BIO_s_mem.pod 7.2 KB

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