
+
+}
+
+namespace Wasm::Wasi::ABI {
+
+template<typename T, typename... Args>
+struct ToCompatibleValue<DistinctNumeric<T, Args...>> {
+    using Type = typename ToCompatibleValue<T>::Type;
+};
+
+template<typename T>
+struct ToCompatibleValue<LittleEndian<T>> {
+    using Type = MakeSigned<T>;
+};
+
+template<typename T>
+requires(requires { declval<typename T::CompatibleType>(); })
+struct ToCompatibleValue<T> {
+    using Type = MakeSigned<typename T::CompatibleType>;
+};
+
+template<Integral T>
+struct ToCompatibleValue<T> {
+    using Type = MakeSigned<T>;
+};
+
+template<Enum T>
+struct ToCompatibleValue<T> {
+    using Type = MakeSigned<UnderlyingType<T>>;
+};
+
+}
+
+template<typename T>
+struct AK::Formatter<Wasm::Wasi::LittleEndian<T>> : AK::Formatter<T> {
+    ErrorOr<void> format(FormatBuilder& builder, Wasm::Wasi::LittleEndian<T> value)
+    {
+        return Formatter<T>::format(builder, value.operator T());
+    }
+};