Direct port of the struct module that provides access to

packed structures in strings. Very useful for network protocol
packing/unpacking. The docs are directly converted from the original.

Review feedback

Fix typo

app/include/user_modules.h

@@ -38,6 +38,7 @@
 #define LUA_USE_MODULES_RTCTIME
 #define LUA_USE_MODULES_SNTP
 #define LUA_USE_MODULES_SPI
+//#define LUA_USE_MODULES_STRUCT
 #define LUA_USE_MODULES_TMR
 #define LUA_USE_MODULES_TSL2561
 #define LUA_USE_MODULES_U8G

app/modules/struct.c

@@ -0,0 +1,425 @@
+/*
+** {======================================================
+** Library for packing/unpacking structures.
+** $Id: struct.c,v 1.4 2012/07/04 18:54:29 roberto Exp $
+** See Copyright Notice at the end of this file
+** =======================================================
+*/
+// Original: http://www.inf.puc-rio.br/~roberto/struct/
+// This was ported to NodeMCU by Philip Gladstone, N1DQ
+/*
+** Valid formats:
+** > - big endian
+** < - little endian
+** ![num] - alignment
+** x - pading
+** b/B - signed/unsigned byte
+** h/H - signed/unsigned short
+** l/L - signed/unsigned long
+** T   - size_t
+** i/In - signed/unsigned integer with size `n' (default is size of int)
+** cn - sequence of `n' chars (from/to a string); when packing, n==0 means
+        the whole string; when unpacking, n==0 means use the previous
+        read number as the string length
+** s - zero-terminated string
+** f - float
+** d - double
+** ' ' - ignored
+*/
+
+
+#include <assert.h>
+#include <ctype.h>
+#include <limits.h>
+#include <stddef.h>
+#include <string.h>
+#include "module.h"
+
+
+#include "lua.h"
+#include "lauxlib.h"
+
+
+/* basic integer type */
+#if !defined(STRUCT_INT)
+#define STRUCT_INT	long
+#endif
+
+typedef STRUCT_INT Inttype;
+
+/* corresponding unsigned version */
+typedef unsigned STRUCT_INT Uinttype;
+
+
+/* maximum size (in bytes) for integral types */
+#ifdef LUA_NUMBER_INTEGRAL
+#ifdef LUA_INTEGRAL_LONGLONG
+#define MAXINTSIZE	8
+#else
+#define MAXINTSIZE	4
+#endif
+#else
+#define MAXINTSIZE	32
+#endif
+
+/* is 'x' a power of 2? */
+#define isp2(x)		((x) > 0 && ((x) & ((x) - 1)) == 0)
+
+/* dummy structure to get alignment requirements */
+struct cD {
+  char c;
+  double d;
+};
+
+
+#define PADDING		(sizeof(struct cD) - sizeof(double))
+#define MAXALIGN  	(PADDING > sizeof(int) ? PADDING : sizeof(int))
+
+
+/* endian options */
+#define BIG	0
+#define LITTLE	1
+
+
+static union {
+  int dummy;
+  char endian;
+} const native = {1};
+
+
+typedef struct Header {
+  int endian;
+  int align;
+} Header;
+
+
+static int getnum (const char **fmt, int df) {
+  if (!isdigit(**fmt))  /* no number? */
+    return df;  /* return default value */
+  else {
+    int a = 0;
+    do {
+      a = a*10 + *((*fmt)++) - '0';
+    } while (isdigit(**fmt));
+    return a;
+  }
+}
+
+
+#define defaultoptions(h)	((h)->endian = native.endian, (h)->align = 1)
+
+
+
+static size_t optsize (lua_State *L, char opt, const char **fmt) {
+  switch (opt) {
+    case 'B': case 'b': return sizeof(char);
+    case 'H': case 'h': return sizeof(short);
+    case 'L': case 'l': return sizeof(long);
+    case 'T': return sizeof(size_t);
+#ifndef LUA_NUMBER_INTEGRAL
+    case 'f':  return sizeof(float);
+    case 'd':  return sizeof(double);
+#endif
+    case 'x': return 1;
+    case 'c': return getnum(fmt, 1);
+    case 'i': case 'I': {
+      int sz = getnum(fmt, sizeof(int));
+      if (sz > MAXINTSIZE)
+        luaL_error(L, "integral size %d is larger than limit of %d",
+                       sz, MAXINTSIZE);
+      return sz;
+    }
+    default: return 0;  /* other cases do not need alignment */
+  }
+}
+
+
+/*
+** return number of bytes needed to align an element of size 'size'
+** at current position 'len'
+*/
+static int gettoalign (size_t len, Header *h, int opt, size_t size) {
+  if (size == 0 || opt == 'c') return 0;
+  if (size > (size_t)h->align)
+    size = h->align;  /* respect max. alignment */
+  return (size - (len & (size - 1))) & (size - 1);
+}
+
+
+/*
+** options to control endianess and alignment
+*/
+static void controloptions (lua_State *L, int opt, const char **fmt,
+                            Header *h) {
+  switch (opt) {
+    case  ' ': return;  /* ignore white spaces */
+    case '>': h->endian = BIG; return;
+    case '<': h->endian = LITTLE; return;
+    case '!': {
+      int a = getnum(fmt, MAXALIGN);
+      if (!isp2(a))
+        luaL_error(L, "alignment %d is not a power of 2", a);
+      h->align = a;
+      return;
+    }
+    default: {
+      const char *msg = lua_pushfstring(L, "invalid format option '%c'", opt);
+      luaL_argerror(L, 1, msg);
+    }
+  }
+}
+
+
+static void putinteger (lua_State *L, luaL_Buffer *b, int arg, int endian,
+                        int size) {
+  lua_Number n = luaL_checknumber(L, arg);
+  Uinttype value;
+  char buff[MAXINTSIZE];
+  if (n < 0)
+    value = (Uinttype)(Inttype)n;
+  else
+    value = (Uinttype)n;
+  if (endian == LITTLE) {
+    int i;
+    for (i = 0; i < size; i++) {
+      buff[i] = (value & 0xff);
+      value >>= 8;
+    }
+  }
+  else {
+    int i;
+    for (i = size - 1; i >= 0; i--) {
+      buff[i] = (value & 0xff);
+      value >>= 8;
+    }
+  }
+  luaL_addlstring(b, buff, size);
+}
+
+
+static void correctbytes (char *b, int size, int endian) {
+  if (endian != native.endian) {
+    int i = 0;
+    while (i < --size) {
+      char temp = b[i];
+      b[i++] = b[size];
+      b[size] = temp;
+    }
+  }
+}
+
+
+static int b_pack (lua_State *L) {
+  luaL_Buffer b;
+  const char *fmt = luaL_checkstring(L, 1);
+  Header h;
+  int arg = 2;
+  size_t totalsize = 0;
+  defaultoptions(&h);
+  lua_pushnil(L);  /* mark to separate arguments from string buffer */
+  luaL_buffinit(L, &b);
+  while (*fmt != '\0') {
+    int opt = *fmt++;
+    size_t size = optsize(L, opt, &fmt);
+    int toalign = gettoalign(totalsize, &h, opt, size);
+    totalsize += toalign;
+    while (toalign-- > 0) luaL_addchar(&b, '\0');
+    switch (opt) {
+      case 'b': case 'B': case 'h': case 'H':
+      case 'l': case 'L': case 'T': case 'i': case 'I': {  /* integer types */
+        putinteger(L, &b, arg++, h.endian, size);
+        break;
+      }
+      case 'x': {
+        luaL_addchar(&b, '\0');
+        break;
+      }
+#ifndef LUA_NUMBER_INTEGRAL
+      case 'f': {
+        float f = (float)luaL_checknumber(L, arg++);
+        correctbytes((char *)&f, size, h.endian);
+        luaL_addlstring(&b, (char *)&f, size);
+        break;
+      }
+      case 'd': {
+        double d = luaL_checknumber(L, arg++);
+        correctbytes((char *)&d, size, h.endian);
+        luaL_addlstring(&b, (char *)&d, size);
+        break;
+      }
+#endif
+      case 'c': case 's': {
+        size_t l;
+        const char *s = luaL_checklstring(L, arg++, &l);
+        if (size == 0) size = l;
+        luaL_argcheck(L, l >= (size_t)size, arg, "string too short");
+        luaL_addlstring(&b, s, size);
+        if (opt == 's') {
+          luaL_addchar(&b, '\0');  /* add zero at the end */
+          size++;
+        }
+        break;
+      }
+      default: controloptions(L, opt, &fmt, &h);
+    }
+    totalsize += size;
+  }
+  luaL_pushresult(&b);
+  return 1;
+}
+
+
+static lua_Number getinteger (const char *buff, int endian,
+                        int issigned, int size) {
+  Uinttype l = 0;
+  int i;
+  if (endian == BIG) {
+    for (i = 0; i < size; i++) {
+      l <<= 8;
+      l |= (Uinttype)(unsigned char)buff[i];
+    }
+  }
+  else {
+    for (i = size - 1; i >= 0; i--) {
+      l <<= 8;
+      l |= (Uinttype)(unsigned char)buff[i];
+    }
+  }
+  if (!issigned)
+    return (lua_Number)l;
+  else {  /* signed format */
+    Uinttype mask = (Uinttype)(~((Uinttype)0)) << (size*8 - 1);
+    if (l & mask)  /* negative value? */
+      l |= mask;  /* signal extension */
+    return (lua_Number)(Inttype)l;
+  }
+}
+
+
+static int b_unpack (lua_State *L) {
+  Header h;
+  const char *fmt = luaL_checkstring(L, 1);
+  size_t ld;
+  const char *data = luaL_checklstring(L, 2, &ld);
+  size_t pos = luaL_optinteger(L, 3, 1) - 1;
+  defaultoptions(&h);
+  lua_settop(L, 2);
+  while (*fmt) {
+    int opt = *fmt++;
+    size_t size = optsize(L, opt, &fmt);
+    pos += gettoalign(pos, &h, opt, size);
+    luaL_argcheck(L, pos+size <= ld, 2, "data string too short");
+    luaL_checkstack(L, 1, "too many results");
+    switch (opt) {
+      case 'b': case 'B': case 'h': case 'H':
+      case 'l': case 'L': case 'T': case 'i':  case 'I': {  /* integer types */
+        int issigned = islower(opt);
+        lua_Number res = getinteger(data+pos, h.endian, issigned, size);
+        lua_pushnumber(L, res);
+        break;
+      }
+      case 'x': {
+        break;
+      }
+#ifndef LUA_NUMBER_INTEGRAL
+      case 'f': {
+        float f;
+        memcpy(&f, data+pos, size);
+        correctbytes((char *)&f, sizeof(f), h.endian);
+        lua_pushnumber(L, f);
+        break;
+      }
+      case 'd': {
+        double d;
+        memcpy(&d, data+pos, size);
+        correctbytes((char *)&d, sizeof(d), h.endian);
+        lua_pushnumber(L, d);
+        break;
+      }
+#endif
+      case 'c': {
+        if (size == 0) {
+          if (!lua_isnumber(L, -1))
+            luaL_error(L, "format `c0' needs a previous size");
+          size = lua_tonumber(L, -1);
+          lua_pop(L, 1);
+          luaL_argcheck(L, pos+size <= ld, 2, "data string too short");
+        }
+        lua_pushlstring(L, data+pos, size);
+        break;
+      }
+      case 's': {
+        const char *e = (const char *)memchr(data+pos, '\0', ld - pos);
+        if (e == NULL)
+          luaL_error(L, "unfinished string in data");
+        size = (e - (data+pos)) + 1;
+        lua_pushlstring(L, data+pos, size - 1);
+        break;
+      }
+      default: controloptions(L, opt, &fmt, &h);
+    }
+    pos += size;
+  }
+  lua_pushinteger(L, pos + 1);
+  return lua_gettop(L) - 2;
+}
+
+
+static int b_size (lua_State *L) {
+  Header h;
+  const char *fmt = luaL_checkstring(L, 1);
+  size_t pos = 0;
+  defaultoptions(&h);
+  while (*fmt) {
+    int opt = *fmt++;
+    size_t size = optsize(L, opt, &fmt);
+    pos += gettoalign(pos, &h, opt, size);
+    if (opt == 's')
+      luaL_argerror(L, 1, "option 's' has no fixed size");
+    else if (opt == 'c' && size == 0)
+      luaL_argerror(L, 1, "option 'c0' has no fixed size");
+    if (!isalnum(opt))
+      controloptions(L, opt, &fmt, &h);
+    pos += size;
+  }
+  lua_pushinteger(L, pos);
+  return 1;
+}
+
+/* }====================================================== */
+
+
+
+static const LUA_REG_TYPE thislib[] = {
+  {LSTRKEY("pack"), LFUNCVAL(b_pack)},
+  {LSTRKEY("unpack"), LFUNCVAL(b_unpack)},
+  {LSTRKEY("size"), LFUNCVAL(b_size)},
+  {LNILKEY, LNILVAL}
+};
+
+
+NODEMCU_MODULE(STRUCT, "struct", thislib, NULL);
+
+/******************************************************************************
+* Copyright (C) 2010-2012 Lua.org, PUC-Rio.  All rights reserved.
+*
+* Permission is hereby granted, free of charge, to any person obtaining
+* a copy of this software and associated documentation files (the
+* "Software"), to deal in the Software without restriction, including
+* without limitation the rights to use, copy, modify, merge, publish,
+* distribute, sublicense, and/or sell copies of the Software, and to
+* permit persons to whom the Software is furnished to do so, subject to
+* the following conditions:
+*
+* The above copyright notice and this permission notice shall be
+* included in all copies or substantial portions of the Software.
+*
+* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+******************************************************************************/
+

docs/en/modules/struct.md

@@ -0,0 +1,172 @@
+# struct module
+
+This module offers basic facilities to convert Lua values to and from C
+structs. Its main functions are `struct.pack`, which packs multiple Lua
+values into a struct-like string; and `struct.unpack`, which unpacks
+multiple Lua values from a given struct-like string.
+
+The first argument to both functions is a *format string*, which
+describes the layout of the structure. The format string is a sequence
+of conversion elements, which respect the current endianess and the
+current alignment requirements. Initially, the current endianess is the
+machine's native endianness and the current alignment requirement is 1
+(meaning no alignment at all). You can change these settings with
+appropriate directives in the format string.
+
+Note that the float and double conversions are only available with
+a floating point NodeMCU build.
+
+### Format String
+
+The elements in the format string are as follows:
+
+-   `" "` (empty space) ignored.
+-   `"!n"` flag to set the current alignment requirement to *n*
+    (necessarily a power of 2); an absent *n* means the machine's native
+    alignment.
+-   `">"` flag to set mode to big endian.
+-   `"<"` flag to set mode to little endian.
+-   `"x"` a padding zero byte with no corresponding Lua value.
+-   `"b"` a signed `char`.
+-   `"B"` an unsigned `char`.
+-   `"h"` a signed `short` (native size).
+-   `"H"` an unsigned `short` (native size).
+-   `"l"` a signed `long` (native size).
+-   `"L"` an unsigned `long` (native size).
+-   `"T"` a `size_t` (native size).
+-   `"in"` a signed integer with *n* bytes. An absent *n* means the
+    native size of an `int`.
+-   `"In"` like `"in"` but unsigned.
+-   `"f"` a `float` (native size).
+-   `"d"` a `double` (native size).
+-   `"s"` a zero-terminated string.
+-   `"cn"` a sequence of exactly *n* chars corresponding to a single Lua
+    string. An absent *n* means 1. When packing, the given string must
+    have at least *n* characters (extra characters are discarded).
+-   `"c0"` this is like `"cn"`, except that the *n* is given by other
+    means: When packing, *n* is the length of the given string; when
+    unpacking, *n* is the value of the previous unpacked value (which
+    must be a number). In that case, this previous value is not
+    returned.
+
+#### Examples
+
+To pack and unpack the structure
+
+        struct Str {
+          char b;
+          int i[4];
+        };
+
+you can use the string `"<!4biiii"`.
+
+To pack a string with its length coded in its first byte, use the
+following code:
+
+        x = struct.pack("Bc0", string.len(s), s)
+
+To unpack that string, do as follows:
+
+        s = struct.unpack("Bc0", x)
+
+Note that the length (read by the element `"B"`) is not returned.
+
+To pack a string in a fixed-width field of 10 characters padded with
+blanks, do as follows:
+
+        x = struct.pack("c10", s .. string.rep(" ", 10))
+
+
+## struct.pack()
+
+Returns a string containing the values `d1`, `d2`, etc. packed
+according to the format string `fmt`.
+
+#### Syntax
+
+`struct.pack (fmt, d1, d2, ...)`
+
+#### Parameters
+
+- `fmt` The format string in the format above
+- `d1` The first data item to be packed
+- `d2` The second data item to be packed etc.
+
+#### Returns
+
+The packed string.
+
+#### Example
+
+```
+s = struct.pack("I", 0x41424344)
+print(s)
+```
+
+## struct.unpack()
+
+Returns the values packed in string `s` according to the format
+string `fmt`. An optional `i` marks where in `s` to start reading
+(default is 1). After the read values, this function also returns
+the index in `s` where it stopped reading, which is also where you
+should start to read the rest of the string.
+
+#### Syntax
+
+`struct.unpack (fmt, s[, offset])`
+
+#### Parameters
+
+- `fmt` The format string in the format above
+- `s` The string holding the data to be unpacked
+- `offset` The position to start in the string (default is 1)
+
+#### Returns
+
+All the unpacked data.
+
+#### Example
+
+Suppose we have to decode a string `s` with an unknown number of
+doubles; the end is marked by a zero value. We can use the following
+code:
+
+        local a = {}
+        local i = 1         -- index where to read
+        while true do
+          local d
+          d, i = struct.unpack("d", s, i)
+          if d == 0 then break end
+          a[#a + 1] = d
+        end
+
+## struct.size()
+
+Returns the size of a string formatted according to the format
+string `fmt`. The format string should contain neither the option
+`s` nor the option `c0`.
+
+#### Syntax
+
+`struct.size (fmt)`
+
+#### Parameters
+
+- `fmt` The format string in the format above
+
+#### Returns
+
+The size of the string that would be output in a pack operation with this format string.
+
+#### Example
+
+```
+print(struct.size("i"))
+```
+
+This prints the size of the native integer type.
+
+### License
+
+This package is distributed under the MIT license. See copyright notice
+at the end of file `struct.c`.

mkdocs.yml

@@ -54,6 +54,7 @@ pages:
         - 'rtcfifo': 'en/modules/rtcfifo.md'
         - 'sntp': 'en/modules/sntp.md'
         - 'spi': 'en/modules/spi.md'
+        - 'struct': 'en/modules/struct.md'
         - 'tmr': 'en/modules/tmr.md'
         - 'tsl2561': 'en/modules/tsl2561.md'
         - 'u8g': 'en/modules/u8g.md'