ei

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.

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.

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.

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().

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.

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

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.

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

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.

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.)

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.

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().

Decodes a GCC long long or Visual C++ __int64 (64-bit) integer from the binary format. This function is missing in the VxWorks port.

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.

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

Decodes a port identifier from the binary format.

Decodes a reference from the binary format.

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.

Decodes a term from the binary format. The term is return in t as a ETERM*, so t is actually an ETERM** (see erl_eterm). The term is later to be deallocated.

Decodes an Erlang trace token from the binary format.

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

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().

Decodes a GCC unsigned long long or Visual C++ unsigned __int64 (64-bit) integer from the binary format. This function is missing in the VxWorks port.

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

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.

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.

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.

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

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.

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

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.

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

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

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

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.

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);

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);

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().

Encodes a GCC long long or Visual C++ __int64 (64-bit) integer in the binary format. This function is missing in the VxWorks port.

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.

Encodes an Erlang process identifier (pid) in the binary format. Parameter p points to an erlang_pid structure (which should have been obtained earlier with ei_decode_pid()).

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

Encodes an Erlang reference in the binary format. Parameter p points to a erlang_ref structure (which should have been obtained earlier with ei_decode_ref()).

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.

Encodes an ETERM, as obtained from erl_interface. Parameter t is actually an ETERM pointer. This function does not free the ETERM.

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()).

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);

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().

Encodes a GCC unsigned long long or Visual C++ unsigned __int64 (64-bit) integer in the binary format. This function is missing in the VxWorks port.

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

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 other types, *size is 0. In all cases, index is left unchanged.

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

If the ei library is used together with the erl_interface library, this function should not be called directly. It will be called by the erl_init() function which should be used to initialize the combination of the two libraries instead.

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

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.

Types

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.

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.

Returns 0 on success, otherwise -1.

Appends data at the end of buffer x.

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.

Frees an ei_x_buff buffer. The memory used by the buffer is returned to the OS.

Allocates a new ei_x_buff buffer. 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.)