1=pod 2 3=head1 NAME 4 5BIO_s_secmem, BIO_s_dgram_mem, 6BIO_s_mem, BIO_set_mem_eof_return, BIO_get_mem_data, BIO_set_mem_buf, 7BIO_get_mem_ptr, BIO_new_mem_buf - memory BIO 8 9=head1 SYNOPSIS 10 11 #include <openssl/bio.h> 12 13 const BIO_METHOD *BIO_s_mem(void); 14 const BIO_METHOD *BIO_s_dgram_mem(void); 15 const BIO_METHOD *BIO_s_secmem(void); 16 17 BIO_set_mem_eof_return(BIO *b, int v); 18 long BIO_get_mem_data(BIO *b, char **pp); 19 BIO_set_mem_buf(BIO *b, BUF_MEM *bm, int c); 20 BIO_get_mem_ptr(BIO *b, BUF_MEM **pp); 21 22 BIO *BIO_new_mem_buf(const void *buf, int len); 23 24=head1 DESCRIPTION 25 26BIO_s_mem() returns the memory BIO method function. 27 28A memory BIO is a source/sink BIO which uses memory for its I/O. Data 29written to a memory BIO is stored in a BUF_MEM structure which is extended 30as appropriate to accommodate the stored data. 31 32BIO_s_secmem() is like BIO_s_mem() except that the secure heap is used 33for buffer storage. 34 35BIO_s_dgram_mem() is a memory BIO that respects datagram semantics. A single 36call to L<BIO_write(3)> will write a single datagram to the memory BIO. A 37subsequent call to L<BIO_read(3)> will read the data in that datagram. The 38L<BIO_read(3)> call will never return more data than was written in the original 39L<BIO_write(3)> call even if there were subsequent L<BIO_write(3)> calls that 40wrote more datagrams. Each successive call to L<BIO_read(3)> will read the next 41datagram. If a L<BIO_read(3)> call supplies a read buffer that is smaller than 42the size of the datagram, then the read buffer will be completely filled and the 43remaining data from the datagram will be discarded. 44 45It is not possible to write a zero length datagram. Calling L<BIO_write(3)> in 46this case will return 0 and no datagrams will be written. Calling L<BIO_read(3)> 47when there are no datagrams in the BIO to read will return a negative result and 48the "retry" flags will be set (i.e. calling L<BIO_should_retry(3)> will return 49true). A datagram mem BIO will never return true from L<BIO_eof(3)>. 50 51Any data written to a memory BIO can be recalled by reading from it. 52Unless the memory BIO is read only any data read from it is deleted from 53the BIO. 54 55Memory BIOs support BIO_gets() and BIO_puts(). 56 57If the BIO_CLOSE flag is set when a memory BIO is freed then the underlying 58BUF_MEM structure is also freed. 59 60Calling BIO_reset() on a read write memory BIO clears any data in it if the 61flag BIO_FLAGS_NONCLEAR_RST is not set, otherwise it just restores the read 62pointer to the state it was just after the last write was performed and the 63data can be read again. On a read only BIO it similarly restores the BIO to 64its original state and the read only data can be read again. 65 66BIO_eof() is true if no data is in the BIO. 67 68BIO_ctrl_pending() returns the number of bytes currently stored. 69 70BIO_set_mem_eof_return() sets the behaviour of memory BIO B<b> when it is 71empty. If the B<v> is zero then an empty memory BIO will return EOF (that is 72it will return zero and BIO_should_retry(b) will be false. If B<v> is non 73zero then it will return B<v> when it is empty and it will set the read retry 74flag (that is BIO_read_retry(b) is true). To avoid ambiguity with a normal 75positive return value B<v> should be set to a negative value, typically -1. 76Calling this macro will fail for datagram mem BIOs. 77 78BIO_get_mem_data() sets *B<pp> to a pointer to the start of the memory BIOs data 79and returns the total amount of data available. It is implemented as a macro. 80 81BIO_set_mem_buf() sets the internal BUF_MEM structure to B<bm> and sets the 82close flag to B<c>, that is B<c> should be either BIO_CLOSE or BIO_NOCLOSE. 83It is a macro. 84 85BIO_get_mem_ptr() places the underlying BUF_MEM structure in *B<pp>. It is 86a macro. 87 88BIO_new_mem_buf() creates a memory BIO using B<len> bytes of data at B<buf>, 89if B<len> is -1 then the B<buf> is assumed to be nul terminated and its 90length is determined by B<strlen>. The BIO is set to a read only state and 91as a result cannot be written to. This is useful when some data needs to be 92made available from a static area of memory in the form of a BIO. The 93supplied data is read directly from the supplied buffer: it is B<not> copied 94first, so the supplied area of memory must be unchanged until the BIO is freed. 95 96=head1 NOTES 97 98Writes to memory BIOs will always succeed if memory is available: that is 99their size can grow indefinitely. 100 101Every write after partial read (not all data in the memory buffer was read) 102to a read write memory BIO will have to move the unread data with an internal 103copy operation, if a BIO contains a lot of data and it is read in small 104chunks intertwined with writes the operation can be very slow. Adding 105a buffering BIO to the chain can speed up the process. 106 107Calling BIO_set_mem_buf() on a secmem or dgram BIO will give undefined results, 108including perhaps a program crash. 109 110Switching a memory BIO from read write to read only is not supported and 111can give undefined results including a program crash. There are two notable 112exceptions to the rule. The first one is to assign a static memory buffer 113immediately after BIO creation and set the BIO as read only. 114 115The other supported sequence is to start with a read write BIO then temporarily 116switch it to read only and call BIO_reset() on the read only BIO immediately 117before switching it back to read write. Before the BIO is freed it must be 118switched back to the read write mode. 119 120Calling BIO_get_mem_ptr() on read only BIO will return a BUF_MEM that 121contains only the remaining data to be read. If the close status of the 122BIO is set to BIO_NOCLOSE, before freeing the BUF_MEM the data pointer 123in it must be set to NULL as the data pointer does not point to an 124allocated memory. 125 126Calling BIO_reset() on a read write memory BIO with BIO_FLAGS_NONCLEAR_RST 127flag set can have unexpected outcome when the reads and writes to the 128BIO are intertwined. As documented above the BIO will be reset to the 129state after the last completed write operation. The effects of reads 130preceding that write operation cannot be undone. 131 132Calling BIO_get_mem_ptr() prior to a BIO_reset() call with 133BIO_FLAGS_NONCLEAR_RST set has the same effect as a write operation. 134 135=head1 RETURN VALUES 136 137BIO_s_mem(), BIO_s_dgram_mem() and BIO_s_secmem() return a valid memory 138B<BIO_METHOD> structure. 139 140BIO_set_mem_eof_return(), BIO_set_mem_buf() and BIO_get_mem_ptr() 141return 1 on success or a value which is less than or equal to 0 if an error occurred. 142 143BIO_get_mem_data() returns the total number of bytes available on success, 1440 if b is NULL, or a negative value in case of other errors. 145 146BIO_new_mem_buf() returns a valid B<BIO> structure on success or NULL on error. 147 148=head1 EXAMPLES 149 150Create a memory BIO and write some data to it: 151 152 BIO *mem = BIO_new(BIO_s_mem()); 153 154 BIO_puts(mem, "Hello World\n"); 155 156Create a read only memory BIO: 157 158 char data[] = "Hello World"; 159 BIO *mem = BIO_new_mem_buf(data, -1); 160 161Extract the BUF_MEM structure from a memory BIO and then free up the BIO: 162 163 BUF_MEM *bptr; 164 165 BIO_get_mem_ptr(mem, &bptr); 166 BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free() leaves BUF_MEM alone */ 167 BIO_free(mem); 168 169 170=head1 COPYRIGHT 171 172Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved. 173 174Licensed under the Apache License 2.0 (the "License"). You may not use 175this file except in compliance with the License. You can obtain a copy 176in the file LICENSE in the source distribution or at 177L<https://www.openssl.org/source/license.html>. 178 179=cut 180
