SchOS/include/socket.h

#pragma once

#include "types.h"

// Unix domain sockets.
//
// These exist for Schcom. A compositor and its clients have to exchange
// messages, and a pipe cannot do it: a pipe is one-directional, has no
// notion of a connection, and gives no way for a server to be *found* by a
// client that starts later. A socket with a name in the filesystem is
// exactly the missing piece.
//
// AF_INET arrived later, and exactly as planned: underneath the same syscalls
// rather than reshaping them. A socket carries its domain and every entry point
// dispatches on it -- kernel/net/unix.c for AF_UNIX, kernel/net/inet.c (lwIP)
// for AF_INET.

#define AF_UNIX         1
#define AF_LOCAL        1
#define AF_INET         2
// Linux's number, because a musl program passes Linux's constant. getifaddrs()
// is implemented over this, which is why it exists here: enumerating interfaces
// is something every networked program does and nothing else offers.
#define AF_NETLINK      16
#define PF_NETLINK      AF_NETLINK
#define NETLINK_ROUTE   0

#define SOCK_STREAM     1
#define SOCK_DGRAM      2
#define SOCK_RAW        3

// Flags ORed into socket()'s and accept4()'s `type`/`flags` argument. Linux's
// values, because a musl program passes Linux's constants.
#define SOCK_NONBLOCK   0x800      // O_NONBLOCK
#define SOCK_CLOEXEC    0x80000    // O_CLOEXEC

// setsockopt/getsockopt levels and names, Linux's numbering.
//
// Only what is listed here is accepted; anything else is answered with
// ENOPROTOOPT rather than a success it did not earn. See the comment above
// sys_setsockopt for why that is worth the risk of failing a caller that never
// checked before.
#define SOL_SOCKET      1
#define IPPROTO_ICMP    1
#define IPPROTO_TCP     6

#define SO_REUSEADDR    2
#define SO_TYPE         3
#define SO_ERROR        4
#define SO_BROADCAST    6
#define SO_SNDBUF       7
#define SO_RCVBUF       8
#define SO_KEEPALIVE    9
#define SO_ACCEPTCONN   30

#define TCP_NODELAY     1

// ---------------------------------------------------------------------------
// Ancillary data -- sendmsg/recvmsg, and SCM_RIGHTS
//
// A descriptor is the only thing that can be passed between two processes that
// is not a number: it names an object the kernel already knows, and handing it
// over is the difference between "here is a buffer" and "here is a *copy* of a
// buffer". Wayland's wl_shm_create_pool passes one and has no integer-shaped
// alternative; docs/plan/hybrid.md's mechanism 1 is this and nothing else.
//
// Every structure below is Linux's, byte for byte, because a musl-linked
// program builds them with Linux's headers and we do not get a vote. The
// offsets that matter on x86-64 are, for msghdr:
//
//     0  msg_name   8  msg_namelen(+4 pad)  16 msg_iov   24 msg_iovlen
//    32  msg_control              40 msg_controllen     48 msg_flags
//
// -- 56 bytes total, which is what musl's int-typed msg_iovlen plus a pad word
// adds up to as well.
// ---------------------------------------------------------------------------

#define MSG_OOB          0x0001
#define MSG_PEEK         0x0002
#define MSG_DONTROUTE    0x0004
#define MSG_CTRUNC       0x0008    // some ancillary data was dropped
#define MSG_TRUNC        0x0020
#define MSG_DONTWAIT     0x0040
#define MSG_EOR          0x0080
#define MSG_WAITALL      0x0100
#define MSG_NOSIGNAL     0x4000
#define MSG_CMSG_CLOEXEC 0x40000000

// The only control message that exists here. SCM_CREDENTIALS is deliberately
// absent rather than stubbed: a caller told it succeeded would read a uid out
// of uninitialised memory and act on it.
#define SCM_RIGHTS      1

// The most descriptors one message may carry. A cap has to exist -- the kernel
// holds a reference to every one of them until it is received -- and saying so
// here means a sender can size its control buffer against the same number the
// kernel will enforce.
#define SCM_MAXFD       8

// struct iovec is declared in two headers on purpose, and guarded so that
// including both is not an error.
//
// posix.h has it because readv/writev need it; this file has it because a
// userspace program including <socket.h> for sendmsg must get a complete
// struct msghdr without also having to know about a kernel header. Both
// definitions are identical and both are Linux's layout.
//
// The guard is not cosmetic. C23 permits redeclaring a struct with identical
// members and GCC 15 defaults to C23, so the duplicate was invisible on the
// gcc path -- while clang defaults to gnu17 and rejected it, which broke the
// one toolchain shell.nix exists to provide and which the UEFI loader needs.
#ifndef SCH_IOVEC_DEFINED
#define SCH_IOVEC_DEFINED
struct iovec {
  void  *iov_base;
  uint64 iov_len;
};
#endif

struct msghdr {
  void         *msg_name;         // struct sockaddr *, or 0
  uint32        msg_namelen;
  uint32        __pad1;
  struct iovec *msg_iov;
  uint64        msg_iovlen;
  void         *msg_control;      // struct cmsghdr *, or 0
  uint64        msg_controllen;
  int           msg_flags;        // out on recvmsg: MSG_CTRUNC
};

struct cmsghdr {
  uint64 cmsg_len;                // CMSG_LEN(payload), NOT including padding
  int    cmsg_level;              // SOL_SOCKET
  int    cmsg_type;               // SCM_RIGHTS
};

// cmsg_len counts the header plus the payload; CMSG_SPACE additionally counts
// the padding to the next header. Conflating the two is the classic way to
// build a control buffer the kernel then rejects, which is why both exist.
#define CMSG_ALIGN(n)    (((uint64)(n) + sizeof(uint64) - 1) & ~(uint64)(sizeof(uint64) - 1))
#define CMSG_LEN(n)      (CMSG_ALIGN(sizeof(struct cmsghdr)) + (uint64)(n))
#define CMSG_SPACE(n)    (CMSG_ALIGN(sizeof(struct cmsghdr)) + CMSG_ALIGN(n))
#define CMSG_DATA(c)     ((unsigned char *)((struct cmsghdr *)(c) + 1))

#define CMSG_FIRSTHDR(m)                                                      \
  ((m)->msg_control && (m)->msg_controllen >= sizeof(struct cmsghdr)          \
     ? (struct cmsghdr *)(m)->msg_control                                     \
     : (struct cmsghdr *)0)

#define CMSG_NXTHDR(m, c)                                                     \
  ((c)->cmsg_len < sizeof(struct cmsghdr) ||                                  \
   (uint64)((char *)(c) + CMSG_ALIGN((c)->cmsg_len) + sizeof(struct cmsghdr)  \
            - (char *)(m)->msg_control) > (m)->msg_controllen                 \
     ? (struct cmsghdr *)0                                                    \
     : (struct cmsghdr *)((char *)(c) + CMSG_ALIGN((c)->cmsg_len)))

#define UNIX_PATH_MAX   108

#define SHUT_RD         0
#define SHUT_WR         1
#define SHUT_RDWR       2

struct sockaddr_un {
  uint16 sun_family;
  char   sun_path[UNIX_PATH_MAX];
};

// The generic form syscalls take. Same shape as Linux's, so a musl-linked
// program's struct lines up byte for byte.
struct sockaddr {
  uint16 sa_family;
  char   sa_data[UNIX_PATH_MAX];
};

// The AF_INET address. Same layout as Linux's, so a musl-linked program's
// struct lines up byte for byte. sin_port and sin_addr are network byte order
// and stay that way: lwIP wants them so, and converting on the way in and out
// again would be two swaps that cancel.
struct sockaddr_in {
  uint16 sin_family;
  uint16 sin_port;
  uint32 sin_addr;
  char   sin_zero[8];
};

// ---------------------------------------------------------------------------
// rtnetlink, enough of it for getifaddrs(3)
//
// Every structure below is Linux's, byte for byte, because musl parses what it
// is handed with Linux's own headers. They are not ours to design.
//
// What musl actually does (src/network/netlink.c) is the whole specification
// this has to meet: open PF_NETLINK/SOCK_RAW/NETLINK_ROUTE, send an
// nlmsghdr+rtgenmsg asking RTM_GETLINK with NLM_F_DUMP, read replies until
// NLMSG_DONE, then do it again for RTM_GETADDR on the same socket.
// ---------------------------------------------------------------------------

struct nlmsghdr {
  uint32 nlmsg_len;
  uint16 nlmsg_type;
  uint16 nlmsg_flags;
  uint32 nlmsg_seq;
  uint32 nlmsg_pid;
};

struct rtgenmsg { uchar rtgen_family; };

struct ifinfomsg {
  uchar  ifi_family;
  uchar  __ifi_pad;
  uint16 ifi_type;              // ARPHRD_*
  int32  ifi_index;
  uint32 ifi_flags;             // IFF_*
  uint32 ifi_change;
};

struct ifaddrmsg {
  uchar  ifa_family;
  uchar  ifa_prefixlen;
  uchar  ifa_flags;
  uchar  ifa_scope;
  uint32 ifa_index;
};

struct rtattr {
  uint16 rta_len;
  uint16 rta_type;
};

#define NLMSG_ERROR     2
#define NLMSG_DONE      3
#define NLM_F_REQUEST   0x001
#define NLM_F_MULTI     0x002
#define NLM_F_DUMP      0x300

#define RTM_NEWLINK     16
#define RTM_GETLINK     18
#define RTM_NEWADDR     20
#define RTM_GETADDR     22

#define IFLA_ADDRESS     1
#define IFLA_IFNAME      3
#define IFA_ADDRESS      1
#define IFA_LOCAL        2
#define IFA_LABEL        3

#define ARPHRD_ETHER     1
#define ARPHRD_LOOPBACK  772

#define IFF_UP           0x1
#define IFF_LOOPBACK     0x8
#define IFF_RUNNING      0x40
#define IFF_BROADCAST    0x2
#define IFF_MULTICAST    0x1000

// Both are four-byte aligned on every architecture Linux supports.
#define NLMSG_ALIGN(n)  (((n) + 3) & ~3)
#define RTA_ALIGN(n)    (((n) + 3) & ~3)

#ifdef _KERNEL_SOCKET_INTERNALS

#define NSOCK       32          // sockets in the system
#define SOCKBUF     4096        // receive buffer per connected socket
#define NBACKLOG    8

// Descriptors in flight.
//
// A batch is pinned to the stream position of the first byte of the message
// that carried it, and that is the whole delivery rule: a reader that arrives
// at that position gets the descriptors, and a reader that has not reached it
// yet is stopped *short* of it rather than allowed to read past. Without the
// second half a program that read 4096 bytes in one call would swallow three
// messages and be handed one message's descriptors, with no way to tell which.
//
// Eight batches in flight is not a guess: a sender that has eight unreceived
// messages carrying descriptors and keeps going is not going to be rescued by
// a ninth slot, and ENOBUFS says so where a larger array would only move the
// same failure further away.
#define NSCM        8           // messages carrying descriptors, in flight

struct file;

struct scm_fds {
  uint  pos;                    // stream position of the message's first byte
  int   n;
  struct file *f[SCM_MAXFD];    // references held by the kernel, not by anyone
};

enum sockstate {
  SS_FREE = 0,
  SS_UNBOUND,
  SS_BOUND,
  SS_LISTENING,
  SS_CONNECTED,
};

// Every field here is protected by the socket table's single lock in
// kernel/net/unix.c -- there is deliberately no per-socket lock; see the
// comment at the top of that file for why.
struct socket {
  int   ref;
  int   type;
  int   state;
  int   domain;                 // AF_UNIX or AF_INET

  // For AF_INET: the lwIP-backed socket in kernel/net/inet.c. Opaque here so
  // that socket.h does not have to drag lwIP's headers into every file that
  // wants a struct socket.
  void *inet;

  char  name[UNIX_PATH_MAX];    // the bound path, for a listener

  // A connected socket's peer. Writing to a socket appends to the *peer's*
  // buffer, which is what makes one buffer per socket enough for a
  // bidirectional connection.
  struct socket *peer;
  int   peer_closed;

  char  data[SOCKBUF];
  uint  nread, nwrite;

  // Connections waiting to be accepted, on a listener.
  struct socket *queue[NBACKLOG];
  int   nqueue;

  // Socket options that are genuinely honoured. Kept here rather than only in
  // lwIP's pcb because getsockopt has to answer for an AF_UNIX socket too, and
  // because a flag set before bind() has to survive until there is a pcb to
  // apply it to.
  int   o_reuseaddr;
  int   o_keepalive;
  int   o_broadcast;
  int   o_nodelay;

  // Descriptors sent to this socket and not yet received. They live on the
  // *receiving* side, next to the bytes they were sent with, because that is
  // the only side that can say when they have been delivered.
  struct scm_fds scm[NSCM];
  int            nscm;
};

#endif