8 files changed, 906 insertions, 2 deletions

diff --git a/.github/workflows/compat53-tests.yml b/.github/workflows/compat53-tests.yml
index d0dd3d4..40819ce 100644
--- a/.github/workflows/compat53-tests.yml
+++ b/.github/workflows/compat53-tests.yml
@@ -55,7 +55,7 @@ jobs:
           if [ "${{ matrix.external }}" = true ]; then DEF="-DCOMPAT53_PREFIX=compat53" SRC="c-api/compat-5.3.c"; fi
           ${CC} ${CFLAGS} -Iold/include ${DEF} -shared -o old/testmod.so tests/testmod.c ${SRC}
           ${CC} ${CFLAGS} -Inew/include ${DEF} -shared -o new/testmod.so tests/testmod.c ${SRC}
-          gcc ${CFLAGS} -Iold/include ${DEF} -shared -o old/compat53.so ltablib.c lutf8lib.c lstrlib.c ${SRC}
+          gcc ${CFLAGS} -Iold/include ${DEF} -shared -o old/compat53.so ltablib.c lutf8lib.c lstrlib.c liolib.c ${SRC}
       - name: run test scripts
         run: |
           (cd old && bin/lua ../tests/test.lua) > old.txt
diff --git a/.travis.yml b/.travis.yml
index af458d8..44ae3a0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -38,7 +38,7 @@ install:
   - if [ "x${EXTERNAL:-}" = xtrue ]; then DEF="-DCOMPAT53_PREFIX=compat53" SRC="c-api/compat-5.3.c"; fi
   - ${CC} ${CFLAGS} -Iold/include ${DEF} -shared -o old/testmod.so tests/testmod.c ${SRC}
   - ${CC} ${CFLAGS} -Inew/include ${DEF} -shared -o new/testmod.so tests/testmod.c ${SRC}
-  - gcc ${CFLAGS} -Iold/include ${DEF} -shared -o old/compat53.so ltablib.c lutf8lib.c lstrlib.c ${SRC}
+  - gcc ${CFLAGS} -Iold/include ${DEF} -shared -o old/compat53.so ltablib.c lutf8lib.c lstrlib.c liolib.c ${SRC}
 
 script:
   - (cd old && bin/lua ../tests/test.lua) > old.txt
diff --git a/README.md b/README.md
index 80e7cbc..3ee6acf 100644
--- a/README.md
+++ b/README.md
@@ -117,6 +117,8 @@ For Lua 5.1 additionally:
 * `io.write` and `file:write` return file handle
 * `io.lines` and `file:lines` accept format arguments (like `io.read`)
   (see [here][10] and [here][11])
+* `file:close` returns three results when a process is opened
+  with `io.popen`
 * `debug.setmetatable` returns object
 * `debug.getuservalue` (see [here][12])
 * `debug.setuservalue` (see [here][13])
diff --git a/compat53/module.lua b/compat53/module.lua
index 30be6b5..225d8ca 100644
--- a/compat53/module.lua
+++ b/compat53/module.lua
@@ -67,6 +67,15 @@ if lua_version < "5.3" then
    end
 
 
+   -- load io functions
+   local io_ok, iolib = pcall(require, "compat53.io")
+   if io_ok then
+      for k,v in pairs(iolib) do
+         M.io[k] = v
+      end
+   end
+
+
    -- load string packing functions
    local str_ok, strlib = pcall(require, "compat53.string")
    if str_ok then
diff --git a/liolib.c b/liolib.c
new file mode 100644
index 0000000..8a9e75c
--- /dev/null
+++ b/liolib.c
@@ -0,0 +1,776 @@
+/*
+** $Id: liolib.c,v 2.151.1.1 2017/04/19 17:29:57 roberto Exp $
+** Standard I/O (and system) library
+** See Copyright Notice in lua.h
+*/
+
+#define liolib_c
+#define LUA_LIB
+
+#include "lprefix.h"
+
+
+#include <ctype.h>
+#include <errno.h>
+#include <locale.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "lua.h"
+
+#include "lauxlib.h"
+#include "lualib.h"
+
+
+
+
+/*
+** Change this macro to accept other modes for 'fopen' besides
+** the standard ones.
+*/
+#if !defined(l_checkmode)
+
+/* accepted extensions to 'mode' in 'fopen' */
+#if !defined(L_MODEEXT)
+#define L_MODEEXT       "b"
+#endif
+
+/* Check whether 'mode' matches '[rwa]%+?[L_MODEEXT]*' */
+static int l_checkmode (const char *mode) {
+  return (*mode != '\0' && strchr("rwa", *(mode++)) != NULL &&
+         (*mode != '+' || (++mode, 1)) &&  /* skip if char is '+' */
+         (strspn(mode, L_MODEEXT) == strlen(mode)));  /* check extensions */
+}
+
+#endif
+
+/*
+** {======================================================
+** l_popen spawns a new process connected to the current
+** one through the file streams.
+** =======================================================
+*/
+
+#if !defined(l_popen)           /* { */
+
+#if defined(LUA_USE_POSIX)      /* { */
+
+#define l_popen(L,c,m)          (fflush(NULL), popen(c,m))
+#define l_pclose(L,file)        (pclose(file))
+
+#elif defined(LUA_USE_WINDOWS)  /* }{ */
+
+#define l_popen(L,c,m)          (_popen(c,m))
+#define l_pclose(L,file)        (_pclose(file))
+
+#else                           /* }{ */
+
+/* ISO C definitions */
+#define l_popen(L,c,m)  \
+          ((void)((void)c, m), \
+          luaL_error(L, "'popen' not supported"), \
+          (FILE*)0)
+#define l_pclose(L,file)                ((void)L, (void)file, -1)
+
+#endif                          /* } */
+
+#endif                          /* } */
+
+/* }====================================================== */
+
+
+#if !defined(l_getc)            /* { */
+
+#if defined(LUA_USE_POSIX)
+#define l_getc(f)               getc_unlocked(f)
+#define l_lockfile(f)           flockfile(f)
+#define l_unlockfile(f)         funlockfile(f)
+#else
+#define l_getc(f)               getc(f)
+#define l_lockfile(f)           ((void)0)
+#define l_unlockfile(f)         ((void)0)
+#endif
+
+#endif                          /* } */
+
+
+/*
+** {======================================================
+** l_fseek: configuration for longer offsets
+** =======================================================
+*/
+
+#if !defined(l_fseek)           /* { */
+
+#if defined(LUA_USE_POSIX)      /* { */
+
+#include <sys/types.h>
+
+#define l_fseek(f,o,w)          fseeko(f,o,w)
+#define l_ftell(f)              ftello(f)
+#define l_seeknum               off_t
+
+#elif defined(LUA_USE_WINDOWS) && !defined(_CRTIMP_TYPEINFO) \
+   && defined(_MSC_VER) && (_MSC_VER >= 1400)   /* }{ */
+
+/* Windows (but not DDK) and Visual C++ 2005 or higher */
+#define l_fseek(f,o,w)          _fseeki64(f,o,w)
+#define l_ftell(f)              _ftelli64(f)
+#define l_seeknum               __int64
+
+#else                           /* }{ */
+
+/* ISO C definitions */
+#define l_fseek(f,o,w)          fseek(f,o,w)
+#define l_ftell(f)              ftell(f)
+#define l_seeknum               long
+
+#endif                          /* } */
+
+#endif                          /* } */
+
+/* }====================================================== */
+
+
+#define IO_PREFIX       "_IO_"
+#define IOPREF_LEN      (sizeof(IO_PREFIX)/sizeof(char) - 1)
+#define IO_INPUT        (IO_PREFIX "input")
+#define IO_OUTPUT       (IO_PREFIX "output")
+
+
+typedef luaL_Stream LStream;
+
+
+#define tolstream(L)    ((LStream *)luaL_checkudata(L, 1, LUA_FILEHANDLE))
+
+#define isclosed(p)     ((p)->closef == NULL)
+
+
+static int io_type (lua_State *L) {
+  LStream *p;
+  luaL_checkany(L, 1);
+  p = (LStream *)luaL_testudata(L, 1, LUA_FILEHANDLE);
+  if (p == NULL)
+    lua_pushnil(L);  /* not a file */
+  else if (isclosed(p))
+    lua_pushliteral(L, "closed file");
+  else
+    lua_pushliteral(L, "file");
+  return 1;
+}
+
+
+static int f_tostring (lua_State *L) {
+  LStream *p = tolstream(L);
+  if (isclosed(p))
+    lua_pushliteral(L, "file (closed)");
+  else
+    lua_pushfstring(L, "file (%p)", p->f);
+  return 1;
+}
+
+
+static FILE *tofile (lua_State *L) {
+  LStream *p = tolstream(L);
+  if (isclosed(p))
+    luaL_error(L, "attempt to use a closed file");
+  lua_assert(p->f);
+  return p->f;
+}
+
+
+/*
+** When creating file handles, always creates a 'closed' file handle
+** before opening the actual file; so, if there is a memory error, the
+** handle is in a consistent state.
+*/
+static LStream *newprefile (lua_State *L) {
+  LStream *p = (LStream *)lua_newuserdata(L, sizeof(LStream));
+  p->closef = NULL;  /* mark file handle as 'closed' */
+  luaL_setmetatable(L, LUA_FILEHANDLE);
+  return p;
+}
+
+
+/*
+** Calls the 'close' function from a file handle. The 'volatile' avoids
+** a bug in some versions of the Clang compiler (e.g., clang 3.0 for
+** 32 bits).
+*/
+static int aux_close (lua_State *L) {
+  LStream *p = tolstream(L);
+  volatile lua_CFunction cf = p->closef;
+  p->closef = NULL;  /* mark stream as closed */
+  return (*cf)(L);  /* close it */
+}
+
+
+static int f_close (lua_State *L) {
+  tofile(L);  /* make sure argument is an open stream */
+  return aux_close(L);
+}
+
+
+static int io_close (lua_State *L) {
+  if (lua_isnone(L, 1))  /* no argument? */
+    lua_getfield(L, LUA_REGISTRYINDEX, IO_OUTPUT);  /* use standard output */
+  return f_close(L);
+}
+
+
+static int f_gc (lua_State *L) {
+  LStream *p = tolstream(L);
+  if (!isclosed(p) && p->f != NULL)
+    aux_close(L);  /* ignore closed and incompletely open files */
+  return 0;
+}
+
+
+/*
+** function to close regular files
+*/
+static int io_fclose (lua_State *L) {
+  LStream *p = tolstream(L);
+  int res = fclose(p->f);
+  return luaL_fileresult(L, (res == 0), NULL);
+}
+
+
+static LStream *newfile (lua_State *L) {
+  LStream *p = newprefile(L);
+  p->f = NULL;
+  p->closef = &io_fclose;
+  return p;
+}
+
+
+static void opencheck (lua_State *L, const char *fname, const char *mode) {
+  LStream *p = newfile(L);
+  p->f = fopen(fname, mode);
+  if (p->f == NULL)
+    luaL_error(L, "cannot open file '%s' (%s)", fname, strerror(errno));
+}
+
+
+static int io_open (lua_State *L) {
+  const char *filename = luaL_checkstring(L, 1);
+  const char *mode = luaL_optstring(L, 2, "r");
+  LStream *p = newfile(L);
+  const char *md = mode;  /* to traverse/check mode */
+  luaL_argcheck(L, l_checkmode(md), 2, "invalid mode");
+  p->f = fopen(filename, mode);
+  return (p->f == NULL) ? luaL_fileresult(L, 0, filename) : 1;
+}
+
+
+/*
+** function to close 'popen' files
+*/
+static int io_pclose (lua_State *L) {
+  LStream *p = tolstream(L);
+  return luaL_execresult(L, l_pclose(L, p->f));
+}
+
+
+static int io_popen (lua_State *L) {
+  const char *filename = luaL_checkstring(L, 1);
+  const char *mode = luaL_optstring(L, 2, "r");
+  LStream *p = newprefile(L);
+  p->f = l_popen(L, filename, mode);
+  p->closef = &io_pclose;
+  return (p->f == NULL) ? luaL_fileresult(L, 0, filename) : 1;
+}
+
+
+static int io_tmpfile (lua_State *L) {
+  LStream *p = newfile(L);
+  p->f = tmpfile();
+  return (p->f == NULL) ? luaL_fileresult(L, 0, NULL) : 1;
+}
+
+
+static FILE *getiofile (lua_State *L, const char *findex) {
+  LStream *p;
+  lua_getfield(L, LUA_REGISTRYINDEX, findex);
+  p = (LStream *)lua_touserdata(L, -1);
+  if (isclosed(p))
+    luaL_error(L, "standard %s file is closed", findex + IOPREF_LEN);
+  return p->f;
+}
+
+
+static int g_iofile (lua_State *L, const char *f, const char *mode) {
+  if (!lua_isnoneornil(L, 1)) {
+    const char *filename = lua_tostring(L, 1);
+    if (filename)
+      opencheck(L, filename, mode);
+    else {
+      tofile(L);  /* check that it's a valid file handle */
+      lua_pushvalue(L, 1);
+    }
+    lua_setfield(L, LUA_REGISTRYINDEX, f);
+  }
+  /* return current value */
+  lua_getfield(L, LUA_REGISTRYINDEX, f);
+  return 1;
+}
+
+
+static int io_input (lua_State *L) {
+  return g_iofile(L, IO_INPUT, "r");
+}
+
+
+static int io_output (lua_State *L) {
+  return g_iofile(L, IO_OUTPUT, "w");
+}
+
+
+static int io_readline (lua_State *L);
+
+
+/*
+** maximum number of arguments to 'f:lines'/'io.lines' (it + 3 must fit
+** in the limit for upvalues of a closure)
+*/
+#define MAXARGLINE      250
+
+static void aux_lines (lua_State *L, int toclose) {
+  int n = lua_gettop(L) - 1;  /* number of arguments to read */
+  luaL_argcheck(L, n <= MAXARGLINE, MAXARGLINE + 2, "too many arguments");
+  lua_pushinteger(L, n);  /* number of arguments to read */
+  lua_pushboolean(L, toclose);  /* close/not close file when finished */
+  lua_rotate(L, 2, 2);  /* move 'n' and 'toclose' to their positions */
+  lua_pushcclosure(L, io_readline, 3 + n);
+}
+
+
+static int f_lines (lua_State *L) {
+  tofile(L);  /* check that it's a valid file handle */
+  aux_lines(L, 0);
+  return 1;
+}
+
+
+static int io_lines (lua_State *L) {
+  int toclose;
+  if (lua_isnone(L, 1)) lua_pushnil(L);  /* at least one argument */
+  if (lua_isnil(L, 1)) {  /* no file name? */
+    lua_getfield(L, LUA_REGISTRYINDEX, IO_INPUT);  /* get default input */
+    lua_replace(L, 1);  /* put it at index 1 */
+    tofile(L);  /* check that it's a valid file handle */
+    toclose = 0;  /* do not close it after iteration */
+  }
+  else {  /* open a new file */
+    const char *filename = luaL_checkstring(L, 1);
+    opencheck(L, filename, "r");
+    lua_replace(L, 1);  /* put file at index 1 */
+    toclose = 1;  /* close it after iteration */
+  }
+  aux_lines(L, toclose);
+  return 1;
+}
+
+
+/*
+** {======================================================
+** READ
+** =======================================================
+*/
+
+
+/* maximum length of a numeral */
+#if !defined (L_MAXLENNUM)
+#define L_MAXLENNUM     200
+#endif
+
+
+/* auxiliary structure used by 'read_number' */
+typedef struct {
+  FILE *f;  /* file being read */
+  int c;  /* current character (look ahead) */
+  int n;  /* number of elements in buffer 'buff' */
+  char buff[L_MAXLENNUM + 1];  /* +1 for ending '\0' */
+} RN;
+
+
+/*
+** Add current char to buffer (if not out of space) and read next one
+*/
+static int nextc (RN *rn) {
+  if (rn->n >= L_MAXLENNUM) {  /* buffer overflow? */
+    rn->buff[0] = '\0';  /* invalidate result */
+    return 0;  /* fail */
+  }
+  else {
+    rn->buff[rn->n++] = rn->c;  /* save current char */
+    rn->c = l_getc(rn->f);  /* read next one */
+    return 1;
+  }
+}
+
+
+/*
+** Accept current char if it is in 'set' (of size 2)
+*/
+static int test2 (RN *rn, const char *set) {
+  if (rn->c == set[0] || rn->c == set[1])
+    return nextc(rn);
+  else return 0;
+}
+
+
+/*
+** Read a sequence of (hex)digits
+*/
+static int readdigits (RN *rn, int hex) {
+  int count = 0;
+  while ((hex ? isxdigit(rn->c) : isdigit(rn->c)) && nextc(rn))
+    count++;
+  return count;
+}
+
+
+/*
+** Read a number: first reads a valid prefix of a numeral into a buffer.
+** Then it calls 'lua_stringtonumber' to check whether the format is
+** correct and to convert it to a Lua number
+*/
+static int read_number (lua_State *L, FILE *f) {
+  RN rn;
+  int count = 0;
+  int hex = 0;
+  char decp[2];
+  rn.f = f; rn.n = 0;
+  decp[0] = lua_getlocaledecpoint();  /* get decimal point from locale */
+  decp[1] = '.';  /* always accept a dot */
+  l_lockfile(rn.f);
+  do { rn.c = l_getc(rn.f); } while (isspace(rn.c));  /* skip spaces */
+  test2(&rn, "-+");  /* optional signal */
+  if (test2(&rn, "00")) {
+    if (test2(&rn, "xX")) hex = 1;  /* numeral is hexadecimal */
+    else count = 1;  /* count initial '0' as a valid digit */
+  }
+  count += readdigits(&rn, hex);  /* integral part */
+  if (test2(&rn, decp))  /* decimal point? */
+    count += readdigits(&rn, hex);  /* fractional part */
+  if (count > 0 && test2(&rn, (hex ? "pP" : "eE"))) {  /* exponent mark? */
+    test2(&rn, "-+");  /* exponent signal */
+    readdigits(&rn, 0);  /* exponent digits */
+  }
+  ungetc(rn.c, rn.f);  /* unread look-ahead char */
+  l_unlockfile(rn.f);
+  rn.buff[rn.n] = '\0';  /* finish string */
+  if (lua_stringtonumber(L, rn.buff))  /* is this a valid number? */
+    return 1;  /* ok */
+  else {  /* invalid format */
+   lua_pushnil(L);  /* "result" to be removed */
+   return 0;  /* read fails */
+  }
+}
+
+
+static int test_eof (lua_State *L, FILE *f) {
+  int c = getc(f);
+  ungetc(c, f);  /* no-op when c == EOF */
+  lua_pushliteral(L, "");
+  return (c != EOF);
+}
+
+
+static int read_line (lua_State *L, FILE *f, int chop) {
+  luaL_Buffer b;
+  int c = '\0';
+  luaL_buffinit(L, &b);
+  while (c != EOF && c != '\n') {  /* repeat until end of line */
+    char *buff = luaL_prepbuffer(&b);  /* preallocate buffer */
+    int i = 0;
+    l_lockfile(f);  /* no memory errors can happen inside the lock */
+    while (i < LUAL_BUFFERSIZE && (c = l_getc(f)) != EOF && c != '\n')
+      buff[i++] = c;
+    l_unlockfile(f);
+    luaL_addsize(&b, i);
+  }
+  if (!chop && c == '\n')  /* want a newline and have one? */
+    luaL_addchar(&b, c);  /* add ending newline to result */
+  luaL_pushresult(&b);  /* close buffer */
+  /* return ok if read something (either a newline or something else) */
+  return (c == '\n' || lua_rawlen(L, -1) > 0);
+}
+
+
+static void read_all (lua_State *L, FILE *f) {
+  size_t nr;
+  luaL_Buffer b;
+  luaL_buffinit(L, &b);
+  do {  /* read file in chunks of LUAL_BUFFERSIZE bytes */
+    char *p = luaL_prepbuffer(&b);
+    nr = fread(p, sizeof(char), LUAL_BUFFERSIZE, f);
+    luaL_addsize(&b, nr);
+  } while (nr == LUAL_BUFFERSIZE);
+  luaL_pushresult(&b);  /* close buffer */
+}
+
+
+static int read_chars (lua_State *L, FILE *f, size_t n) {
+  size_t nr;  /* number of chars actually read */
+  char *p;
+  luaL_Buffer b;
+  luaL_buffinit(L, &b);
+  p = luaL_prepbuffsize(&b, n);  /* prepare buffer to read whole block */
+  nr = fread(p, sizeof(char), n, f);  /* try to read 'n' chars */
+  luaL_addsize(&b, nr);
+  luaL_pushresult(&b);  /* close buffer */
+  return (nr > 0);  /* true iff read something */
+}
+
+
+static int g_read (lua_State *L, FILE *f, int first) {
+  int nargs = lua_gettop(L) - 1;
+  int success;
+  int n;
+  clearerr(f);
+  if (nargs == 0) {  /* no arguments? */
+    success = read_line(L, f, 1);
+    n = first+1;  /* to return 1 result */
+  }
+  else {  /* ensure stack space for all results and for auxlib's buffer */
+    luaL_checkstack(L, nargs+LUA_MINSTACK, "too many arguments");
+    success = 1;
+    for (n = first; nargs-- && success; n++) {
+      if (lua_type(L, n) == LUA_TNUMBER) {
+        size_t l = (size_t)luaL_checkinteger(L, n);
+        success = (l == 0) ? test_eof(L, f) : read_chars(L, f, l);
+      }
+      else {
+        const char *p = luaL_checkstring(L, n);
+        if (*p == '*') p++;  /* skip optional '*' (for compatibility) */
+        switch (*p) {
+          case 'n':  /* number */
+            success = read_number(L, f);
+            break;
+          case 'l':  /* line */
+            success = read_line(L, f, 1);
+            break;
+          case 'L':  /* line with end-of-line */
+            success = read_line(L, f, 0);
+            break;
+          case 'a':  /* file */
+            read_all(L, f);  /* read entire file */
+            success = 1; /* always success */
+            break;
+          default:
+            return luaL_argerror(L, n, "invalid format");
+        }
+      }
+    }
+  }
+  if (ferror(f))
+    return luaL_fileresult(L, 0, NULL);
+  if (!success) {
+    lua_pop(L, 1);  /* remove last result */
+    lua_pushnil(L);  /* push nil instead */
+  }
+  return n - first;
+}
+
+
+static int io_read (lua_State *L) {
+  return g_read(L, getiofile(L, IO_INPUT), 1);
+}
+
+
+static int f_read (lua_State *L) {
+  return g_read(L, tofile(L), 2);
+}
+
+
+static int io_readline (lua_State *L) {
+  LStream *p = (LStream *)lua_touserdata(L, lua_upvalueindex(1));
+  int i;
+  int n = (int)lua_tointeger(L, lua_upvalueindex(2));
+  if (isclosed(p))  /* file is already closed? */
+    return luaL_error(L, "file is already closed");
+  lua_settop(L , 1);
+  luaL_checkstack(L, n, "too many arguments");
+  for (i = 1; i <= n; i++)  /* push arguments to 'g_read' */
+    lua_pushvalue(L, lua_upvalueindex(3 + i));
+  n = g_read(L, p->f, 2);  /* 'n' is number of results */
+  lua_assert(n > 0);  /* should return at least a nil */
+  if (lua_toboolean(L, -n))  /* read at least one value? */
+    return n;  /* return them */
+  else {  /* first result is nil: EOF or error */
+    if (n > 1) {  /* is there error information? */
+      /* 2nd result is error message */
+      return luaL_error(L, "%s", lua_tostring(L, -n + 1));
+    }
+    if (lua_toboolean(L, lua_upvalueindex(3))) {  /* generator created file? */
+      lua_settop(L, 0);
+      lua_pushvalue(L, lua_upvalueindex(1));
+      aux_close(L);  /* close it */
+    }
+    return 0;
+  }
+}
+
+/* }====================================================== */
+
+
+static int g_write (lua_State *L, FILE *f, int arg) {
+  int nargs = lua_gettop(L) - arg;
+  int status = 1;
+  for (; nargs--; arg++) {
+    if (lua_type(L, arg) == LUA_TNUMBER) {
+      /* optimization: could be done exactly as for strings */
+      int len = lua_isinteger(L, arg)
+                ? fprintf(f, LUA_INTEGER_FMT,
+                             (LUAI_UACINT)lua_tointeger(L, arg))
+                : fprintf(f, LUA_NUMBER_FMT,
+                             (LUAI_UACNUMBER)lua_tonumber(L, arg));
+      status = status && (len > 0);
+    }
+    else {
+      size_t l;
+      const char *s = luaL_checklstring(L, arg, &l);
+      status = status && (fwrite(s, sizeof(char), l, f) == l);
+    }
+  }
+  if (status) return 1;  /* file handle already on stack top */
+  else return luaL_fileresult(L, status, NULL);
+}
+
+
+static int io_write (lua_State *L) {
+  return g_write(L, getiofile(L, IO_OUTPUT), 1);
+}
+
+
+static int f_write (lua_State *L) {
+  FILE *f = tofile(L);
+  lua_pushvalue(L, 1);  /* push file at the stack top (to be returned) */
+  return g_write(L, f, 2);
+}
+
+
+static int f_seek (lua_State *L) {
+  static const int mode[] = {SEEK_SET, SEEK_CUR, SEEK_END};
+  static const char *const modenames[] = {"set", "cur", "end", NULL};
+  FILE *f = tofile(L);
+  int op = luaL_checkoption(L, 2, "cur", modenames);
+  lua_Integer p3 = luaL_optinteger(L, 3, 0);
+  l_seeknum offset = (l_seeknum)p3;
+  luaL_argcheck(L, (lua_Integer)offset == p3, 3,
+                  "not an integer in proper range");
+  op = l_fseek(f, offset, mode[op]);
+  if (op)
+    return luaL_fileresult(L, 0, NULL);  /* error */
+  else {
+    lua_pushinteger(L, (lua_Integer)l_ftell(f));
+    return 1;
+  }
+}
+
+
+static int f_setvbuf (lua_State *L) {
+  static const int mode[] = {_IONBF, _IOFBF, _IOLBF};
+  static const char *const modenames[] = {"no", "full", "line", NULL};
+  FILE *f = tofile(L);
+  int op = luaL_checkoption(L, 2, NULL, modenames);
+  lua_Integer sz = luaL_optinteger(L, 3, LUAL_BUFFERSIZE);
+  int res = setvbuf(f, NULL, mode[op], (size_t)sz);
+  return luaL_fileresult(L, res == 0, NULL);
+}
+
+
+
+static int io_flush (lua_State *L) {
+  return luaL_fileresult(L, fflush(getiofile(L, IO_OUTPUT)) == 0, NULL);
+}
+
+
+static int f_flush (lua_State *L) {
+  return luaL_fileresult(L, fflush(tofile(L)) == 0, NULL);
+}
+
+
+/*
+** functions for 'io' library
+*/
+static const luaL_Reg iolib[] = {
+  {"close", io_close},
+  {"flush", io_flush},
+  {"input", io_input},
+  {"lines", io_lines},
+  {"open", io_open},
+  {"output", io_output},
+  {"popen", io_popen},
+  {"read", io_read},
+  {"tmpfile", io_tmpfile},
+  {"type", io_type},
+  {"write", io_write},
+  {NULL, NULL}
+};
+
+
+/*
+** methods for file handles
+*/
+static const luaL_Reg flib[] = {
+  {"close", f_close},
+  {"flush", f_flush},
+  {"lines", f_lines},
+  {"read", f_read},
+  {"seek", f_seek},
+  {"setvbuf", f_setvbuf},
+  {"write", f_write},
+  {"__gc", f_gc},
+  {"__tostring", f_tostring},
+  {NULL, NULL}
+};
+
+
+static void createmeta (lua_State *L) {
+  luaL_newmetatable(L, LUA_FILEHANDLE);  /* create metatable for file handles */
+  lua_pushvalue(L, -1);  /* push metatable */
+  lua_setfield(L, -2, "__index");  /* metatable.__index = metatable */
+  luaL_setfuncs(L, flib, 0);  /* add file methods to new metatable */
+  lua_pop(L, 1);  /* pop new metatable */
+}
+
+
+/*
+** function to (not) close the standard files stdin, stdout, and stderr
+*/
+static int io_noclose (lua_State *L) {
+  LStream *p = tolstream(L);
+  p->closef = &io_noclose;  /* keep file opened */
+  lua_pushnil(L);
+  lua_pushliteral(L, "cannot close standard file");
+  return 2;
+}
+
+
+static void createstdfile (lua_State *L, FILE *f, const char *k,
+                           const char *fname) {
+  LStream *p = newprefile(L);
+  p->f = f;
+  p->closef = &io_noclose;
+  if (k != NULL) {
+    lua_pushvalue(L, -1);
+    lua_setfield(L, LUA_REGISTRYINDEX, k);  /* add file to registry */
+  }
+  lua_setfield(L, -2, fname);  /* add file to module */
+}
+
+
+LUAMOD_API int luaopen_io (lua_State *L) {
+  luaL_newlib(L, iolib);  /* new module */
+  createmeta(L);
+  /* create (and set) default files */
+  createstdfile(L, stdin, IO_INPUT, "stdin");
+  createstdfile(L, stdout, IO_OUTPUT, "stdout");
+  createstdfile(L, stderr, NULL, "stderr");
+  return 1;
+}
+
diff --git a/lprefix.h b/lprefix.h
index 0eb149f..2a7651a 100644
--- a/lprefix.h
+++ b/lprefix.h
@@ -173,3 +173,105 @@ LUAMOD_API int luaopen_compat53_string (lua_State *L) {
 
 #endif
 
+
+#ifdef liolib_c
+/* move the io library open function out of the way (we only take
+ * the popen and type functions)!
+ */
+#  define luaopen_io luaopen_io_XXX
+
+#include <locale.h>
+#include <lualib.h>
+
+#  if !defined(lua_getlocaledecpoint)
+#    define lua_getlocaledecpoint() (localeconv()->decimal_point[0])
+#  endif
+
+#  ifndef LUA_INTEGER_FMT
+#    define LUA_INTEGER_FMT "%ld"
+#  endif
+#  ifndef LUAI_UACINT
+#    define LUAI_UACINT lua_Integer
+#  endif
+
+/* choose which popen implementation to pick */
+#  if (defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 200112L) || \
+      (defined(_XOPEN_SOURCE) && _XOPEN_SOURCE >= 600) || \
+      defined(__APPLE__)
+#    define LUA_USE_POSIX 1
+#  elif (defined(_MSC_VER)
+#    define LUA_USE_WINDOWS 0
+#  endif
+
+typedef struct COMPAT53_luaL_Stream {
+  FILE *f;  /* stream (NULL for incompletely created streams) */
+  lua_CFunction closef;  /* to close stream (NULL for closed streams) */
+} COMPAT53_luaL_Stream;
+
+#define luaL_Stream COMPAT53_luaL_Stream
+
+#define COMPAT53_LUA_PFILEHANDLE "PFILE*"
+
+static int io_ptype (lua_State *L) {
+  luaL_Stream *p;
+  luaL_checkany(L, 1);
+  p = (luaL_Stream *)luaL_testudata(L, 1, COMPAT53_LUA_PFILEHANDLE);
+  if (p) {
+    /* Lua 5.3 implementation, for popen files */
+    if (p->closef == NULL)
+      lua_pushliteral(L, "closed file");
+    else
+      lua_pushliteral(L, "file");
+    return 1;
+  } else {
+    /* Lua 5.1 implementation, for plain files */
+    void *ud = lua_touserdata(L, 1);
+    lua_getfield(L, LUA_REGISTRYINDEX, LUA_FILEHANDLE);
+    if (ud == NULL || !lua_getmetatable(L, 1) || !lua_rawequal(L, -2, -1))
+      lua_pushnil(L);  /* not a file */
+    else if (*((FILE **)ud) == NULL)
+      lua_pushliteral(L, "closed file");
+    else
+      lua_pushliteral(L, "file");
+    return 1;
+  }
+}
+
+static int io_popen (lua_State *L);
+static void createmeta (lua_State *L);
+
+#  undef LUA_FILEHANDLE
+#  define LUA_FILEHANDLE COMPAT53_LUA_PFILEHANDLE
+
+/* for PUC-Rio Lua 5.1 only */
+#  if defined(LUA_VERSION_NUM) && LUA_VERSION_NUM == 501 && !defined(LUA_JITLIBNAME)
+
+LUAMOD_API int luaopen_compat53_io (lua_State *L) {
+  luaL_Reg const funcs[] = {
+    { "popen", io_popen },
+    { "type", io_ptype },
+    { NULL, NULL }
+  };
+  luaL_newlib(L, funcs);
+  createmeta(L);
+  return 1;
+}
+
+#  endif /* for PUC-Rio Lua 5.1 only */
+
+/* fake CLANG feature detection on other compilers */
+#  ifndef __has_attribute
+#    define __has_attribute(x) 0
+#  endif
+/* make luaopen_io(_XXX) static, so it (and all other referenced
+ * io functions) won't be included in the resulting dll
+ * (hopefully).
+ */
+#  undef LUAMOD_API
+#  if defined(__GNUC__) || __has_attribute(__unused__)
+#    define LUAMOD_API __attribute__((__unused__)) static
+#  else
+#    define LUAMOD_API static
+#  endif
+
+#endif /* iolib.c */
diff --git a/rockspecs/compat53-scm-0.rockspec b/rockspecs/compat53-scm-0.rockspec
index db9f4e7..e0820d4 100644
--- a/rockspecs/compat53-scm-0.rockspec
+++ b/rockspecs/compat53-scm-0.rockspec
@@ -27,6 +27,7 @@ build = {
       ["compat53.utf8"] = "lutf8lib.c",
       ["compat53.table"] = "ltablib.c",
       ["compat53.string"] = "lstrlib.c",
+      ["compat53.io"] = "liolib.c",
    }
 }
 
diff --git a/tests/test.lua b/tests/test.lua
index 0640cae..443f6f7 100755
--- a/tests/test.lua
+++ b/tests/test.lua
@@ -625,11 +625,13 @@ do
    end))
    if mode ~= "module" then
      local f = assert(io.open(self, "r"))
+     print("io.type()", io.type(f))
      for a,b in f:lines(2, "*l") do
         print("file:lines()", a, b)
         break
      end
      f:close()
+     print("io.type()", io.type(f))
      f = assert(io.open("data.txt", "r"))
      for n1,n2,rest in f:lines("*n", "n", "*a") do
         print("file:lines()", n1, n2, rest)
@@ -650,6 +652,18 @@ do
      end))
    end
    os.remove("data.txt")
+   print("io.popen()", pcall(function()
+      local f = assert(io.popen("echo 'hello' && exit 0", "r"))
+      print("io.popen()", f:read("*a"))
+      print("io.popen()", f:close())
+   end))
+   print("io.popen()", pcall(function()
+      local f = assert(io.popen("echo 'hello' && exit 5", "r"))
+      print("io.type()", io.type(f))
+      print("io.popen()", f:read("*a"))
+      print("io.popen()", f:close())
+      print("io.type()", io.type(f))
+   end))
 end
 ___''