diff options
Diffstat (limited to 'lib/erl_interface/doc/src/ei.xml')
| -rw-r--r-- | lib/erl_interface/doc/src/ei.xml | 138 |
1 files changed, 112 insertions, 26 deletions
diff --git a/lib/erl_interface/doc/src/ei.xml b/lib/erl_interface/doc/src/ei.xml index 179dbbd966..70af5642da 100644 --- a/lib/erl_interface/doc/src/ei.xml +++ b/lib/erl_interface/doc/src/ei.xml @@ -35,6 +35,9 @@ <lib>ei</lib> <libsummary>Routines for handling the Erlang binary term format.</libsummary> <description> + <note><p>The support for VxWorks is deprecated as of OTP 22, and + will be removed in OTP 23.</p></note> + <p>The library <c>ei</c> contains macros and functions to encode and decode the Erlang binary term format.</p> @@ -180,6 +183,43 @@ typedef enum { </func> <func> + <name since="OTP 22.0"><ret>int</ret><nametext>ei_decode_bitstring(const char *buf, int *index, const char **pp, unsigned int *bitoffsp, size_t *nbitsp)</nametext></name> + <fsummary>Decode a bitstring.</fsummary> + <desc> + <p>Decodes a bit string from the binary format.</p> + <taglist> + <tag><c>pp</c></tag> + <item><p>Either <c>NULL</c> or <c>*pp</c> 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 <c>buf</c> is + readable and not written to.</p> + </item> + <tag><c>bitoffsp</c></tag> + <item><p>Either <c>NULL</c> or <c>*bitoffsp</c> returns the + number of unused bits in the first byte pointed to by + <c>*pp</c>. The value of <c>*bitoffsp</c> is between 0 and 7. + Unused bits in the first byte are the most significant bits.</p> + </item> + <tag><c>nbitsp</c></tag> + <item><p>Either <c>NULL</c> or <c>*nbitsp</c> returns the length + of the bit string in <em>bits</em>.</p> + </item> + </taglist> + <p>Returns <c>0</c> if it was a bit string term.</p> + <p>The number of <em>bytes</em> pointed to by <c>*pp</c>, which are + part of the bit string, is <c>(*bitoffsp + *nbitsp + 7)/8</c>. If + <c>(*bitoffsp + *bitsp)%8 > 0</c> then only <c>(*bitoffsp + + *bitsp)%8</c> bits of the last byte are used. Unused bits in + the last byte are the least significant bits.</p> + <p>The values of unused bits in the first and last byte are undefined + and cannot be relied on.</p> + <p>Number of bits may be divisible by 8, which means a binary + decodable by <c>ei_decode_binary</c> is also decodable by + <c>ei_decode_bitstring</c>.</p> + </desc> + </func> + + <func> <name since=""><ret>int</ret><nametext>ei_decode_boolean(const char *buf, int *index, int *p)</nametext></name> <fsummary>Decode a boolean.</fsummary> <desc> @@ -346,8 +386,10 @@ typedef enum { <c>t</c> is actually an <c>ETERM**</c> (see <seealso marker="erl_eterm"><c>erl_eterm</c></seealso>). The term is later to be deallocated.</p> - <p>Notice that this function is located in the <c>Erl_Interface</c> - library.</p> + <note><p>This function is deprecated as of OTP 22 and will be removed in + OTP 23 together with the old legacy <c>erl_interface</c> library (functions + with prefix <c>erl_</c>).</p> + </note> </desc> </func> @@ -456,6 +498,28 @@ typedef enum { </func> <func> + <name since="OTP 22.0"><ret>int</ret> + <nametext>ei_encode_bitstring(char *buf, int *index, const char *p, size_t bitoffs, size_t nbits)</nametext></name> + <name since="OTP 22.0"><ret>int</ret> + <nametext>ei_x_encode_bitstring(ei_x_buff* x, const char *p, size_t bitoffs, size_t nbits)</nametext></name> + <fsummary>Encode a bitstring.</fsummary> + <desc> + <p>Encodes a bit string in the binary format.</p> + <p>The data is at <c>p</c>. The length of the bit string is <c>nbits</c> + bits. The first <c>bitoffs</c> bits of the data at <c>p</c> are unused. + The first byte which is part of the bit string is + <c>p[bitoffs/8]</c>. The <c>bitoffs%8</c> most significant bits of + the first byte <c>p[bitoffs/8]</c> are unused.</p> + <p>The number of bytes which is part of the bit string is <c>(bitoffs + + nbits + 7)/8</c>. If <c>(bitoffs + nbits)%8 > 0</c> then only <c>(bitoffs + + nbits)%8</c> bits of the last byte are used. Unused bits in + the last byte are the least significant bits.</p> + <p>The values of unused bits are disregarded and does not need to be + cleared.</p> + </desc> + </func> + + <func> <name since=""><ret>int</ret><nametext>ei_encode_boolean(char *buf, int *index, int p)</nametext></name> <name since=""><ret>int</ret><nametext>ei_x_encode_boolean(ei_x_buff* x, int p)</nametext></name> <fsummary>Encode a boolean.</fsummary> @@ -653,6 +717,10 @@ ei_x_encode_string(&x, "Banana");</pre> <c>erl_interface</c>. Parameter <c>t</c> is actually an <c>ETERM</c> pointer. This function does not free the <c>ETERM</c>.</p> + <note><p>These functions are deprecated as of OTP 22 and will be removed in + OTP 23 together with the old legacy <c>erl_interface</c> library + (functions with prefix <c>erl_</c>).</p> + </note> </desc> </func> <func> @@ -722,12 +790,12 @@ ei_encode_tuple_header(buf, &i, 0);</pre> <name since=""><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>Returns the type in <c>type</c> and size in - <c>size</c> of the encoded term. For strings and atoms, + <p>Returns the type in <c>*type</c> and size in + <c>*size</c> of the encoded term. For strings and atoms, size is the number of characters <em>not</em> including the - terminating <c>NULL</c>. For binaries, <c>size</c> is the number of - bytes. For lists and tuples, <c>size</c> is the arity of - the object. For other types, <c>size</c> is 0. In all + terminating <c>NULL</c>. For binaries and bitstrings, <c>*size</c> is + the number of bytes. For lists, tuples and maps, <c>*size</c> is the + arity of the object. For other types, <c>*size</c> is 0. In all cases, <c>index</c> is left unchanged.</p> </desc> </func> @@ -781,30 +849,48 @@ ei_encode_tuple_header(buf, &i, 0);</pre> </type> <desc> <marker id="ei_set_compat_rel"></marker> - <p>By default, the <c>ei</c> library is only guaranteed - to be compatible with other Erlang/OTP components from the same - release as the <c>ei</c> library itself. For example, - <c>ei</c> from - Erlang/OTP R10 is not compatible with an Erlang emulator - from Erlang/OTP R9 by default.</p> - <p>A call to <c>ei_set_compat_rel(release_number)</c> sets - the <c>ei</c> library in compatibility mode of release - <c>release_number</c>. Valid range of - <c>release_number</c> - is <c>[7, current release]</c>. This makes it possible to - communicate with Erlang/OTP components from earlier releases.</p> + <p>In general, the <c>ei</c> library is guaranteed + to be compatible with other Erlang/OTP components that are 2 major + releases older or newer than the <c>ei</c> library itself.</p> + <p>Sometimes an exception to the above rule has to be made to make new + features (or even bug fixes) possible. A call to + <c>ei_set_compat_rel(release_number)</c> sets + the <c>ei</c> library in compatibility mode of OTP release + <c>release_number</c>.</p> + <p>The only useful value for <c>release_number</c> is currently + <c>21</c>. This will only be useful and have an effect if <em>bit + strings</em> or <em>export funs</em> are received from a connected + node. Before OTP 22, bit strings and export funs were not supported by + <c>ei</c>. They were instead encoded using an undocumented fallback + tuple format when sent from the emulator to <c>ei</c>:</p> + <taglist> + <tag><c>Bit string</c></tag> + <item><p>The term <c><<42, 1:1>></c> was encoded as + <c>{<<42, 128>>, 1}</c>. 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.</p> + </item> + <tag><c>Export fun</c></tag> + <item><p>The term <c>fun lists:map/2</c> was encoded as + <c>{lists,map}</c>. A tuple with the module, function and a missing + arity.</p> + </item> + </taglist> + <p>If <c>ei_set_compat_rel(21)</c> is <em>not</em> called then a connected + emulator will send bit strings and export funs correctly encoded. The + functions <seealso marker="#ei_decode_bitstring"><c>ei_decode_bitstring</c></seealso> + and <seealso marker="#ei_decode_fun"><c>ei_decode_fun</c></seealso> + has to be used to decode such terms. Calling + <c>ei_set_compat_rel(21)</c> 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. + </p> <note> <p>If this function is called, it can only be called once and must be called before any other functions in the <c>ei</c> library are called.</p> </note> - <warning> - <p>You can run into trouble if this feature is used - carelessly. Always ensure 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> |