d2i_X509(3)

     NAME
          d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio,
          i2d_X509_fp - X509 encode and decode functions

     SYNOPSIS
           #include <openssl/x509.h>

           X509 *d2i_X509(X509 **px, unsigned char **in, int len);
           int i2d_X509(X509 *x, unsigned char **out);

           X509 *d2i_X509_bio(BIO *bp, X509 **x);
           X509 *d2i_X509_fp(FILE *fp, X509 **x);

           int i2d_X509_bio(X509 *x, BIO *bp);
           int i2d_X509_fp(X509 *x, FILE *fp);


     DESCRIPTION
          The X509 encode and decode routines encode and parse an X509
          structure, which represents an X509 certificate.

          d2i_X509() attempts to decode len bytes at *out. If
          successful a pointer to the X509 structure is returned. If
          an error occurred then NULL is returned. If px is not NULL
          then the returned structure is written to *px. If *px is not
          NULL then it is assumed that *px contains a valid X509
          structure and an attempt is made to reuse it. If the call is
          successful *out is incremented to the byte following the
          parsed data.

          i2d_X509() encodes the structure pointed to by x into DER
          format.  If out is not NULL is writes the DER encoded data
          to the buffer at *out, and increments it to point after the
          data just written.  If the return value is negative an error
          occurred, otherwise it returns the length of the encoded
          data.

          For OpenSSL 0.9.7 and later if *out is NULL memory will be
          allocated for a buffer and the encoded data written to it.
          In this case *out is not incremented and it points to the
          start of the data just written.

          d2i_X509_bio() is similar to d2i_X509() except it attempts
          to parse data from BIO bp.

          d2i_X509_fp() is similar to d2i_X509() except it attempts to
          parse data from FILE pointer fp.

          i2d_X509_bio() is similar to i2d_X509() except it writes the
          encoding of the structure x to BIO bp and it returns 1 for
          success and 0 for failure.

          i2d_X509_fp() is similar to i2d_X509() except it writes the
          encoding of the structure x to BIO bp and it returns 1 for
          success and 0 for failure.

     NOTES
          The letters i and d in for example i2d_X509 stand for
          "internal" (that is an internal C structure) and "DER". So
          that i2d_X509 converts from internal to DER.

          The functions can also understand BER forms.

          The actual X509 structure passed to i2d_X509() must be a
          valid populated X509 structure it can not simply be fed with
          an empty structure such as that returned by X509_new().

          The encoded data is in binary form and may contain embedded
          zeroes.  Therefore any FILE pointers or BIOs should be
          opened in binary mode.  Functions such as strlen() will not
          return the correct length of the encoded structure.

          The ways that *in and *out are incremented after the
          operation can trap the unwary. See the WARNINGS section for
          some common errors.

          The reason for the auto increment behaviour is to reflect a
          typical usage of ASN1 functions: after one structure is
          encoded or decoded another will processed after it.

     EXAMPLES
          Allocate and encode the DER encoding of an X509 structure:

           int len;
           unsigned char *buf, *p;

           len = i2d_X509(x, NULL);

           buf = OPENSSL_malloc(len);

           if (buf == NULL)
                  /* error */

           p = buf;

           i2d_X509(x, &p);

          If you are using OpenSSL 0.9.7 or later then this can be
          simplified to:

           int len;
           unsigned char *buf;

           buf = NULL;
           len = i2d_X509(x, &buf);

           if (len < 0)
                  /* error */

          Attempt to decode a buffer:

           X509 *x;

           unsigned char *buf, *p;

           int len;

           /* Something to setup buf and len */

           p = buf;

           x = d2i_X509(NULL, &p, len);

           if (x == NULL)
              /* Some error */

          Alternative technique:

           X509 *x;

           unsigned char *buf, *p;

           int len;

           /* Something to setup buf and len */

           p = buf;

           x = NULL;

           if(!d2i_X509(&x, &p, len))
              /* Some error */


     WARNINGS
          The use of temporary variable is mandatory. A common mistake
          is to attempt to use a buffer directly as follows:

           int len;
           unsigned char *buf;

           len = i2d_X509(x, NULL);

           buf = OPENSSL_malloc(len);

           if (buf == NULL)
                  /* error */

           i2d_X509(x, &buf);

           /* Other stuff ... */

           OPENSSL_free(buf);

          This code will result in buf apparently containing garbage
          because it was incremented after the call to point after the
          data just written.  Also buf will no longer contain the
          pointer allocated by OPENSSL_malloc() and the subsequent
          call to OPENSSL_free() may well crash.

          The auto allocation feature (setting buf to NULL) only works
          on OpenSSL 0.9.7 and later. Attempts to use it on earlier
          versions will typically cause a segmentation violation.

          Another trap to avoid is misuse of the xp argument to
          d2i_X509():

           X509 *x;

           if (!d2i_X509(&x, &p, len))
                  /* Some error */

          This will probably crash somewhere in d2i_X509(). The reason
          for this is that the variable x is uninitialized and an
          attempt will be made to interpret its (invalid) value as an
          X509 structure, typically causing a segmentation violation.
          If x is set to NULL first then this will not happen.

     BUGS
          In some versions of OpenSSL the "reuse" behaviour of
          d2i_X509() when *px is valid is broken and some parts of the
          reused structure may persist if they are not present in the
          new one. As a result the use of this "reuse" behaviour is
          strongly discouraged.

          i2d_X509() will not return an error in many versions of
          OpenSSL, if mandatory fields are not initialized due to a
          programming error then the encoded structure may contain
          invalid data or omit the fields entirely and will not be
          parsed by d2i_X509(). This may be fixed in future so code
          should not assume that i2d_X509() will always succeed.

     RETURN VALUES
          d2i_X509(), d2i_X509_bio() and d2i_X509_fp() return a valid
          X509 structure or NULL if an error occurs. The error code
          that can be obtained by ERR_get_error(3).

          i2d_X509(), i2d_X509_bio() and i2d_X509_fp() return a the
          number of bytes successfully encoded or a negative value if
          an error occurs. The error code can be obtained by
          ERR_get_error(3).

          i2d_X509_bio() and i2d_X509_fp() returns 1 for success and 0
          if an error occurs The error code can be obtained by
          ERR_get_error(3).

     SEE ALSO
          ERR_get_error(3)

     HISTORY
          d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio
          and i2d_X509_fp are available in all versions of SSLeay and
          OpenSSL.