doc/man3/BIO_s_mem.pod

   1 =pod
   2
   3 =head1 NAME
   4
   5 BIO_s_secmem, BIO_s_dgram_mem,
   6 BIO_s_mem, BIO_set_mem_eof_return, BIO_get_mem_data, BIO_set_mem_buf,
   7 BIO_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
  26 BIO_s_mem() returns the memory BIO method function.
  27
  28 A memory BIO is a source/sink BIO which uses memory for its I/O. Data
  29 written to a memory BIO is stored in a BUF_MEM structure which is extended
  30 as appropriate to accommodate the stored data.
  31
  32 BIO_s_secmem() is like BIO_s_mem() except that the secure heap is used
  33 for buffer storage.
  34
  35 BIO_s_dgram_mem() is a memory BIO that respects datagram semantics. A single
  36 call to L<BIO_write(3)> will write a single datagram to the memory BIO. A
  37 subsequent call to L<BIO_read(3)> will read the data in that datagram. The
  38 L<BIO_read(3)> call will never return more data than was written in the original
  39 L<BIO_write(3)> call even if there were subsequent L<BIO_write(3)> calls that
  40 wrote more datagrams. Each successive call to L<BIO_read(3)> will read the next
  41 datagram. If a L<BIO_read(3)> call supplies a read buffer that is smaller than
  42 the size of the datagram, then the read buffer will be completely filled and the
  43 remaining data from the datagram will be discarded.
  44
  45 It is not possible to write a zero length datagram. Calling L<BIO_write(3)> in
  46 this case will return 0 and no datagrams will be written. Calling L<BIO_read(3)>
  47 when there are no datagrams in the BIO to read will return a negative result and
  48 the "retry" flags will be set (i.e. calling L<BIO_should_retry(3)> will return
  49 true). A datagram mem BIO will never return true from L<BIO_eof(3)>.
  50
  51 Any data written to a memory BIO can be recalled by reading from it.
  52 Unless the memory BIO is read only any data read from it is deleted from
  53 the BIO.
  54
  55 Memory BIOs except BIO_s_dgram_mem() support BIO_gets() and BIO_puts().
  56
  57 BIO_s_dgram_mem() supports L<BIO_sendmmsg(3)> and L<BIO_recvmmsg(3)> calls
  58 and calls related to B<BIO_ADDR> and MTU handling similarly to the
  59 L<BIO_s_dgram_pair(3)>.
  60
  61 If the BIO_CLOSE flag is set when a memory BIO is freed then the underlying
  62 BUF_MEM structure is also freed.
  63
  64 Calling BIO_reset() on a read write memory BIO clears any data in it if the
  65 flag BIO_FLAGS_NONCLEAR_RST is not set, otherwise it just restores the read
  66 pointer to the state it was just after the last write was performed and the
  67 data can be read again. On a read only BIO it similarly restores the BIO to
  68 its original state and the read only data can be read again.
  69
  70 BIO_eof() is true if no data is in the BIO.
  71
  72 BIO_ctrl_pending() returns the number of bytes currently stored.
  73
  74 BIO_set_mem_eof_return() sets the behaviour of memory BIO B<b> when it is
  75 empty. If the B<v> is zero then an empty memory BIO will return EOF (that is
  76 it will return zero and BIO_should_retry(b) will be false. If B<v> is non
  77 zero then it will return B<v> when it is empty and it will set the read retry
  78 flag (that is BIO_read_retry(b) is true). To avoid ambiguity with a normal
  79 positive return value B<v> should be set to a negative value, typically -1.
  80 Calling this macro will fail for datagram mem BIOs.
  81
  82 BIO_get_mem_data() sets *B<pp> to a pointer to the start of the memory BIOs data
  83 and returns the total amount of data available. It is implemented as a macro.
  84 Note the pointer returned by this call is informative, no transfer of ownership
  85 of this memory is implied.  See notes on BIO_set_close().
  86
  87 BIO_set_mem_buf() sets the internal BUF_MEM structure to B<bm> and sets the
  88 close flag to B<c>, that is B<c> should be either BIO_CLOSE or BIO_NOCLOSE.
  89 It is a macro.
  90
  91 BIO_get_mem_ptr() places the underlying BUF_MEM structure in *B<pp>. It is
  92 a macro.
  93
  94 BIO_new_mem_buf() creates a memory BIO using B<len> bytes of data at B<buf>,
  95 if B<len> is -1 then the B<buf> is assumed to be nul terminated and its
  96 length is determined by B<strlen>. The BIO is set to a read only state and
  97 as a result cannot be written to. This is useful when some data needs to be
  98 made available from a static area of memory in the form of a BIO. The
  99 supplied data is read directly from the supplied buffer: it is B<not> copied
 100 first, so the supplied area of memory must be unchanged until the BIO is freed.
 101
 102 All of the five functions described above return an error with
 103 BIO_s_dgram_mem().
 104
 105 =head1 NOTES
 106
 107 Writes to memory BIOs will always succeed if memory is available: that is
 108 their size can grow indefinitely. An exception is BIO_s_dgram_mem() when
 109 L<BIO_set_write_buf_size(3)> is called on it. In such case the write buffer
 110 size will be fixed and any writes that would overflow the buffer will return
 111 an error.
 112
 113 Every write after partial read (not all data in the memory buffer was read)
 114 to a read write memory BIO will have to move the unread data with an internal
 115 copy operation, if a BIO contains a lot of data and it is read in small
 116 chunks intertwined with writes the operation can be very slow. Adding
 117 a buffering BIO to the chain can speed up the process.
 118
 119 Calling BIO_set_mem_buf() on a secmem or dgram BIO will give undefined results,
 120 including perhaps a program crash.
 121
 122 Switching a memory BIO from read write to read only is not supported and
 123 can give undefined results including a program crash. There are two notable
 124 exceptions to the rule. The first one is to assign a static memory buffer
 125 immediately after BIO creation and set the BIO as read only.
 126
 127 The other supported sequence is to start with a read write BIO then temporarily
 128 switch it to read only and call BIO_reset() on the read only BIO immediately
 129 before switching it back to read write. Before the BIO is freed it must be
 130 switched back to the read write mode.
 131
 132 Calling BIO_get_mem_ptr() on read only BIO will return a BUF_MEM that
 133 contains only the remaining data to be read. If the close status of the
 134 BIO is set to BIO_NOCLOSE, before freeing the BUF_MEM the data pointer
 135 in it must be set to NULL as the data pointer does not point to an
 136 allocated memory.
 137
 138 Calling BIO_reset() on a read write memory BIO with BIO_FLAGS_NONCLEAR_RST
 139 flag set can have unexpected outcome when the reads and writes to the
 140 BIO are intertwined. As documented above the BIO will be reset to the
 141 state after the last completed write operation. The effects of reads
 142 preceding that write operation cannot be undone.
 143
 144 Calling BIO_get_mem_ptr() prior to a BIO_reset() call with
 145 BIO_FLAGS_NONCLEAR_RST set has the same effect as a write operation.
 146
 147 Calling BIO_set_close() with BIO_NOCLOSE orphans the BUF_MEM internal to the
 148 BIO, _not_ its actual data buffer. See the examples section for the proper
 149 method for claiming ownership of the data pointer for a deferred free operation.
 150
 151 =head1 RETURN VALUES
 152
 153 BIO_s_mem(), BIO_s_dgram_mem() and BIO_s_secmem() return a valid memory
 154 B<BIO_METHOD> structure.
 155
 156 BIO_set_mem_eof_return(), BIO_set_mem_buf() and BIO_get_mem_ptr()
 157 return 1 on success or a value which is less than or equal to 0 if an error occurred.
 158
 159 BIO_get_mem_data() returns the total number of bytes available on success,
 160 0 if b is NULL, or a negative value in case of other errors.
 161
 162 BIO_new_mem_buf() returns a valid B<BIO> structure on success or NULL on error.
 163
 164 =head1 EXAMPLES
 165
 166 Create 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
 172 Create a read only memory BIO:
 173
 174  char data[] = "Hello World";
 175  BIO *mem = BIO_new_mem_buf(data, -1);
 176
 177 Extract 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
 185 Extract the BUF_MEM ptr, claim ownership of the internal data and free the BIO
 186 and 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 COPYRIGHT
 201
 202 Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved.
 203
 204 Licensed under the Apache License 2.0 (the "License").  You may not use
 205 this file except in compliance with the License.  You can obtain a copy
 206 in the file LICENSE in the source distribution or at
 207 L<https://www.openssl.org/source/license.html>.
 208
 209 =cut