1 internals.txt, 8 May 1996
2 Written by David Chappell <David.Chappell@mail.trincoll.edu>.
4 This document describes some of the internal functions which must be
5 understood by anyone wishing to add features to Samba.
9 =============================================================================
10 This section describes character set handling in Samba, as implemented in
13 In the past Samba had very ad-hoc character set handling. Scattered
14 throughout the code were numerous calls which converted particular
15 strings to/from DOS codepages. The problem is that there was no way of
16 telling if a particular char* is in dos codepage or unix
17 codepage. This led to a nightmare of code that tried to cope with
18 particular cases without handlingt the general case.
20 The new system works like this:
22 - all char* strings inside Samba are "unix" strings. These are
23 multi-byte strings that are in the charset defined by the "unix
24 charset" option in smb.conf.
26 - there is no single fixed character set for unix strings, but any
27 character set that is used does need the following properties:
28 * must not contain NULLs except for termination
29 * must be 7-bit compatible with C strings, so that a constant
30 string or character in C will be byte-for-byte identical to the
31 equivalent string in the chosen character set.
32 * when you uppercase or lowercase a string it does not become
33 longer than the original string
34 * must be able to correctly hold all characters that your client
36 For example, UTF-8 is fine, and most multi-byte asian character sets
37 are fine, but UCS2 could not be used for unix strings as they
40 - when you need to put a string into a buffer that will be sent on the
41 wire, or you need a string in a character set format that is
42 compatible with the clients character set then you need to use a
43 pull_ or push_ function. The pull_ functions pull a string from a
44 wire buffer into a (multi-byte) unix string. The push_ functions
45 push a string out to a wire buffer.
47 - the two main pull_ and push_ functions you need to understand are
48 pull_string and push_string. These functions take a base pointer
49 that should point at the start of the SMB packet that the string is
50 in. The functions will check the flags field in this packet to
51 automatically determine if the packet is marked as a unicode packet,
52 and they will choose whether to use unicode for this string based on
53 that flag. You may also force this decision using the STR_UNICODE or
54 STR_ASCII flags. For use in smbd/ and libsmb/ there are wrapper
55 functions clistr_ and srvstr_ that call the pull_/push_ functions
56 with the appropriate first argument.
58 You may also call the pull_ascii/pull_ucs2 or push_ascii/push_ucs2
59 functions if you know that a particular string is ascii or
60 unicode. There are also a number of other convenience functions in
61 charcnv.c that call the pull_/push_ functions with particularly
62 common arguments, such as pull_ascii_pstring()
64 The biggest thing to remember is that internal (unix) strings in Samba
65 may now contain multi-byte characters. This means you cannot assume
66 that characters are always 1 byte long. Often this means that you will
67 have to convert strings to ucs2 and back again in order to do some
68 (seemingly) simple task. For examples of how to do this see functions
69 like strchr_m(). I know this is very slow, and we will eventually
70 speed it up but right now we want this stuff correct not fast.
74 - all lp_ functions now return unix strings. The magic "DOS" flag on
76 - all vfs functions take unix strings. Don't convert when passing to
80 =============================================================================
81 This section describes the macros defined in byteorder.h. These macros
82 are used extensively in the Samba code.
84 -----------------------------------------------------------------------------
87 returns the byte at offset pos within buffer buf as an unsigned character.
89 -----------------------------------------------------------------------------
92 returns the value of CVAL(buf,pos) cast to type unsigned integer.
94 -----------------------------------------------------------------------------
97 sets the byte at offset pos within buffer buf to value val.
99 -----------------------------------------------------------------------------
102 returns the value of the unsigned short (16 bit) little-endian integer at
103 offset pos within buffer buf. An integer of this type is sometimes
104 refered to as "USHORT".
106 -----------------------------------------------------------------------------
109 returns the value of the unsigned 32 bit little-endian integer at offset
110 pos within buffer buf.
112 -----------------------------------------------------------------------------
115 returns the value of the signed short (16 bit) little-endian integer at
116 offset pos within buffer buf.
118 -----------------------------------------------------------------------------
121 returns the value of the signed 32 bit little-endian integer at offset pos
124 -----------------------------------------------------------------------------
127 sets the unsigned short (16 bit) little-endian integer at offset pos within
128 buffer buf to value val.
130 -----------------------------------------------------------------------------
133 sets the unsigned 32 bit little-endian integer at offset pos within buffer
134 buf to the value val.
136 -----------------------------------------------------------------------------
139 sets the short (16 bit) signed little-endian integer at offset pos within
140 buffer buf to the value val.
142 -----------------------------------------------------------------------------
145 sets the signed 32 bit little-endian integer at offset pos withing buffer
146 buf to the value val.
148 -----------------------------------------------------------------------------
151 returns the value of the unsigned short (16 bit) big-endian integer at
152 offset pos within buffer buf.
154 -----------------------------------------------------------------------------
157 returns the value of the unsigned 32 bit big-endian integer at offset
158 pos within buffer buf.
160 -----------------------------------------------------------------------------
163 sets the value of the unsigned short (16 bit) big-endian integer at
164 offset pos within buffer buf to value val.
165 refered to as "USHORT".
167 -----------------------------------------------------------------------------
170 sets the value of the unsigned 32 bit big-endian integer at offset
171 pos within buffer buf to value val.
177 =============================================================================
178 This section describes the functions need to make a LAN Manager RPC call.
179 This information had been obtained by examining the Samba code and the LAN
180 Manager 2.0 API documentation. It should not be considered entirely
183 -----------------------------------------------------------------------------
184 call_api(int prcnt, int drcnt, int mprcnt, int mdrcnt,
185 char *param, char *data, char **rparam, char **rdata);
187 This function is defined in client.c. It uses an SMB transaction to call a
190 The parameters are as follows:
192 prcnt: the number of bytes of parameters begin sent.
193 drcnt: the number of bytes of data begin sent.
194 mprcnt: the maximum number of bytes of parameters which should be returned
195 mdrcnt: the maximum number of bytes of data which should be returned
196 param: a pointer to the parameters to be sent.
197 data: a pointer to the data to be sent.
198 rparam: a pointer to a pointer which will be set to point to the returned
199 paramters. The caller of call_api() must deallocate this memory.
200 rdata: a pointer to a pointer which will be set to point to the returned
201 data. The caller of call_api() must deallocate this memory.
203 -----------------------------------------------------------------------------
204 These are the parameters which you ought to send, in the order of their
205 appearance in the parameter block:
207 * An unsigned 16 bit integer API number. You should set this value with
208 SSVAL(). I do not know where these numbers are described.
210 * An ASCIIZ string describing the parameters to the API function as defined
211 in the LAN Manager documentation. The first parameter, which is the server
212 name, is ommited. This string is based uppon the API function as described
213 in the manual, not the data which is actually passed.
215 * An ASCIIZ string describing the data structure which ought to be returned.
217 * Any parameters which appear in the function call, as defined in the LAN
218 Manager API documentation, after the "Server" and up to and including the
221 * An unsigned 16 bit integer which gives the size in bytes of the buffer we
222 will use to receive the returned array of data structures. Presumably this
223 should be the same as mdrcnt. This value should be set with SSVAL().
225 * An ASCIIZ string describing substructures which should be returned. If no
226 substructures apply, this string is of zero length.
228 -----------------------------------------------------------------------------
229 The code in client.c always calls call_api() with no data. It is unclear
230 when a non-zero length data buffer would be sent.
232 -----------------------------------------------------------------------------
233 The returned parameters (pointed to by rparam), in their order of appearance
236 * An unsigned 16 bit integer which contains the API function's return code.
237 This value should be read with SVAL().
239 * An adjustment which tells the amount by which pointers in the returned
240 data should be adjusted. This value should be read with SVAL(). Basically,
241 the address of the start of the returned data buffer should have the returned
242 pointer value added to it and then have this value subtracted from it in
243 order to obtain the currect offset into the returned data buffer.
245 * A count of the number of elements in the array of structures returned.
246 It is also possible that this may sometimes be the number of bytes returned.
248 -----------------------------------------------------------------------------
249 When call_api() returns, rparam points to the returned parameters. The
250 first if these is the result code. It will be zero if the API call
251 suceeded. This value by be read with "SVAL(rparam,0)".
253 The second parameter may be read as "SVAL(rparam,2)". It is a 16 bit offset
254 which indicates what the base address of the returned data buffer was when
255 it was built on the server. It should be used to correct pointer before
258 The returned data buffer contains the array of returned data structures.
259 Note that all pointers must be adjusted before use. The function
260 fix_char_ptr() in client.c can be used for this purpose.
262 The third parameter (which may be read as "SVAL(rparam,4)") has something to
263 do with indicating the amount of data returned or possibly the amount of
264 data which can be returned if enough buffer space is allowed.
266 -----------------------------------------------------------------------------
267 Certain data structures are described by means of ASCIIz strings containing
268 code characters. These are the code characters:
270 W a type byte little-endian unsigned integer
271 N a count of substructures which follow
272 D a four byte little-endian unsigned integer
273 B a byte (with optional count expressed as trailing ASCII digits)
274 z a four byte offset to a NULL terminated string
275 l a four byte offset to non-string user data
276 b an offset to data (with count expressed as trailing ASCII digits)
277 r pointer to returned data buffer???
278 L length in bytes of returned data buffer???
279 h number of bytes of information available???
281 ----------------------------------------------------------------------------