BIO_read.pod 5.1 KB

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  1. =pod
  2. =head1 NAME
  3. BIO_read_ex, BIO_write_ex, BIO_read, BIO_write,
  4. BIO_gets, BIO_get_line, BIO_puts
  5. - BIO I/O functions
  6. =head1 SYNOPSIS
  7. #include <openssl/bio.h>
  8. int BIO_read_ex(BIO *b, void *data, size_t dlen, size_t *readbytes);
  9. int BIO_write_ex(BIO *b, const void *data, size_t dlen, size_t *written);
  10. int BIO_read(BIO *b, void *data, int dlen);
  11. int BIO_gets(BIO *b, char *buf, int size);
  12. int BIO_get_line(BIO *b, char *buf, int size);
  13. int BIO_write(BIO *b, const void *data, int dlen);
  14. int BIO_puts(BIO *b, const char *buf);
  15. =head1 DESCRIPTION
  16. BIO_read_ex() attempts to read I<dlen> bytes from BIO I<b> and places the data
  17. in I<data>. If any bytes were successfully read then the number of bytes read is
  18. stored in I<*readbytes>.
  19. BIO_write_ex() attempts to write I<dlen> bytes from I<data> to BIO I<b>.
  20. If successful then the number of bytes written is stored in I<*written>
  21. unless I<written> is NULL.
  22. BIO_read() attempts to read I<len> bytes from BIO I<b> and places
  23. the data in I<buf>.
  24. BIO_gets() performs the BIOs "gets" operation and places the data
  25. in I<buf>. Usually this operation will attempt to read a line of data
  26. from the BIO of maximum length I<size-1>. There are exceptions to this,
  27. however; for example, BIO_gets() on a digest BIO will calculate and
  28. return the digest and other BIOs may not support BIO_gets() at all.
  29. The returned string is always NUL-terminated and the '\n' is preserved
  30. if present in the input data.
  31. On binary input there may be NUL characters within the string;
  32. in this case the return value (if nonnegative) may give an incorrect length.
  33. BIO_get_line() attempts to read from BIO I<b> a line of data up to the next '\n'
  34. or the maximum length I<size-1> is reached and places the data in I<buf>.
  35. The returned string is always NUL-terminated and the '\n' is preserved
  36. if present in the input data.
  37. On binary input there may be NUL characters within the string;
  38. in this case the return value (if nonnegative) gives the actual length read.
  39. For implementing this, unfortunately the data needs to be read byte-by-byte.
  40. BIO_write() attempts to write I<len> bytes from I<buf> to BIO I<b>.
  41. BIO_puts() attempts to write a NUL-terminated string I<buf> to BIO I<b>.
  42. =head1 RETURN VALUES
  43. BIO_read_ex() returns 1 if data was successfully read, and 0 otherwise.
  44. BIO_write_ex() returns 1 if no error was encountered writing data, 0 otherwise.
  45. Requesting to write 0 bytes is not considered an error.
  46. BIO_write() returns -2 if the "write" operation is not implemented by the BIO
  47. or -1 on other errors.
  48. Otherwise it returns the number of bytes written.
  49. This may be 0 if the BIO I<b> is NULL or I<dlen <= 0>.
  50. BIO_gets() returns -2 if the "gets" operation is not implemented by the BIO
  51. or -1 on other errors.
  52. Otherwise it typically returns the amount of data read,
  53. but depending on the implementation it may return only the length up to
  54. the first NUL character contained in the data read.
  55. In any case the trailing NUL that is added after the data read
  56. is not included in the length returned.
  57. All other functions return either the amount of data successfully read or
  58. written (if the return value is positive) or that no data was successfully
  59. read or written if the result is 0 or -1. If the return value is -2 then
  60. the operation is not implemented in the specific BIO type.
  61. =head1 NOTES
  62. A 0 or -1 return is not necessarily an indication of an error. In
  63. particular when the source/sink is nonblocking or of a certain type
  64. it may merely be an indication that no data is currently available and that
  65. the application should retry the operation later.
  66. One technique sometimes used with blocking sockets is to use a system call
  67. (such as select(), poll() or equivalent) to determine when data is available
  68. and then call read() to read the data. The equivalent with BIOs (that is call
  69. select() on the underlying I/O structure and then call BIO_read() to
  70. read the data) should B<not> be used because a single call to BIO_read()
  71. can cause several reads (and writes in the case of SSL BIOs) on the underlying
  72. I/O structure and may block as a result. Instead select() (or equivalent)
  73. should be combined with non blocking I/O so successive reads will request
  74. a retry instead of blocking.
  75. See L<BIO_should_retry(3)> for details of how to
  76. determine the cause of a retry and other I/O issues.
  77. If the "gets" method is not supported by a BIO then BIO_get_line() can be used.
  78. It is also possible to make BIO_gets() usable even if the "gets" method is not
  79. supported by adding a buffering BIO L<BIO_f_buffer(3)> to the chain.
  80. =head1 SEE ALSO
  81. L<BIO_should_retry(3)>
  82. =head1 HISTORY
  83. BIO_gets() on 1.1.0 and older when called on BIO_fd() based BIO did not
  84. keep the '\n' at the end of the line in the buffer.
  85. BIO_get_line() was added in OpenSSL 3.0.
  86. BIO_write_ex() returns 1 if the size of the data to write is 0 and the
  87. I<written> parameter of the function can be NULL since OpenSSL 3.0.
  88. =head1 COPYRIGHT
  89. Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved.
  90. Licensed under the Apache License 2.0 (the "License"). You may not use
  91. this file except in compliance with the License. You can obtain a copy
  92. in the file LICENSE in the source distribution or at
  93. L<https://www.openssl.org/source/license.html>.
  94. =cut