Hi, 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>. I am not using cygwin directly so I can’t provide the output from `cygcheck`. Regards -Mark
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