More new BIO docs, correct some old ones.

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

diff --git a/doc/crypto/BIO_f_md.pod b/doc/crypto/BIO_f_md.pod
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+=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