More new BIO docs, correct some old ones.

=pod

=head1 NAME

	BIO_f_md - message digest BIO

=head1 SYNOPSIS

 #include <openssl/bio.h>

 #include <openssl/evp.h>

 BIO_METHOD *	BIO_f_md(void);

 int BIO_set_md(BIO *b,EVP_MD *md);

 int BIO_get_md(BIO *b,EVP_MD **mdp);

 int BIO_get_md_ctx(BIO *b,EVP_MD_CTX **mdcp);

=head1 DESCRIPTION

BIO_f_md() returns the message digest BIO method. This is a filter

BIO that digests any data passed through it, it is a BIO wrapper

for the digest routines EVP_DigestInit(), EVP_DigestUpdate()

and EVP_DigestFinal().

Any data written or read through a digest BIO using BIO_read() and

BIO_write() is digested.

BIO_gets(), if its B<size> parameter is large enough finishes the

digest calculation and returns the digest value. BIO_puts() is

not supported.

BIO_reset() reinitializes a digest BIO.

BIO_set_md() sets the message digest of BIO B<b> to B<md>: this

must be called to initialise a digest BIO before any data is

passed through it. It is a BIO_ctrl() macro.

BIO_get_md() places the a pointer to the digest BIOs digest method

in B<mdp>, it is a BIO_ctrl() macro.

BIO_get_md_ctx() returns the digest BIOs context into B<mdcp>.

=head1 NOTES

The context returned by BIO_get_md_ctx() can be used in calls

to EVP_DigestFinal() and also the signature routines EVP_SignFinal()

and EVP_VerifyFinal().

The context returned by BIO_get_md_ctx() is an internal context

structure. Changes made to this context will affect the digest

BIO itself and the context pointer will become invalid when the digest

BIO is freed.

After the digest has been retrieved from a digest BIO it must be

reinitialized by calling BIO_reset(), or BIO_set_md() before any more

data is passed through it.

If an application needs to call BIO_gets() or BIO_puts() through

a chain containing digest BIOs then this can be done by prepending

a buffering BIO.

=head1 RETURN VALUES

BIO_f_md() returns the digest BIO method.

BIO_set_md(), BIO_get_md() and BIO_md_ctx() return 1 for success and

0 for failure.

=head1 EXAMPLES

The following example creates a BIO chain containing an SHA1 and MD5

digest BIO and passes the string "Hello World" through it. Error

checking has been omitted for clarity.

 BIO *bio, *mdtmp;

 char message[] = "Hello World";

 bio = BIO_new(BIO_s_null());

 mdtmp = BIO_new(BIO_f_md());

 BIO_set_md(mdtmp, EVP_sha1());

 /* For BIO_push() we want to append the sink BIO and keep a note of

  * the start of the chain.

  */

 bio = BIO_push(mdtmp, bio);

 mdtmp = BIO_new(BIO_f_md());

 BIO_set_md(mdtmp, EVP_md5());

 bio = BIO_push(mdtmp, bio);

 /* Note: mdtmp can now be discarded */

 BIO_write(bio, message, strlen(message));

The next example digests data by reading through a chain instead:

 BIO *bio, *mdtmp;

 char buf[1024];

 int rdlen;

 bio = BIO_new_file(file, "rb");

 mdtmp = BIO_new(BIO_f_md());

 BIO_set_md(mdtmp, EVP_sha1());

 bio = BIO_push(mdtmp, bio);

 mdtmp = BIO_new(BIO_f_md());

 BIO_set_md(mdtmp, EVP_md5());

 bio = BIO_push(mdtmp, bio);

 do {

 	rdlen = BIO_read(bio, buf, sizeof(buf));

        /* Might want to do something with the data here */

 } while(rdlen > 0);

This next example retrieves the message digests from a BIO chain and

outputs them. This could be used with the examples above.

 BIO *mdtmp;

 unsigned char mdbuf[EVP_MAX_MD_SIZE];

 int mdlen;

 int i;

 mdtmp = bio;	/* Assume bio has previously been set up */

 do {

	EVP_MD *md;

 	mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);

        if(!mdtmp) break;

	BIO_get_md(mdtmp, &md);

        printf("%s digest", OBJ_nid2sn(EVP_MD_type(md)));

	mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE);

	for(i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]);

	printf("\n");

	mdtmp = BIO_next(mdtmp);

 } while(mdtmp);

 BIO_free_all(bio);

=head1 BUGS

The lack of support for BIO_puts() and the non standard behaviour of

BIO_gets() could be regarded as anomalous. It could be argued that BIO_gets()

and BIO_puts() should be passed to the next BIO in the chain and digest

the data passed through and that digests should be retrieved using a

separate BIO_ctrl() call.

=head1 SEE ALSO

TBA

=pod

=head1 NAME

	BIO_f_null - null filter

=head1 SYNOPSIS

 #include <openssl/bio.h>

 BIO_METHOD *	BIO_f_null(void);

=head1 DESCRIPTION

BIO_f_null() returns the null filter BIO method. This is a filter BIO

that does nothing.

All requests to a null filter BIO are passed through to the next BIO in

the chain: this means that a BIO chain containing a null filter BIO

behaves just as though the BIO was not there.

=head1 NOTES

As may be apparent a null filter BIO is not particularly useful.

=head1 RETURN VALUES

BIO_f_null() returns the null filter BIO method.

=head1 SEE ALSO

TBA

=pod

=head1 NAME

	BIO_s_null - null data sink

=head1 SYNOPSIS

 #include <openssl/bio.h>

 BIO_METHOD *	BIO_s_null(void);

=head1 DESCRIPTION

BIO_s_null() returns the null sink BIO method. Data written to

the null sink is discraded, reads return EOF.

=head1 NOTES

A null sink BIO behaves in a similar manner to the Unix /dev/null

device.

A null bio can be placed on the end of a chain to discard any data

passed through it.

A null sink is useful if, for example, an application wishes to digest some

data but not write the result anywhere. Since a BIO chain must normally

include a source/sink BIO this can be achieved by adding a null sink BIO

to the end of the chain

=head1 RETURN VALUES

BIO_s_null() returns the null sink BIO method.

=head1 SEE ALSO

TBA

BIOs can be joined together to form a chain (a single BIO is a chain

with one component). A chain normally consist of one source/sink

BIO and one or more filter BIOs. Data read from or written to the

end BIO then traverses the chain to the end (normally a source/sink

first BIO then traverses the chain to the end (normally a source/sink

BIO).

=head1 SEE ALSO