Ensure =cut is last line in every file.

[openssl.git] / doc / crypto / BIO_read.pod

diff --git a/doc/crypto/BIO_read.pod b/doc/crypto/BIO_read.pod
index 6c001a309242a3bde2b83744dc0a01c78430ad65..4df8c7e044b2e9e1ab34988a370f98946457d04e 100644 (file)
--- a/doc/crypto/BIO_read.pod
+++ b/doc/crypto/BIO_read.pod
@@ -2,16 +2,16 @@
 
 =head1 NAME
 
-       BIO_read, BIO_write, BIO_gets, BIO_puts - BIO I/O functions
+BIO_read, BIO_write, BIO_gets, BIO_puts - BIO I/O functions
 
 =head1 SYNOPSIS
 
  #include <openssl/bio.h>
 
-int    BIO_read(BIO *b, void *buf, int len);
-int    BIO_gets(BIO *b,char *buf, int size);
-int    BIO_write(BIO *b, const void *buf, int len);
-int    BIO_puts(BIO *b,const char *buf);
+ int   BIO_read(BIO *b, void *buf, int len);
+ int   BIO_gets(BIO *b, char *buf, int size);
+ int   BIO_write(BIO *b, const void *buf, int len);
+ int   BIO_puts(BIO *b, const char *buf);
 
 =head1 DESCRIPTION
 
@@ -20,34 +20,51 @@ the data in B<buf>.
 
 BIO_gets() performs the BIOs "gets" operation and places the data
 in B<buf>. Usually this operation will attempt to read a line of data
-from the BIO of maximum length B<len>. There are exceptions to this
-however, for example BIO_gets() on a digest BIO will calculate and
+from the BIO of maximum length B<len-1>. There are exceptions to this,
+however; for example, BIO_gets() on a digest BIO will calculate and
 return the digest and other BIOs may not support BIO_gets() at all.
+The returned string is always NUL-terminated.
 
 BIO_write() attempts to write B<len> bytes from B<buf> to BIO B<b>.
 
-BIO_puts() attempts to write a null terminated string B<buf> to BIO B<b>
+BIO_puts() attempts to write a NUL-terminated string B<buf> to BIO B<b>.
 
 =head1 RETURN VALUES
 
 All these functions return either the amount of data successfully read or
 written (if the return value is positive) or that no data was successfully
 read or written if the result is 0 or -1. If the return value is -2 then
-the operation is not implemented in the specific BIO type.
+the operation is not implemented in the specific BIO type.  The trailing
+NUL is not included in the length returned by BIO_gets().
 
 =head1 NOTES
 
 A 0 or -1 return is not necessarily an indication of an error. In
-particular when the source/sink is non-blocking or of a certain type (for
-example an SSL BIO can retry even if the underlying connection is blocking)
+particular when the source/sink is non-blocking or of a certain type
 it may merely be an indication that no data is currently available and that
-the application should retry the operation later. L<BIO_should_retry(3)|BIO_should_retry(3)>
-can be called to determine the precise cause.
+the application should retry the operation later.
+
+One technique sometimes used with blocking sockets is to use a system call
+(such as select(), poll() or equivalent) to determine when data is available
+and then call read() to read the data. The equivalent with BIOs (that is call
+select() on the underlying I/O structure and then call BIO_read() to
+read the data) should B<not> be used because a single call to BIO_read()
+can cause several reads (and writes in the case of SSL BIOs) on the underlying
+I/O structure and may block as a result. Instead select() (or equivalent)
+should be combined with non blocking I/O so successive reads will request
+a retry instead of blocking.
+
+See L<BIO_should_retry(3)> for details of how to
+determine the cause of a retry and other I/O issues.
 
 If the BIO_gets() function is not supported by a BIO then it possible to
-work around this by adding a buffering BIO L<BIO_f_buffer(3)|BIO_f_buffer(3)>
+work around this by adding a buffering BIO L<BIO_f_buffer(3)>
 to the chain.
 
 =head1 SEE ALSO
 
+L<BIO_should_retry(3)>
+
 TBA
+
+=cut