src/basic/fileio.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include <ctype.h>
   4 #include <errno.h>
   5 #include <fcntl.h>
   6 #include <limits.h>
   7 #include <stdarg.h>
   8 #include <stdint.h>
   9 #include <stdio_ext.h>
  10 #include <stdlib.h>
  11 #include <string.h>
  12 #include <sys/stat.h>
  13 #include <sys/types.h>
  14 #include <unistd.h>
  15
  16 #include "alloc-util.h"
  17 #include "fd-util.h"
  18 #include "fileio.h"
  19 #include "fs-util.h"
  20 #include "hexdecoct.h"
  21 #include "log.h"
  22 #include "macro.h"
  23 #include "missing.h"
  24 #include "parse-util.h"
  25 #include "path-util.h"
  26 #include "stdio-util.h"
  27 #include "string-util.h"
  28 #include "tmpfile-util.h"
  29
  30 #define READ_FULL_BYTES_MAX (4U*1024U*1024U)
  31
  32 int write_string_stream_ts(
  33                 FILE *f,
  34                 const char *line,
  35                 WriteStringFileFlags flags,
  36                 struct timespec *ts) {
  37
  38         bool needs_nl;
  39         int r;
  40
  41         assert(f);
  42         assert(line);
  43
  44         if (ferror(f))
  45                 return -EIO;
  46
  47         needs_nl = !(flags & WRITE_STRING_FILE_AVOID_NEWLINE) && !endswith(line, "\n");
  48
  49         if (needs_nl && (flags & WRITE_STRING_FILE_DISABLE_BUFFER)) {
  50                 /* If STDIO buffering was disabled, then let's append the newline character to the string itself, so
  51                  * that the write goes out in one go, instead of two */
  52
  53                 line = strjoina(line, "\n");
  54                 needs_nl = false;
  55         }
  56
  57         if (fputs(line, f) == EOF)
  58                 return -errno;
  59
  60         if (needs_nl)
  61                 if (fputc('\n', f) == EOF)
  62                         return -errno;
  63
  64         if (flags & WRITE_STRING_FILE_SYNC)
  65                 r = fflush_sync_and_check(f);
  66         else
  67                 r = fflush_and_check(f);
  68         if (r < 0)
  69                 return r;
  70
  71         if (ts) {
  72                 struct timespec twice[2] = {*ts, *ts};
  73
  74                 if (futimens(fileno(f), twice) < 0)
  75                         return -errno;
  76         }
  77
  78         return 0;
  79 }
  80
  81 static int write_string_file_atomic(
  82                 const char *fn,
  83                 const char *line,
  84                 WriteStringFileFlags flags,
  85                 struct timespec *ts) {
  86
  87         _cleanup_fclose_ FILE *f = NULL;
  88         _cleanup_free_ char *p = NULL;
  89         int r;
  90
  91         assert(fn);
  92         assert(line);
  93
  94         r = fopen_temporary(fn, &f, &p);
  95         if (r < 0)
  96                 return r;
  97
  98         (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
  99         (void) fchmod_umask(fileno(f), 0644);
 100
 101         r = write_string_stream_ts(f, line, flags, ts);
 102         if (r < 0)
 103                 goto fail;
 104
 105         if (rename(p, fn) < 0) {
 106                 r = -errno;
 107                 goto fail;
 108         }
 109
 110         return 0;
 111
 112 fail:
 113         (void) unlink(p);
 114         return r;
 115 }
 116
 117 int write_string_file_ts(
 118                 const char *fn,
 119                 const char *line,
 120                 WriteStringFileFlags flags,
 121                 struct timespec *ts) {
 122
 123         _cleanup_fclose_ FILE *f = NULL;
 124         int q, r;
 125
 126         assert(fn);
 127         assert(line);
 128
 129         /* We don't know how to verify whether the file contents was already on-disk. */
 130         assert(!((flags & WRITE_STRING_FILE_VERIFY_ON_FAILURE) && (flags & WRITE_STRING_FILE_SYNC)));
 131
 132         if (flags & WRITE_STRING_FILE_ATOMIC) {
 133                 assert(flags & WRITE_STRING_FILE_CREATE);
 134
 135                 r = write_string_file_atomic(fn, line, flags, ts);
 136                 if (r < 0)
 137                         goto fail;
 138
 139                 return r;
 140         } else
 141                 assert(!ts);
 142
 143         if (flags & WRITE_STRING_FILE_CREATE) {
 144                 f = fopen(fn, "we");
 145                 if (!f) {
 146                         r = -errno;
 147                         goto fail;
 148                 }
 149         } else {
 150                 int fd;
 151
 152                 /* We manually build our own version of fopen(..., "we") that
 153                  * works without O_CREAT */
 154                 fd = open(fn, O_WRONLY|O_CLOEXEC|O_NOCTTY | ((flags & WRITE_STRING_FILE_NOFOLLOW) ? O_NOFOLLOW : 0));
 155                 if (fd < 0) {
 156                         r = -errno;
 157                         goto fail;
 158                 }
 159
 160                 f = fdopen(fd, "w");
 161                 if (!f) {
 162                         r = -errno;
 163                         safe_close(fd);
 164                         goto fail;
 165                 }
 166         }
 167
 168         (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
 169
 170         if (flags & WRITE_STRING_FILE_DISABLE_BUFFER)
 171                 setvbuf(f, NULL, _IONBF, 0);
 172
 173         r = write_string_stream_ts(f, line, flags, ts);
 174         if (r < 0)
 175                 goto fail;
 176
 177         return 0;
 178
 179 fail:
 180         if (!(flags & WRITE_STRING_FILE_VERIFY_ON_FAILURE))
 181                 return r;
 182
 183         f = safe_fclose(f);
 184
 185         /* OK, the operation failed, but let's see if the right
 186          * contents in place already. If so, eat up the error. */
 187
 188         q = verify_file(fn, line, !(flags & WRITE_STRING_FILE_AVOID_NEWLINE));
 189         if (q <= 0)
 190                 return r;
 191
 192         return 0;
 193 }
 194
 195 int write_string_filef(
 196                 const char *fn,
 197                 WriteStringFileFlags flags,
 198                 const char *format, ...) {
 199
 200         _cleanup_free_ char *p = NULL;
 201         va_list ap;
 202         int r;
 203
 204         va_start(ap, format);
 205         r = vasprintf(&p, format, ap);
 206         va_end(ap);
 207
 208         if (r < 0)
 209                 return -ENOMEM;
 210
 211         return write_string_file(fn, p, flags);
 212 }
 213
 214 int read_one_line_file(const char *fn, char **line) {
 215         _cleanup_fclose_ FILE *f = NULL;
 216
 217         assert(fn);
 218         assert(line);
 219
 220         f = fopen(fn, "re");
 221         if (!f)
 222                 return -errno;
 223
 224         (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
 225
 226         return read_line(f, LONG_LINE_MAX, line);
 227 }
 228
 229 int verify_file(const char *fn, const char *blob, bool accept_extra_nl) {
 230         _cleanup_fclose_ FILE *f = NULL;
 231         _cleanup_free_ char *buf = NULL;
 232         size_t l, k;
 233
 234         assert(fn);
 235         assert(blob);
 236
 237         l = strlen(blob);
 238
 239         if (accept_extra_nl && endswith(blob, "\n"))
 240                 accept_extra_nl = false;
 241
 242         buf = malloc(l + accept_extra_nl + 1);
 243         if (!buf)
 244                 return -ENOMEM;
 245
 246         f = fopen(fn, "re");
 247         if (!f)
 248                 return -errno;
 249
 250         (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
 251
 252         /* We try to read one byte more than we need, so that we know whether we hit eof */
 253         errno = 0;
 254         k = fread(buf, 1, l + accept_extra_nl + 1, f);
 255         if (ferror(f))
 256                 return errno > 0 ? -errno : -EIO;
 257
 258         if (k != l && k != l + accept_extra_nl)
 259                 return 0;
 260         if (memcmp(buf, blob, l) != 0)
 261                 return 0;
 262         if (k > l && buf[l] != '\n')
 263                 return 0;
 264
 265         return 1;
 266 }
 267
 268 int read_full_stream_full(
 269                 FILE *f,
 270                 const char *filename,
 271                 ReadFullFileFlags flags,
 272                 char **ret_contents,
 273                 size_t *ret_size) {
 274
 275         _cleanup_free_ char *buf = NULL;
 276         struct stat st;
 277         size_t n, n_next, l;
 278         int fd, r;
 279
 280         assert(f);
 281         assert(ret_contents);
 282         assert(!(flags & READ_FULL_FILE_UNBASE64) || ret_size);
 283
 284         n_next = LINE_MAX; /* Start size */
 285
 286         fd = fileno(f);
 287         if (fd >= 0) { /* If the FILE* object is backed by an fd (as opposed to memory or such, see fmemopen(), let's
 288                         * optimize our buffering) */
 289
 290                 if (fstat(fd, &st) < 0)
 291                         return -errno;
 292
 293                 if (S_ISREG(st.st_mode)) {
 294
 295                         /* Safety check */
 296                         if (st.st_size > READ_FULL_BYTES_MAX)
 297                                 return -E2BIG;
 298
 299                         /* Start with the right file size, but be prepared for files from /proc which generally report a file
 300                          * size of 0. Note that we increase the size to read here by one, so that the first read attempt
 301                          * already makes us notice the EOF. */
 302                         if (st.st_size > 0)
 303                                 n_next = st.st_size + 1;
 304
 305                         if (flags & READ_FULL_FILE_SECURE)
 306                                 (void) warn_file_is_world_accessible(filename, &st, NULL, 0);
 307                 }
 308         }
 309
 310         n = l = 0;
 311         for (;;) {
 312                 char *t;
 313                 size_t k;
 314
 315                 if (flags & READ_FULL_FILE_SECURE) {
 316                         t = malloc(n_next + 1);
 317                         if (!t) {
 318                                 r = -ENOMEM;
 319                                 goto finalize;
 320                         }
 321                         memcpy_safe(t, buf, n);
 322                         explicit_bzero_safe(buf, n);
 323                 } else {
 324                         t = realloc(buf, n_next + 1);
 325                         if (!t)
 326                                 return -ENOMEM;
 327                 }
 328
 329                 buf = t;
 330                 n = n_next;
 331
 332                 errno = 0;
 333                 k = fread(buf + l, 1, n - l, f);
 334                 if (k > 0)
 335                         l += k;
 336
 337                 if (ferror(f)) {
 338                         r = errno > 0 ? -errno : -EIO;
 339                         goto finalize;
 340                 }
 341
 342                 if (feof(f))
 343                         break;
 344
 345                 /* We aren't expecting fread() to return a short read outside
 346                  * of (error && eof), assert buffer is full and enlarge buffer.
 347                  */
 348                 assert(l == n);
 349
 350                 /* Safety check */
 351                 if (n >= READ_FULL_BYTES_MAX) {
 352                         r = -E2BIG;
 353                         goto finalize;
 354                 }
 355
 356                 n_next = MIN(n * 2, READ_FULL_BYTES_MAX);
 357         }
 358
 359         if (flags & READ_FULL_FILE_UNBASE64) {
 360                 buf[l++] = 0;
 361                 r = unbase64mem_full(buf, l, flags & READ_FULL_FILE_SECURE, (void **) ret_contents, ret_size);
 362                 goto finalize;
 363         }
 364
 365         if (!ret_size) {
 366                 /* Safety check: if the caller doesn't want to know the size of what we just read it will rely on the
 367                  * trailing NUL byte. But if there's an embedded NUL byte, then we should refuse operation as otherwise
 368                  * there'd be ambiguity about what we just read. */
 369
 370                 if (memchr(buf, 0, l)) {
 371                         r = -EBADMSG;
 372                         goto finalize;
 373                 }
 374         }
 375
 376         buf[l] = 0;
 377         *ret_contents = TAKE_PTR(buf);
 378
 379         if (ret_size)
 380                 *ret_size = l;
 381
 382         return 0;
 383
 384 finalize:
 385         if (flags & READ_FULL_FILE_SECURE)
 386                 explicit_bzero_safe(buf, n);
 387
 388         return r;
 389 }
 390
 391 int read_full_file_full(const char *filename, ReadFullFileFlags flags, char **contents, size_t *size) {
 392         _cleanup_fclose_ FILE *f = NULL;
 393
 394         assert(filename);
 395         assert(contents);
 396
 397         f = fopen(filename, "re");
 398         if (!f)
 399                 return -errno;
 400
 401         (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
 402
 403         return read_full_stream_full(f, filename, flags, contents, size);
 404 }
 405
 406 int executable_is_script(const char *path, char **interpreter) {
 407         _cleanup_free_ char *line = NULL;
 408         size_t len;
 409         char *ans;
 410         int r;
 411
 412         assert(path);
 413
 414         r = read_one_line_file(path, &line);
 415         if (r == -ENOBUFS) /* First line overly long? if so, then it's not a script */
 416                 return 0;
 417         if (r < 0)
 418                 return r;
 419
 420         if (!startswith(line, "#!"))
 421                 return 0;
 422
 423         ans = strstrip(line + 2);
 424         len = strcspn(ans, " \t");
 425
 426         if (len == 0)
 427                 return 0;
 428
 429         ans = strndup(ans, len);
 430         if (!ans)
 431                 return -ENOMEM;
 432
 433         *interpreter = ans;
 434         return 1;
 435 }
 436
 437 /**
 438  * Retrieve one field from a file like /proc/self/status.  pattern
 439  * should not include whitespace or the delimiter (':'). pattern matches only
 440  * the beginning of a line. Whitespace before ':' is skipped. Whitespace and
 441  * zeros after the ':' will be skipped. field must be freed afterwards.
 442  * terminator specifies the terminating characters of the field value (not
 443  * included in the value).
 444  */
 445 int get_proc_field(const char *filename, const char *pattern, const char *terminator, char **field) {
 446         _cleanup_free_ char *status = NULL;
 447         char *t, *f;
 448         size_t len;
 449         int r;
 450
 451         assert(terminator);
 452         assert(filename);
 453         assert(pattern);
 454         assert(field);
 455
 456         r = read_full_file(filename, &status, NULL);
 457         if (r < 0)
 458                 return r;
 459
 460         t = status;
 461
 462         do {
 463                 bool pattern_ok;
 464
 465                 do {
 466                         t = strstr(t, pattern);
 467                         if (!t)
 468                                 return -ENOENT;
 469
 470                         /* Check that pattern occurs in beginning of line. */
 471                         pattern_ok = (t == status || t[-1] == '\n');
 472
 473                         t += strlen(pattern);
 474
 475                 } while (!pattern_ok);
 476
 477                 t += strspn(t, " \t");
 478                 if (!*t)
 479                         return -ENOENT;
 480
 481         } while (*t != ':');
 482
 483         t++;
 484
 485         if (*t) {
 486                 t += strspn(t, " \t");
 487
 488                 /* Also skip zeros, because when this is used for
 489                  * capabilities, we don't want the zeros. This way the
 490                  * same capability set always maps to the same string,
 491                  * irrespective of the total capability set size. For
 492                  * other numbers it shouldn't matter. */
 493                 t += strspn(t, "0");
 494                 /* Back off one char if there's nothing but whitespace
 495                    and zeros */
 496                 if (!*t || isspace(*t))
 497                         t--;
 498         }
 499
 500         len = strcspn(t, terminator);
 501
 502         f = strndup(t, len);
 503         if (!f)
 504                 return -ENOMEM;
 505
 506         *field = f;
 507         return 0;
 508 }
 509
 510 DIR *xopendirat(int fd, const char *name, int flags) {
 511         int nfd;
 512         DIR *d;
 513
 514         assert(!(flags & O_CREAT));
 515
 516         nfd = openat(fd, name, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|flags, 0);
 517         if (nfd < 0)
 518                 return NULL;
 519
 520         d = fdopendir(nfd);
 521         if (!d) {
 522                 safe_close(nfd);
 523                 return NULL;
 524         }
 525
 526         return d;
 527 }
 528
 529 static int search_and_fopen_internal(const char *path, const char *mode, const char *root, char **search, FILE **_f) {
 530         char **i;
 531
 532         assert(path);
 533         assert(mode);
 534         assert(_f);
 535
 536         if (!path_strv_resolve_uniq(search, root))
 537                 return -ENOMEM;
 538
 539         STRV_FOREACH(i, search) {
 540                 _cleanup_free_ char *p = NULL;
 541                 FILE *f;
 542
 543                 if (root)
 544                         p = strjoin(root, *i, "/", path);
 545                 else
 546                         p = strjoin(*i, "/", path);
 547                 if (!p)
 548                         return -ENOMEM;
 549
 550                 f = fopen(p, mode);
 551                 if (f) {
 552                         *_f = f;
 553                         return 0;
 554                 }
 555
 556                 if (errno != ENOENT)
 557                         return -errno;
 558         }
 559
 560         return -ENOENT;
 561 }
 562
 563 int search_and_fopen(const char *path, const char *mode, const char *root, const char **search, FILE **_f) {
 564         _cleanup_strv_free_ char **copy = NULL;
 565
 566         assert(path);
 567         assert(mode);
 568         assert(_f);
 569
 570         if (path_is_absolute(path)) {
 571                 FILE *f;
 572
 573                 f = fopen(path, mode);
 574                 if (f) {
 575                         *_f = f;
 576                         return 0;
 577                 }
 578
 579                 return -errno;
 580         }
 581
 582         copy = strv_copy((char**) search);
 583         if (!copy)
 584                 return -ENOMEM;
 585
 586         return search_and_fopen_internal(path, mode, root, copy, _f);
 587 }
 588
 589 int search_and_fopen_nulstr(const char *path, const char *mode, const char *root, const char *search, FILE **_f) {
 590         _cleanup_strv_free_ char **s = NULL;
 591
 592         if (path_is_absolute(path)) {
 593                 FILE *f;
 594
 595                 f = fopen(path, mode);
 596                 if (f) {
 597                         *_f = f;
 598                         return 0;
 599                 }
 600
 601                 return -errno;
 602         }
 603
 604         s = strv_split_nulstr(search);
 605         if (!s)
 606                 return -ENOMEM;
 607
 608         return search_and_fopen_internal(path, mode, root, s, _f);
 609 }
 610
 611 int fflush_and_check(FILE *f) {
 612         assert(f);
 613
 614         errno = 0;
 615         fflush(f);
 616
 617         if (ferror(f))
 618                 return errno > 0 ? -errno : -EIO;
 619
 620         return 0;
 621 }
 622
 623 int fflush_sync_and_check(FILE *f) {
 624         int r;
 625
 626         assert(f);
 627
 628         r = fflush_and_check(f);
 629         if (r < 0)
 630                 return r;
 631
 632         if (fsync(fileno(f)) < 0)
 633                 return -errno;
 634
 635         r = fsync_directory_of_file(fileno(f));
 636         if (r < 0)
 637                 return r;
 638
 639         return 0;
 640 }
 641
 642 int write_timestamp_file_atomic(const char *fn, usec_t n) {
 643         char ln[DECIMAL_STR_MAX(n)+2];
 644
 645         /* Creates a "timestamp" file, that contains nothing but a
 646          * usec_t timestamp, formatted in ASCII. */
 647
 648         if (n <= 0 || n >= USEC_INFINITY)
 649                 return -ERANGE;
 650
 651         xsprintf(ln, USEC_FMT "\n", n);
 652
 653         return write_string_file(fn, ln, WRITE_STRING_FILE_CREATE|WRITE_STRING_FILE_ATOMIC);
 654 }
 655
 656 int read_timestamp_file(const char *fn, usec_t *ret) {
 657         _cleanup_free_ char *ln = NULL;
 658         uint64_t t;
 659         int r;
 660
 661         r = read_one_line_file(fn, &ln);
 662         if (r < 0)
 663                 return r;
 664
 665         r = safe_atou64(ln, &t);
 666         if (r < 0)
 667                 return r;
 668
 669         if (t <= 0 || t >= (uint64_t) USEC_INFINITY)
 670                 return -ERANGE;
 671
 672         *ret = (usec_t) t;
 673         return 0;
 674 }
 675
 676 int fputs_with_space(FILE *f, const char *s, const char *separator, bool *space) {
 677         int r;
 678
 679         assert(s);
 680
 681         /* Outputs the specified string with fputs(), but optionally prefixes it with a separator. The *space parameter
 682          * when specified shall initially point to a boolean variable initialized to false. It is set to true after the
 683          * first invocation. This call is supposed to be use in loops, where a separator shall be inserted between each
 684          * element, but not before the first one. */
 685
 686         if (!f)
 687                 f = stdout;
 688
 689         if (space) {
 690                 if (!separator)
 691                         separator = " ";
 692
 693                 if (*space) {
 694                         r = fputs(separator, f);
 695                         if (r < 0)
 696                                 return r;
 697                 }
 698
 699                 *space = true;
 700         }
 701
 702         return fputs(s, f);
 703 }
 704
 705 /* A bitmask of the EOL markers we know */
 706 typedef enum EndOfLineMarker {
 707         EOL_NONE     = 0,
 708         EOL_ZERO     = 1 << 0,  /* \0 (aka NUL) */
 709         EOL_TEN      = 1 << 1,  /* \n (aka NL, aka LF)  */
 710         EOL_THIRTEEN = 1 << 2,  /* \r (aka CR)  */
 711 } EndOfLineMarker;
 712
 713 static EndOfLineMarker categorize_eol(char c, ReadLineFlags flags) {
 714
 715         if (!IN_SET(flags, READ_LINE_ONLY_NUL)) {
 716                 if (c == '\n')
 717                         return EOL_TEN;
 718                 if (c == '\r')
 719                         return EOL_THIRTEEN;
 720         }
 721
 722         if (c == '\0')
 723                 return EOL_ZERO;
 724
 725         return EOL_NONE;
 726 }
 727
 728 DEFINE_TRIVIAL_CLEANUP_FUNC(FILE*, funlockfile);
 729
 730 int read_line_full(FILE *f, size_t limit, ReadLineFlags flags, char **ret) {
 731         size_t n = 0, allocated = 0, count = 0;
 732         _cleanup_free_ char *buffer = NULL;
 733         int r;
 734
 735         assert(f);
 736
 737         /* Something like a bounded version of getline().
 738          *
 739          * Considers EOF, \n, \r and \0 end of line delimiters (or combinations of these), and does not include these
 740          * delimiters in the string returned. Specifically, recognizes the following combinations of markers as line
 741          * endings:
 742          *
 743          *     • \n        (UNIX)
 744          *     • \r        (old MacOS)
 745          *     • \0        (C strings)
 746          *     • \n\0
 747          *     • \r\0
 748          *     • \r\n      (Windows)
 749          *     • \n\r
 750          *     • \r\n\0
 751          *     • \n\r\0
 752          *
 753          * Returns the number of bytes read from the files (i.e. including delimiters — this hence usually differs from
 754          * the number of characters in the returned string). When EOF is hit, 0 is returned.
 755          *
 756          * The input parameter limit is the maximum numbers of characters in the returned string, i.e. excluding
 757          * delimiters. If the limit is hit we fail and return -ENOBUFS.
 758          *
 759          * If a line shall be skipped ret may be initialized as NULL. */
 760
 761         if (ret) {
 762                 if (!GREEDY_REALLOC(buffer, allocated, 1))
 763                         return -ENOMEM;
 764         }
 765
 766         {
 767                 _unused_ _cleanup_(funlockfilep) FILE *flocked = f;
 768                 EndOfLineMarker previous_eol = EOL_NONE;
 769                 flockfile(f);
 770
 771                 for (;;) {
 772                         EndOfLineMarker eol;
 773                         char c;
 774
 775                         if (n >= limit)
 776                                 return -ENOBUFS;
 777
 778                         if (count >= INT_MAX) /* We couldn't return the counter anymore as "int", hence refuse this */
 779                                 return -ENOBUFS;
 780
 781                         r = safe_fgetc(f, &c);
 782                         if (r < 0)
 783                                 return r;
 784                         if (r == 0) /* EOF is definitely EOL */
 785                                 break;
 786
 787                         eol = categorize_eol(c, flags);
 788
 789                         if (FLAGS_SET(previous_eol, EOL_ZERO) ||
 790                             (eol == EOL_NONE && previous_eol != EOL_NONE) ||
 791                             (eol != EOL_NONE && (previous_eol & eol) != 0)) {
 792                                 /* Previous char was a NUL? This is not an EOL, but the previous char was? This type of
 793                                  * EOL marker has been seen right before?  In either of these three cases we are
 794                                  * done. But first, let's put this character back in the queue. (Note that we have to
 795                                  * cast this to (unsigned char) here as ungetc() expects a positive 'int', and if we
 796                                  * are on an architecture where 'char' equals 'signed char' we need to ensure we don't
 797                                  * pass a negative value here. That said, to complicate things further ungetc() is
 798                                  * actually happy with most negative characters and implicitly casts them back to
 799                                  * positive ones as needed, except for \xff (aka -1, aka EOF), which it refuses. What a
 800                                  * godawful API!) */
 801                                 assert_se(ungetc((unsigned char) c, f) != EOF);
 802                                 break;
 803                         }
 804
 805                         count++;
 806
 807                         if (eol != EOL_NONE) {
 808                                 previous_eol |= eol;
 809                                 continue;
 810                         }
 811
 812                         if (ret) {
 813                                 if (!GREEDY_REALLOC(buffer, allocated, n + 2))
 814                                         return -ENOMEM;
 815
 816                                 buffer[n] = c;
 817                         }
 818
 819                         n++;
 820                 }
 821         }
 822
 823         if (ret) {
 824                 buffer[n] = 0;
 825
 826                 *ret = TAKE_PTR(buffer);
 827         }
 828
 829         return (int) count;
 830 }
 831
 832 int safe_fgetc(FILE *f, char *ret) {
 833         int k;
 834
 835         assert(f);
 836
 837         /* A safer version of plain fgetc(): let's propagate the error that happened while reading as such, and
 838          * separate the EOF condition from the byte read, to avoid those confusion signed/unsigned issues fgetc()
 839          * has. */
 840
 841         errno = 0;
 842         k = fgetc(f);
 843         if (k == EOF) {
 844                 if (ferror(f))
 845                         return errno > 0 ? -errno : -EIO;
 846
 847                 if (ret)
 848                         *ret = 0;
 849
 850                 return 0;
 851         }
 852
 853         if (ret)
 854                 *ret = k;
 855
 856         return 1;
 857 }
 858
 859 int warn_file_is_world_accessible(const char *filename, struct stat *st, const char *unit, unsigned line) {
 860         struct stat _st;
 861
 862         if (!filename)
 863                 return 0;
 864
 865         if (!st) {
 866                 if (stat(filename, &_st) < 0)
 867                         return -errno;
 868                 st = &_st;
 869         }
 870
 871         if ((st->st_mode & S_IRWXO) == 0)
 872                 return 0;
 873
 874         if (unit)
 875                 log_syntax(unit, LOG_WARNING, filename, line, 0,
 876                            "%s has %04o mode that is too permissive, please adjust the access mode.",
 877                            filename, st->st_mode & 07777);
 878         else
 879                 log_warning("%s has %04o mode that is too permissive, please adjust the access mode.",
 880                             filename, st->st_mode & 07777);
 881         return 0;
 882 }