Clarify (non-)blocking behavior of EGD socket interface used by RAND_egd().

[oweals/openssl.git] / doc / crypto / BIO_s_bio.pod

diff --git a/doc/crypto/BIO_s_bio.pod b/doc/crypto/BIO_s_bio.pod
index 7a3b2db141461cee9168166e8b07409d6220302f..8d0a55a025c73f49a49d5d29afec0f43056b2793 100644 (file)
--- a/doc/crypto/BIO_s_bio.pod
+++ b/doc/crypto/BIO_s_bio.pod
@@ -2,10 +2,10 @@
 
 =head1 NAME
 
 
 =head1 NAME
 

-BIO_s_bio, BIO_make_bio_pair, BIO_destroy_bio_pair, BIO_set_write_buf_size,
-BIO_get_write_buf_size, BIO_new_bio_pair, BIO_get_write_guarantee,
-BIO_ctrl_get_write_guarantee, BIO_get_read_request, BIO_ctrl_get_read_request,
-BIO_ctrl_reset_read_request - BIO pair BIO
+BIO_s_bio, BIO_make_bio_pair, BIO_destroy_bio_pair, BIO_shutdown_wr, 
+BIO_set_write_buf_size, BIO_get_write_buf_size, BIO_new_bio_pair,
+BIO_get_write_guarantee, BIO_ctrl_get_write_guarantee, BIO_get_read_request,
+BIO_ctrl_get_read_request, BIO_ctrl_reset_read_request - BIO pair BIO

 
 =head1 SYNOPSIS
 
 
 =head1 SYNOPSIS
 


@@ -16,6 +16,8 @@ BIO_ctrl_reset_read_request - BIO pair BIO
  #define BIO_make_bio_pair(b1,b2)   (int)BIO_ctrl(b1,BIO_C_MAKE_BIO_PAIR,0,b2)
  #define BIO_destroy_bio_pair(b)    (int)BIO_ctrl(b,BIO_C_DESTROY_BIO_PAIR,0,NULL)
 
  #define BIO_make_bio_pair(b1,b2)   (int)BIO_ctrl(b1,BIO_C_MAKE_BIO_PAIR,0,b2)
  #define BIO_destroy_bio_pair(b)    (int)BIO_ctrl(b,BIO_C_DESTROY_BIO_PAIR,0,NULL)
 

+ #define BIO_shutdown_wr(b) (int)BIO_ctrl(b, BIO_C_SHUTDOWN_WR, 0, NULL)
+

  #define BIO_set_write_buf_size(b,size) (int)BIO_ctrl(b,BIO_C_SET_WRITE_BUF_SIZE,size,NULL)
  #define BIO_get_write_buf_size(b,size) (size_t)BIO_ctrl(b,BIO_C_GET_WRITE_BUF_SIZE,size,NULL)
 
  #define BIO_set_write_buf_size(b,size) (int)BIO_ctrl(b,BIO_C_SET_WRITE_BUF_SIZE,size,NULL)
  #define BIO_get_write_buf_size(b,size) (size_t)BIO_ctrl(b,BIO_C_GET_WRITE_BUF_SIZE,size,NULL)
 


@@ -60,6 +62,11 @@ BIO_make_bio_pair() joins two separate BIOs into a connected pair.
 BIO_destroy_pair() destroys the association between two connected BIOs. Freeing
 up any half of the pair will automatically destroy the association.
 
 BIO_destroy_pair() destroys the association between two connected BIOs. Freeing
 up any half of the pair will automatically destroy the association.
 

+BIO_shutdown_wr() is used to close down a BIO B<b>. After this call no further
+writes on BIO B<b> are allowed (they will return an error). Reads on the other
+half of the pair will return any pending data or EOF when all pending data has
+been read. 
+

 BIO_set_write_buf_size() sets the write buffer size of BIO B<b> to B<size>.
 If the size is not initialized a default value is used. This is currently
 17K, sufficient for a maximum size TLS record.
 BIO_set_write_buf_size() sets the write buffer size of BIO B<b> to B<size>.
 If the size is not initialized a default value is used. This is currently
 17K, sufficient for a maximum size TLS record.


@@ -69,7 +76,9 @@ BIO_get_write_buf_size() returns the size of the write buffer.
 BIO_new_bio_pair() combines the calls to BIO_new(), BIO_make_bio_pair() and
 BIO_set_write_buf_size() to create a connected pair of BIOs B<bio1>, B<bio2>
 with write buffer sizes B<writebuf1> and B<writebuf2>. If either size is
 BIO_new_bio_pair() combines the calls to BIO_new(), BIO_make_bio_pair() and
 BIO_set_write_buf_size() to create a connected pair of BIOs B<bio1>, B<bio2>
 with write buffer sizes B<writebuf1> and B<writebuf2>. If either size is

-zero then the default size is used.
+zero then the default size is used.  BIO_new_bio_pair() does not check whether
+B<bio1> or B<bio2> do point to some other BIO, the values are overwritten,
+BIO_free() is not called.

 
 BIO_get_write_guarantee() and BIO_ctrl_get_write_guarantee() return the maximum
 length of data that can be currently written to the BIO. Writes larger than this
 
 BIO_get_write_guarantee() and BIO_ctrl_get_write_guarantee() return the maximum
 length of data that can be currently written to the BIO. Writes larger than this


@@ -77,12 +86,17 @@ value will return a value from BIO_write() less than the amount requested or if
 buffer is full request a retry. BIO_ctrl_get_write_guarantee() is a function
 whereas BIO_get_write_guarantee() is a macro.
 
 buffer is full request a retry. BIO_ctrl_get_write_guarantee() is a function
 whereas BIO_get_write_guarantee() is a macro.
 

-BIO_get_read_request() and BIO_ctrl_get_read_request() return the amount of data
-requested (or the buffer size if it is less) if the last read failed due to an
-empty buffer. This can be used to determine how much data should be written to the
-other half of the pair so the next read will succeed: this is most useful in TLS/SSL
-applications where the amount of data read is usually meaningful rather than just
-a buffer size. After a successful read this call will return zero.
+BIO_get_read_request() and BIO_ctrl_get_read_request() return the
+amount of data requested, or the buffer size if it is less, if the
+last read attempt at the other half of the BIO pair failed due to an
+empty buffer.  This can be used to determine how much data should be
+written to the BIO so the next read will succeed: this is most useful
+in TLS/SSL applications where the amount of data read is usually
+meaningful rather than just a buffer size. After a successful read
+this call will return zero.  It also will return zero once new data
+has been written satisfying the read request or part of it.
+Note that BIO_get_read_request() never returns an amount larger
+than that returned by BIO_get_write_guarantee().

 
 BIO_ctrl_reset_read_request() can also be used to reset the value returned by
 BIO_get_read_request() to zero.
 
 BIO_ctrl_reset_read_request() can also be used to reset the value returned by
 BIO_get_read_request() to zero.


@@ -106,9 +120,59 @@ the application then waits for data to be available on the underlying transport
 before flushing the write buffer it will never succeed because the request was
 never sent!
 
 before flushing the write buffer it will never succeed because the request was
 never sent!
 

+=head1 RETURN VALUES
+
+BIO_new_bio_pair() returns 1 on success, with the new BIOs available in
+B<bio1> and B<bio2>, or 0 on failure, with NULL pointers stored into the
+locations for B<bio1> and B<bio2>. Check the error stack for more information.
+
+[XXXXX: More return values need to be added here]
+

 =head1 EXAMPLE
 
 =head1 EXAMPLE
 

-TBA
+The BIO pair can be used to have full control over the network access of an
+application. The application can call select() on the socket as required
+without having to go through the SSL-interface.
+
+ BIO *internal_bio, *network_bio;
+ ...
+ BIO_new_bio_pair(internal_bio, 0, network_bio, 0);
+ SSL_set_bio(ssl, internal_bio, internal_bio);
+ SSL_operations();
+ ...
+
+ application |   TLS-engine
+    |        |
+    +----------> SSL_operations()
+             |     /\    ||
+             |     ||    \/
+             |   BIO-pair (internal_bio)
+    +----------< BIO-pair (network_bio)
+    |        |
+  socket     |
+
+  ...
+  SSL_free(ssl);               /* implicitly frees internal_bio */
+  BIO_free(network_bio);
+  ...
+
+As the BIO pair will only buffer the data and never directly access the
+connection, it behaves non-blocking and will return as soon as the write
+buffer is full or the read buffer is drained. Then the application has to
+flush the write buffer and/or fill the read buffer.
+
+Use the BIO_ctrl_pending(), to find out whether data is buffered in the BIO
+and must be transfered to the network. Use BIO_ctrl_get_read_request() to
+find out, how many bytes must be written into the buffer before the
+SSL_operation() can successfully be continued.
+
+=head1 WARNING
+
+As the data is buffered, SSL_operation() may return with a ERROR_SSL_WANT_READ
+condition, but there is still data in the write buffer. An application must
+not rely on the error value of SSL_operation() but must assure that the
+write buffer is always flushed first. Otherwise a deadlock may occur as
+the peer might be waiting for the data before being able to continue.

 
 =head1 SEE ALSO
 
 
 =head1 SEE ALSO