1 <?xml version="1.0" encoding="iso-8859-1"?>
2 <!DOCTYPE chapter PUBLIC "-//Samba-Team//DTD DocBook V4.2-Based Variant V1.0//EN" "http://www.samba.org/samba/DTD/samba-doc">
3 <chapter id="internals">
6 <firstname>David</firstname><surname>Chappell</surname>
8 <address><email>David.Chappell@mail.trincoll.edu</email></address>
11 <pubdate>8 May 1996</pubdate>
14 <title>Samba Internals</title>
17 <title>Character Handling</title>
19 This section describes character set handling in Samba, as implemented in
24 In the past Samba had very ad-hoc character set handling. Scattered
25 throughout the code were numerous calls which converted particular
26 strings to/from DOS codepages. The problem is that there was no way of
27 telling if a particular char* is in dos codepage or unix
28 codepage. This led to a nightmare of code that tried to cope with
29 particular cases without handlingt the general case.
34 <title>The new functions</title>
37 The new system works like this:
42 all char* strings inside Samba are "unix" strings. These are
43 multi-byte strings that are in the charset defined by the "unix
44 charset" option in smb.conf.
48 there is no single fixed character set for unix strings, but any
49 character set that is used does need the following properties:
54 must not contain NULLs except for termination
58 must be 7-bit compatible with C strings, so that a constant
59 string or character in C will be byte-for-byte identical to the
60 equivalent string in the chosen character set.
64 when you uppercase or lowercase a string it does not become
65 longer than the original string
69 must be able to correctly hold all characters that your client
75 For example, UTF-8 is fine, and most multi-byte asian character sets
76 are fine, but UCS2 could not be used for unix strings as they
82 when you need to put a string into a buffer that will be sent on the
83 wire, or you need a string in a character set format that is
84 compatible with the clients character set then you need to use a
85 pull_ or push_ function. The pull_ functions pull a string from a
86 wire buffer into a (multi-byte) unix string. The push_ functions
87 push a string out to a wire buffer.
91 the two main pull_ and push_ functions you need to understand are
92 pull_string and push_string. These functions take a base pointer
93 that should point at the start of the SMB packet that the string is
94 in. The functions will check the flags field in this packet to
95 automatically determine if the packet is marked as a unicode packet,
96 and they will choose whether to use unicode for this string based on
97 that flag. You may also force this decision using the STR_UNICODE or
98 STR_ASCII flags. For use in smbd/ and libsmb/ there are wrapper
99 functions clistr_ and srvstr_ that call the pull_/push_ functions
100 with the appropriate first argument.
104 You may also call the pull_ascii/pull_ucs2 or push_ascii/push_ucs2
105 functions if you know that a particular string is ascii or
106 unicode. There are also a number of other convenience functions in
107 charcnv.c that call the pull_/push_ functions with particularly
108 common arguments, such as pull_ascii_pstring()
113 The biggest thing to remember is that internal (unix) strings in Samba
114 may now contain multi-byte characters. This means you cannot assume
115 that characters are always 1 byte long. Often this means that you will
116 have to convert strings to ucs2 and back again in order to do some
117 (seemingly) simple task. For examples of how to do this see functions
118 like strchr_m(). I know this is very slow, and we will eventually
119 speed it up but right now we want this stuff correct not fast.
123 all lp_ functions now return unix strings. The magic "DOS" flag on
128 all vfs functions take unix strings. Don't convert when passing to them
136 <title>Macros in byteorder.h</title>
139 This section describes the macros defined in byteorder.h. These macros
140 are used extensively in the Samba code.
144 <title>CVAL(buf,pos)</title>
147 returns the byte at offset pos within buffer buf as an unsigned character.
152 <title>PVAL(buf,pos)</title>
153 <para>returns the value of CVAL(buf,pos) cast to type unsigned integer.</para>
157 <title>SCVAL(buf,pos,val)</title>
158 <para>sets the byte at offset pos within buffer buf to value val.</para>
162 <title>SVAL(buf,pos)</title>
164 returns the value of the unsigned short (16 bit) little-endian integer at
165 offset pos within buffer buf. An integer of this type is sometimes
166 refered to as "USHORT".
171 <title>IVAL(buf,pos)</title>
172 <para>returns the value of the unsigned 32 bit little-endian integer at offset
173 pos within buffer buf.</para>
177 <title>SVALS(buf,pos)</title>
178 <para>returns the value of the signed short (16 bit) little-endian integer at
179 offset pos within buffer buf.</para>
183 <title>IVALS(buf,pos)</title>
184 <para>returns the value of the signed 32 bit little-endian integer at offset pos
185 within buffer buf.</para>
189 <title>SSVAL(buf,pos,val)</title>
190 <para>sets the unsigned short (16 bit) little-endian integer at offset pos within
191 buffer buf to value val.</para>
195 <title>SIVAL(buf,pos,val)</title>
196 <para>sets the unsigned 32 bit little-endian integer at offset pos within buffer
197 buf to the value val.</para>
201 <title>SSVALS(buf,pos,val)</title>
202 <para>sets the short (16 bit) signed little-endian integer at offset pos within
203 buffer buf to the value val.</para>
207 <title>SIVALS(buf,pos,val)</title>
208 <para>sets the signed 32 bit little-endian integer at offset pos withing buffer
209 buf to the value val.</para>
213 <title>RSVAL(buf,pos)</title>
214 <para>returns the value of the unsigned short (16 bit) big-endian integer at
215 offset pos within buffer buf.</para>
219 <title>RIVAL(buf,pos)</title>
220 <para>returns the value of the unsigned 32 bit big-endian integer at offset
221 pos within buffer buf.</para>
225 <title>RSSVAL(buf,pos,val)</title>
226 <para>sets the value of the unsigned short (16 bit) big-endian integer at
227 offset pos within buffer buf to value val.
228 refered to as "USHORT".</para>
232 <title>RSIVAL(buf,pos,val)</title>
233 <para>sets the value of the unsigned 32 bit big-endian integer at offset
234 pos within buffer buf to value val.</para>
241 <title>LAN Manager Samba API</title>
244 This section describes the functions need to make a LAN Manager RPC call.
245 This information had been obtained by examining the Samba code and the LAN
246 Manager 2.0 API documentation. It should not be considered entirely
252 call_api(int prcnt, int drcnt, int mprcnt, int mdrcnt,
253 char *param, char *data, char **rparam, char **rdata);
258 This function is defined in client.c. It uses an SMB transaction to call a
263 <title>Parameters</title>
265 <para>The parameters are as follows:</para>
269 prcnt: the number of bytes of parameters begin sent.
272 drcnt: the number of bytes of data begin sent.
275 mprcnt: the maximum number of bytes of parameters which should be returned
278 mdrcnt: the maximum number of bytes of data which should be returned
281 param: a pointer to the parameters to be sent.
284 data: a pointer to the data to be sent.
287 rparam: a pointer to a pointer which will be set to point to the returned
288 parameters. The caller of call_api() must deallocate this memory.
291 rdata: a pointer to a pointer which will be set to point to the returned
292 data. The caller of call_api() must deallocate this memory.
297 These are the parameters which you ought to send, in the order of their
298 appearance in the parameter block:
304 An unsigned 16 bit integer API number. You should set this value with
305 SSVAL(). I do not know where these numbers are described.
309 An ASCIIZ string describing the parameters to the API function as defined
310 in the LAN Manager documentation. The first parameter, which is the server
311 name, is ommited. This string is based uppon the API function as described
312 in the manual, not the data which is actually passed.
316 An ASCIIZ string describing the data structure which ought to be returned.
320 Any parameters which appear in the function call, as defined in the LAN
321 Manager API documentation, after the "Server" and up to and including the
326 An unsigned 16 bit integer which gives the size in bytes of the buffer we
327 will use to receive the returned array of data structures. Presumably this
328 should be the same as mdrcnt. This value should be set with SSVAL().
332 An ASCIIZ string describing substructures which should be returned. If no
333 substructures apply, this string is of zero length.
339 The code in client.c always calls call_api() with no data. It is unclear
340 when a non-zero length data buffer would be sent.
346 <title>Return value</title>
349 The returned parameters (pointed to by rparam), in their order of appearance
355 An unsigned 16 bit integer which contains the API function's return code.
356 This value should be read with SVAL().
360 An adjustment which tells the amount by which pointers in the returned
361 data should be adjusted. This value should be read with SVAL(). Basically,
362 the address of the start of the returned data buffer should have the returned
363 pointer value added to it and then have this value subtracted from it in
364 order to obtain the currect offset into the returned data buffer.
368 A count of the number of elements in the array of structures returned.
369 It is also possible that this may sometimes be the number of bytes returned.
374 When call_api() returns, rparam points to the returned parameters. The
375 first if these is the result code. It will be zero if the API call
376 suceeded. This value by be read with "SVAL(rparam,0)".
380 The second parameter may be read as "SVAL(rparam,2)". It is a 16 bit offset
381 which indicates what the base address of the returned data buffer was when
382 it was built on the server. It should be used to correct pointer before
387 The returned data buffer contains the array of returned data structures.
388 Note that all pointers must be adjusted before use. The function
389 fix_char_ptr() in client.c can be used for this purpose.
393 The third parameter (which may be read as "SVAL(rparam,4)") has something to
394 do with indicating the amount of data returned or possibly the amount of
395 data which can be returned if enough buffer space is allowed.
402 <title>Code character table</title>
404 Certain data structures are described by means of ASCIIz strings containing
405 code characters. These are the code characters:
410 W a type byte little-endian unsigned integer
413 N a count of substructures which follow
416 D a four byte little-endian unsigned integer
419 B a byte (with optional count expressed as trailing ASCII digits)
422 z a four byte offset to a NULL terminated string
425 l a four byte offset to non-string user data
428 b an offset to data (with count expressed as trailing ASCII digits)
431 r pointer to returned data buffer???
434 L length in bytes of returned data buffer???
437 h number of bytes of information available???
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