mergefiles.ipp

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#include <sys/sendfile.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <glob.h>
#include <cerrno>
#include <vector>
#include <string>
 
/*! \brief use sendfile to join all files matching pattern in new dest file.
 * \param dest file to write merge result.
 * \param pattern glob pattern to match possible input files.
 * \param merged list of files added
 * \return 0 and updated merged list or errno and merged content undefined.
 */
int glob_sendfile_join(const char *dest, const char *pattern, int perm, std::vector<std::string>& merged)
{
    glob_t glob_results;
    merged.clear();
    int err = glob(pattern, GLOB_NOSORT|GLOB_TILDE, NULL, &glob_results);
    switch(err) {
    case 0:
        break;
    case GLOB_NOSPACE:
        globfree(&glob_results);
        return ENOMEM;
    case GLOB_ABORTED:
        globfree(&glob_results);
        return EPERM;
    case GLOB_NOMATCH:
        globfree(&glob_results);
        return 0;
    }
 
    int dest_fd = open(dest, O_WRONLY | O_CREAT |O_CLOEXEC | O_TRUNC , perm);
    if (dest_fd == -1) {
        globfree(&glob_results);
        return errno;
    }
 
    for (size_t i = 0; i < glob_results.gl_pathc; i++) {
        int src_fd = open(glob_results.gl_pathv[i], O_RDONLY);
        if (src_fd == -1) continue;
 
        struct stat stat_buf;
        if (fstat(src_fd, &stat_buf) == 0 && S_ISREG(stat_buf.st_mode)) {
            off_t offset = 0;
            size_t remaining = stat_buf.st_size;
 
            // Loop until the entire file is transferred
            while (remaining > 0) {
                ssize_t sent = sendfile(dest_fd, src_fd, &offset, remaining);
 
                if (sent <= 0) {
                    // Handle errors or unexpected EOF
                    if (sent == -1 && errno == EINTR) continue; // Interrupted by signal, retry
                    break;
                }
                remaining -= sent;
            }
        }
        close(src_fd);
        merged.push_back(glob_results.gl_pathv[i]);
    }
 
    close(dest_fd);
    globfree(&glob_results);
    return 0;
}