Arch Linux

Iulian

Member

Registered: 2019-08-01

Posts: 24

fopen() fails on symlinks to directories

void TarMaker::writeFileToArchive(const std::string& path)
{
    static const size_t BUFF_SIZE = 1024;
    char buffer[BUFF_SIZE] = {};

    FILE* file = fopen(path.c_str(), "rw");
    if (file == NULL)
    {
        throw archive_exception("Cannot open file " + path + " reason: " + std::to_string(errno));
    }

    while(true)
    {
        size_t read = fread(buffer, sizeof(*buffer), BUFF_SIZE, file);
        
        if(fread > 0)
            archive_write_data(m_pArchiveDescrptor, buffer, read);
        if(feof(file))
            break;
        if(ferror(file))
        {
            fclose(file);
            throw archive_exception("Failed to read from file " + path + " : " + std::to_string(errno));
        }
    }
    fclose(file);
}

i have this snippet that i call to read the contents of a file so i can add it to a tar file that i am making,
the problem is that on symlinks to directories it fails what.

what's different i would assume that a symlink to a file is the same as a symlink to a directory

dimich

Member

From: Kharkiv, Ukraine

Registered: 2009-11-03

Posts: 315

Re: fopen() fails on symlinks to directories

I'm not sure i understand the question correctly. Do you want to distinguish symlink to a file from symlink to a directory? You can `stat()` path and `readlink()` if it is a symlink. Probably you need to do it recursively to handle symlink pointing to another symlink. However i'd do it on upper level and call WriteFileToArchive() with regular file path only.

rowdog

Member

From: East Texas

Registered: 2009-08-19

Posts: 118

Re: fopen() fails on symlinks to directories

You can use realpath(3) to get the absolute path and then open that.

You can use open(2) to get a file descriptor and then fdopen(3) the fd.

int fd = open(path, O_RDONLY);
if (fd == -1) {
    perror("open");
    exit(-1);
}
FILE *handle = fdopen(fd, "r");
...
fclose(handle);