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05fbeb03 | 1 | .\" -*-nroff-*- |
fbf20b5b | 2 | .TH lbuf 3 "6 July 1999" "Straylight/Edgeware" "mLib utilities library" |
05fbeb03 | 3 | .SH "NAME" |
4 | lbuf \- split lines out of asynchronously received blocks | |
5 | .\" @lbuf_flush | |
6 | .\" @lbuf_close | |
7 | .\" @lbuf_free | |
8 | .\" @lbuf_snarf | |
31e83d07 | 9 | .\" @lbuf_setsize |
05fbeb03 | 10 | .\" @lbuf_init |
31e83d07 | 11 | .\" @lbuf_destroy |
05fbeb03 | 12 | .SH "SYNOPSIS" |
13 | .nf | |
adec5584 | 14 | .ta 2n |
05fbeb03 | 15 | .B "#include <mLib/lbuf.h>" |
d056fbdf | 16 | .PP |
4729aa69 | 17 | .B "enum {" |
adec5584 MW |
18 | .B " LBUF_CRLF," |
19 | .B " LBUF_STRICTCRLF," | |
20 | .B " ..." | |
4729aa69 MW |
21 | .B "};" |
22 | .B "#define LBUF_ENABLE ..." | |
d056fbdf | 23 | .PP |
4729aa69 | 24 | .B "typedef struct {" |
adec5584 MW |
25 | .B " unsigned f;" |
26 | .B " ..." | |
4729aa69 | 27 | .B "} lbuf;" |
d056fbdf | 28 | .PP |
4729aa69 | 29 | .B "typedef void lbuf_func(char *" s ", size_t " len ", void *" p ); |
d056fbdf | 30 | .PP |
05fbeb03 | 31 | .BI "void lbuf_flush(lbuf *" b ", char *" p ", size_t " len ); |
32 | .BI "void lbuf_close(lbuf *" b ); | |
33 | .BI "size_t lbuf_free(lbuf *" b ", char **" p ); | |
34 | .BI "void lbuf_snarf(lbuf *" b ", const void *" p ", size_t " sz ); | |
cededfbe | 35 | .BI "void lbuf_setsize(lbuf *" b ", size_t " sz ); |
83c63e03 | 36 | .BI "void lbuf_init(lbuf *" b ", lbuf_func *" func ", void *" p ); |
cededfbe | 37 | .BI "void lbuf_destroy(lbuf *" b ); |
05fbeb03 | 38 | .fi |
39 | .SH "DESCRIPTION" | |
40 | The declarations in | |
41 | .B <mLib/lbuf.h> | |
42 | implement a handy object called a | |
43 | .IR "line buffer" . | |
44 | Given unpredictably-sized chunks of data, the line buffer extracts | |
45 | completed lines of text and passes them to a caller-supplied function. | |
46 | This is useful in nonblocking network servers, for example: the server | |
47 | can feed input from a client into a line buffer as it arrives and deal | |
48 | with completed text lines as they appear without having to wait for | |
49 | newline characters. | |
50 | .PP | |
51 | The state of a line buffer is stored in an object of type | |
52 | .BR lbuf . | |
53 | This is a structure which must be allocated by the caller. The | |
54 | structure should normally be considered opaque (see the section on | |
55 | .B Disablement | |
56 | for an exception to this). | |
57 | .SS "Initialization and finalization" | |
58 | The function | |
59 | .B lbuf_init | |
60 | initializes a line buffer ready for use. It is given three arguments: | |
61 | .TP | |
ff76c38f | 62 | .BI "lbuf *" b |
31e83d07 | 63 | A pointer to the block of memory to use for the line buffer. The line |
64 | buffer will allocate memory to store incoming data automatically: this | |
65 | structure just contains bookkeeping information. | |
05fbeb03 | 66 | .TP |
83c63e03 | 67 | .BI "lbuf_func *" func |
05fbeb03 | 68 | The |
69 | .I line-handler | |
70 | function to which the line buffer should pass completed lines of text. | |
83c63e03 | 71 | See |
72 | .B "Line-handler functions" | |
73 | below for a description of this function. | |
05fbeb03 | 74 | .TP |
ff76c38f | 75 | .BI "void *" p |
05fbeb03 | 76 | A pointer argument to be passed to the function when a completed line of |
77 | text arrives. | |
78 | .PP | |
cededfbe | 79 | The amount of memory set aside for reading lines is configurable. It |
80 | may be set by calling | |
81 | .B lbuf_setsize | |
82 | at any time when the buffer is empty. The default limit is 256 bytes. | |
83 | Lines longer than the limit are truncated. By default, the buffer is | |
84 | allocated from the current arena, | |
85 | .BR arena_global (3); | |
86 | this may be changed by altering the buffer's | |
87 | .B a | |
88 | member to refer to a different arena at any time when the buffer is | |
89 | unallocated. | |
90 | .PP | |
91 | A line buffer must be destroyed after use by calling | |
92 | .BR lbuf_destroy , | |
93 | passing it the address of the buffer block. | |
05fbeb03 | 94 | .SS "Inserting data into the buffer" |
95 | There are two interfaces for inserting data into the buffer. One's much | |
96 | simpler than the other, although it's less expressive. | |
97 | .PP | |
98 | The simple interface is | |
99 | .BR lbuf_snarf . | |
100 | This function is given three arguments: a pointer | |
101 | .I b | |
102 | to a line buffer structure; a pointer | |
103 | .I p | |
d0053e2e | 104 | to a chunk of data to read; and the size |
05fbeb03 | 105 | .I sz |
106 | of the chunk of data. The data is pushed through the line buffer and | |
107 | any complete lines are passed on to the line handler. | |
108 | .PP | |
109 | The complex interface is the pair of functions | |
d0053e2e | 110 | .B lbuf_free |
05fbeb03 | 111 | and |
d0053e2e | 112 | .BR lbuf_flush . |
05fbeb03 | 113 | .PP |
d4efbcd9 | 114 | The |
05fbeb03 | 115 | .B lbuf_free |
116 | function returns the address and size of a free portion of the line | |
117 | buffer's memory into which data may be written. The function is passed | |
d4efbcd9 | 118 | the address |
31e83d07 | 119 | .I b |
05fbeb03 | 120 | of the line buffer. Its result is the size of the free area, and it |
121 | writes the base address of this free space to the location pointed to by | |
122 | the argument | |
123 | .IR p . | |
124 | The caller's data must be written to ascending memory locations starting | |
125 | at | |
126 | .BI * p | |
127 | and no data may be written beyond the end of the free space. However, | |
128 | it isn't necessary to completely fill the buffer. | |
129 | .PP | |
130 | Once the free area has had some data written to it, | |
131 | .B lbuf_flush | |
132 | is called to examine the new data and break it into text lines. This is | |
133 | given three arguments: | |
134 | .TP | |
ff76c38f | 135 | .BI "lbuf *" b |
05fbeb03 | 136 | The address of the line buffer. |
137 | .TP | |
ff76c38f | 138 | .BI "char *" p |
05fbeb03 | 139 | The address at which the new data has been written. This must be the |
140 | base address returned from | |
141 | .BR lbuf_free . | |
142 | .TP | |
ff76c38f | 143 | .BI "size_t " len |
05fbeb03 | 144 | The number of bytes which have been written to the buffer. |
145 | .PP | |
146 | The | |
147 | .B lbuf_flush | |
148 | function breaks the new data into lines as described below, and passes | |
149 | each one in turn to the line-handler function. | |
150 | .PP | |
151 | The | |
152 | .B lbuf_snarf | |
153 | function is trivially implemented in terms of the more complex | |
d0053e2e | 154 | .BR lbuf_free / lbuf_flush |
05fbeb03 | 155 | interface. |
156 | .SS "Line breaking" | |
83c63e03 | 157 | By default, the line buffer considers a line to end with either a simple |
158 | linefeed character (the normal Unix convention) or a | |
159 | carriage-return/linefeed pair (the Internet convention). This can be | |
160 | changed by modifying the | |
161 | .B delim | |
162 | member of the | |
163 | .B lbuf | |
164 | structure: the default value is | |
165 | .BR LBUF_CRLF . | |
166 | If set to | |
167 | .BR LBUF_STRICTCRLF , | |
168 | only a carriage-return/linefeed pair will terminate a line. Any other | |
169 | value is a single character which is considered to be the line terminator. | |
05fbeb03 | 170 | .PP |
171 | The line buffer has a fixed amount of memory available to it. This is | |
172 | deliberate, to prevent a trivial attack whereby a remote user sends a | |
173 | stream of data containing no newline markers, wasting the server's | |
174 | memory. Instead, the buffer will truncate overly long lines (silently) | |
175 | and return only the initial portion. It will ignore the rest of the | |
176 | line completely. | |
177 | .SS "Line-handler functions" | |
178 | Completed lines, as already said, are passed to the caller's | |
4729aa69 | 179 | line-handler function. It is given three arguments: the address |
05fbeb03 | 180 | .I s |
83c63e03 | 181 | of the line which has just been read; the length |
182 | .I len | |
183 | of the line (not including the null terminator), and the pointer | |
05fbeb03 | 184 | .I p |
185 | which was set up in the call to | |
d0053e2e | 186 | .BR lbuf_init . |
05fbeb03 | 187 | The line passed is null-terminated, and has had its trailing newline |
188 | stripped. The area of memory in which the string is located may be | |
189 | overwritten by the line-handler function, although writing beyond the | |
190 | terminating zero byte is not permitted. | |
191 | .PP | |
192 | The line pointer argument | |
193 | .I s | |
83c63e03 | 194 | may be null to signify end-of-file; in this case, the length |
195 | .I len | |
196 | will be zero. See the next section. | |
05fbeb03 | 197 | .SS "Flushing the remaining data" |
198 | When the client program knows that there's no more data arriving (for | |
199 | example, an end-of-file condition exists on its data source) it should | |
200 | call the function | |
201 | .BR lbuf_close | |
202 | to flush out the remaining data in the buffer as one last (improperly | |
203 | terminated) line. This will pass the remaining text to the line | |
204 | handler, if there is any, and then call the handler one final time with | |
205 | a null pointer rather than the address of a text line to inform it of | |
206 | the end-of-file. | |
207 | .SS "Disablement" | |
208 | The line buffer is intended to be used in higher-level program objects, | |
209 | such as the buffer selector described in | |
210 | .BR selbuf (3). | |
211 | Unfortunately, a concept from this high level needs to exist at the line | |
212 | buffer level, which complicates the description somewhat. The idea is | |
213 | that, when a line-handler attached to some higher-level object decides | |
214 | that it's read enough, it can | |
215 | .I disable | |
216 | the object so that it doesn't see any more data. | |
217 | .PP | |
218 | Clearly, since an | |
219 | .B lbuf_flush | |
528c8b4d | 220 | call can emit more than one line, it must be aware that the line handler |
221 | isn't interested in any more lines. However, this fact must also be | |
222 | signalled to the higher-level object so that it can detach itself from | |
223 | its data source. | |
05fbeb03 | 224 | .PP |
225 | Rather than invent some complex interface for this, the line buffer | |
3bc42912 | 226 | exports one of its structure members, a flags word called |
227 | .BR f . | |
05fbeb03 | 228 | A higher-level object wishing to disable the line buffer simply clears |
229 | the bit | |
230 | .B LBUF_ENABLE | |
3bc42912 | 231 | in this flags word. |
05fbeb03 | 232 | .PP |
233 | Disabling a buffer causes an immediate return from | |
234 | .BR lbuf_flush . | |
235 | However, it is not permitted for the functions | |
236 | .B lbuf_flush | |
237 | or | |
238 | .B lbuf_close | |
239 | to be called on a disabled buffer. (This condition isn't checked for; | |
240 | it'll just do the wrong thing.) Furthermore, the | |
241 | .B lbuf_snarf | |
242 | function does not handle disablement at all, because it would complicate | |
243 | the interface so much that it wouldn't have any advantage over the more | |
244 | general | |
245 | .BR lbuf_free / lbuf_flush . | |
246 | .SH "SEE ALSO" | |
247 | .BR selbuf (3), | |
248 | .BR mLib (3). | |
249 | .SH "AUTHOR" | |
9b5ac6ff | 250 | Mark Wooding, <mdw@distorted.org.uk> |