Add tcp syn packet fingerprinting to redbean

This change also fixes bugs in enoprotoopt reporting with setsockopt and
getsockopt error returns.

tool/net/lfinger.c

@@ -0,0 +1,98 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "net/finger/finger.h"
+#include "third_party/lua/lauxlib.h"
+
+// finger.DescribeSyn(syn_packet_bytes:str)
+//     ├─→ description:str
+//     └─→ nil, error:str
+static int LuaDescribeSyn(lua_State *L) {
+  char *q, *r;
+  size_t n, m;
+  const char *p;
+  luaL_Buffer b;
+  if (!lua_isnoneornil(L, 1)) {
+    p = luaL_checklstring(L, 1, &n);
+    m = 128;
+    q = luaL_buffinitsize(L, &b, m);
+    if ((r = DescribeSyn(q, m, p, n))) {
+      luaL_pushresultsize(&b, r - q);
+      return 1;
+    } else {
+      lua_pushnil(L);
+      lua_pushstring(L, "bad syn packet");
+      return 2;
+    }
+  } else {
+    return lua_gettop(L);
+  }
+}
+
+// finger.FingerSyn(syn_packet_bytes:str)
+//     ├─→ synfinger:uint32
+//     └─→ nil, error:str
+static int LuaFingerSyn(lua_State *L) {
+  size_t n;
+  uint32_t x;
+  const char *p;
+  if (!lua_isnoneornil(L, 1)) {
+    p = luaL_checklstring(L, 1, &n);
+    if ((x = FingerSyn(p, n))) {
+      lua_pushinteger(L, x);
+      return 1;
+    } else {
+      lua_pushnil(L);
+      lua_pushstring(L, "bad syn packet");
+      return 2;
+    }
+  } else {
+    return lua_gettop(L);
+  }
+}
+
+// finger.GetSynFingerOs(synfinger:uint32)
+//     ├─→ osname:str
+//     └─→ nil, error:str
+static int LuaGetSynFingerOs(lua_State *L) {
+  int os;
+  if (!lua_isnoneornil(L, 1)) {
+    if ((os = GetSynFingerOs(luaL_checkinteger(L, 1)))) {
+      lua_pushstring(L, GetOsName(os));
+      return 1;
+    } else {
+      lua_pushnil(L);
+      lua_pushstring(L, "unknown syn os fingerprint");
+      return 2;
+    }
+  } else {
+    return lua_gettop(L);
+  }
+}
+
+static const luaL_Reg kLuaFinger[] = {
+    {"DescribeSyn", LuaDescribeSyn},        //
+    {"FingerSyn", LuaFingerSyn},            //
+    {"GetSynFingerOs", LuaGetSynFingerOs},  //
+    {0},                                    //
+};
+
+int LuaFinger(lua_State *L) {
+  luaL_newlib(L, kLuaFinger);
+  return 1;
+}