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Date: | Tue, 15 Aug 2023 09:30:42 +0900 |
To: | cygwin AT cygwin DOT com |
Cc: | =?ISO-2022-JP?B?GyRCJS0lYyVtJSYhISVeITwlLxsoQg==?= <github AT callow DOT im> |
Subject: | Re: Pipes truncating data in cygwin from main and cygwin-3_4-branch |
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From: | Takashi Yano via Cygwin <cygwin AT cygwin DOT com> |
Reply-To: | Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp> |
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On Mon, 14 Aug 2023 20:51:39 +0900 $B%-%c%m%&!!%^!<%/(B wrote: > I have a problem that looks like pipes are truncating data when I cat a file to my program$B!G(Bs stdin. A simple `cat foo | cat > bar` works fine. bar ends up identical to foo. It is more complicated than that. My application is doing this > std::stringstream buffer; > buffer << std::cin.rdbuf(); > std::istream* isp = &buffer; > Initial reads after this work fine. Once the app has read everything up to the payload data in the file, it does > > off_t dataStart = (off_t)(isp->tellg()); > isp->seekg(0, ios_base::end); > off_t dataEnd = (off_t)(isp->tellg()); > dataSizeInFile = dataEnd - dataStart; > The tellg result shows the size is significantly less than the actual file data. 43k less in a 170k file. It is seemingly being truncated somewhere. > > Later the app does > > isp->seekg(0); > std::streambuf* _streambuf = (isp->rdbuf()); > and starts reading from _streambuf. All data read from _streambuf is gibberish. > > The application code makes no distinction between a pipe and stdin redirection from a file. It just uses std::cin. stdin redirection still works. > > I created a minimal reproducer. More on that in a moment. > > I first encountered this in Git for Windows 2.41.0. I had no problem in previous versions. I reported this to the Git for Windows project. See https://github.com/git-for-windows/git/issues/4464. You can find the minimal reproducer over there. It consists of 2 parts, a script and a small c++ program. The script finds the size of the target file then cats it to the test program passing the file size as a command line option. The test program does what I have described above and compares the file size determined from the seek to the end with the provided size. > > A G4W project member reports that the problem reproduces on vanilla Cygwin in the branches mentioned in the subject and that G4W and MSYS2 are on the cygwin-3_4-branch release train. He recommends reporting the bug to you, You can find his(?) full comment here <https://github.com/git-for-windows/git/issues/4464#issuecomment-1671137446>. Your test case does not work in command prompt as well. Try type testfile | test-pipe sizeoftestfile in command prompt. It will fail. New pipe implementation since cygwin 3.4.x provides the pipes more similar to pipe in command prompt for non-cygwin apps. Since your test case is compiled with cl.exe, it is non-cygwin apps. -- Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp> -- Problem reports: https://cygwin.com/problems.html FAQ: https://cygwin.com/faq/ Documentation: https://cygwin.com/docs.html Unsubscribe info: https://cygwin.com/ml/#unsubscribe-simple
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