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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 "2018-11-20" "1.0.2q" "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 |
