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NAME

       ei - Routines for handling the Erlang binary term format.

DESCRIPTION

       The  library  ei contains macros and functions to encode and decode the Erlang binary term
       format.

       ei allows you to convert atoms, lists, numbers,  and  binaries  to  and  from  the  binary
       format.  This is useful when writing port programs and drivers. ei uses a given buffer, no
       dynamic memory (except ei_decode_fun()) and is often quite fast.

       ei also handles C-nodes, C-programs that talks Erlang distribution with Erlang  nodes  (or
       other  C-nodes)  using  the  Erlang distribution format.The ei library is thread safe, and
       using threads, one process can handle multiple C-nodes.

       The decode and encode functions use a buffer and an index into the buffer, which points at
       the  point  where to encode and decode. The index is updated to point right after the term
       encoded/decoded. No checking is done whether the term  fits  in  the  buffer  or  not.  If
       encoding goes outside the buffer, the program can crash.

       All functions take two parameters:

         * buf is a pointer to the buffer where the binary data is or will be.

         * index is a pointer to an index into the buffer. This parameter is incremented with the
           size of the term decoded/encoded.

       The data is thus at buf[*index] when an ei function is called.

       All encode functions assume that the buf and index parameters  point  to  a  buffer  large
       enough  for  the  data. To get the size of an encoded term, without encoding it, pass NULL
       instead of a buffer pointer. Parameter index is incremented, but nothing will be  encoded.
       This is the way in ei to "preflight" term encoding.

       There  are also encode functions that use a dynamic buffer. It is often more convenient to
       use these to encode data. All encode functions comes in two versions; those starting  with
       ei_x_ use a dynamic buffer of type ei_x_buff.

       All  functions  return 0 if successful, otherwise -1 (for example, if a term is not of the
       expected type, or the data to decode is an invalid Erlang term).

       Some of the decode functions need a pre-allocated buffer. This buffer  must  be  allocated
       large  enough,  and  for  non-compound  types  the ei_get_type() function returns the size
       required (notice that for strings an extra byte is needed for the NULL-terminator).

DATA TYPES

         ei_term:

         typedef struct {
             char ei_type;
             int arity;
             int size;
             union {
              long i_val;
              double d_val;
              char atom_name[MAXATOMLEN_UTF8];
              erlang_pid pid;
              erlang_port port;
              erlang_ref ref;
             } value;
         } ei_term;

           Structure written by ei_decode_ei_term(). The ei_type field is the type  of  the  term
           which equals to what ei_get_type() sets *type to.

         ei_x_buff:
           A dynamically resized buffer. It is a struct with two fields of interest for the user:

           char *buff:
             Pointer to the dynamically allocated buffer.

           int index:
             Offset  to  the  next  byte to write which also equals the amount of bytes currently
             written.

           An ei_x_buff is initialized by calling either ei_x_new()  or  ei_x_new_with_version().
           The memory used by an initialized ei_x_buff is released by calling ei_x_free().

         erlang_char_encoding:

         typedef enum {
             ERLANG_ASCII = 1,
             ERLANG_LATIN1 = 2,
             ERLANG_UTF8 = 4
         } erlang_char_encoding;

           The  character  encodings used for atoms. ERLANG_ASCII represents 7-bit ASCII. Latin-1
           and UTF-8 are different extensions of 7-bit ASCII.  All  7-bit  ASCII  characters  are
           valid Latin-1 and UTF-8 characters. ASCII and Latin-1 both represent each character by
           one byte. An UTF-8 character can consist of 1-4 bytes. Notice that these constants are
           bit-flags and can be combined with bitwise OR.

         erlang_fun:
           Opaque data type representing an Erlang fun.

         erlang_pid:
           Opaque data type representing an Erlang process identifier.

         erlang_port:
           Opaque data type representing an Erlang port identifier.

         erlang_ref:
           Opaque data type representing an Erlang reference.

         erlang_trace:
           Opaque data type representing an Erlang sequential trace token.

EXPORTS

       int ei_cmp_pids(erlang_pid *a, erlang_pid *b)

              Types:

                 erlang_pid

              Compare  two  process  identifiers.  The  comparison is done the same way as Erlang
              does.

              Returns 0 if a and b are equal. Returns a value less than 0 if a compares  as  less
              than b. Returns a value larger than 0 if a compares as larger than b.

       int ei_cmp_ports(erlang_port *a, erlang_port *b)

              Types:

                 erlang_port

              Compare two port identifiers. The comparison is done the same way as Erlang does.

              Returns  0  if a and b are equal. Returns a value less than 0 if a compares as less
              than b. Returns a value larger than 0 if a compares as larger than b.

       int ei_cmp_refs(erlang_ref *a, erlang_ref *b)

              Types:

                 erlang_ref

              Compare two references. The comparison is done the same way as Erlang does.

              Returns 0 if a and b are equal. Returns a value less than 0 if a compares  as  less
              than b. Returns a value larger than 0 if a compares as larger than b.

       int ei_decode_atom(const char *buf, int *index, char *p)

              Decodes  an  atom  from  the binary format. The NULL-terminated name of the atom is
              placed at p. At most MAXATOMLEN bytes can be placed in the buffer.

       int ei_decode_atom_as(const char *buf, int *index, char *p, int plen, erlang_char_encoding
       want, erlang_char_encoding* was, erlang_char_encoding* result)

              Types:

                 erlang_char_encoding

              Decodes  an  atom  from  the binary format. The NULL-terminated name of the atom is
              placed in buffer at p of length plen bytes.

              The wanted string encoding is specified by want. The original encoding used in  the
              binary  format  (Latin-1  or  UTF-8) can be obtained from *was. The encoding of the
              resulting string (7-bit ASCII, Latin-1, or UTF-8) can  be  obtained  from  *result.
              Both  was and result can be NULL. *result can differ from want if want is a bitwise
              OR'd combination like ERLANG_LATIN1|ERLANG_UTF8 or if *result turns out to be  pure
              7-bit ASCII (compatible with both Latin-1 and UTF-8).

              This  function  fails  if  the  atom  is too long for the buffer or if it cannot be
              represented with encoding want.

              This function was introduced in Erlang/OTP R16 as part of a first step  to  support
              UTF-8 atoms.

       int ei_decode_bignum(const char *buf, int *index, mpz_t obj)

              Decodes  an  integer  in  the  binary  format  to  a GMP mpz_t integer. To use this
              function, the ei library must be configured and compiled to use the GMP library.

       int ei_decode_binary(const char *buf, int *index, void *p, long *len)

              Decodes a binary from the binary format. Parameter len is set to the actual size of
              the  binary.  Notice  that ei_decode_binary() assumes that there is enough room for
              the binary. The size required can be fetched by ei_get_type().

       int ei_decode_bitstring(const char  *buf,  int  *index,  const  char  **pp,  unsigned  int
       *bitoffsp, size_t *nbitsp)

              Decodes a bit string from the binary format.

                pp:
                  Either  NULL  or *pp returns a pointer to the first byte of the bit string. The
                  returned bit string is readable as long as the buffer  pointed  to  by  buf  is
                  readable and not written to.

                bitoffsp:
                  Either  NULL  or  *bitoffsp returns the number of unused bits in the first byte
                  pointed to by *pp. The value of *bitoffsp is between 0 and 7.  Unused  bits  in
                  the first byte are the most significant bits.

                nbitsp:
                  Either NULL or *nbitsp returns the length of the bit string in bits.

              Returns 0 if it was a bit string term.

              The  number  of  bytes  pointed  to  by  *pp,  which are part of the bit string, is
              (*bitoffsp + *nbitsp + 7)/8. If (*bitoffsp + *bitsp)%8 > 0 then only  (*bitoffsp  +
              *bitsp)%8  bits  of  the  last  byte are used. Unused bits in the last byte are the
              least significant bits.

              The values of unused bits in the first and last byte are undefined  and  cannot  be
              relied on.

              Number  of  bits  may  be  divisible  by  8,  which  means  a  binary  decodable by
              ei_decode_binary is also decodable by ei_decode_bitstring.

       int ei_decode_boolean(const char *buf, int *index, int *p)

              Decodes a boolean value from the binary format. A boolean is actually an atom, true
              decodes 1 and false decodes 0.

       int ei_decode_char(const char *buf, int *index, char *p)

              Decodes a char (8-bit) integer between 0-255 from the binary format. For historical
              reasons the returned integer is of type char.  Your  C  code  is  to  consider  the
              returned  value  to be of type unsigned char even if the C compilers and system can
              define char to be signed.

       int ei_decode_double(const char *buf, int *index, double *p)

              Decodes a double-precision (64-bit) floating point number from the binary format.

       int ei_decode_ei_term(const char* buf, int* index, ei_term* term)

              Types:

                 ei_term

              Decodes any term, or at least tries to. If the term pointed at  by  *index  in  buf
              fits  in the term union, it is decoded, and the appropriate field in term->value is
              set, and *index is incremented by the term size.

              The function returns 1 on successful decoding, -1 on error, and 0 if the term seems
              alright,  but  does  not  fit in the term structure. If 1 is returned, the index is
              incremented, and term contains the decoded term.

              The term structure contains the arity for a tuple  or  list,  size  for  a  binary,
              string,  or atom. It contains a term if it is any of the following: integer, float,
              atom, pid, port, or ref.

       int ei_decode_fun(const char *buf, int *index, erlang_fun *p)
       void free_fun(erlang_fun* f)

              Types:

                 erlang_fun

              Decodes a fun from the binary format. Parameter p is to be  NULL  or  point  to  an
              erlang_fun  structure. This is the only decode function that allocates memory. When
              the erlang_fun is no longer needed, it is to be freed with free_fun. (This  has  to
              do with the arbitrary size of the environment for a fun.)

       int ei_decode_iodata(const char *buf, int *index, int *size, char *outbuf)

              Decodes a term of the type iodata(). The iodata() term will be flattened an written
              into the buffer pointed to by the outbuf argument. The byte size of the  iodata  is
              written  into  the  integer variable pointed to by the size argument. Both size and
              outbuf can be set to NULL. The integer pointed to by the index argument is  updated
              to  refer to the term following after the iodata() term regardless of the the state
              of the size and the outbuf arguments.

              Note that the buffer pointed to by the outbuf argument must be large  enough  if  a
              non  NULL  value is passed as outbuf. You typically want to call ei_decode_iodata()
              twice. First with a non NULL size argument and a NULL outbuf argument in  order  to
              determine  the  size  of  the buffer needed, and then once again in order to do the
              actual decoding. Note that the integer pointed to by index will be updated  by  the
              call  determining  the size as well, so you need to reset it before the second call
              doing the actual decoding.

              Returns 0 on success and -1 on failure. Failure might  be  either  due  to  invalid
              encoding of the term or due to the term not being of the type iodata(). On failure,
              the integer pointed to by the index argument will be updated to refer  to  the  sub
              term where the failure was detected.

       int ei_decode_list_header(const char *buf, int *index, int *arity)

              Decodes a list header from the binary format. The number of elements is returned in
              arity. The arity+1 elements follow (the last one is the tail of the list,  normally
              an empty list). If arity is 0, it is an empty list.

              Notice  that  lists  are encoded as strings if they consist entirely of integers in
              the range 0..255. This function do not decode such strings, use  ei_decode_string()
              instead.

       int ei_decode_long(const char *buf, int *index, long *p)

              Decodes a long integer from the binary format. If the code is 64 bits, the function
              ei_decode_long() is the same as ei_decode_longlong().

       int ei_decode_longlong(const char *buf, int *index, long long *p)

              Decodes a GCC long long or Visual C++ __int64  (64-bit)  integer  from  the  binary
              format.

       int ei_decode_map_header(const char *buf, int *index, int *arity)

              Decodes  a  map  header  from  the  binary format. The number of key-value pairs is
              returned in *arity. Keys and values follow in this order: K1, V1, K2, V2, ...,  Kn,
              Vn.  This  makes  a total of arity*2 terms. If arity is zero, it is an empty map. A
              correctly encoded map does not have duplicate keys.

       int ei_decode_pid(const char *buf, int *index, erlang_pid *p)

              Types:

                 erlang_pid

              Decodes a process identifier (pid) from the binary format.

       int ei_decode_port(const char *buf, int *index, erlang_port *p)

              Types:

                 erlang_port

              Decodes a port identifier from the binary format.

       int ei_decode_ref(const char *buf, int *index, erlang_ref *p)

              Types:

                 erlang_ref

              Decodes a reference from the binary format.

       int ei_decode_string(const char *buf, int *index, char *p)

              Decodes a string from the binary format. A string in Erlang is a list  of  integers
              between  0  and  255. Notice that as the string is just a list, sometimes lists are
              encoded as strings by term_to_binary/1, even if it was not intended.

              The string is copied to p, and enough space must be allocated. The returned  string
              is NULL-terminated, so you must add an extra byte to the memory requirement.

       int ei_decode_trace(const char *buf, int *index, erlang_trace *p)

              Types:

                 erlang_trace

              Decodes an Erlang trace token from the binary format.

       int ei_decode_tuple_header(const char *buf, int *index, int *arity)

              Decodes  a  tuple  header,  the  number of elements is returned in arity. The tuple
              elements follow in order in the buffer.

       int ei_decode_ulong(const char *buf, int *index, unsigned long *p)

              Decodes an unsigned long integer from the binary format. If the code  is  64  bits,
              the function ei_decode_ulong() is the same as ei_decode_ulonglong().

       int ei_decode_ulonglong(const char *buf, int *index, unsigned long long *p)

              Decodes  a  GCC  unsigned long long or Visual C++ unsigned __int64 (64-bit) integer
              from the binary format.

       int ei_decode_version(const char *buf, int *index, int *version)

              Decodes the version magic number for the Erlang binary term format. It must be  the
              first token in a binary term.

       int ei_encode_atom(char *buf, int *index, const char *p)
       int ei_encode_atom_len(char *buf, int *index, const char *p, int len)
       int ei_x_encode_atom(ei_x_buff* x, const char *p)
       int ei_x_encode_atom_len(ei_x_buff* x, const char *p, int len)

              Types:

                 ei_x_buff

              Encodes  an  atom  in  the  binary  format.  Parameter p is the name of the atom in
              Latin-1 encoding. Only up to MAXATOMLEN-1 bytes are encoded.  The  name  is  to  be
              NULL-terminated, except for the ei_x_encode_atom_len() function.

       int ei_encode_atom_as(char *buf, int *index, const char *p, erlang_char_encoding from_enc,
       erlang_char_encoding to_enc)
       int   ei_encode_atom_len_as(char   *buf,   int   *index,   const   char   *p,   int   len,
       erlang_char_encoding from_enc, erlang_char_encoding to_enc)
       int  ei_x_encode_atom_as(ei_x_buff*  x,  const  char  *p,  erlang_char_encoding  from_enc,
       erlang_char_encoding to_enc)
       int ei_x_encode_atom_len_as(ei_x_buff* x, const char  *p,  int  len,  erlang_char_encoding
       from_enc, erlang_char_encoding to_enc)

              Types:

                 ei_x_buff
                 erlang_char_encoding

              Encodes  an  atom  in  the  binary format. Parameter p is the name of the atom with
              character encoding from_enc (ASCII, Latin-1, or UTF-8). The  name  must  either  be
              NULL-terminated or a function variant with a len parameter must be used.

              The encoding fails if p is not a valid string in encoding from_enc.

              Argument  to_enc  is  ignored. As from Erlang/OTP 20 the encoding is always done in
              UTF-8 which is readable by nodes as old as Erlang/OTP R16.

       int ei_encode_bignum(char *buf, int *index, mpz_t obj)
       int ei_x_encode_bignum(ei_x_buff *x, mpz_t obj)

              Types:

                 ei_x_buff

              Encodes a GMP mpz_t integer to binary format. To use this function, the ei  library
              must be configured and compiled to use the GMP library.

       int ei_encode_binary(char *buf, int *index, const void *p, long len)
       int ei_x_encode_binary(ei_x_buff* x, const void *p, long len)

              Types:

                 ei_x_buff

              Encodes a binary in the binary format. The data is at p, of len bytes length.

       int  ei_encode_bitstring(char  *buf,  int  *index,  const  char *p, size_t bitoffs, size_t
       nbits)
       int ei_x_encode_bitstring(ei_x_buff* x, const char *p, size_t bitoffs, size_t nbits)

              Types:

                 ei_x_buff

              Encodes a bit string in the binary format.

              The data is at p. The length of the bit string is nbits  bits.  The  first  bitoffs
              bits of the data at p are unused. The first byte which is part of the bit string is
              p[bitoffs/8]. The bitoffs%8 most significant bits of the  first  byte  p[bitoffs/8]
              are unused.

              The  number of bytes which is part of the bit string is (bitoffs + nbits + 7)/8. If
              (bitoffs + nbits)%8 > 0 then only (bitoffs + nbits)%8 bits of  the  last  byte  are
              used. Unused bits in the last byte are the least significant bits.

              The values of unused bits are disregarded and does not need to be cleared.

       int ei_encode_boolean(char *buf, int *index, int p)
       int ei_x_encode_boolean(ei_x_buff* x, int p)

              Types:

                 ei_x_buff

              Encodes a boolean value as the atom true if p is not zero, or false if p is zero.

       int ei_encode_char(char *buf, int *index, char p)
       int ei_x_encode_char(ei_x_buff* x, char p)

              Types:

                 ei_x_buff

              Encodes  a  char  (8-bit)  as  an  integer  between 0-255 in the binary format. For
              historical reasons the integer argument is of type char. Your C code is to consider
              the  specified  argument  to  be  of type unsigned char even if the C compilers and
              system may define char to be signed.

       int ei_encode_double(char *buf, int *index, double p)
       int ei_x_encode_double(ei_x_buff* x, double p)

              Types:

                 ei_x_buff

              Encodes a double-precision (64-bit) floating point number in the binary format.

              Returns -1 if the floating point number is not finite.

       int ei_encode_empty_list(char* buf, int* index)
       int ei_x_encode_empty_list(ei_x_buff* x)

              Types:

                 ei_x_buff

              Encodes an empty list. It is often used at the tail of a list.

       int ei_encode_fun(char *buf, int *index, const erlang_fun *p)
       int ei_x_encode_fun(ei_x_buff* x, const erlang_fun* fun)

              Types:

                 ei_x_buff
                 erlang_fun

              Encodes a fun in the binary format. Parameter p points to an erlang_fun  structure.
              The  erlang_fun is not freed automatically, the free_fun is to be called if the fun
              is not needed after encoding.

       int ei_encode_list_header(char *buf, int *index, int arity)
       int ei_x_encode_list_header(ei_x_buff* x, int arity)

              Types:

                 ei_x_buff

              Encodes a list header, with a specified arity.  The  next  arity+1  terms  are  the
              elements (actually its arity cons cells) and the tail of the list. Lists and tuples
              are encoded recursively, so that a list can contain another list or tuple.

              For example, to encode the list [c, d, [e | f]]:

              ei_encode_list_header(buf, &i, 3);
              ei_encode_atom(buf, &i, "c");
              ei_encode_atom(buf, &i, "d");
              ei_encode_list_header(buf, &i, 1);
              ei_encode_atom(buf, &i, "e");
              ei_encode_atom(buf, &i, "f");
              ei_encode_empty_list(buf, &i);

          Note:
              It may seem that there is no way to create a list without  knowing  the  number  of
              elements  in advance. But indeed there is a way. Notice that the list [a, b, c] can
              be written as [a | [b | [c]]]. Using this, a list can be written as conses.

              To encode a list, without knowing the arity in advance:

              while (something()) {
                  ei_x_encode_list_header(&x, 1);
                  ei_x_encode_ulong(&x, i); /* just an example */
              }
              ei_x_encode_empty_list(&x);

       int ei_encode_long(char *buf, int *index, long p)
       int ei_x_encode_long(ei_x_buff* x, long p)

              Types:

                 ei_x_buff

              Encodes a long integer in the binary format. If the code is 64 bits,  the  function
              ei_encode_long() is the same as ei_encode_longlong().

       int ei_encode_longlong(char *buf, int *index, long long p)
       int ei_x_encode_longlong(ei_x_buff* x, long long p)

              Types:

                 ei_x_buff

              Encodes  a  GCC  long  long  or  Visual  C++ __int64 (64-bit) integer in the binary
              format.

       int ei_encode_map_header(char *buf, int *index, int arity)
       int ei_x_encode_map_header(ei_x_buff* x, int arity)

              Types:

                 ei_x_buff

              Encodes a map header, with a specified arity. The next arity*2 terms  encoded  will
              be  the  keys and values of the map encoded in the following order: K1, V1, K2, V2,
              ..., Kn, Vn.

              For example, to encode the map #{a => "Apple", b => "Banana"}:

              ei_x_encode_map_header(&x, 2);
              ei_x_encode_atom(&x, "a");
              ei_x_encode_string(&x, "Apple");
              ei_x_encode_atom(&x, "b");
              ei_x_encode_string(&x, "Banana");

              A correctly encoded map cannot have duplicate keys.

       int ei_encode_pid(char *buf, int *index, const erlang_pid *p)
       int ei_x_encode_pid(ei_x_buff* x, const erlang_pid *p)

              Types:

                 ei_x_buff
                 erlang_pid

              Encodes an Erlang process identifier (pid) in the binary format. Parameter p points
              to  an  erlang_pid  structure  which  should either have been obtained earlier with
              ei_decode_pid(), ei_self() or created by ei_make_pid().

       int ei_encode_port(char *buf, int *index, const erlang_port *p)
       int ei_x_encode_port(ei_x_buff* x, const erlang_port *p)

              Types:

                 ei_x_buff
                 erlang_port

              Encodes an Erlang port in the binary format. Parameter p points to  an  erlang_port
              structure which should have been obtained earlier with ei_decode_port(),

       int ei_encode_ref(char *buf, int *index, const erlang_ref *p)
       int ei_x_encode_ref(ei_x_buff* x, const erlang_ref *p)

              Types:

                 ei_x_buff
                 erlang_ref

              Encodes  an  Erlang  reference  in  the  binary  format.  Parameter  p points to an
              erlang_ref  structure  which  either  should  have  been  obtained   earlier   with
              ei_decode_ref(), or created by ei_make_ref().

       int ei_encode_string(char *buf, int *index, const char *p)
       int ei_encode_string_len(char *buf, int *index, const char *p, int len)
       int ei_x_encode_string(ei_x_buff* x, const char *p)
       int ei_x_encode_string_len(ei_x_buff* x, const char* s, int len)

              Types:

                 ei_x_buff

              Encodes  a  string  in  the  binary  format.  (A string in Erlang is a list, but is
              encoded as a character array in the binary format.)  The  string  is  to  be  NULL-
              terminated, except for the ei_x_encode_string_len() function.

       int ei_encode_trace(char *buf, int *index, const erlang_trace *p)
       int ei_x_encode_trace(ei_x_buff* x, const erlang_trace *p)

              Types:

                 ei_x_buff
                 erlang_trace

              Encodes  an  Erlang  trace  token  in  the  binary  format. Parameter p points to a
              erlang_trace   structure   which   should   have   been   obtained   earlier   with
              ei_decode_trace().

       int ei_encode_tuple_header(char *buf, int *index, int arity)
       int ei_x_encode_tuple_header(ei_x_buff* x, int arity)

              Types:

                 ei_x_buff

              Encodes  a  tuple header, with a specified arity. The next arity terms encoded will
              be the elements of the tuple. Tuples and lists are encoded recursively, so  that  a
              tuple can contain another tuple or list.

              For example, to encode the tuple {a, {b, {}}}:

              ei_encode_tuple_header(buf, &i, 2);
              ei_encode_atom(buf, &i, "a");
              ei_encode_tuple_header(buf, &i, 2);
              ei_encode_atom(buf, &i, "b");
              ei_encode_tuple_header(buf, &i, 0);

       int ei_encode_ulong(char *buf, int *index, unsigned long p)
       int ei_x_encode_ulong(ei_x_buff* x, unsigned long p)

              Types:

                 ei_x_buff

              Encodes  an unsigned long integer in the binary format. If the code is 64 bits, the
              function ei_encode_ulong() is the same as ei_encode_ulonglong().

       int ei_encode_ulonglong(char *buf, int *index, unsigned long long p)
       int ei_x_encode_ulonglong(ei_x_buff* x, unsigned long long p)

              Types:

                 ei_x_buff

              Encodes a GCC unsigned long long or Visual C++ unsigned __int64 (64-bit) integer in
              the binary format.

       int ei_encode_version(char *buf, int *index)
       int ei_x_encode_version(ei_x_buff* x)

              Types:

                 ei_x_buff

              Encodes  a version magic number for the binary format. Must be the first token in a
              binary term.

       int ei_get_type(const char *buf, const int *index, int *type, int *size)

              Returns the type in *type and size in *size of the encoded term.  For  strings  and
              atoms,  size  is  the  number of characters not including the terminating NULL. For
              binaries and bitstrings, *size is the number of bytes. For lists, tuples and  maps,
              *size is the arity of the object. For bignum integers, *size is the number of bytes
              for the absolute value of the bignum. For other types, *size is 0.  In  all  cases,
              index is left unchanged.

              Currently *type is one of:

                ERL_ATOM_EXT:
                  Decode     using     either     ei_decode_atom(),    ei_decode_atom_as(),    or
                  ei_decode_boolean().

                ERL_BINARY_EXT:
                  Decode   using    either    ei_decode_binary(),    ei_decode_bitstring(),    or
                  ei_decode_iodata().

                ERL_BIT_BINARY_EXT:
                  Decode using ei_decode_bitstring().

                ERL_FLOAT_EXT:
                  Decode using ei_decode_double().

                ERL_NEW_FUN_EXT
                  ERL_FUN_EXT
                  ERL_EXPORT_EXT: Decode using ei_decode_fun().

                ERL_SMALL_INTEGER_EXT
                  ERL_INTEGER_EXT
                  ERL_SMALL_BIG_EXT
                  ERL_LARGE_BIG_EXT:  Decode  using  either  ei_decode_char(),  ei_decode_long(),
                  ei_decode_longlong(),     ei_decode_ulong(),     ei_decode_ulonglong(),      or
                  ei_decode_bignum().

                ERL_LIST_EXT
                  ERL_NIL_EXT:     Decode     using     either     ei_decode_list_header(),    or
                  ei_decode_iodata().

                ERL_STRING_EXT:
                  Decode using either ei_decode_string(), or ei_decode_iodata().

                ERL_MAP_EXT:
                  Decode using ei_decode_map_header().

                ERL_PID_EXT:
                  Decode using ei_decode_pid().

                ERL_PORT_EXT:
                  Decode using ei_decode_port().

                ERL_NEW_REFERENCE_EXT:
                  Decode using ei_decode_ref().

                ERL_SMALL_TUPLE_EXT
                  ERL_LARGE_TUPLE_EXT: Decode using ei_decode_tuple_header().

              Instead of decoding a term you can also skipped past it if you are  not  interested
              in the data by usage of ei_skip_term().

       int ei_init(void)

              Initialize  the  ei  library.  This  function should be called once (and only once)
              before calling any other functionality in the ei library.

              On success zero is returned. On failure a posix error code is returned.

       int ei_print_term(FILE* fp, const char* buf, int* index)
       int ei_s_print_term(char** s, const char* buf, int* index)

              Prints a term, in clear text, to the file specified by fp, or the buffer pointed to
              by s. It tries to resemble the term printing in the Erlang shell.

              In  ei_s_print_term(),  parameter s is to point to a dynamically (malloc) allocated
              string of BUFSIZ bytes or a NULL pointer. The string can be reallocated (and *s can
              be  updated)  by  this  function  if the result is more than BUFSIZ characters. The
              string returned is NULL-terminated.

              The return value is the number of characters written to the file or string,  or  -1
              if buf[index] does not contain a valid term. Unfortunately, I/O errors on fp is not
              checked.

              Argument index is updated, that is,  this  function  can  be  viewed  as  a  decode
              function that decodes a term into a human-readable format.

       void ei_set_compat_rel(unsigned release_number)

              In  general,  the  ei  library is guaranteed to be compatible with other Erlang/OTP
              components that are 2 major releases older or newer than the ei library itself.

              Sometimes an exception to the above rule has to be made to make  new  features  (or
              even  bug  fixes) possible. A call to ei_set_compat_rel(release_number) sets the ei
              library in compatibility mode of OTP release release_number.

              The only useful value for release_number is currently 21. This will only be  useful
              and  have  an  effect  if  bit strings or export funs are received from a connected
              node. Before OTP 22, bit strings and export funs were not  supported  by  ei.  They
              were instead encoded using an undocumented fallback tuple format when sent from the
              emulator to ei:

                Bit string:
                  The term <<42, 1:1>> was encoded as {<<42, 128>>, 1}. The first element of  the
                  tuple  is  a  binary  and  the second element denotes how many bits of the last
                  bytes are part of the bit string. In this example only the most significant bit
                  of the last byte (128) is part of the bit string.

                Export fun:
                  The  term  fun lists:map/2 was encoded as {lists,map}. A tuple with the module,
                  function and a missing arity.

              If ei_set_compat_rel(21) is not called then a  connected  emulator  will  send  bit
              strings  and  export  funs correctly encoded. The functions ei_decode_bitstring and
              ei_decode_fun has to be used to decode such  terms.  Calling  ei_set_compat_rel(21)
              should  only  be  done  as  a workaround to keep an old implementation alive, which
              expects to receive the undocumented tuple formats for  bit  strings  and/or  export
              funs.

          Note:
              If  this  function  is called, it can only be called once and must be called before
              any other functions in the ei library are called.

       int ei_skip_term(const char* buf, int* index)

              Skips a term in the specified buffer;  recursively  skips  elements  of  lists  and
              tuples,  so that a full term is skipped. This is a way to get the size of an Erlang
              term.

              buf is the buffer.

              index is updated to point right after the term in the buffer.

          Note:
              This can be useful when you want to hold arbitrary terms: skip them  and  copy  the
              binary term data to some buffer.

              Returns 0 on success, otherwise -1.

       int ei_x_append(ei_x_buff* x, const ei_x_buff* x2)
       int ei_x_append_buf(ei_x_buff* x, const char* buf, int len)

              Types:

                 ei_x_buff

              Appends data at the end of buffer x.

       int ei_x_format(ei_x_buff* x, const char* fmt, ...)
       int ei_x_format_wo_ver(ei_x_buff* x, const char *fmt, ... )

              Types:

                 ei_x_buff
                 erlang_pid

              Formats  a  term,  given  as a string, to a buffer. Works like a sprintf for Erlang
              terms. fmt contains a format string, with arguments like ~d, to insert  terms  from
              variables. The following formats are supported (with the C types given):

              ~a  An atom, char*
              ~c  A character, char
              ~s  A string, char*
              ~i  An integer, int
              ~l  A long integer, long int
              ~u  A unsigned long integer, unsigned long int
              ~f  A float, float
              ~d  A double float, double float
              ~p  An Erlang pid, erlang_pid*

              For example, to encode a tuple with some stuff:

              ei_x_format("{~a,~i,~d}", "numbers", 12, 3.14159)
              encodes the tuple {numbers,12,3.14159}

              ei_x_format_wo_ver() formats into a buffer, without the initial version byte.

       int ei_x_free(ei_x_buff* x)

              Types:

                 ei_x_buff

              Deallocates  the  dynamically  allocated content of the buffer referred by x. After
              deallocation, the buff field is set to NULL.

       int ei_x_new(ei_x_buff* x)
       int ei_x_new_with_version(ei_x_buff* x)

              Types:

                 ei_x_buff

              Initialize the dynamically realizable buffer referred to by x. The  fields  of  the
              structure  pointed  to  by  parameter  x  is  filled  in,  and  a default buffer is
              allocated. ei_x_new_with_version() also puts an initial version byte, which is used
              in the binary format (so that ei_x_encode_version() will not be needed.)

DEBUG INFORMATION

       Some  tips  on what to check when the emulator does not seem to receive the terms that you
       send:

         * Be careful with the version header, use ei_x_new_with_version() when appropriate.

         * Turn on distribution tracing on the Erlang node.

         * Check the result codes from ei_decode_-calls.