Error 36 Incorrect Gzip Crc Checksum
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Gunzip Invalid Compressed Data Crc Error
Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 4.7 million repair gzip file programmers, just like you, helping each other. Join them; it only takes a minute: Sign up GZipStream doesn't detect corrupt data (even CRC32 passes)? up vote 4 down vote favorite I'm using GZipStream to compress / gzip invalid compressed data--format violated decompress data. I chose this over DeflateStream since the documentation states that GZipStream also adds a CRC to detect corrupt data, which is another feature I wanted. My "positive" unit tests are working well in that I can compress some data, save the compressed byte array and then successfully decompress it again. The .NET GZipStream compress and decompress problem post helped me realize that I needed to close the GZipStream before accessing the compressed
Gunzip Unexpected End Of File Ignore
or decompressed data. Next, I continued to write a "negative" unit test to be sure corrupt data could be detected. I had previously used the example for the GZipStream class from MSDN to compress a file, open the compressed file with a text editor, change a byte to corrupt it (as if opening it with a text editor wasn't bad enough!), save it and then decompress it to be sure that I got an InvalidDataException as expected. When I wrote the unit test, I picked an arbitrary byte to corrupt (e.g., compressedDataBytes[50] = 0x99) and got an InvalidDataException. So far so good. I was curious, so I chose another byte, but to my surprise I did not get an exception. This may be okay (e.g., I coincidentally hit an unused byte in a block of data), so long as the data could still be recovered successfully. However, I didn't get the correct data back either! To be sure "it wasn't me", I took the cleaned up code from the bottom of .NET GZipStream compress and decompress problem and modified it to sequentially corrupt each byte of the compressed data until it failed to decompress properly. Here's the changes (note that I'm using the Visual Studio 2010 test framework): // successful compress / decompress example code from: // http://stackoverflow.com/questio
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us gzrecover Learn more about Stack Overflow the company Business Learn more about hiring developers or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up Force gzip to decompress despite CRC error up http://stackoverflow.com/questions/9456563/gzipstream-doesnt-detect-corrupt-data-even-crc32-passes vote 5 down vote favorite 1 I think there's a way to do this but I'm not sure how? Basically, I was writing a compression program that resulted in a crc error when I tried to unzip the compressed data. Normally this means that the decompressor actually recognized my data as being in the right format and decompressed it, but when it compared the result to the expected http://stackoverflow.com/questions/13149751/force-gzip-to-decompress-despite-crc-error length as indicated by the CRC, they weren't the same. However, for comparison reasons, I actually do want to see the output to see if it's just a concatenation issue (which should be relatively obvious if the decompressed output isn't gibberish but just in the wrong order). java gzip decompression share|improve this question edited Oct 31 '12 at 1:13 alphazero 21.8k32124 asked Oct 31 '12 at 0:53 user1777900 4391719 add a comment| 2 Answers 2 active oldest votes up vote 7 down vote You said "unzip", but the question says "gzip". Which is it? Those are two different programs that operate on two different formats. I will assume gzip. Also the length is not "indicated by the CRC". The gzip trailer contains a CRC and an uncompressed length (modulo 232), which are two different things. The gzip command will decompress all valid deflate data and write it out before checking the crc. So if, for example, I take a .gz file and corrupt just the crc (or length) at the end, and do: gzip -dc < corrupt.gz > result then result will be the entire, correct uncompressed data stream. There is no need to modify and recompile gzip, nor to
41 Last updated: 28 Oct, 2014 Print Email to friend Views: 114020 About CRC Errors A CRC error indicates that some data in your Zip file (.zip or .zipx) is damaged. CRC stands for cyclic redundancy check. It http://kb.winzip.com/kb/entry/41/ is a calculation made from all the data in a file to insure accuracy. When you add a file to a Zip file, WinZip calculates a CRC value for the file and saves the value in the Zip file. When you later extract the file from the Zip file, WinZip calculates the CRC of the extracted file and compares it to the value stored when the file was zipped. If these two invalid compressed CRC values do not match, the file that was extracted does not match the original file, and WinZip will display a CRC Error message. When the data in a Zip file is damaged, it may not be possible to extract all of the files from the Zip file correctly. Damaged data can affect the entire Zip file, multiple files, or just one file. Why CRC Errors Occur There are many possible causes for invalid compressed data data damage. Among the most common is a transfer error when downloading a Zip file from the internet. Such an error can introduce invalid data into a Zip file. Some other possible causes include exposure of media to excessive temperatures or magnetic fields, cross linked disk sectors, and mechanical problems with disk drives. What to do if a CRC Error Occurs The best solution to the problem of a damaged Zip file is to try to obtain another copy of the file. For example, use your backup copy of the file or get a new copy from the original source. If you obtained the Zip file by downloading it, then downloading it again will almost always solve the problem. A "Last Resort" for CRC Errors If you cannot download a new copy of the Zip file, obtain a replacement disk, or use a backup copy, you may still be able to recover some of your files, and even save portions of the files that are damaged in the Zip file. Here is the recommended procedure. Start WinZip and open the damaged Zip file Use the current available method for unzipping files to a particular folder In the Unzip dialog, select a target folder and click Unzip (XP users - Select the All files/folders in archive rad