ei

Types

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.

Types

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.

Types

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.

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.

Types

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.

Types

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.

Types

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 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.

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.

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.

Types

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

Types

Decodes a port identifier from the binary format.

Types

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.

Types

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.

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

Types

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.

Types

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.

Types

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.

Types

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

Types

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.

Types

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

Types

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.

Types

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

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

Types

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

Types

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.

Types

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);

Types

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().

Types

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

Types

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.

Types

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().

Types

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(),

Types

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().

Types

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.

Types

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().

Types

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);

Types

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().

Types

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

Types

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 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().

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.

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.

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.

Types

Appends data at the end of buffer x.

Types

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.

Types

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

Types

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.)