On Mon, 14 Aug 2023 20:51:39 +0900 キャロウ マーク wrote: > I have a problem that looks like pipes are truncating data when I cat a file > to my program’s 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.y...@nifty.ne.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
