CMS_compress.pod 2.3 KB

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  1. =pod
  2. =head1 NAME
  3. CMS_compress - create a CMS CompressedData structure
  4. =head1 SYNOPSIS
  5. #include <openssl/cms.h>
  6. CMS_ContentInfo *CMS_compress(BIO *in, int comp_nid, unsigned int flags);
  7. =head1 DESCRIPTION
  8. CMS_compress() creates and returns a CMS CompressedData structure. B<comp_nid>
  9. is the compression algorithm to use or B<NID_undef> to use the default
  10. algorithm (zlib compression). B<in> is the content to be compressed.
  11. B<flags> is an optional set of flags.
  12. =head1 NOTES
  13. The only currently supported compression algorithm is zlib using the NID
  14. NID_zlib_compression.
  15. If zlib support is not compiled into OpenSSL then CMS_compress() will return
  16. an error.
  17. If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are
  18. prepended to the data.
  19. Normally the supplied content is translated into MIME canonical format (as
  20. required by the S/MIME specifications) if B<CMS_BINARY> is set no translation
  21. occurs. This option should be used if the supplied data is in binary format
  22. otherwise the translation will corrupt it. If B<CMS_BINARY> is set then
  23. B<CMS_TEXT> is ignored.
  24. If the B<CMS_STREAM> flag is set a partial B<CMS_ContentInfo> structure is
  25. returned suitable for streaming I/O: no data is read from the BIO B<in>.
  26. The compressed data is included in the CMS_ContentInfo structure, unless
  27. B<CMS_DETACHED> is set in which case it is omitted. This is rarely used in
  28. practice and is not supported by SMIME_write_CMS().
  29. =head1 NOTES
  30. If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is
  31. B<not> complete and outputting its contents via a function that does not
  32. properly finalize the B<CMS_ContentInfo> structure will give unpredictable
  33. results.
  34. Several functions including SMIME_write_CMS(), i2d_CMS_bio_stream(),
  35. PEM_write_bio_CMS_stream() finalize the structure. Alternatively finalization
  36. can be performed by obtaining the streaming ASN1 B<BIO> directly using
  37. BIO_new_CMS().
  38. Additional compression parameters such as the zlib compression level cannot
  39. currently be set.
  40. =head1 RETURN VALUES
  41. CMS_compress() returns either a CMS_ContentInfo structure or NULL if an error
  42. occurred. The error can be obtained from ERR_get_error(3).
  43. =head1 SEE ALSO
  44. L<ERR_get_error(3)|ERR_get_error(3)>, L<CMS_uncompress(3)|CMS_uncompress(3)>
  45. =head1 HISTORY
  46. CMS_compress() was added to OpenSSL 0.9.8
  47. The B<CMS_STREAM> flag was first supported in OpenSSL 1.0.0.
  48. =cut