https://forums.ni.com/t5/Example-Code/GZip-Compression/ta-p/3534832 Using this code, gzipped file only partially uncompressed. Its a large XML File. I am wondering if because it works partially that means there is some sort of buffer ratio I can change within the OpenG library? The file unzippes perfectly when using 7zip. But I need a way to extract this using Labview. I cannot guarantee 7zip is installed on every machine. What other options do I have?

The routine in the linked article does a number of things wrong. First it prepends a zlib header (0x789C) to the deflate stream. This tells the inflate algorithm that it is a valid zlib stream and that it should use the adler32 algorithm for the crc calculation. But it is a gzip stream which should use the crc32 algorithm for checking. The inflate routine also checks the actual last 4 bytes in the stream to be a correct crc, so that of course will fail, which is why the routine returns -3 (DATA_ERROR) which is translated into LabVIEW error 42. The inflate algorithm internally also would allow direct gzip stream decoding including the header but this is not currently exposed to the API. I do have an idea how that can be done but it will take a few days. However the attached VI works on my computer (with oglib_lvzip-5.0.4-1.ogp) but generates of course the error 42 because of the CRC mismatch. So I'm curious if you still see corrupted output.

LabVIEW

GZip De-Compression failure, possible buffer oversize? File unzips in 7zip but not with the OpenG library.

Solved!

I released 5.0.5 of the OpenG ZIP Library with additional support for header encoding in Deflate and header decoding in Inflate.

Included VI can handle the entire gzip file from your first post as a whole! And it is better than just blindly cutting of 10 bytes from the file and trying to decode it without header at all, since the gzip header can contain additional information such as file name and extra stuff that you should try to properly decode if you want to make it truly gzip compliant.

Attached VI is LabVIEW 2020 and requires OpenG ZIP Library 5.0.5.

PS: I bet you used the Read from Text File node instead of the Read from Binary File one. This was the reason your binary gzip stream got corrupted!

Rolf Kalbermatter
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