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135 .IX Title "BIO_s_mem 3"
136 .TH BIO_s_mem 3 "2015-03-19" "1.0.1m" "OpenSSL"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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142 BIO_s_mem, BIO_set_mem_eof_return, BIO_get_mem_data, BIO_set_mem_buf,
143 BIO_get_mem_ptr, BIO_new_mem_buf \- memory BIO
145 .IX Header "SYNOPSIS"
147 \& #include <openssl/bio.h>
149 \& BIO_METHOD * BIO_s_mem(void);
151 \& BIO_set_mem_eof_return(BIO *b,int v)
152 \& long BIO_get_mem_data(BIO *b, char **pp)
153 \& BIO_set_mem_buf(BIO *b,BUF_MEM *bm,int c)
154 \& BIO_get_mem_ptr(BIO *b,BUF_MEM **pp)
156 \& BIO *BIO_new_mem_buf(void *buf, int len);
159 .IX Header "DESCRIPTION"
160 \&\fIBIO_s_mem()\fR return the memory \s-1BIO\s0 method function.
162 A memory \s-1BIO\s0 is a source/sink \s-1BIO\s0 which uses memory for its I/O. Data
163 written to a memory \s-1BIO\s0 is stored in a \s-1BUF_MEM\s0 structure which is extended
164 as appropriate to accommodate the stored data.
166 Any data written to a memory \s-1BIO\s0 can be recalled by reading from it.
167 Unless the memory \s-1BIO\s0 is read only any data read from it is deleted from
170 Memory BIOs support \fIBIO_gets()\fR and \fIBIO_puts()\fR.
172 If the \s-1BIO_CLOSE\s0 flag is set when a memory \s-1BIO\s0 is freed then the underlying
173 \&\s-1BUF_MEM\s0 structure is also freed.
175 Calling \fIBIO_reset()\fR on a read write memory \s-1BIO\s0 clears any data in it. On a
176 read only \s-1BIO\s0 it restores the \s-1BIO\s0 to its original state and the read only
177 data can be read again.
179 \&\fIBIO_eof()\fR is true if no data is in the \s-1BIO.\s0
181 \&\fIBIO_ctrl_pending()\fR returns the number of bytes currently stored.
183 \&\fIBIO_set_mem_eof_return()\fR sets the behaviour of memory \s-1BIO \s0\fBb\fR when it is
184 empty. If the \fBv\fR is zero then an empty memory \s-1BIO\s0 will return \s-1EOF \s0(that is
185 it will return zero and BIO_should_retry(b) will be false. If \fBv\fR is non
186 zero then it will return \fBv\fR when it is empty and it will set the read retry
187 flag (that is BIO_read_retry(b) is true). To avoid ambiguity with a normal
188 positive return value \fBv\fR should be set to a negative value, typically \-1.
190 \&\fIBIO_get_mem_data()\fR sets \fBpp\fR to a pointer to the start of the memory BIOs data
191 and returns the total amount of data available. It is implemented as a macro.
193 \&\fIBIO_set_mem_buf()\fR sets the internal \s-1BUF_MEM\s0 structure to \fBbm\fR and sets the
194 close flag to \fBc\fR, that is \fBc\fR should be either \s-1BIO_CLOSE\s0 or \s-1BIO_NOCLOSE.\s0
197 \&\fIBIO_get_mem_ptr()\fR places the underlying \s-1BUF_MEM\s0 structure in \fBpp\fR. It is
200 \&\fIBIO_new_mem_buf()\fR creates a memory \s-1BIO\s0 using \fBlen\fR bytes of data at \fBbuf\fR,
201 if \fBlen\fR is \-1 then the \fBbuf\fR is assumed to be null terminated and its
202 length is determined by \fBstrlen\fR. The \s-1BIO\s0 is set to a read only state and
203 as a result cannot be written to. This is useful when some data needs to be
204 made available from a static area of memory in the form of a \s-1BIO.\s0 The
205 supplied data is read directly from the supplied buffer: it is \fBnot\fR copied
206 first, so the supplied area of memory must be unchanged until the \s-1BIO\s0 is freed.
209 Writes to memory BIOs will always succeed if memory is available: that is
210 their size can grow indefinitely.
212 Every read from a read write memory \s-1BIO\s0 will remove the data just read with
213 an internal copy operation, if a \s-1BIO\s0 contains a lot of data and it is
214 read in small chunks the operation can be very slow. The use of a read only
215 memory \s-1BIO\s0 avoids this problem. If the \s-1BIO\s0 must be read write then adding
216 a buffering \s-1BIO\s0 to the chain will speed up the process.
219 There should be an option to set the maximum size of a memory \s-1BIO.\s0
221 There should be a way to \*(L"rewind\*(R" a read write \s-1BIO\s0 without destroying
224 The copying operation should not occur after every small read of a large \s-1BIO\s0
225 to improve efficiency.
228 Create a memory \s-1BIO\s0 and write some data to it:
231 \& BIO *mem = BIO_new(BIO_s_mem());
232 \& BIO_puts(mem, "Hello World\en");
235 Create a read only memory \s-1BIO:\s0
238 \& char data[] = "Hello World";
240 \& mem = BIO_new_mem_buf(data, \-1);
243 Extract the \s-1BUF_MEM\s0 structure from a memory \s-1BIO\s0 and then free up the \s-1BIO:\s0
247 \& BIO_get_mem_ptr(mem, &bptr);
248 \& BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free() leaves BUF_MEM alone */
252 .IX Header "SEE ALSO"