Source

gevent / c-ares / ares_process.c

   1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
/* Copyright 1998 by the Massachusetts Institute of Technology.
 * Copyright (C) 2004-2010 by Daniel Stenberg
 *
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting
 * documentation, and that the name of M.I.T. not be used in
 * advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is"
 * without express or implied warranty.
 */

#include "ares_setup.h"

#ifdef HAVE_SYS_SOCKET_H
#  include <sys/socket.h>
#endif
#ifdef HAVE_SYS_UIO_H
#  include <sys/uio.h>
#endif
#ifdef HAVE_NETINET_IN_H
#  include <netinet/in.h>
#endif
#ifdef HAVE_NETINET_TCP_H
#  include <netinet/tcp.h>
#endif
#ifdef HAVE_NETDB_H
#  include <netdb.h>
#endif
#ifdef HAVE_ARPA_NAMESER_H
#  include <arpa/nameser.h>
#else
#  include "nameser.h"
#endif
#ifdef HAVE_ARPA_NAMESER_COMPAT_H
#  include <arpa/nameser_compat.h>
#endif

#ifdef HAVE_SYS_TIME_H
#  include <sys/time.h>
#endif

#ifdef HAVE_STRINGS_H
#  include <strings.h>
#endif
#ifdef HAVE_UNISTD_H
#  include <unistd.h>
#endif
#ifdef HAVE_SYS_IOCTL_H
#  include <sys/ioctl.h>
#endif
#ifdef NETWARE
#  include <sys/filio.h>
#endif

#include <assert.h>
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
#include <time.h>

#include "ares.h"
#include "ares_dns.h"
#include "ares_nowarn.h"
#include "ares_private.h"


static int try_again(int errnum);
static void write_tcp_data(ares_channel channel, fd_set *write_fds,
                           ares_socket_t write_fd, struct timeval *now);
static void read_tcp_data(ares_channel channel, fd_set *read_fds,
                          ares_socket_t read_fd, struct timeval *now);
static void read_udp_packets(ares_channel channel, fd_set *read_fds,
                             ares_socket_t read_fd, struct timeval *now);
static void advance_tcp_send_queue(ares_channel channel, int whichserver,
                                   ssize_t num_bytes);
static void process_timeouts(ares_channel channel, struct timeval *now);
static void process_broken_connections(ares_channel channel,
                                       struct timeval *now);
static void process_answer(ares_channel channel, unsigned char *abuf,
                           int alen, int whichserver, int tcp,
                           struct timeval *now);
static void handle_error(ares_channel channel, int whichserver,
                         struct timeval *now);
static void skip_server(ares_channel channel, struct query *query,
                        int whichserver);
static void next_server(ares_channel channel, struct query *query,
                        struct timeval *now);
static int open_tcp_socket(ares_channel channel, struct server_state *server);
static int open_udp_socket(ares_channel channel, struct server_state *server);
static int same_questions(const unsigned char *qbuf, int qlen,
                          const unsigned char *abuf, int alen);
static int same_address(struct sockaddr *sa, struct ares_addr *aa);
static void end_query(ares_channel channel, struct query *query, int status,
                      unsigned char *abuf, int alen);

/* return true if now is exactly check time or later */
int ares__timedout(struct timeval *now,
                   struct timeval *check)
{
  long secs = (now->tv_sec - check->tv_sec);

  if(secs > 0)
    return 1; /* yes, timed out */
  if(secs < 0)
    return 0; /* nope, not timed out */

  /* if the full seconds were identical, check the sub second parts */
  return (now->tv_usec - check->tv_usec >= 0);
}

/* add the specific number of milliseconds to the time in the first argument */
int ares__timeadd(struct timeval *now,
                  int millisecs)
{
  now->tv_sec += millisecs/1000;
  now->tv_usec += (millisecs%1000)*1000;

  if(now->tv_usec >= 1000000) {
    ++(now->tv_sec);
    now->tv_usec -= 1000000;
  }

  return 0;
}

/* return time offset between now and (future) check, in milliseconds */
long ares__timeoffset(struct timeval *now,
                      struct timeval *check)
{
  return (check->tv_sec - now->tv_sec)*1000 +
         (check->tv_usec - now->tv_usec)/1000;
}


/*
 * generic process function
 */
static void processfds(ares_channel channel,
                       fd_set *read_fds, ares_socket_t read_fd,
                       fd_set *write_fds, ares_socket_t write_fd)
{
  struct timeval now = ares__tvnow();

  write_tcp_data(channel, write_fds, write_fd, &now);
  read_tcp_data(channel, read_fds, read_fd, &now);
  read_udp_packets(channel, read_fds, read_fd, &now);
  process_timeouts(channel, &now);
  process_broken_connections(channel, &now);
}

/* Something interesting happened on the wire, or there was a timeout.
 * See what's up and respond accordingly.
 */
void ares_process(ares_channel channel, fd_set *read_fds, fd_set *write_fds)
{
  processfds(channel, read_fds, ARES_SOCKET_BAD, write_fds, ARES_SOCKET_BAD);
}

/* Something interesting happened on the wire, or there was a timeout.
 * See what's up and respond accordingly.
 */
void ares_process_fd(ares_channel channel,
                     ares_socket_t read_fd, /* use ARES_SOCKET_BAD or valid
                                               file descriptors */
                     ares_socket_t write_fd)
{
  processfds(channel, NULL, read_fd, NULL, write_fd);
}


/* Return 1 if the specified error number describes a readiness error, or 0
 * otherwise. This is mostly for HP-UX, which could return EAGAIN or
 * EWOULDBLOCK. See this man page
 *
 * http://devrsrc1.external.hp.com/STKS/cgi-bin/man2html?
 *     manpage=/usr/share/man/man2.Z/send.2
 */
static int try_again(int errnum)
{
#if !defined EWOULDBLOCK && !defined EAGAIN
#error "Neither EWOULDBLOCK nor EAGAIN defined"
#endif
  switch (errnum)
    {
#ifdef EWOULDBLOCK
    case EWOULDBLOCK:
      return 1;
#endif
#if defined EAGAIN && EAGAIN != EWOULDBLOCK
    case EAGAIN:
      return 1;
#endif
    }
  return 0;
}

/* If any TCP sockets select true for writing, write out queued data
 * we have for them.
 */
static void write_tcp_data(ares_channel channel,
                           fd_set *write_fds,
                           ares_socket_t write_fd,
                           struct timeval *now)
{
  struct server_state *server;
  struct send_request *sendreq;
  struct iovec *vec;
  int i;
  ssize_t scount;
  ssize_t wcount;
  size_t n;

  if(!write_fds && (write_fd == ARES_SOCKET_BAD))
    /* no possible action */
    return;

  for (i = 0; i < channel->nservers; i++)
    {
      /* Make sure server has data to send and is selected in write_fds or
         write_fd. */
      server = &channel->servers[i];
      if (!server->qhead || server->tcp_socket == ARES_SOCKET_BAD ||
          server->is_broken)
        continue;

      if(write_fds) {
        if(!FD_ISSET(server->tcp_socket, write_fds))
          continue;
      }
      else {
        if(server->tcp_socket != write_fd)
          continue;
      }

      if(write_fds)
        /* If there's an error and we close this socket, then open
         * another with the same fd to talk to another server, then we
         * don't want to think that it was the new socket that was
         * ready. This is not disastrous, but is likely to result in
         * extra system calls and confusion. */
        FD_CLR(server->tcp_socket, write_fds);

      /* Count the number of send queue items. */
      n = 0;
      for (sendreq = server->qhead; sendreq; sendreq = sendreq->next)
        n++;

      /* Allocate iovecs so we can send all our data at once. */
      vec = malloc(n * sizeof(struct iovec));
      if (vec)
        {
          /* Fill in the iovecs and send. */
          n = 0;
          for (sendreq = server->qhead; sendreq; sendreq = sendreq->next)
            {
              vec[n].iov_base = (char *) sendreq->data;
              vec[n].iov_len = sendreq->len;
              n++;
            }
          wcount = (ssize_t)writev(server->tcp_socket, vec, (int)n);
          free(vec);
          if (wcount < 0)
            {
              if (!try_again(SOCKERRNO))
                  handle_error(channel, i, now);
              continue;
            }

          /* Advance the send queue by as many bytes as we sent. */
          advance_tcp_send_queue(channel, i, wcount);
        }
      else
        {
          /* Can't allocate iovecs; just send the first request. */
          sendreq = server->qhead;

          scount = swrite(server->tcp_socket, sendreq->data, sendreq->len);
          if (scount < 0)
            {
              if (!try_again(SOCKERRNO))
                  handle_error(channel, i, now);
              continue;
            }

          /* Advance the send queue by as many bytes as we sent. */
          advance_tcp_send_queue(channel, i, scount);
        }
    }
}

/* Consume the given number of bytes from the head of the TCP send queue. */
static void advance_tcp_send_queue(ares_channel channel, int whichserver,
                                   ssize_t num_bytes)
{
  struct send_request *sendreq;
  struct server_state *server = &channel->servers[whichserver];
  while (num_bytes > 0) {
    sendreq = server->qhead;
    if ((size_t)num_bytes >= sendreq->len) {
      num_bytes -= sendreq->len;
      server->qhead = sendreq->next;
      if (sendreq->data_storage)
        free(sendreq->data_storage);
      free(sendreq);
      if (server->qhead == NULL) {
        SOCK_STATE_CALLBACK(channel, server->tcp_socket, 1, 0);
        server->qtail = NULL;

        /* qhead is NULL so we cannot continue this loop */
        break;
      }
    }
    else {
      sendreq->data += num_bytes;
      sendreq->len -= num_bytes;
      num_bytes = 0;
    }
  }
}

/* If any TCP socket selects true for reading, read some data,
 * allocate a buffer if we finish reading the length word, and process
 * a packet if we finish reading one.
 */
static void read_tcp_data(ares_channel channel, fd_set *read_fds,
                          ares_socket_t read_fd, struct timeval *now)
{
  struct server_state *server;
  int i;
  ssize_t count;

  if(!read_fds && (read_fd == ARES_SOCKET_BAD))
    /* no possible action */
    return;

  for (i = 0; i < channel->nservers; i++)
    {
      /* Make sure the server has a socket and is selected in read_fds. */
      server = &channel->servers[i];
      if (server->tcp_socket == ARES_SOCKET_BAD || server->is_broken)
        continue;

      if(read_fds) {
        if(!FD_ISSET(server->tcp_socket, read_fds))
          continue;
      }
      else {
        if(server->tcp_socket != read_fd)
          continue;
      }

      if(read_fds)
        /* If there's an error and we close this socket, then open
         * another with the same fd to talk to another server, then we
         * don't want to think that it was the new socket that was
         * ready. This is not disastrous, but is likely to result in
         * extra system calls and confusion. */
        FD_CLR(server->tcp_socket, read_fds);

      if (server->tcp_lenbuf_pos != 2)
        {
          /* We haven't yet read a length word, so read that (or
           * what's left to read of it).
           */
          count = sread(server->tcp_socket,
                        server->tcp_lenbuf + server->tcp_lenbuf_pos,
                        2 - server->tcp_lenbuf_pos);
          if (count <= 0)
            {
              if (!(count == -1 && try_again(SOCKERRNO)))
                  handle_error(channel, i, now);
              continue;
            }

          server->tcp_lenbuf_pos += (int)count;
          if (server->tcp_lenbuf_pos == 2)
            {
              /* We finished reading the length word.  Decode the
               * length and allocate a buffer for the data.
               */
              server->tcp_length = server->tcp_lenbuf[0] << 8
                | server->tcp_lenbuf[1];
              server->tcp_buffer = malloc(server->tcp_length);
              if (!server->tcp_buffer)
                handle_error(channel, i, now);
              server->tcp_buffer_pos = 0;
            }
        }
      else
        {
          /* Read data into the allocated buffer. */
          count = sread(server->tcp_socket,
                        server->tcp_buffer + server->tcp_buffer_pos,
                        server->tcp_length - server->tcp_buffer_pos);
          if (count <= 0)
            {
              if (!(count == -1 && try_again(SOCKERRNO)))
                  handle_error(channel, i, now);
              continue;
            }

          server->tcp_buffer_pos += (int)count;
          if (server->tcp_buffer_pos == server->tcp_length)
            {
              /* We finished reading this answer; process it and
               * prepare to read another length word.
               */
              process_answer(channel, server->tcp_buffer, server->tcp_length,
                             i, 1, now);
          if (server->tcp_buffer)
                        free(server->tcp_buffer);
              server->tcp_buffer = NULL;
              server->tcp_lenbuf_pos = 0;
              server->tcp_buffer_pos = 0;
            }
        }
    }
}

/* If any UDP sockets select true for reading, process them. */
static void read_udp_packets(ares_channel channel, fd_set *read_fds,
                             ares_socket_t read_fd, struct timeval *now)
{
  struct server_state *server;
  int i;
  ssize_t count;
  unsigned char buf[PACKETSZ + 1];
#ifdef HAVE_RECVFROM
  ares_socklen_t fromlen;
  union {
    struct sockaddr     sa;
    struct sockaddr_in  sa4;
    struct sockaddr_in6 sa6;
  } from;
#endif

  if(!read_fds && (read_fd == ARES_SOCKET_BAD))
    /* no possible action */
    return;

  for (i = 0; i < channel->nservers; i++)
    {
      /* Make sure the server has a socket and is selected in read_fds. */
      server = &channel->servers[i];

      if (server->udp_socket == ARES_SOCKET_BAD || server->is_broken)
        continue;

      if(read_fds) {
        if(!FD_ISSET(server->udp_socket, read_fds))
          continue;
      }
      else {
        if(server->udp_socket != read_fd)
          continue;
      }

      if(read_fds)
        /* If there's an error and we close this socket, then open
         * another with the same fd to talk to another server, then we
         * don't want to think that it was the new socket that was
         * ready. This is not disastrous, but is likely to result in
         * extra system calls and confusion. */
        FD_CLR(server->udp_socket, read_fds);

      /* To reduce event loop overhead, read and process as many
       * packets as we can. */
      do {
#ifdef HAVE_RECVFROM
        if (server->addr.family == AF_INET)
          fromlen = sizeof(from.sa4);
        else
          fromlen = sizeof(from.sa6);
        count = (ssize_t)recvfrom(server->udp_socket, (void *)buf, sizeof(buf),
                                  0, &from.sa, &fromlen);
#else
        count = sread(server->udp_socket, buf, sizeof(buf));
#endif
        if (count == -1 && try_again(SOCKERRNO))
          continue;
        else if (count <= 0)
          handle_error(channel, i, now);
#ifdef HAVE_RECVFROM
        else if (!same_address(&from.sa, &server->addr))
          /* The address the response comes from does not match
           * the address we sent the request to. Someone may be
           * attempting to perform a cache poisoning attack. */
          break;
#endif
        else
          process_answer(channel, buf, (int)count, i, 0, now);
       } while (count > 0);
    }
}

/* If any queries have timed out, note the timeout and move them on. */
static void process_timeouts(ares_channel channel, struct timeval *now)
{
  time_t t;  /* the time of the timeouts we're processing */
  struct query *query;
  struct list_node* list_head;
  struct list_node* list_node;

  /* Process all the timeouts that have fired since the last time we
   * processed timeouts. If things are going well, then we'll have
   * hundreds/thousands of queries that fall into future buckets, and
   * only a handful of requests that fall into the "now" bucket, so
   * this should be quite quick.
   */
  for (t = channel->last_timeout_processed; t <= now->tv_sec; t++)
    {
      list_head = &(channel->queries_by_timeout[t % ARES_TIMEOUT_TABLE_SIZE]);
      for (list_node = list_head->next; list_node != list_head; )
        {
          query = list_node->data;
          list_node = list_node->next;  /* in case the query gets deleted */
          if (query->timeout.tv_sec && ares__timedout(now, &query->timeout))
            {
              query->error_status = ARES_ETIMEOUT;
              ++query->timeouts;
              next_server(channel, query, now);
            }
        }
     }
  channel->last_timeout_processed = now->tv_sec;
}

/* Handle an answer from a server. */
static void process_answer(ares_channel channel, unsigned char *abuf,
                           int alen, int whichserver, int tcp,
                           struct timeval *now)
{
  int tc, rcode;
  unsigned short id;
  struct query *query;
  struct list_node* list_head;
  struct list_node* list_node;

  /* If there's no room in the answer for a header, we can't do much
   * with it. */
  if (alen < HFIXEDSZ)
    return;

  /* Grab the query ID, truncate bit, and response code from the packet. */
  id = DNS_HEADER_QID(abuf);
  tc = DNS_HEADER_TC(abuf);
  rcode = DNS_HEADER_RCODE(abuf);

  /* Find the query corresponding to this packet. The queries are
   * hashed/bucketed by query id, so this lookup should be quick.
   * Note that both the query id and the questions must be the same;
   * when the query id wraps around we can have multiple outstanding
   * queries with the same query id, so we need to check both the id and
   * question.
   */
  query = NULL;
  list_head = &(channel->queries_by_qid[id % ARES_QID_TABLE_SIZE]);
  for (list_node = list_head->next; list_node != list_head;
       list_node = list_node->next)
    {
      struct query *q = list_node->data;
      if ((q->qid == id) && same_questions(q->qbuf, q->qlen, abuf, alen))
        {
          query = q;
          break;
        }
    }
  if (!query)
    return;

  /* If we got a truncated UDP packet and are not ignoring truncation,
   * don't accept the packet, and switch the query to TCP if we hadn't
   * done so already.
   */
  if ((tc || alen > PACKETSZ) && !tcp && !(channel->flags & ARES_FLAG_IGNTC))
    {
      if (!query->using_tcp)
        {
          query->using_tcp = 1;
          ares__send_query(channel, query, now);
        }
      return;
    }

  /* Limit alen to PACKETSZ if we aren't using TCP (only relevant if we
   * are ignoring truncation.
   */
  if (alen > PACKETSZ && !tcp)
    alen = PACKETSZ;

  /* If we aren't passing through all error packets, discard packets
   * with SERVFAIL, NOTIMP, or REFUSED response codes.
   */
  if (!(channel->flags & ARES_FLAG_NOCHECKRESP))
    {
      if (rcode == SERVFAIL || rcode == NOTIMP || rcode == REFUSED)
        {
          skip_server(channel, query, whichserver);
          if (query->server == whichserver)
            next_server(channel, query, now);
          return;
        }
    }

  end_query(channel, query, ARES_SUCCESS, abuf, alen);
}

/* Close all the connections that are no longer usable. */
static void process_broken_connections(ares_channel channel,
                                       struct timeval *now)
{
  int i;
  for (i = 0; i < channel->nservers; i++)
    {
      struct server_state *server = &channel->servers[i];
      if (server->is_broken)
        {
          handle_error(channel, i, now);
        }
    }
}

static void handle_error(ares_channel channel, int whichserver,
                         struct timeval *now)
{
  struct server_state *server;
  struct query *query;
  struct list_node list_head;
  struct list_node* list_node;

  server = &channel->servers[whichserver];

  /* Reset communications with this server. */
  ares__close_sockets(channel, server);

  /* Tell all queries talking to this server to move on and not try
   * this server again. We steal the current list of queries that were
   * in-flight to this server, since when we call next_server this can
   * cause the queries to be re-sent to this server, which will
   * re-insert these queries in that same server->queries_to_server
   * list.
   */
  ares__init_list_head(&list_head);
  ares__swap_lists(&list_head, &(server->queries_to_server));
  for (list_node = list_head.next; list_node != &list_head; )
    {
      query = list_node->data;
      list_node = list_node->next;  /* in case the query gets deleted */
      assert(query->server == whichserver);
      skip_server(channel, query, whichserver);
      next_server(channel, query, now);
    }
  /* Each query should have removed itself from our temporary list as
   * it re-sent itself or finished up...
   */
  assert(ares__is_list_empty(&list_head));
}

static void skip_server(ares_channel channel, struct query *query,
                        int whichserver) {
  /* The given server gave us problems with this query, so if we have
   * the luxury of using other servers, then let's skip the
   * potentially broken server and just use the others. If we only
   * have one server and we need to retry then we should just go ahead
   * and re-use that server, since it's our only hope; perhaps we
   * just got unlucky, and retrying will work (eg, the server timed
   * out our TCP connection just as we were sending another request).
   */
  if (channel->nservers > 1)
    {
      query->server_info[whichserver].skip_server = 1;
    }
}

static void next_server(ares_channel channel, struct query *query,
                        struct timeval *now)
{
  /* We need to try each server channel->tries times. We have channel->nservers
   * servers to try. In total, we need to do channel->nservers * channel->tries
   * attempts. Use query->try to remember how many times we already attempted
   * this query. Use modular arithmetic to find the next server to try. */
  while (++(query->try_count) < (channel->nservers * channel->tries))
    {
      struct server_state *server;

      /* Move on to the next server. */
      query->server = (query->server + 1) % channel->nservers;
      server = &channel->servers[query->server];

      /* We don't want to use this server if (1) we decided this
       * connection is broken, and thus about to be closed, (2)
       * we've decided to skip this server because of earlier
       * errors we encountered, or (3) we already sent this query
       * over this exact connection.
       */
      if (!server->is_broken &&
           !query->server_info[query->server].skip_server &&
           !(query->using_tcp &&
             (query->server_info[query->server].tcp_connection_generation ==
              server->tcp_connection_generation)))
        {
           ares__send_query(channel, query, now);
           return;
        }

      /* You might think that with TCP we only need one try. However,
       * even when using TCP, servers can time-out our connection just
       * as we're sending a request, or close our connection because
       * they die, or never send us a reply because they get wedged or
       * tickle a bug that drops our request.
       */
    }

  /* If we are here, all attempts to perform query failed. */
  end_query(channel, query, query->error_status, NULL, 0);
}

void ares__send_query(ares_channel channel, struct query *query,
                      struct timeval *now)
{
  struct send_request *sendreq;
  struct server_state *server;
  int timeplus;

  server = &channel->servers[query->server];
  if (query->using_tcp)
    {
      /* Make sure the TCP socket for this server is set up and queue
       * a send request.
       */
      if (server->tcp_socket == ARES_SOCKET_BAD)
        {
          if (open_tcp_socket(channel, server) == -1)
            {
              skip_server(channel, query, query->server);
              next_server(channel, query, now);
              return;
            }
        }
      sendreq = calloc(1, sizeof(struct send_request));
      if (!sendreq)
        {
        end_query(channel, query, ARES_ENOMEM, NULL, 0);
          return;
        }
      /* To make the common case fast, we avoid copies by using the
       * query's tcpbuf for as long as the query is alive. In the rare
       * case where the query ends while it's queued for transmission,
       * then we give the sendreq its own copy of the request packet
       * and put it in sendreq->data_storage.
       */
      sendreq->data_storage = NULL;
      sendreq->data = query->tcpbuf;
      sendreq->len = query->tcplen;
      sendreq->owner_query = query;
      sendreq->next = NULL;
      if (server->qtail)
        server->qtail->next = sendreq;
      else
        {
          SOCK_STATE_CALLBACK(channel, server->tcp_socket, 1, 1);
          server->qhead = sendreq;
        }
      server->qtail = sendreq;
      query->server_info[query->server].tcp_connection_generation =
        server->tcp_connection_generation;
    }
  else
    {
      if (server->udp_socket == ARES_SOCKET_BAD)
        {
          if (open_udp_socket(channel, server) == -1)
            {
              skip_server(channel, query, query->server);
              next_server(channel, query, now);
              return;
            }
        }
      if (swrite(server->udp_socket, query->qbuf, query->qlen) == -1)
        {
          /* FIXME: Handle EAGAIN here since it likely can happen. */
          skip_server(channel, query, query->server);
          next_server(channel, query, now);
          return;
        }
    }
    timeplus = channel->timeout << (query->try_count / channel->nservers);
    timeplus = (timeplus * (9 + (rand () & 7))) / 16;
    query->timeout = *now;
    ares__timeadd(&query->timeout,
                  timeplus);
    /* Keep track of queries bucketed by timeout, so we can process
     * timeout events quickly.
     */
    ares__remove_from_list(&(query->queries_by_timeout));
    ares__insert_in_list(
        &(query->queries_by_timeout),
        &(channel->queries_by_timeout[query->timeout.tv_sec %
                                      ARES_TIMEOUT_TABLE_SIZE]));

    /* Keep track of queries bucketed by server, so we can process server
     * errors quickly.
     */
    ares__remove_from_list(&(query->queries_to_server));
    ares__insert_in_list(&(query->queries_to_server),
                         &(server->queries_to_server));
}

/*
 * setsocknonblock sets the given socket to either blocking or non-blocking
 * mode based on the 'nonblock' boolean argument. This function is highly
 * portable.
 */
static int setsocknonblock(ares_socket_t sockfd,    /* operate on this */
                    int nonblock   /* TRUE or FALSE */)
{
#if defined(USE_BLOCKING_SOCKETS)

  return 0; /* returns success */

#elif defined(HAVE_FCNTL_O_NONBLOCK)

  /* most recent unix versions */
  int flags;
  flags = fcntl(sockfd, F_GETFL, 0);
  if (FALSE != nonblock)
    return fcntl(sockfd, F_SETFL, flags | O_NONBLOCK);
  else
    return fcntl(sockfd, F_SETFL, flags & (~O_NONBLOCK));

#elif defined(HAVE_IOCTL_FIONBIO)

  /* older unix versions */
  int flags;
  flags = nonblock;
  return ioctl(sockfd, FIONBIO, &flags);

#elif defined(HAVE_IOCTLSOCKET_FIONBIO)

#ifdef WATT32
  char flags;
#else
  /* Windows */
  unsigned long flags;
#endif
  flags = nonblock;
  return ioctlsocket(sockfd, FIONBIO, &flags);

#elif defined(HAVE_IOCTLSOCKET_CAMEL_FIONBIO)

  /* Amiga */
  return IoctlSocket(sockfd, FIONBIO, (long)nonblock);

#elif defined(HAVE_SETSOCKOPT_SO_NONBLOCK)

  /* BeOS */
  long b = nonblock ? 1 : 0;
  return setsockopt(sockfd, SOL_SOCKET, SO_NONBLOCK, &b, sizeof(b));

#else
#  error "no non-blocking method was found/used/set"
#endif
}

static int configure_socket(ares_socket_t s, int family, ares_channel channel)
{
  union {
    struct sockaddr     sa;
    struct sockaddr_in  sa4;
    struct sockaddr_in6 sa6;
  } local;

  setsocknonblock(s, TRUE);

#if defined(FD_CLOEXEC) && !defined(MSDOS)
  /* Configure the socket fd as close-on-exec. */
  if (fcntl(s, F_SETFD, FD_CLOEXEC) == -1)
    return -1;
#endif

  /* Set the socket's send and receive buffer sizes. */
  if ((channel->socket_send_buffer_size > 0) &&
      setsockopt(s, SOL_SOCKET, SO_SNDBUF,
                 (void *)&channel->socket_send_buffer_size,
                 sizeof(channel->socket_send_buffer_size)) == -1)
    return -1;

  if ((channel->socket_receive_buffer_size > 0) &&
      setsockopt(s, SOL_SOCKET, SO_RCVBUF,
                 (void *)&channel->socket_receive_buffer_size,
                 sizeof(channel->socket_receive_buffer_size)) == -1)
    return -1;

#ifdef SO_BINDTODEVICE
  if (channel->local_dev_name[0]) {
    if (setsockopt(s, SOL_SOCKET, SO_BINDTODEVICE,
                   channel->local_dev_name, sizeof(channel->local_dev_name))) {
      /* Only root can do this, and usually not fatal if it doesn't work, so */
      /* just continue on. */
    }
  }
#endif

  if (family == AF_INET) {
    if (channel->local_ip4) {
      memset(&local.sa4, 0, sizeof(local.sa4));
      local.sa4.sin_family = AF_INET;
      local.sa4.sin_addr.s_addr = htonl(channel->local_ip4);
      if (bind(s, &local.sa, sizeof(local.sa4)) < 0)
        return -1;
    }
  }
  else if (family == AF_INET6) {
    if (memcmp(channel->local_ip6, &ares_in6addr_any, sizeof(channel->local_ip6)) != 0) {
      memset(&local.sa6, 0, sizeof(local.sa6));
      local.sa6.sin6_family = AF_INET6;
      memcpy(&local.sa6.sin6_addr, channel->local_ip6, sizeof(channel->local_ip6));
      if (bind(s, &local.sa, sizeof(local.sa6)) < 0)
        return -1;
    }
  }

  return 0;
}

static int open_tcp_socket(ares_channel channel, struct server_state *server)
{
  ares_socket_t s;
  int opt;
  ares_socklen_t salen;
  union {
    struct sockaddr_in  sa4;
    struct sockaddr_in6 sa6;
  } saddr;
  struct sockaddr *sa;

  switch (server->addr.family)
    {
      case AF_INET:
        sa = (void *)&saddr.sa4;
        salen = sizeof(saddr.sa4);
        memset(sa, 0, salen);
        saddr.sa4.sin_family = AF_INET;
        saddr.sa4.sin_port = (unsigned short)(channel->tcp_port & 0xffff);
        memcpy(&saddr.sa4.sin_addr, &server->addr.addrV4,
               sizeof(server->addr.addrV4));
        break;
      case AF_INET6:
        sa = (void *)&saddr.sa6;
        salen = sizeof(saddr.sa6);
        memset(sa, 0, salen);
        saddr.sa6.sin6_family = AF_INET6;
        saddr.sa6.sin6_port = (unsigned short)(channel->tcp_port & 0xffff);
        memcpy(&saddr.sa6.sin6_addr, &server->addr.addrV6,
               sizeof(server->addr.addrV6));
        break;
      default:
        return -1;
    }

  /* Acquire a socket. */
  s = socket(server->addr.family, SOCK_STREAM, 0);
  if (s == ARES_SOCKET_BAD)
    return -1;

  /* Configure it. */
  if (configure_socket(s, server->addr.family, channel) < 0)
    {
       sclose(s);
       return -1;
    }

#ifdef TCP_NODELAY
  /*
   * Disable the Nagle algorithm (only relevant for TCP sockets, and thus not
   * in configure_socket). In general, in DNS lookups we're pretty much
   * interested in firing off a single request and then waiting for a reply,
   * so batching isn't very interesting.
   */
  opt = 1;
  if (setsockopt(s, IPPROTO_TCP, TCP_NODELAY,
                 (void *)&opt, sizeof(opt)) == -1)
    {
       sclose(s);
       return -1;
    }
#endif

  /* Connect to the server. */
  if (connect(s, sa, salen) == -1)
    {
      int err = SOCKERRNO;

      if (err != EINPROGRESS && err != EWOULDBLOCK)
        {
          sclose(s);
          return -1;
        }
    }

  if (channel->sock_create_cb)
    {
      int err = channel->sock_create_cb(s, SOCK_STREAM,
                                        channel->sock_create_cb_data);
      if (err < 0)
        {
          sclose(s);
          return err;
        }
    }

  SOCK_STATE_CALLBACK(channel, s, 1, 0);
  server->tcp_buffer_pos = 0;
  server->tcp_socket = s;
  server->tcp_connection_generation = ++channel->tcp_connection_generation;
  return 0;
}

static int open_udp_socket(ares_channel channel, struct server_state *server)
{
  ares_socket_t s;
  ares_socklen_t salen;
  union {
    struct sockaddr_in  sa4;
    struct sockaddr_in6 sa6;
  } saddr;
  struct sockaddr *sa;

  switch (server->addr.family)
    {
      case AF_INET:
        sa = (void *)&saddr.sa4;
        salen = sizeof(saddr.sa4);
        memset(sa, 0, salen);
        saddr.sa4.sin_family = AF_INET;
        saddr.sa4.sin_port = (unsigned short)(channel->udp_port & 0xffff);
        memcpy(&saddr.sa4.sin_addr, &server->addr.addrV4,
               sizeof(server->addr.addrV4));
        break;
      case AF_INET6:
        sa = (void *)&saddr.sa6;
        salen = sizeof(saddr.sa6);
        memset(sa, 0, salen);
        saddr.sa6.sin6_family = AF_INET6;
        saddr.sa6.sin6_port = (unsigned short)(channel->udp_port & 0xffff);
        memcpy(&saddr.sa6.sin6_addr, &server->addr.addrV6,
               sizeof(server->addr.addrV6));
        break;
      default:
        return -1;
    }

  /* Acquire a socket. */
  s = socket(server->addr.family, SOCK_DGRAM, 0);
  if (s == ARES_SOCKET_BAD)
    return -1;

  /* Set the socket non-blocking. */
  if (configure_socket(s, server->addr.family, channel) < 0)
    {
       sclose(s);
       return -1;
    }

  /* Connect to the server. */
  if (connect(s, sa, salen) == -1)
    {
      int err = SOCKERRNO;

      if (err != EINPROGRESS && err != EWOULDBLOCK)
        {
          sclose(s);
          return -1;
        }
    }

  if (channel->sock_create_cb)
    {
      int err = channel->sock_create_cb(s, SOCK_DGRAM,
                                        channel->sock_create_cb_data);
      if (err < 0)
        {
          sclose(s);
          return err;
        }
    }

  SOCK_STATE_CALLBACK(channel, s, 1, 0);

  server->udp_socket = s;
  return 0;
}

static int same_questions(const unsigned char *qbuf, int qlen,
                          const unsigned char *abuf, int alen)
{
  struct {
    const unsigned char *p;
    int qdcount;
    char *name;
    long namelen;
    int type;
    int dnsclass;
  } q, a;
  int i, j;

  if (qlen < HFIXEDSZ || alen < HFIXEDSZ)
    return 0;

  /* Extract qdcount from the request and reply buffers and compare them. */
  q.qdcount = DNS_HEADER_QDCOUNT(qbuf);
  a.qdcount = DNS_HEADER_QDCOUNT(abuf);
  if (q.qdcount != a.qdcount)
    return 0;

  /* For each question in qbuf, find it in abuf. */
  q.p = qbuf + HFIXEDSZ;
  for (i = 0; i < q.qdcount; i++)
    {
      /* Decode the question in the query. */
      if (ares_expand_name(q.p, qbuf, qlen, &q.name, &q.namelen)
          != ARES_SUCCESS)
        return 0;
      q.p += q.namelen;
      if (q.p + QFIXEDSZ > qbuf + qlen)
        {
          free(q.name);
          return 0;
        }
      q.type = DNS_QUESTION_TYPE(q.p);
      q.dnsclass = DNS_QUESTION_CLASS(q.p);
      q.p += QFIXEDSZ;

      /* Search for this question in the answer. */
      a.p = abuf + HFIXEDSZ;
      for (j = 0; j < a.qdcount; j++)
        {
          /* Decode the question in the answer. */
          if (ares_expand_name(a.p, abuf, alen, &a.name, &a.namelen)
              != ARES_SUCCESS)
            {
              free(q.name);
              return 0;
            }
          a.p += a.namelen;
          if (a.p + QFIXEDSZ > abuf + alen)
            {
              free(q.name);
              free(a.name);
              return 0;
            }
          a.type = DNS_QUESTION_TYPE(a.p);
          a.dnsclass = DNS_QUESTION_CLASS(a.p);
          a.p += QFIXEDSZ;

          /* Compare the decoded questions. */
          if (strcasecmp(q.name, a.name) == 0 && q.type == a.type
              && q.dnsclass == a.dnsclass)
            {
              free(a.name);
              break;
            }
          free(a.name);
        }

      free(q.name);
      if (j == a.qdcount)
        return 0;
    }
  return 1;
}

static int same_address(struct sockaddr *sa, struct ares_addr *aa)
{
  void *addr1;
  void *addr2;

  if (sa->sa_family == aa->family)
    {
      switch (aa->family)
        {
          case AF_INET:
            addr1 = &aa->addrV4;
            addr2 = &((struct sockaddr_in *)sa)->sin_addr;
            if (memcmp(addr1, addr2, sizeof(aa->addrV4)) == 0)
              return 1; /* match */
            break;
          case AF_INET6:
            addr1 = &aa->addrV6;
            addr2 = &((struct sockaddr_in6 *)sa)->sin6_addr;
            if (memcmp(addr1, addr2, sizeof(aa->addrV6)) == 0)
              return 1; /* match */
            break;
          default:
            break;
        }
    }
  return 0; /* different */
}

static void end_query (ares_channel channel, struct query *query, int status,
                       unsigned char *abuf, int alen)
{
  int i;

  /* First we check to see if this query ended while one of our send
   * queues still has pointers to it.
   */
  for (i = 0; i < channel->nservers; i++)
    {
      struct server_state *server = &channel->servers[i];
      struct send_request *sendreq;
      for (sendreq = server->qhead; sendreq; sendreq = sendreq->next)
        if (sendreq->owner_query == query)
          {
            sendreq->owner_query = NULL;
            assert(sendreq->data_storage == NULL);
            if (status == ARES_SUCCESS)
              {
                /* We got a reply for this query, but this queued
                 * sendreq points into this soon-to-be-gone query's
                 * tcpbuf. Probably this means we timed out and queued
                 * the query for retransmission, then received a
                 * response before actually retransmitting. This is
                 * perfectly fine, so we want to keep the connection
                 * running smoothly if we can. But in the worst case
                 * we may have sent only some prefix of the query,
                 * with some suffix of the query left to send. Also,
                 * the buffer may be queued on multiple queues. To
                 * prevent dangling pointers to the query's tcpbuf and
                 * handle these cases, we just give such sendreqs
                 * their own copy of the query packet.
                 */
               sendreq->data_storage = malloc(sendreq->len);
               if (sendreq->data_storage != NULL)
                 {
                   memcpy(sendreq->data_storage, sendreq->data, sendreq->len);
                   sendreq->data = sendreq->data_storage;
                 }
              }
            if ((status != ARES_SUCCESS) || (sendreq->data_storage == NULL))
              {
                /* We encountered an error (probably a timeout,
                 * suggesting the DNS server we're talking to is
                 * probably unreachable, wedged, or severely
                 * overloaded) or we couldn't copy the request, so
                 * mark the connection as broken. When we get to
                 * process_broken_connections() we'll close the
                 * connection and try to re-send requests to another
                 * server.
                 */
               server->is_broken = 1;
               /* Just to be paranoid, zero out this sendreq... */
               sendreq->data = NULL;
               sendreq->len = 0;
             }
          }
    }

  /* Invoke the callback */
  query->callback(query->arg, status, query->timeouts, abuf, alen);
  ares__free_query(query);

  /* Simple cleanup policy: if no queries are remaining, close all
   * network sockets unless STAYOPEN is set.
   */
  if (!(channel->flags & ARES_FLAG_STAYOPEN) &&
      ares__is_list_empty(&(channel->all_queries)))
    {
      for (i = 0; i < channel->nservers; i++)
        ares__close_sockets(channel, &channel->servers[i]);
    }
}

void ares__free_query(struct query *query)
{
  /* Remove the query from all the lists in which it is linked */
  ares__remove_from_list(&(query->queries_by_qid));
  ares__remove_from_list(&(query->queries_by_timeout));
  ares__remove_from_list(&(query->queries_to_server));
  ares__remove_from_list(&(query->all_queries));
  /* Zero out some important stuff, to help catch bugs */
  query->callback = NULL;
  query->arg = NULL;
  /* Deallocate the memory associated with the query */
  free(query->tcpbuf);
  free(query->server_info);
  free(query);
}
Tip: Filter by directory path e.g. /media app.js to search for public/media/app.js.
Tip: Use camelCasing e.g. ProjME to search for ProjectModifiedEvent.java.
Tip: Filter by extension type e.g. /repo .js to search for all .js files in the /repo directory.
Tip: Separate your search with spaces e.g. /ssh pom.xml to search for src/ssh/pom.xml.
Tip: Use ↑ and ↓ arrow keys to navigate and return to view the file.
Tip: You can also navigate files with Ctrl+j (next) and Ctrl+k (previous) and view the file with Ctrl+o.
Tip: You can also navigate files with Alt+j (next) and Alt+k (previous) and view the file with Alt+o.