BIO_s_mem.pod 3.8 KB

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  1. =pod
  2. =head1 NAME
  3. BIO_s_mem, BIO_set_mem_eof_return, BIO_get_mem_data, BIO_set_mem_buf,
  4. BIO_get_mem_ptr, BIO_new_mem_buf - memory BIO
  5. =head1 SYNOPSIS
  6. #include <openssl/bio.h>
  7. BIO_METHOD * BIO_s_mem(void);
  8. BIO_set_mem_eof_return(BIO *b,int v)
  9. long BIO_get_mem_data(BIO *b, char **pp)
  10. BIO_set_mem_buf(BIO *b,BUF_MEM *bm,int c)
  11. BIO_get_mem_ptr(BIO *b,BUF_MEM **pp)
  12. BIO *BIO_new_mem_buf(void *buf, int len);
  13. =head1 DESCRIPTION
  14. BIO_s_mem() return the memory BIO method function.
  15. A memory BIO is a source/sink BIO which uses memory for its I/O. Data
  16. written to a memory BIO is stored in a BUF_MEM structure which is extended
  17. as appropriate to accommodate the stored data.
  18. Any data written to a memory BIO can be recalled by reading from it.
  19. Unless the memory BIO is read only any data read from it is deleted from
  20. the BIO.
  21. Memory BIOs support BIO_gets() and BIO_puts().
  22. If the BIO_CLOSE flag is set when a memory BIO is freed then the underlying
  23. BUF_MEM structure is also freed.
  24. Calling BIO_reset() on a read write memory BIO clears any data in it. On a
  25. read only BIO it restores the BIO to its original state and the read only
  26. data can be read again.
  27. BIO_eof() is true if no data is in the BIO.
  28. BIO_ctrl_pending() returns the number of bytes currently stored.
  29. BIO_set_mem_eof_return() sets the behaviour of memory BIO B<b> when it is
  30. empty. If the B<v> is zero then an empty memory BIO will return EOF (that is
  31. it will return zero and BIO_should_retry(b) will be false. If B<v> is non
  32. zero then it will return B<v> when it is empty and it will set the read retry
  33. flag (that is BIO_read_retry(b) is true). To avoid ambiguity with a normal
  34. positive return value B<v> should be set to a negative value, typically -1.
  35. BIO_get_mem_data() sets B<pp> to a pointer to the start of the memory BIOs data
  36. and returns the total amount of data available. It is implemented as a macro.
  37. BIO_set_mem_buf() sets the internal BUF_MEM structure to B<bm> and sets the
  38. close flag to B<c>, that is B<c> should be either BIO_CLOSE or BIO_NOCLOSE.
  39. It is a macro.
  40. BIO_get_mem_ptr() places the underlying BUF_MEM structure in B<pp>. It is
  41. a macro.
  42. BIO_new_mem_buf() creates a memory BIO using B<len> bytes of data at B<buf>,
  43. if B<len> is -1 then the B<buf> is assumed to be null terminated and its
  44. length is determined by B<strlen>. The BIO is set to a read only state and
  45. as a result cannot be written to. This is useful when some data needs to be
  46. made available from a static area of memory in the form of a BIO. The
  47. supplied data is read directly from the supplied buffer: it is B<not> copied
  48. first, so the supplied area of memory must be unchanged until the BIO is freed.
  49. =head1 NOTES
  50. Writes to memory BIOs will always succeed if memory is available: that is
  51. their size can grow indefinitely.
  52. Every read from a read write memory BIO will remove the data just read with
  53. an internal copy operation, if a BIO contains a lot of data and it is
  54. read in small chunks the operation can be very slow. The use of a read only
  55. memory BIO avoids this problem. If the BIO must be read write then adding
  56. a buffering BIO to the chain will speed up the process.
  57. =head1 BUGS
  58. There should be an option to set the maximum size of a memory BIO.
  59. There should be a way to "rewind" a read write BIO without destroying
  60. its contents.
  61. The copying operation should not occur after every small read of a large BIO
  62. to improve efficiency.
  63. =head1 EXAMPLE
  64. Create a memory BIO and write some data to it:
  65. BIO *mem = BIO_new(BIO_s_mem());
  66. BIO_puts(mem, "Hello World\n");
  67. Create a read only memory BIO:
  68. char data[] = "Hello World";
  69. BIO *mem;
  70. mem = BIO_new_mem_buf(data, -1);
  71. Extract the BUF_MEM structure from a memory BIO and then free up the BIO:
  72. BUF_MEM *bptr;
  73. BIO_get_mem_ptr(mem, &bptr);
  74. BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free() leaves BUF_MEM alone */
  75. BIO_free(mem);
  76. =head1 SEE ALSO
  77. TBA