1=pod 2 3=head1 NAME 4 5BIO_s_secmem, 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_secmem(void); 15 16 BIO_set_mem_eof_return(BIO *b, int v); 17 long BIO_get_mem_data(BIO *b, char **pp); 18 BIO_set_mem_buf(BIO *b, BUF_MEM *bm, int c); 19 BIO_get_mem_ptr(BIO *b, BUF_MEM **pp); 20 21 BIO *BIO_new_mem_buf(const void *buf, int len); 22 23=head1 DESCRIPTION 24 25BIO_s_mem() returns the memory BIO method function. 26 27A memory BIO is a source/sink BIO which uses memory for its I/O. Data 28written to a memory BIO is stored in a BUF_MEM structure which is extended 29as appropriate to accommodate the stored data. 30 31BIO_s_secmem() is like BIO_s_mem() except that the secure heap is used 32for buffer storage. 33 34Any data written to a memory BIO can be recalled by reading from it. 35Unless the memory BIO is read only any data read from it is deleted from 36the BIO. 37 38Memory BIOs support BIO_gets() and BIO_puts(). 39 40If the BIO_CLOSE flag is set when a memory BIO is freed then the underlying 41BUF_MEM structure is also freed. 42 43Calling BIO_reset() on a read write memory BIO clears any data in it if the 44flag BIO_FLAGS_NONCLEAR_RST is not set, otherwise it just restores the read 45pointer to the state it was just after the last write was performed and the 46data can be read again. On a read only BIO it similarly restores the BIO to 47its original state and the read only data can be read again. 48 49BIO_eof() is true if no data is in the BIO. 50 51BIO_ctrl_pending() returns the number of bytes currently stored. 52 53BIO_set_mem_eof_return() sets the behaviour of memory BIO B<b> when it is 54empty. If the B<v> is zero then an empty memory BIO will return EOF (that is 55it will return zero and BIO_should_retry(b) will be false. If B<v> is non 56zero then it will return B<v> when it is empty and it will set the read retry 57flag (that is BIO_read_retry(b) is true). To avoid ambiguity with a normal 58positive return value B<v> should be set to a negative value, typically -1. 59 60BIO_get_mem_data() sets *B<pp> to a pointer to the start of the memory BIOs data 61and returns the total amount of data available. It is implemented as a macro. 62Note the pointer returned by this call is informative, no transfer of ownership 63of this memory is implied. See notes on BIO_set_close(). 64 65BIO_set_mem_buf() sets the internal BUF_MEM structure to B<bm> and sets the 66close flag to B<c>, that is B<c> should be either BIO_CLOSE or BIO_NOCLOSE. 67It is a macro. 68 69BIO_get_mem_ptr() places the underlying BUF_MEM structure in *B<pp>. It is 70a macro. 71 72BIO_new_mem_buf() creates a memory BIO using B<len> bytes of data at B<buf>, 73if B<len> is -1 then the B<buf> is assumed to be nul terminated and its 74length is determined by B<strlen>. The BIO is set to a read only state and 75as a result cannot be written to. This is useful when some data needs to be 76made available from a static area of memory in the form of a BIO. The 77supplied data is read directly from the supplied buffer: it is B<not> copied 78first, so the supplied area of memory must be unchanged until the BIO is freed. 79 80=head1 NOTES 81 82Writes to memory BIOs will always succeed if memory is available: that is 83their size can grow indefinitely. 84 85Every write after partial read (not all data in the memory buffer was read) 86to a read write memory BIO will have to move the unread data with an internal 87copy operation, if a BIO contains a lot of data and it is read in small 88chunks intertwined with writes the operation can be very slow. Adding 89a buffering BIO to the chain can speed up the process. 90 91Calling BIO_set_mem_buf() on a BIO created with BIO_new_secmem() will 92give undefined results, including perhaps a program crash. 93 94Switching the memory BIO from read write to read only is not supported and 95can give undefined results including a program crash. There are two notable 96exceptions to the rule. The first one is to assign a static memory buffer 97immediately after BIO creation and set the BIO as read only. 98 99The other supported sequence is to start with read write BIO then temporarily 100switch it to read only and call BIO_reset() on the read only BIO immediately 101before switching it back to read write. Before the BIO is freed it must be 102switched back to the read write mode. 103 104Calling BIO_get_mem_ptr() on read only BIO will return a BUF_MEM that 105contains only the remaining data to be read. If the close status of the 106BIO is set to BIO_NOCLOSE, before freeing the BUF_MEM the data pointer 107in it must be set to NULL as the data pointer does not point to an 108allocated memory. 109 110Calling BIO_reset() on a read write memory BIO with BIO_FLAGS_NONCLEAR_RST 111flag set can have unexpected outcome when the reads and writes to the 112BIO are intertwined. As documented above the BIO will be reset to the 113state after the last completed write operation. The effects of reads 114preceding that write operation cannot be undone. 115 116Calling BIO_get_mem_ptr() prior to a BIO_reset() call with 117BIO_FLAGS_NONCLEAR_RST set has the same effect as a write operation. 118 119Calling BIO_set_close() with BIO_NOCLOSE orphans the BUF_MEM internal to the 120BIO, _not_ its actual data buffer. See the examples section for the proper 121method for claiming ownership of the data pointer for a deferred free operation. 122 123=head1 BUGS 124 125There should be an option to set the maximum size of a memory BIO. 126 127=head1 RETURN VALUES 128 129BIO_s_mem() and BIO_s_secmem() return a valid memory B<BIO_METHOD> structure. 130 131BIO_set_mem_eof_return(), BIO_set_mem_buf() and BIO_get_mem_ptr() 132return 1 on success or a value which is less than or equal to 0 if an error occurred. 133 134BIO_get_mem_data() returns the total number of bytes available on success, 1350 if b is NULL, or a negative value in case of other errors. 136 137BIO_new_mem_buf() returns a valid B<BIO> structure on success or NULL on error. 138 139=head1 EXAMPLES 140 141Create a memory BIO and write some data to it: 142 143 BIO *mem = BIO_new(BIO_s_mem()); 144 145 BIO_puts(mem, "Hello World\n"); 146 147Create a read only memory BIO: 148 149 char data[] = "Hello World"; 150 BIO *mem = BIO_new_mem_buf(data, -1); 151 152Extract the BUF_MEM structure from a memory BIO and then free up the BIO: 153 154 BUF_MEM *bptr; 155 156 BIO_get_mem_ptr(mem, &bptr); 157 BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free() leaves BUF_MEM alone */ 158 BIO_free(mem); 159 160Extract the BUF_MEM ptr, claim ownership of the internal data and free the BIO 161and BUF_MEM structure: 162 163 BUF_MEM *bptr; 164 char *data; 165 166 BIO_get_mem_data(bio, &data); 167 BIO_get_mem_ptr(bio, &bptr); 168 BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free orphans BUF_MEM */ 169 BIO_free(bio); 170 bptr->data = NULL; /* Tell BUF_MEM to orphan data */ 171 BUF_MEM_free(bptr); 172 ... 173 free(data); 174 175=head1 COPYRIGHT 176 177Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved. 178 179Licensed under the Apache License 2.0 (the "License"). You may not use 180this file except in compliance with the License. You can obtain a copy 181in the file LICENSE in the source distribution or at 182L<https://www.openssl.org/source/license.html>. 183 184=cut 185