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 except BIO_s_dgram_mem() support BIO_gets() and BIO_puts(). 56 57BIO_s_dgram_mem() supports L<BIO_sendmmsg(3)> and L<BIO_recvmmsg(3)> calls 58and calls related to B<BIO_ADDR> and MTU handling similarly to the 59L<BIO_s_dgram_pair(3)>. 60 61If the BIO_CLOSE flag is set when a memory BIO is freed then the underlying 62BUF_MEM structure is also freed. 63 64Calling BIO_reset() on a read write memory BIO clears any data in it if the 65flag BIO_FLAGS_NONCLEAR_RST is not set, otherwise it just restores the read 66pointer to the state it was just after the last write was performed and the 67data can be read again. On a read only BIO it similarly restores the BIO to 68its original state and the read only data can be read again. 69 70BIO_eof() is true if no data is in the BIO. 71 72BIO_ctrl_pending() returns the number of bytes currently stored. 73 74BIO_set_mem_eof_return() sets the behaviour of memory BIO B<b> when it is 75empty. If the B<v> is zero then an empty memory BIO will return EOF (that is 76it will return zero and BIO_should_retry(b) will be false. If B<v> is non 77zero then it will return B<v> when it is empty and it will set the read retry 78flag (that is BIO_read_retry(b) is true). To avoid ambiguity with a normal 79positive return value B<v> should be set to a negative value, typically -1. 80Calling this macro will fail for datagram mem BIOs. 81 82BIO_get_mem_data() sets *B<pp> to a pointer to the start of the memory BIOs data 83and returns the total amount of data available. It is implemented as a macro. 84Note the pointer returned by this call is informative, no transfer of ownership 85of this memory is implied. See notes on BIO_set_close(). 86 87BIO_set_mem_buf() sets the internal BUF_MEM structure to B<bm> and sets the 88close flag to B<c>, that is B<c> should be either BIO_CLOSE or BIO_NOCLOSE. 89It is a macro. 90 91BIO_get_mem_ptr() places the underlying BUF_MEM structure in *B<pp>. It is 92a macro. 93 94BIO_new_mem_buf() creates a memory BIO using B<len> bytes of data at B<buf>, 95if B<len> is -1 then the B<buf> is assumed to be nul terminated and its 96length is determined by B<strlen>. The BIO is set to a read only state and 97as a result cannot be written to. This is useful when some data needs to be 98made available from a static area of memory in the form of a BIO. The 99supplied data is read directly from the supplied buffer: it is B<not> copied 100first, so the supplied area of memory must be unchanged until the BIO is freed. 101 102All of the five functions described above return an error with 103BIO_s_dgram_mem(). 104 105=head1 NOTES 106 107Writes to memory BIOs will always succeed if memory is available: that is 108their size can grow indefinitely. An exception is BIO_s_dgram_mem() when 109L<BIO_set_write_buf_size(3)> is called on it. In such case the write buffer 110size will be fixed and any writes that would overflow the buffer will return 111an error. 112 113Every write after partial read (not all data in the memory buffer was read) 114to a read write memory BIO will have to move the unread data with an internal 115copy operation, if a BIO contains a lot of data and it is read in small 116chunks intertwined with writes the operation can be very slow. Adding 117a buffering BIO to the chain can speed up the process. 118 119Calling BIO_set_mem_buf() on a secmem or dgram BIO will give undefined results, 120including perhaps a program crash. 121 122Switching a memory BIO from read write to read only is not supported and 123can give undefined results including a program crash. There are two notable 124exceptions to the rule. The first one is to assign a static memory buffer 125immediately after BIO creation and set the BIO as read only. 126 127The other supported sequence is to start with a read write BIO then temporarily 128switch it to read only and call BIO_reset() on the read only BIO immediately 129before switching it back to read write. Before the BIO is freed it must be 130switched back to the read write mode. 131 132Calling BIO_get_mem_ptr() on read only BIO will return a BUF_MEM that 133contains only the remaining data to be read. If the close status of the 134BIO is set to BIO_NOCLOSE, before freeing the BUF_MEM the data pointer 135in it must be set to NULL as the data pointer does not point to an 136allocated memory. 137 138Calling BIO_reset() on a read write memory BIO with BIO_FLAGS_NONCLEAR_RST 139flag set can have unexpected outcome when the reads and writes to the 140BIO are intertwined. As documented above the BIO will be reset to the 141state after the last completed write operation. The effects of reads 142preceding that write operation cannot be undone. 143 144Calling BIO_get_mem_ptr() prior to a BIO_reset() call with 145BIO_FLAGS_NONCLEAR_RST set has the same effect as a write operation. 146 147Calling BIO_set_close() with BIO_NOCLOSE orphans the BUF_MEM internal to the 148BIO, _not_ its actual data buffer. See the examples section for the proper 149method for claiming ownership of the data pointer for a deferred free operation. 150 151=head1 RETURN VALUES 152 153BIO_s_mem(), BIO_s_dgram_mem() and BIO_s_secmem() return a valid memory 154B<BIO_METHOD> structure. 155 156BIO_set_mem_eof_return(), BIO_set_mem_buf() and BIO_get_mem_ptr() 157return 1 on success or a value which is less than or equal to 0 if an error occurred. 158 159BIO_get_mem_data() returns the total number of bytes available on success, 1600 if b is NULL, or a negative value in case of other errors. 161 162BIO_new_mem_buf() returns a valid B<BIO> structure on success or NULL on error. 163 164=head1 EXAMPLES 165 166Create a memory BIO and write some data to it: 167 168 BIO *mem = BIO_new(BIO_s_mem()); 169 170 BIO_puts(mem, "Hello World\n"); 171 172Create a read only memory BIO: 173 174 char data[] = "Hello World"; 175 BIO *mem = BIO_new_mem_buf(data, -1); 176 177Extract the BUF_MEM structure from a memory BIO and then free up the BIO: 178 179 BUF_MEM *bptr; 180 181 BIO_get_mem_ptr(mem, &bptr); 182 BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free() leaves BUF_MEM alone */ 183 BIO_free(mem); 184 185Extract the BUF_MEM ptr, claim ownership of the internal data and free the BIO 186and BUF_MEM structure: 187 188 BUF_MEM *bptr; 189 char *data; 190 191 BIO_get_mem_data(bio, &data); 192 BIO_get_mem_ptr(bio, &bptr); 193 BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free orphans BUF_MEM */ 194 BIO_free(bio); 195 bptr->data = NULL; /* Tell BUF_MEM to orphan data */ 196 BUF_MEM_free(bptr); 197 ... 198 free(data); 199 200=head1 HISTORY 201 202BIO_s_dgram_mem() was added in OpenSSL 3.2. 203 204=head1 COPYRIGHT 205 206Copyright 2000-2024 The OpenSSL Project Authors. All Rights Reserved. 207 208Licensed under the Apache License 2.0 (the "License"). You may not use 209this file except in compliance with the License. You can obtain a copy 210in the file LICENSE in the source distribution or at 211L<https://www.openssl.org/source/license.html>. 212 213=cut 214
