250 lines
8.2 KiB
Groff
250 lines
8.2 KiB
Groff
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.\" ========================================================================
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.\"
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.IX Title "BIO_s_mem 3"
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.TH BIO_s_mem 3 "2017-05-25" "1.0.2l" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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BIO_s_mem, BIO_set_mem_eof_return, BIO_get_mem_data, BIO_set_mem_buf,
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BIO_get_mem_ptr, BIO_new_mem_buf \- memory BIO
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/bio.h>
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\&
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\& BIO_METHOD * BIO_s_mem(void);
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\&
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\& BIO_set_mem_eof_return(BIO *b,int v)
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\& long BIO_get_mem_data(BIO *b, char **pp)
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\& BIO_set_mem_buf(BIO *b,BUF_MEM *bm,int c)
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\& BIO_get_mem_ptr(BIO *b,BUF_MEM **pp)
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\&
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\& BIO *BIO_new_mem_buf(const void *buf, int len);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fIBIO_s_mem()\fR return the memory \s-1BIO\s0 method function.
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.PP
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A memory \s-1BIO\s0 is a source/sink \s-1BIO\s0 which uses memory for its I/O. Data
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written to a memory \s-1BIO\s0 is stored in a \s-1BUF_MEM\s0 structure which is extended
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as appropriate to accommodate the stored data.
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.PP
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Any data written to a memory \s-1BIO\s0 can be recalled by reading from it.
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Unless the memory \s-1BIO\s0 is read only any data read from it is deleted from
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the \s-1BIO.\s0
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.PP
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Memory BIOs support \fIBIO_gets()\fR and \fIBIO_puts()\fR.
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.PP
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If the \s-1BIO_CLOSE\s0 flag is set when a memory \s-1BIO\s0 is freed then the underlying
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\&\s-1BUF_MEM\s0 structure is also freed.
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.PP
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Calling \fIBIO_reset()\fR on a read write memory \s-1BIO\s0 clears any data in it. On a
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read only \s-1BIO\s0 it restores the \s-1BIO\s0 to its original state and the read only
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data can be read again.
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.PP
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\&\fIBIO_eof()\fR is true if no data is in the \s-1BIO.\s0
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.PP
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\&\fIBIO_ctrl_pending()\fR returns the number of bytes currently stored.
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.PP
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\&\fIBIO_set_mem_eof_return()\fR sets the behaviour of memory \s-1BIO \s0\fBb\fR when it is
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empty. If the \fBv\fR is zero then an empty memory \s-1BIO\s0 will return \s-1EOF \s0(that is
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it will return zero and BIO_should_retry(b) will be false. If \fBv\fR is non
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zero then it will return \fBv\fR when it is empty and it will set the read retry
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flag (that is BIO_read_retry(b) is true). To avoid ambiguity with a normal
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positive return value \fBv\fR should be set to a negative value, typically \-1.
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.PP
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\&\fIBIO_get_mem_data()\fR sets \fBpp\fR to a pointer to the start of the memory BIOs data
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and returns the total amount of data available. It is implemented as a macro.
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.PP
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\&\fIBIO_set_mem_buf()\fR sets the internal \s-1BUF_MEM\s0 structure to \fBbm\fR and sets the
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close flag to \fBc\fR, that is \fBc\fR should be either \s-1BIO_CLOSE\s0 or \s-1BIO_NOCLOSE.\s0
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It is a macro.
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.PP
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\&\fIBIO_get_mem_ptr()\fR places the underlying \s-1BUF_MEM\s0 structure in \fBpp\fR. It is
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a macro.
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.PP
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\&\fIBIO_new_mem_buf()\fR creates a memory \s-1BIO\s0 using \fBlen\fR bytes of data at \fBbuf\fR,
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if \fBlen\fR is \-1 then the \fBbuf\fR is assumed to be nul terminated and its
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length is determined by \fBstrlen\fR. The \s-1BIO\s0 is set to a read only state and
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as a result cannot be written to. This is useful when some data needs to be
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made available from a static area of memory in the form of a \s-1BIO.\s0 The
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supplied data is read directly from the supplied buffer: it is \fBnot\fR copied
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first, so the supplied area of memory must be unchanged until the \s-1BIO\s0 is freed.
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.SH "NOTES"
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.IX Header "NOTES"
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Writes to memory BIOs will always succeed if memory is available: that is
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their size can grow indefinitely.
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.PP
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Every read from a read write memory \s-1BIO\s0 will remove the data just read with
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an internal copy operation, if a \s-1BIO\s0 contains a lot of data and it is
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read in small chunks the operation can be very slow. The use of a read only
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memory \s-1BIO\s0 avoids this problem. If the \s-1BIO\s0 must be read write then adding
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a buffering \s-1BIO\s0 to the chain will speed up the process.
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.SH "BUGS"
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.IX Header "BUGS"
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There should be an option to set the maximum size of a memory \s-1BIO.\s0
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.PP
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There should be a way to \*(L"rewind\*(R" a read write \s-1BIO\s0 without destroying
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its contents.
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.PP
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The copying operation should not occur after every small read of a large \s-1BIO\s0
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to improve efficiency.
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.SH "EXAMPLE"
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.IX Header "EXAMPLE"
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Create a memory \s-1BIO\s0 and write some data to it:
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.PP
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.Vb 2
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\& BIO *mem = BIO_new(BIO_s_mem());
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\& BIO_puts(mem, "Hello World\en");
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.Ve
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.PP
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Create a read only memory \s-1BIO:\s0
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.PP
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.Vb 3
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\& char data[] = "Hello World";
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\& BIO *mem;
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\& mem = BIO_new_mem_buf(data, \-1);
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.Ve
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.PP
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Extract the \s-1BUF_MEM\s0 structure from a memory \s-1BIO\s0 and then free up the \s-1BIO:\s0
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.PP
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.Vb 4
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\& BUF_MEM *bptr;
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\& BIO_get_mem_ptr(mem, &bptr);
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\& BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free() leaves BUF_MEM alone */
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\& BIO_free(mem);
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.Ve
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\s-1TBA\s0
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