.\" $OpenBSD: BIO_s_mem.3,v 1.5 2016/12/06 14:45:08 schwarze Exp $ .\" OpenSSL 8711efb4 Mon Apr 20 11:33:12 2009 +0000 .\" .\" This file was written by Dr. Stephen Henson . .\" Copyright (c) 2000 The OpenSSL Project. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" 3. All advertising materials mentioning features or use of this .\" software must display the following acknowledgment: .\" "This product includes software developed by the OpenSSL Project .\" for use in the OpenSSL Toolkit. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: December 6 2016 $ .Dt BIO_S_MEM 3 .Os .Sh NAME .Nm BIO_s_mem , .Nm BIO_set_mem_eof_return , .Nm BIO_get_mem_data , .Nm BIO_set_mem_buf , .Nm BIO_get_mem_ptr , .Nm BIO_new_mem_buf .Nd memory BIO .Sh SYNOPSIS .In openssl/bio.h .Ft BIO_METHOD * .Fo BIO_s_mem .Fa "void" .Fc .Ft long .Fo BIO_set_mem_eof_return .Fa "BIO *b" .Fa "int v" .Fc .Ft long .Fo BIO_get_mem_data .Fa "BIO *b" .Fa "char **pp" .Fc .Ft long .Fo BIO_set_mem_buf .Fa "BIO *b" .Fa "BUF_MEM *bm" .Fa "int c" .Fc .Ft long .Fo BIO_get_mem_ptr .Fa "BIO *b" .Fa "BUF_MEM **pp" .Fc .Ft BIO * .Fo BIO_new_mem_buf .Fa "void *buf" .Fa "int len" .Fc .Sh DESCRIPTION .Fn BIO_s_mem returns the memory BIO method function. .Pp A memory BIO is a source/sink BIO which uses memory for its I/O. Data written to a memory BIO is stored in a .Vt BUF_MEM structure which is extended as appropriate to accommodate the stored data. .Pp Any data written to a memory BIO can be recalled by reading from it. Unless the memory BIO is read only, any data read from it is deleted from the BIO. .Pp Memory BIOs support .Xr BIO_gets 3 and .Xr BIO_puts 3 . .Pp If the .Dv BIO_CLOSE flag is set when a memory BIO is freed, the underlying .Dv BUF_MEM structure is also freed. .Pp Calling .Xr BIO_reset 3 on a read/write memory BIO clears any data in it. On a read only BIO it restores the BIO to its original state and the read only data can be read again. .Pp .Xr BIO_eof 3 is true if no data is in the BIO. .Pp .Xr BIO_ctrl_pending 3 returns the number of bytes currently stored. .Pp .Fn BIO_set_mem_eof_return sets the behaviour of memory BIO .Fa b when it is empty. If .Fa v is zero, then an empty memory BIO will return EOF: it will return zero and .Fn BIO_should_retry will be false. If .Fa v is non-zero then it will return .Fa v when it is empty and it will set the read retry flag: .Fn BIO_read_retry is true. To avoid ambiguity with a normal positive return value .Fa v should be set to a negative value, typically -1. .Pp .Fn BIO_get_mem_data sets .Fa pp to a pointer to the start of the memory BIO's data and returns the total amount of data available. It is implemented as a macro. .Pp .Fn BIO_set_mem_buf sets the internal BUF_MEM structure to .Fa bm and sets the close flag to .Fa c . That is, .Fa c should be either .Dv BIO_CLOSE or .Dv BIO_NOCLOSE . .Fn BIO_set_mem_buf is a macro. .Pp .Fn BIO_get_mem_ptr places the underlying .Vt BUF_MEM structure in .Fa pp . It is a macro. .Pp .Fn BIO_new_mem_buf creates a memory BIO using .Fa len bytes of data at .Fa buf . If .Fa len is -1, then .Fa buf is assumed to be NUL terminated and its length is determined by .Xr strlen 3 . The BIO is set to a read only state and as a result cannot be written to. This is useful when some data needs to be made available from a static area of memory in the form of a BIO. The supplied data is read directly from the supplied buffer: it is .Em not copied first, so the supplied area of memory must be unchanged until the BIO is freed. .Pp Writes to memory BIOs will always succeed if memory is available: their size can grow indefinitely. .Pp Every read from a read/write memory BIO will remove the data just read with an internal copy operation. If a BIO contains a lot of data and it is read in small chunks, the operation can be very slow. The use of a read only memory BIO avoids this problem. If the BIO must be read/write then adding a buffering BIO to the chain will speed up the process. .Sh EXAMPLES Create a memory BIO and write some data to it: .Bd -literal -offset indent BIO *mem = BIO_new(BIO_s_mem()); BIO_puts(mem, "Hello World\en"); .Ed .Pp Create a read only memory BIO: .Bd -literal -offset indent char data[] = "Hello World"; BIO *mem; mem = BIO_new_mem_buf(data, -1); .Ed .Pp Extract the .Vt BUF_MEM structure from a memory BIO and then free up the BIO: .Bd -literal -offset indent BUF_MEM *bptr; BIO_get_mem_ptr(mem, &bptr); /* Make sure BIO_free() leaves BUF_MEM alone. */ BIO_set_close(mem, BIO_NOCLOSE); BIO_free(mem); .Ed .Sh SEE ALSO .Xr BIO_new 3 .Sh BUGS There should be an option to set the maximum size of a memory BIO. .Pp There should be a way to "rewind" a read/write BIO without destroying its contents. .Pp The copying operation should not occur after every small read of a large BIO to improve efficiency.