<?xml version="1.0" encoding="latin1" ?> <!DOCTYPE cref SYSTEM "cref.dtd"> <cref> <header> <copyright> <year>2001</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> The contents of this file are subject to the Erlang Public License, Version 1.1, (the "License"); you may not use this file except in compliance with the License. You should have received a copy of the Erlang Public License along with this software. If not, it can be retrieved online at http://www.erlang.org/. Software distributed under the License is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for the specific language governing rights and limitations under the License. </legalnotice> <title>ei</title> <prepared>Jakob Cederlund</prepared> <responsible>Kent Boortz</responsible> <docno>1</docno> <approved>Kenneth Lundin</approved> <checked></checked> <date>2000-11-27</date> <rev>PA1</rev> <file>ei.sgml</file> </header> <lib>ei</lib> <libsummary>routines for handling the erlang binary term format</libsummary> <description> <p>The library <c><![CDATA[ei]]></c> contains macros and functions to encode and decode the erlang binary term format.</p> <p>With <c><![CDATA[ei]]></c>, you can convert atoms, lists, numbers and binaries to and from the binary format. This is useful when writing port programs and drivers. <c><![CDATA[ei]]></c> uses a given buffer, and no dynamic memory (with the exception of <c><![CDATA[ei_decode_fun()]]></c>), and is often quite fast.</p> <p>It also handles C-nodes, C-programs that talks erlang distribution with erlang nodes (or other C-nodes) using the erlang distribution format. The difference between <c><![CDATA[ei]]></c> and <c><![CDATA[erl_interface]]></c> is that <c><![CDATA[ei]]></c> uses the binary format directly when sending and receiving terms. It is also thread safe, and using threads, one process can handle multiple C-nodes. The <c><![CDATA[erl_interface]]></c> library is built on top of <c><![CDATA[ei]]></c>, but of legacy reasons, it doesn't allow for multiple C-nodes. In general, <c><![CDATA[ei]]></c> is the preferred way of doing C-nodes.</p> <p>The decode and encode functions use a buffer 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 may crash.</p> <p>All functions takes two parameter, <c><![CDATA[buf]]></c> is a pointer to the buffer where the binary data is / will be, <c><![CDATA[index]]></c> is a pointer to an index into the buffer. This parameter will be incremented with the size of the term decoded / encoded. The data is thus at <c><![CDATA[buf[*index]]]></c> when an <c><![CDATA[ei]]></c> function is called.</p> <p>The encode functions all assumes that the <c><![CDATA[buf]]></c> and <c><![CDATA[index]]></c> parameters points to a buffer big enough for the data. To get the size of an encoded term, without encoding it, pass <c><![CDATA[NULL]]></c> instead of a buffer pointer. The <c><![CDATA[index]]></c> parameter will be incremented, but nothing will be encoded. This is the way in <c><![CDATA[ei]]></c> to "preflight" term encoding.</p> <p>There are also encode-functions that uses a dynamic buffer. It is often more convenient to use these to encode data. All encode functions comes in two versions: those starting with <c><![CDATA[ei_x]]></c>, uses a dynamic buffer.</p> <p>All functions return <c><![CDATA[0]]></c> if successful, and <c><![CDATA[-1]]></c> if not. (For instance, if a term is not of the expected type, or the data to decode is not a valid erlang term.)</p> <p>Some of the decode-functions needs a preallocated buffer. This buffer must be allocated big enough, and for non compound types the <c><![CDATA[ei_get_type()]]></c> function returns the size required (note that for strings an extra byte is needed for the 0 string terminator).</p> </description> <section> <title>DATA TYPES</title> <taglist> <tag><marker id="erlang_char_encoding"/>erlang_char_encoding</tag> <item> <p/> <code type="none"> typedef enum { ERLANG_ASCII = 1, ERLANG_LATIN1 = 2, ERLANG_UTF8 = 4 }erlang_char_encoding; </code> <p>The character encodings used for atoms. <c>ERLANG_ASCII</c> represents 7-bit ASCII. Latin1 and UTF8 are different extensions of 7-bit ASCII. All 7-bit ASCII characters are valid Latin1 and UTF8 characters. ASCII and Latin1 both represent each character by one byte. A UTF8 character can consist of one to four bytes. Note that these constants are bit-flags and can be combined with bitwise-or.</p> </item> </taglist> </section> <funcs> <func> <name><ret>void</ret><nametext>ei_set_compat_rel(release_number)</nametext></name> <fsummary>Set the ei library in compatibility mode</fsummary> <type> <v>unsigned release_number;</v> </type> <desc> <marker id="ei_set_compat_rel"></marker> <p>By default, the <c><![CDATA[ei]]></c> library is only guaranteed to be compatible with other Erlang/OTP components from the same release as the <c><![CDATA[ei]]></c> library itself. For example, <c><![CDATA[ei]]></c> from the OTP R10 release is not compatible with an Erlang emulator from the OTP R9 release by default.</p> <p>A call to <c><![CDATA[ei_set_compat_rel(release_number)]]></c> sets the <c><![CDATA[ei]]></c> library in compatibility mode of release <c><![CDATA[release_number]]></c>. Valid range of <c><![CDATA[release_number]]></c> is [7, current release]. This makes it possible to communicate with Erlang/OTP components from earlier releases.</p> <note> <p>If this function is called, it may only be called once and must be called before any other functions in the <c><![CDATA[ei]]></c> library is called.</p> </note> <warning> <p>You may run into trouble if this feature is used carelessly. Always make sure that all communicating components are either from the same Erlang/OTP release, or from release X and release Y where all components from release Y are in compatibility mode of release X.</p> </warning> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_version(char *buf, int *index)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_version(ei_x_buff* x)</nametext></name> <fsummary>Encode version</fsummary> <desc> <p>Encodes a version magic number for the binary format. Must be the first token in a binary term.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_long(char *buf, int *index, long p)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_long(ei_x_buff* x, long p)</nametext></name> <fsummary>Encode integer</fsummary> <desc> <p>Encodes a long integer in the binary format. Note that if the code is 64 bits the function ei_encode_long() is exactly the same as ei_encode_longlong().</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_ulong(char *buf, int *index, unsigned long p)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_ulong(ei_x_buff* x, unsigned long p)</nametext></name> <fsummary>Encode unsigned integer</fsummary> <desc> <p>Encodes an unsigned long integer in the binary format. Note that if the code is 64 bits the function ei_encode_ulong() is exactly the same as ei_encode_ulonglong().</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_longlong(char *buf, int *index, long long p)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_longlong(ei_x_buff* x, long long p)</nametext></name> <fsummary>Encode integer</fsummary> <desc> <p>Encodes a GCC <c><![CDATA[long long]]></c> or Visual C++ <c><![CDATA[__int64]]></c> (64 bit) integer in the binary format. Note that this function is missing in the VxWorks port.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_ulonglong(char *buf, int *index, unsigned long long p)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_ulonglong(ei_x_buff* x, unsigned long long p)</nametext></name> <fsummary>Encode unsigned integer</fsummary> <desc> <p>Encodes a GCC <c><![CDATA[unsigned long long]]></c> or Visual C++ <c><![CDATA[unsigned __int64]]></c> (64 bit) integer in the binary format. Note that this function is missing in the VxWorks port.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_bignum(char *buf, int *index, mpz_t obj)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_bignum(ei_x_buff *x, mpz_t obj)</nametext></name> <fsummary>Encode an arbitrary precision integer</fsummary> <desc> <p>Encodes a GMP <c><![CDATA[mpz_t]]></c> integer to binary format. To use this function the ei library needs to be configured and compiled to use the GMP library. </p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_double(char *buf, int *index, double p)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_double(ei_x_buff* x, double p)</nametext></name> <fsummary>Encode a double float</fsummary> <desc> <p>Encodes a double-precision (64 bit) floating point number in the binary format.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_boolean(char *buf, int *index, int p)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_boolean(ei_x_buff* x, int p)</nametext></name> <fsummary>Encode a boolean</fsummary> <desc> <p>Encodes a boolean value, as the atom <c><![CDATA[true]]></c> if p is not zero or <c><![CDATA[false]]></c> if p is zero.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_char(char *buf, int *index, char p)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_char(ei_x_buff* x, char p)</nametext></name> <fsummary>Encode an 8-bit integer between 0-255</fsummary> <desc> <p>Encodes a char (8-bit) as an integer between 0-255 in the binary format. Note that for historical reasons the integer argument is of type <c><![CDATA[char]]></c>. Your C code should consider the given argument to be of type <c><![CDATA[unsigned char]]></c> even if the C compilers and system may define <c><![CDATA[char]]></c> to be signed.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_string(char *buf, int *index, const char *p)</nametext></name> <name><ret>int</ret><nametext>ei_encode_string_len(char *buf, int *index, const char *p, int len)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_string(ei_x_buff* x, const char *p)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_string_len(ei_x_buff* x, const char* s, int len)</nametext></name> <fsummary>Encode a string</fsummary> <desc> <p>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 should be zero-terminated, except for the <c><![CDATA[ei_x_encode_string_len()]]></c> function.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_atom(char *buf, int *index, const char *p)</nametext></name> <name><ret>int</ret><nametext>ei_encode_atom_len(char *buf, int *index, const char *p, int len)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_atom(ei_x_buff* x, const char *p)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_atom_len(ei_x_buff* x, const char *p, int len)</nametext></name> <fsummary>Encode an atom</fsummary> <desc> <p>Encodes an atom in the binary format. The <c><![CDATA[p]]></c> parameter is the name of the atom in latin1 encoding. Only upto <c>MAXATOMLEN-1</c> bytes are encoded. The name should be zero-terminated, except for the <c><![CDATA[ei_x_encode_atom_len()]]></c> function.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_atom_as(char *buf, int *index, const char *p, erlang_char_encoding from_enc, erlang_char_encoding to_enc)</nametext></name> <name><ret>int</ret><nametext>ei_encode_atom_len_as(char *buf, int *index, const char *p, int len, erlang_char_encoding from_enc, erlang_char_encoding to_enc)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_atom_as(ei_x_buff* x, const char *p, erlang_char_encoding from_enc, erlang_char_encoding to_enc)</nametext></name> <name><ret>int</ret><nametext>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)</nametext></name> <fsummary>Encode an atom</fsummary> <desc> <p>Encodes an atom in the binary format with character encoding <c><seealso marker="#erlang_char_encoding">to_enc</seealso></c> (latin1 or utf8). The <c>p</c> parameter is the name of the atom with character encoding <c><seealso marker="#erlang_char_encoding">from_enc</seealso></c> (ascii, latin1 or utf8). The name must either be zero-terminated or a function variant with a <c>len</c> parameter must be used. If <c>to_enc</c> is set to the bitwise-or'd combination <c>(ERLANG_LATIN1|ERLANG_UTF8)</c>, utf8 encoding is only used if the atom string can not be represented in latin1 encoding.</p> <p>The encoding will fail if <c>p</c> is not a valid string in encoding <c>from_enc</c>, if the string is too long or if it can not be represented with character encoding <c>to_enc</c>.</p> <p>These functions were introduced in R16 release of Erlang/OTP as part of a first step to support UTF8 atoms. Atoms encoded with <c>ERLANG_UTF8</c> can not be decoded by earlier releases than R16.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_binary(char *buf, int *index, const void *p, long len)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_binary(ei_x_buff* x, const void *p, long len)</nametext></name> <fsummary>Encode a binary</fsummary> <desc> <p>Encodes a binary in the binary format. The data is at <c><![CDATA[p]]></c>, of <c><![CDATA[len]]></c> bytes length.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_pid(char *buf, int *index, const erlang_pid *p)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_pid(ei_x_buff* x, const erlang_pid *p)</nametext></name> <fsummary>Encode a pid</fsummary> <desc> <p>Encodes an erlang process identifier, pid, in the binary format. The <c><![CDATA[p]]></c> parameter points to an <c><![CDATA[erlang_pid]]></c> structure (which should have been obtained earlier with <c><![CDATA[ei_decode_pid()]]></c>).</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_fun(char *buf, int *index, const erlang_fun *p)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_fun(ei_x_buff* x, const erlang_fun* fun)</nametext></name> <fsummary>Encode a fun</fsummary> <desc> <p>Encodes a fun in the binary format. The <c><![CDATA[p]]></c> parameter points to an <c><![CDATA[erlang_fun]]></c> structure. The <c><![CDATA[erlang_fun]]></c> is not freed automatically, the <c><![CDATA[free_fun]]></c> should be called if the fun is not needed after encoding.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_port(char *buf, int *index, const erlang_port *p)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_port(ei_x_buff* x, const erlang_port *p)</nametext></name> <fsummary>Encodes a port</fsummary> <desc> <p>Encodes an erlang port in the binary format. The <c><![CDATA[p]]></c> parameter points to a <c><![CDATA[erlang_port]]></c> structure (which should have been obtained earlier with <c><![CDATA[ei_decode_port()]]></c>.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_ref(char *buf, int *index, const erlang_ref *p)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_ref(ei_x_buff* x, const erlang_ref *p)</nametext></name> <fsummary>Encodes a ref</fsummary> <desc> <p>Encodes an erlang reference in the binary format. The <c><![CDATA[p]]></c> parameter points to a <c><![CDATA[erlang_ref]]></c> structure (which should have been obtained earlier with <c><![CDATA[ei_decode_ref()]]></c>.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_term(char *buf, int *index, void *t)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_term(ei_x_buff* x, void *t)</nametext></name> <fsummary>Encode an <c><![CDATA[erl_interface]]></c>term</fsummary> <desc> <p>This function encodes an <c><![CDATA[ETERM]]></c>, as obtained from <c><![CDATA[erl_interface]]></c>. The <c><![CDATA[t]]></c> parameter is actually an <c><![CDATA[ETERM]]></c> pointer. This function doesn't free the <c><![CDATA[ETERM]]></c>.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_trace(char *buf, int *index, const erlang_trace *p)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_trace(ei_x_buff* x, const erlang_trace *p)</nametext></name> <fsummary>Encode a trace token</fsummary> <desc> <p>This function encodes an erlang trace token in the binary format. The <c><![CDATA[p]]></c> parameter points to a <c><![CDATA[erlang_trace]]></c> structure (which should have been obtained earlier with <c><![CDATA[ei_decode_trace()]]></c>.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_tuple_header(char *buf, int *index, int arity)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_tuple_header(ei_x_buff* x, int arity)</nametext></name> <fsummary>Encode a tuple</fsummary> <desc> <p>This function encodes a tuple header, with a specified arity. The next <c><![CDATA[arity]]></c> terms encoded will be the elements of the tuple. Tuples and lists are encoded recursively, so that a tuple may contain another tuple or list.</p> <p>E.g. to encode the tuple <c><![CDATA[{a, {b, {}}}]]></c>:</p> <pre> 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); </pre> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_list_header(char *buf, int *index, int arity)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_list_header(ei_x_buff* x, int arity)</nametext></name> <fsummary>Encode a list</fsummary> <desc> <p>This function encodes a list header, with a specified arity. The next <c><![CDATA[arity+1]]></c> terms are the elements (actually its <c><![CDATA[arity]]></c> cons cells) and the tail of the list. Lists and tuples are encoded recursively, so that a list may contain another list or tuple.</p> <p>E.g. to encode the list <c><![CDATA[[c, d, [e | f]]]]></c>:</p> <pre> 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); </pre> <note> <p>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. Note that the list <c><![CDATA[[a, b, c]]]></c> can be written as <c><![CDATA[[a | [b | [c]]]]]></c>. Using this, a list can be written as conses.</p> </note> <p>To encode a list, without knowing the arity in advance:</p> <pre> while (something()) { ei_x_encode_list_header(&x, 1); ei_x_encode_ulong(&x, i); /* just an example */ } ei_x_encode_empty_list(&x); </pre> </desc> </func> <func> <name><ret>int</ret><nametext>ei_encode_empty_list(char* buf, int* index)</nametext></name> <name><ret>int</ret><nametext>ei_x_encode_empty_list(ei_x_buff* x)</nametext></name> <fsummary>Encode an empty list (<c><![CDATA[nil]]></c>)</fsummary> <desc> <p>This function encodes an empty list. It's often used at the tail of a list.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_get_type(const char *buf, const int *index, int *type, int *size)</nametext></name> <fsummary>Fetch the type and size of an encoded term</fsummary> <desc> <p>This function returns the type in <c><![CDATA[type]]></c> and size in <c><![CDATA[size]]></c> of the encoded term. For strings and atoms, size is the number of characters <em>not</em> including the terminating 0. For binaries, <c><![CDATA[size]]></c> is the number of bytes. For lists and tuples, <c><![CDATA[size]]></c> is the arity of the object. For other types, <c><![CDATA[size]]></c> is 0. In all cases, <c><![CDATA[index]]></c> is left unchanged.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_version(const char *buf, int *index, int *version)</nametext></name> <fsummary>Encode an empty list (<c><![CDATA[nil]]></c>)</fsummary> <desc> <p>This function decodes the version magic number for the erlang binary term format. It must be the first token in a binary term.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_long(const char *buf, int *index, long *p)</nametext></name> <fsummary>Decode integer</fsummary> <desc> <p>This function decodes a long integer from the binary format. Note that if the code is 64 bits the function ei_decode_long() is exactly the same as ei_decode_longlong().</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_ulong(const char *buf, int *index, unsigned long *p)</nametext></name> <fsummary>Decode unsigned integer</fsummary> <desc> <p>This function decodes an unsigned long integer from the binary format. Note that if the code is 64 bits the function ei_decode_ulong() is exactly the same as ei_decode_ulonglong().</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_longlong(const char *buf, int *index, long long *p)</nametext></name> <fsummary>Decode integer</fsummary> <desc> <p>This function decodes a GCC <c><![CDATA[long long]]></c> or Visual C++ <c><![CDATA[__int64]]></c> (64 bit) integer from the binary format. Note that this function is missing in the VxWorks port.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_ulonglong(const char *buf, int *index, unsigned long long *p)</nametext></name> <fsummary>Decode unsigned integer</fsummary> <desc> <p>This function decodes a GCC <c><![CDATA[unsigned long long]]></c> or Visual C++ <c><![CDATA[unsigned __int64]]></c> (64 bit) integer from the binary format. Note that this function is missing in the VxWorks port.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_bignum(const char *buf, int *index, mpz_t obj)</nametext></name> <fsummary>Decode a GMP arbitrary precision integer</fsummary> <desc> <p>This function decodes an integer in the binary format to a GMP <c><![CDATA[mpz_t]]></c> integer. To use this function the ei library needs to be configured and compiled to use the GMP library. </p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_double(const char *buf, int *index, double *p)</nametext></name> <fsummary>Decode a double</fsummary> <desc> <p>This function decodes an double-precision (64 bit) floating point number from the binary format.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_boolean(const char *buf, int *index, int *p)</nametext></name> <fsummary>Decode a boolean</fsummary> <desc> <p>This function decodes a boolean value from the binary format. A boolean is actually an atom, <c><![CDATA[true]]></c> decodes 1 and <c><![CDATA[false]]></c> decodes 0.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_char(const char *buf, int *index, char *p)</nametext></name> <fsummary>Decode an 8-bit integer between 0-255</fsummary> <desc> <p>This function decodes a char (8-bit) integer between 0-255 from the binary format. Note that for historical reasons the returned integer is of type <c><![CDATA[char]]></c>. Your C code should consider the returned value to be of type <c><![CDATA[unsigned char]]></c> even if the C compilers and system may define <c><![CDATA[char]]></c> to be signed.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_string(const char *buf, int *index, char *p)</nametext></name> <fsummary>Decode a string</fsummary> <desc> <p>This function decodes a string from the binary format. A string in erlang is a list of integers between 0 and 255. Note that since the string is just a list, sometimes lists are encoded as strings by <c><![CDATA[term_to_binary/1]]></c>, even if it was not intended.</p> <p>The string is copied to <c><![CDATA[p]]></c>, and enough space must be allocated. The returned string is null terminated so you need to add an extra byte to the memory requirement.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_atom(const char *buf, int *index, char *p)</nametext></name> <fsummary>Decode an atom</fsummary> <desc> <p>This function decodes an atom from the binary format. The null terminated name of the atom is placed at <c><![CDATA[p]]></c>. There can be at most <c><![CDATA[MAXATOMLEN]]></c> bytes placed in the buffer.</p> </desc> </func> <func> <name><ret>int</ret><nametext>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)</nametext></name> <fsummary>Decode an atom</fsummary> <desc> <p>This function decodes an atom from the binary format. The null terminated name of the atom is placed in buffer at <c>p</c> of length <c>plen</c> bytes.</p> <p>The wanted string encoding is specified by <c><seealso marker="#erlang_char_encoding"> want</seealso></c>. The original encoding used in the binary format (latin1 or utf8) can be obtained from <c>*was</c>. The actual encoding of the resulting string (7-bit ascii, latin1 or utf8) can be obtained from <c>*result</c>. Both <c>was</c> and <c>result</c> can be <c>NULL</c>. <c>*result</c> may differ from <c>want</c> if <c>want</c> is a bitwise-or'd combination like <c>ERLANG_LATIN1|ERLANG_UTF8</c> or if <c>*result</c> turn out to be pure 7-bit ascii (compatible with both latin1 and utf8).</p> <p>This function fails if the atom is too long for the buffer or if it can not be represented with encoding <c>want</c>.</p> <p>This function was introduced in R16 release of Erlang/OTP as part of a first step to support UTF8 atoms.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_binary(const char *buf, int *index, void *p, long *len)</nametext></name> <fsummary>Decode a binary</fsummary> <desc> <p>This function decodes a binary from the binary format. The <c><![CDATA[len]]></c> parameter is set to the actual size of the binary. Note that <c><![CDATA[ei_decode_binary()]]></c> assumes that there are enough room for the binary. The size required can be fetched by <c><![CDATA[ei_get_type()]]></c>.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_fun(const char *buf, int *index, erlang_fun *p)</nametext></name> <name><ret>void</ret><nametext>free_fun(erlang_fun* f)</nametext></name> <fsummary>Decode a fun</fsummary> <desc> <p>This function decodes a fun from the binary format. The <c><![CDATA[p]]></c> parameter should be NULL or point to an <c><![CDATA[erlang_fun]]></c> structure. This is the only decode function that allocates memory; when the <c><![CDATA[erlang_fun]]></c> is no longer needed, it should be freed with <c><![CDATA[free_fun]]></c>. (This has to do with the arbitrary size of the environment for a fun.)</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_pid(const char *buf, int *index, erlang_pid *p)</nametext></name> <fsummary>Decode a <c><![CDATA[pid]]></c></fsummary> <desc> <p>Decodes a pid, process identifier, from the binary format.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_port(const char *buf, int *index, erlang_port *p)</nametext></name> <fsummary>Decode a port</fsummary> <desc> <p>This function decodes a port identifier from the binary format.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_ref(const char *buf, int *index, erlang_ref *p)</nametext></name> <fsummary>Decode a reference</fsummary> <desc> <p>This function decodes a reference from the binary format.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_trace(const char *buf, int *index, erlang_trace *p)</nametext></name> <fsummary>Decode a trace token</fsummary> <desc> <p>Decodes an erlang trace token from the binary format.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_tuple_header(const char *buf, int *index, int *arity)</nametext></name> <fsummary>Decode a tuple</fsummary> <desc> <p>This function decodes a tuple header, the number of elements is returned in <c><![CDATA[arity]]></c>. The tuple elements follows in order in the buffer.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_list_header(const char *buf, int *index, int *arity)</nametext></name> <fsummary>Decode a list</fsummary> <desc> <p>This function decodes a list header from the binary format. The number of elements is returned in <c><![CDATA[arity]]></c>. The <c><![CDATA[arity+1]]></c> elements follows (the last one is the tail of the list, normally an empty list.) If <c><![CDATA[arity]]></c> is <c><![CDATA[0]]></c>, it's an empty list.</p> <p>Note that lists are encoded as strings, if they consist entirely of integers in the range 0..255. This function will not decode such strings, use <c><![CDATA[ei_decode_string()]]></c> instead.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_ei_term(const char* buf, int* index, ei_term* term)</nametext></name> <fsummary>Decode a term, without prior knowledge of type</fsummary> <desc> <p>This function decodes any term, or at least tries to. If the term pointed at by <c><![CDATA[*index]]></c> in <c><![CDATA[buf]]></c> fits in the <c><![CDATA[term]]></c> union, it is decoded, and the appropriate field in <c><![CDATA[term->value]]></c> is set, and <c><![CDATA[*index]]></c> is incremented by the term size.</p> <p>The function returns 1 on successful decoding, -1 on error, and 0 if the term seems alright, but does not fit in the <c><![CDATA[term]]></c> structure. If it returns 1, the <c><![CDATA[index]]></c> will be incremented, and the <c><![CDATA[term]]></c> contains the decoded term.</p> <p>The <c><![CDATA[term]]></c> structure will contain the arity for a tuple or list, size for a binary, string or atom. It will contains a term if it's any of the following: integer, float, atom, pid, port or ref.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_decode_term(const char *buf, int *index, void *t)</nametext></name> <fsummary>Decode a <c><![CDATA[ETERM]]></c></fsummary> <desc> <p>This function decodes a term from the binary format. The term is return in <c><![CDATA[t]]></c> as a <c><![CDATA[ETERM*]]></c>, so <c><![CDATA[t]]></c> is actually an <c><![CDATA[ETERM**]]></c> (see <c><![CDATA[erl_interface(3)]]></c>. The term should later be deallocated.</p> <p>Note that this function is located in the erl_interface library.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_print_term(FILE* fp, const char* buf, int* index)</nametext></name> <name><ret>int</ret><nametext>ei_s_print_term(char** s, const char* buf, int* index)</nametext></name> <fsummary>Print a term in clear text</fsummary> <desc> <p>This function prints a term, in clear text, to the file given by <c><![CDATA[fp]]></c>, or the buffer pointed to by <c><![CDATA[s]]></c>. It tries to resemble the term printing in the erlang shell.</p> <p>In <c><![CDATA[ei_s_print_term()]]></c>, the parameter <c><![CDATA[s]]></c> should point to a dynamically (malloc) allocated string of <c><![CDATA[BUFSIZ]]></c> bytes or a NULL pointer. The string may be reallocated (and <c><![CDATA[*s]]></c> may be updated) by this function if the result is more than <c><![CDATA[BUFSIZ]]></c> characters. The string returned is zero-terminated.</p> <p>The return value is the number of characters written to the file or string, or -1 if <c><![CDATA[buf[index]]]></c> doesn't contain a valid term. Unfortunately, I/O errors on <c><![CDATA[fp]]></c> is not checked.</p> <p>The argument <c><![CDATA[index]]></c> is updated, i.e. this function can be viewed as en decode function that decodes a term into a human readable format.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_x_format(ei_x_buff* x, const char* fmt, ...)</nametext></name> <name><ret>int</ret><nametext>ei_x_format_wo_ver(ei_x_buff* x, const char *fmt, ... )</nametext></name> <fsummary>Format a term from a format string and parameters.</fsummary> <desc> <p>Format a term, given as a string, to a buffer. This functions works like a sprintf for erlang terms. The <c><![CDATA[fmt]]></c> contains a format string, with arguments like <c><![CDATA[~d]]></c>, to insert terms from variables. The following formats are supported (with the C types given):</p> <p></p> <pre> ~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* </pre> <p>For instance, to encode a tuple with some stuff:</p> <pre> ei_x_format("{~a,~i,~d}", "numbers", 12, 3.14159) encodes the tuple {numbers,12,3.14159} </pre> <p>The <c><![CDATA[ei_x_format_wo_ver()]]></c> formats into a buffer, without the initial version byte.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_x_new(ei_x_buff* x)</nametext></name> <name><ret>int</ret><nametext>ei_x_new_with_version(ei_x_buff* x)</nametext></name> <fsummary>Allocate a new buffer</fsummary> <desc> <p>This function allocates a new <c><![CDATA[ei_x_buff]]></c> buffer. The fields of the structure pointed to by <c><![CDATA[x]]></c> parameter is filled in, and a default buffer is allocated. The <c><![CDATA[ei_x_new_with_version()]]></c> also puts an initial version byte, that is used in the binary format. (So that <c><![CDATA[ei_x_encode_version()]]></c> won't be needed.)</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_x_free(ei_x_buff* x)</nametext></name> <fsummary>Frees a buffer</fsummary> <desc> <p>This function frees an <c><![CDATA[ei_x_buff]]></c> buffer. The memory used by the buffer is returned to the OS.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_x_append(ei_x_buff* x, const ei_x_buff* x2)</nametext></name> <name><ret>int</ret><nametext>ei_x_append_buf(ei_x_buff* x, const char* buf, int len)</nametext></name> <fsummary>Appends a buffer at the end</fsummary> <desc> <p>These functions appends data at the end of the buffer <c><![CDATA[x]]></c>.</p> </desc> </func> <func> <name><ret>int</ret><nametext>ei_skip_term(const char* buf, int* index)</nametext></name> <fsummary>skip a term</fsummary> <desc> <p>This function skips a term in the given buffer, it 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.</p> <p><c><![CDATA[buf]]></c> is the buffer.</p> <p><c><![CDATA[index]]></c> is updated to point right after the term in the buffer.</p> <note> <p>This can be useful when you want to hold arbitrary terms: just skip them and copy the binary term data to some buffer.</p> </note> <p>The function returns <c><![CDATA[0]]></c> on success and <c><![CDATA[-1]]></c> on failure.</p> </desc> </func> </funcs> <section> <title>Debug Information</title> <p>Some tips on what to check when the emulator doesn't seem to receive the terms that you send.</p> <list type="bulleted"> <item>be careful with the version header, use <c><![CDATA[ei_x_new_with_version()]]></c> when appropriate</item> <item>turn on distribution tracing on the erlang node</item> <item>check the result codes from ei_decode_-calls</item> </list> </section> <section> <title>See Also</title> <p>erl_interface(3)</p> </section> </cref>