lib/stream.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2010, 2011 Nicira Networks.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #include <config.h>
  18 #include "stream-provider.h"
  19 #include <assert.h>
  20 #include <errno.h>
  21 #include <inttypes.h>
  22 #include <netinet/in.h>
  23 #include <poll.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26 #include "coverage.h"
  27 #include "dynamic-string.h"
  28 #include "fatal-signal.h"
  29 #include "flow.h"
  30 #include "ofp-print.h"
  31 #include "ofpbuf.h"
  32 #include "openflow/nicira-ext.h"
  33 #include "openflow/openflow.h"
  34 #include "packets.h"
  35 #include "poll-loop.h"
  36 #include "random.h"
  37 #include "util.h"
  38 #include "vlog.h"
  39
  40 VLOG_DEFINE_THIS_MODULE(stream);
  41
  42 COVERAGE_DEFINE(pstream_open);
  43 COVERAGE_DEFINE(stream_open);
  44
  45 /* State of an active stream.*/
  46 enum stream_state {
  47     SCS_CONNECTING,             /* Underlying stream is not connected. */
  48     SCS_CONNECTED,              /* Connection established. */
  49     SCS_DISCONNECTED            /* Connection failed or connection closed. */
  50 };
  51
  52 static struct stream_class *stream_classes[] = {
  53     &tcp_stream_class,
  54     &unix_stream_class,
  55 #ifdef HAVE_OPENSSL
  56     &ssl_stream_class,
  57 #endif
  58 };
  59
  60 static struct pstream_class *pstream_classes[] = {
  61     &ptcp_pstream_class,
  62     &punix_pstream_class,
  63 #ifdef HAVE_OPENSSL
  64     &pssl_pstream_class,
  65 #endif
  66 };
  67
  68 /* Check the validity of the stream class structures. */
  69 static void
  70 check_stream_classes(void)
  71 {
  72 #ifndef NDEBUG
  73     size_t i;
  74
  75     for (i = 0; i < ARRAY_SIZE(stream_classes); i++) {
  76         struct stream_class *class = stream_classes[i];
  77         assert(class->name != NULL);
  78         assert(class->open != NULL);
  79         if (class->close || class->recv || class->send || class->run
  80             || class->run_wait || class->wait) {
  81             assert(class->close != NULL);
  82             assert(class->recv != NULL);
  83             assert(class->send != NULL);
  84             assert(class->wait != NULL);
  85         } else {
  86             /* This class delegates to another one. */
  87         }
  88     }
  89
  90     for (i = 0; i < ARRAY_SIZE(pstream_classes); i++) {
  91         struct pstream_class *class = pstream_classes[i];
  92         assert(class->name != NULL);
  93         assert(class->listen != NULL);
  94         if (class->close || class->accept || class->wait) {
  95             assert(class->close != NULL);
  96             assert(class->accept != NULL);
  97             assert(class->wait != NULL);
  98         } else {
  99             /* This class delegates to another one. */
 100         }
 101     }
 102 #endif
 103 }
 104
 105 /* Prints information on active (if 'active') and passive (if 'passive')
 106  * connection methods supported by the stream. */
 107 void
 108 stream_usage(const char *name, bool active, bool passive,
 109              bool bootstrap OVS_UNUSED)
 110 {
 111     /* Really this should be implemented via callbacks into the stream
 112      * providers, but that seems too heavy-weight to bother with at the
 113      * moment. */
 114
 115     printf("\n");
 116     if (active) {
 117         printf("Active %s connection methods:\n", name);
 118         printf("  tcp:IP:PORT             "
 119                "PORT at remote IP\n");
 120 #ifdef HAVE_OPENSSL
 121         printf("  ssl:IP:PORT             "
 122                "SSL PORT at remote IP\n");
 123 #endif
 124         printf("  unix:FILE               "
 125                "Unix domain socket named FILE\n");
 126     }
 127
 128     if (passive) {
 129         printf("Passive %s connection methods:\n", name);
 130         printf("  ptcp:PORT[:IP]          "
 131                "listen to TCP PORT on IP\n");
 132 #ifdef HAVE_OPENSSL
 133         printf("  pssl:PORT[:IP]          "
 134                "listen for SSL on PORT on IP\n");
 135 #endif
 136         printf("  punix:FILE              "
 137                "listen on Unix domain socket FILE\n");
 138     }
 139
 140 #ifdef HAVE_OPENSSL
 141     printf("PKI configuration (required to use SSL):\n"
 142            "  -p, --private-key=FILE  file with private key\n"
 143            "  -c, --certificate=FILE  file with certificate for private key\n"
 144            "  -C, --ca-cert=FILE      file with peer CA certificate\n");
 145     if (bootstrap) {
 146         printf("  --bootstrap-ca-cert=FILE  file with peer CA certificate "
 147                "to read or create\n");
 148     }
 149 #endif
 150 }
 151
 152 /* Given 'name', a stream name in the form "TYPE:ARGS", stores the class
 153  * named "TYPE" into '*classp' and returns 0.  Returns EAFNOSUPPORT and stores
 154  * a null pointer into '*classp' if 'name' is in the wrong form or if no such
 155  * class exists. */
 156 static int
 157 stream_lookup_class(const char *name, struct stream_class **classp)
 158 {
 159     size_t prefix_len;
 160     size_t i;
 161
 162     check_stream_classes();
 163
 164     *classp = NULL;
 165     prefix_len = strcspn(name, ":");
 166     if (name[prefix_len] == '\0') {
 167         return EAFNOSUPPORT;
 168     }
 169     for (i = 0; i < ARRAY_SIZE(stream_classes); i++) {
 170         struct stream_class *class = stream_classes[i];
 171         if (strlen(class->name) == prefix_len
 172             && !memcmp(class->name, name, prefix_len)) {
 173             *classp = class;
 174             return 0;
 175         }
 176     }
 177     return EAFNOSUPPORT;
 178 }
 179
 180 /* Returns 0 if 'name' is a stream name in the form "TYPE:ARGS" and TYPE is
 181  * a supported stream type, otherwise EAFNOSUPPORT.  */
 182 int
 183 stream_verify_name(const char *name)
 184 {
 185     struct stream_class *class;
 186     return stream_lookup_class(name, &class);
 187 }
 188
 189 /* Attempts to connect a stream to a remote peer.  'name' is a connection name
 190  * in the form "TYPE:ARGS", where TYPE is an active stream class's name and
 191  * ARGS are stream class-specific.
 192  *
 193  * Returns 0 if successful, otherwise a positive errno value.  If successful,
 194  * stores a pointer to the new connection in '*streamp', otherwise a null
 195  * pointer.  */
 196 int
 197 stream_open(const char *name, struct stream **streamp)
 198 {
 199     struct stream_class *class;
 200     struct stream *stream;
 201     char *suffix_copy;
 202     int error;
 203
 204     COVERAGE_INC(stream_open);
 205
 206     /* Look up the class. */
 207     error = stream_lookup_class(name, &class);
 208     if (!class) {
 209         goto error;
 210     }
 211
 212     /* Call class's "open" function. */
 213     suffix_copy = xstrdup(strchr(name, ':') + 1);
 214     error = class->open(name, suffix_copy, &stream);
 215     free(suffix_copy);
 216     if (error) {
 217         goto error;
 218     }
 219
 220     /* Success. */
 221     *streamp = stream;
 222     return 0;
 223
 224 error:
 225     *streamp = NULL;
 226     return error;
 227 }
 228
 229 /* Blocks until a previously started stream connection attempt succeeds or
 230  * fails.  'error' should be the value returned by stream_open() and 'streamp'
 231  * should point to the stream pointer set by stream_open().  Returns 0 if
 232  * successful, otherwise a positive errno value other than EAGAIN or
 233  * EINPROGRESS.  If successful, leaves '*streamp' untouched; on error, closes
 234  * '*streamp' and sets '*streamp' to null.
 235  *
 236  * Typical usage:
 237  *   error = stream_open_block(stream_open("tcp:1.2.3.4:5", &stream), &stream);
 238  */
 239 int
 240 stream_open_block(int error, struct stream **streamp)
 241 {
 242     struct stream *stream = *streamp;
 243
 244     fatal_signal_run();
 245
 246     if (!error) {
 247         while ((error = stream_connect(stream)) == EAGAIN) {
 248             stream_run(stream);
 249             stream_run_wait(stream);
 250             stream_connect_wait(stream);
 251             poll_block();
 252         }
 253         assert(error != EINPROGRESS);
 254     }
 255
 256     if (error) {
 257         stream_close(stream);
 258         *streamp = NULL;
 259     } else {
 260         *streamp = stream;
 261     }
 262     return error;
 263 }
 264
 265 /* Closes 'stream'. */
 266 void
 267 stream_close(struct stream *stream)
 268 {
 269     if (stream != NULL) {
 270         char *name = stream->name;
 271         (stream->class->close)(stream);
 272         free(name);
 273     }
 274 }
 275
 276 /* Returns the name of 'stream', that is, the string passed to
 277  * stream_open(). */
 278 const char *
 279 stream_get_name(const struct stream *stream)
 280 {
 281     return stream ? stream->name : "(null)";
 282 }
 283
 284 /* Returns the IP address of the peer, or 0 if the peer is not connected over
 285  * an IP-based protocol or if its IP address is not yet known. */
 286 ovs_be32
 287 stream_get_remote_ip(const struct stream *stream)
 288 {
 289     return stream->remote_ip;
 290 }
 291
 292 /* Returns the transport port of the peer, or 0 if the connection does not
 293  * contain a port or if the port is not yet known. */
 294 ovs_be16
 295 stream_get_remote_port(const struct stream *stream)
 296 {
 297     return stream->remote_port;
 298 }
 299
 300 /* Returns the IP address used to connect to the peer, or 0 if the connection
 301  * is not an IP-based protocol or if its IP address is not yet known. */
 302 ovs_be32
 303 stream_get_local_ip(const struct stream *stream)
 304 {
 305     return stream->local_ip;
 306 }
 307
 308 /* Returns the transport port used to connect to the peer, or 0 if the
 309  * connection does not contain a port or if the port is not yet known. */
 310 ovs_be16
 311 stream_get_local_port(const struct stream *stream)
 312 {
 313     return stream->local_port;
 314 }
 315
 316 static void
 317 scs_connecting(struct stream *stream)
 318 {
 319     int retval = (stream->class->connect)(stream);
 320     assert(retval != EINPROGRESS);
 321     if (!retval) {
 322         stream->state = SCS_CONNECTED;
 323     } else if (retval != EAGAIN) {
 324         stream->state = SCS_DISCONNECTED;
 325         stream->error = retval;
 326     }
 327 }
 328
 329 /* Tries to complete the connection on 'stream'.  If 'stream''s connection is
 330  * complete, returns 0 if the connection was successful or a positive errno
 331  * value if it failed.  If the connection is still in progress, returns
 332  * EAGAIN. */
 333 int
 334 stream_connect(struct stream *stream)
 335 {
 336     enum stream_state last_state;
 337
 338     do {
 339         last_state = stream->state;
 340         switch (stream->state) {
 341         case SCS_CONNECTING:
 342             scs_connecting(stream);
 343             break;
 344
 345         case SCS_CONNECTED:
 346             return 0;
 347
 348         case SCS_DISCONNECTED:
 349             return stream->error;
 350
 351         default:
 352             NOT_REACHED();
 353         }
 354     } while (stream->state != last_state);
 355
 356     return EAGAIN;
 357 }
 358
 359 /* Tries to receive up to 'n' bytes from 'stream' into 'buffer', and returns:
 360  *
 361  *     - If successful, the number of bytes received (between 1 and 'n').
 362  *
 363  *     - On error, a negative errno value.
 364  *
 365  *     - 0, if the connection has been closed in the normal fashion, or if 'n'
 366  *       is zero.
 367  *
 368  * The recv function will not block waiting for a packet to arrive.  If no
 369  * data have been received, it returns -EAGAIN immediately. */
 370 int
 371 stream_recv(struct stream *stream, void *buffer, size_t n)
 372 {
 373     int retval = stream_connect(stream);
 374     return (retval ? -retval
 375             : n == 0 ? 0
 376             : (stream->class->recv)(stream, buffer, n));
 377 }
 378
 379 /* Tries to send up to 'n' bytes of 'buffer' on 'stream', and returns:
 380  *
 381  *     - If successful, the number of bytes sent (between 1 and 'n').  0 is
 382  *       only a valid return value if 'n' is 0.
 383  *
 384  *     - On error, a negative errno value.
 385  *
 386  * The send function will not block.  If no bytes can be immediately accepted
 387  * for transmission, it returns -EAGAIN immediately. */
 388 int
 389 stream_send(struct stream *stream, const void *buffer, size_t n)
 390 {
 391     int retval = stream_connect(stream);
 392     return (retval ? -retval
 393             : n == 0 ? 0
 394             : (stream->class->send)(stream, buffer, n));
 395 }
 396
 397 /* Allows 'stream' to perform maintenance activities, such as flushing
 398  * output buffers. */
 399 void
 400 stream_run(struct stream *stream)
 401 {
 402     if (stream->class->run) {
 403         (stream->class->run)(stream);
 404     }
 405 }
 406
 407 /* Arranges for the poll loop to wake up when 'stream' needs to perform
 408  * maintenance activities. */
 409 void
 410 stream_run_wait(struct stream *stream)
 411 {
 412     if (stream->class->run_wait) {
 413         (stream->class->run_wait)(stream);
 414     }
 415 }
 416
 417 /* Arranges for the poll loop to wake up when 'stream' is ready to take an
 418  * action of the given 'type'. */
 419 void
 420 stream_wait(struct stream *stream, enum stream_wait_type wait)
 421 {
 422     assert(wait == STREAM_CONNECT || wait == STREAM_RECV
 423            || wait == STREAM_SEND);
 424
 425     switch (stream->state) {
 426     case SCS_CONNECTING:
 427         wait = STREAM_CONNECT;
 428         break;
 429
 430     case SCS_DISCONNECTED:
 431         poll_immediate_wake();
 432         return;
 433     }
 434     (stream->class->wait)(stream, wait);
 435 }
 436
 437 void
 438 stream_connect_wait(struct stream *stream)
 439 {
 440     stream_wait(stream, STREAM_CONNECT);
 441 }
 442
 443 void
 444 stream_recv_wait(struct stream *stream)
 445 {
 446     stream_wait(stream, STREAM_RECV);
 447 }
 448
 449 void
 450 stream_send_wait(struct stream *stream)
 451 {
 452     stream_wait(stream, STREAM_SEND);
 453 }
 454
 455 /* Given 'name', a pstream name in the form "TYPE:ARGS", stores the class
 456  * named "TYPE" into '*classp' and returns 0.  Returns EAFNOSUPPORT and stores
 457  * a null pointer into '*classp' if 'name' is in the wrong form or if no such
 458  * class exists. */
 459 static int
 460 pstream_lookup_class(const char *name, struct pstream_class **classp)
 461 {
 462     size_t prefix_len;
 463     size_t i;
 464
 465     check_stream_classes();
 466
 467     *classp = NULL;
 468     prefix_len = strcspn(name, ":");
 469     if (name[prefix_len] == '\0') {
 470         return EAFNOSUPPORT;
 471     }
 472     for (i = 0; i < ARRAY_SIZE(pstream_classes); i++) {
 473         struct pstream_class *class = pstream_classes[i];
 474         if (strlen(class->name) == prefix_len
 475             && !memcmp(class->name, name, prefix_len)) {
 476             *classp = class;
 477             return 0;
 478         }
 479     }
 480     return EAFNOSUPPORT;
 481 }
 482
 483 /* Returns 0 if 'name' is a pstream name in the form "TYPE:ARGS" and TYPE is
 484  * a supported pstream type, otherwise EAFNOSUPPORT.  */
 485 int
 486 pstream_verify_name(const char *name)
 487 {
 488     struct pstream_class *class;
 489     return pstream_lookup_class(name, &class);
 490 }
 491
 492 /* Attempts to start listening for remote stream connections.  'name' is a
 493  * connection name in the form "TYPE:ARGS", where TYPE is an passive stream
 494  * class's name and ARGS are stream class-specific.
 495  *
 496  * Returns 0 if successful, otherwise a positive errno value.  If successful,
 497  * stores a pointer to the new connection in '*pstreamp', otherwise a null
 498  * pointer.  */
 499 int
 500 pstream_open(const char *name, struct pstream **pstreamp)
 501 {
 502     struct pstream_class *class;
 503     struct pstream *pstream;
 504     char *suffix_copy;
 505     int error;
 506
 507     COVERAGE_INC(pstream_open);
 508
 509     /* Look up the class. */
 510     error = pstream_lookup_class(name, &class);
 511     if (!class) {
 512         goto error;
 513     }
 514
 515     /* Call class's "open" function. */
 516     suffix_copy = xstrdup(strchr(name, ':') + 1);
 517     error = class->listen(name, suffix_copy, &pstream);
 518     free(suffix_copy);
 519     if (error) {
 520         goto error;
 521     }
 522
 523     /* Success. */
 524     *pstreamp = pstream;
 525     return 0;
 526
 527 error:
 528     *pstreamp = NULL;
 529     return error;
 530 }
 531
 532 /* Returns the name that was used to open 'pstream'.  The caller must not
 533  * modify or free the name. */
 534 const char *
 535 pstream_get_name(const struct pstream *pstream)
 536 {
 537     return pstream->name;
 538 }
 539
 540 /* Closes 'pstream'. */
 541 void
 542 pstream_close(struct pstream *pstream)
 543 {
 544     if (pstream != NULL) {
 545         char *name = pstream->name;
 546         (pstream->class->close)(pstream);
 547         free(name);
 548     }
 549 }
 550
 551 /* Tries to accept a new connection on 'pstream'.  If successful, stores the
 552  * new connection in '*new_stream' and returns 0.  Otherwise, returns a
 553  * positive errno value.
 554  *
 555  * pstream_accept() will not block waiting for a connection.  If no connection
 556  * is ready to be accepted, it returns EAGAIN immediately. */
 557 int
 558 pstream_accept(struct pstream *pstream, struct stream **new_stream)
 559 {
 560     int retval = (pstream->class->accept)(pstream, new_stream);
 561     if (retval) {
 562         *new_stream = NULL;
 563     } else {
 564         assert((*new_stream)->state != SCS_CONNECTING
 565                || (*new_stream)->class->connect);
 566     }
 567     return retval;
 568 }
 569
 570 /* Tries to accept a new connection on 'pstream'.  If successful, stores the
 571  * new connection in '*new_stream' and returns 0.  Otherwise, returns a
 572  * positive errno value.
 573  *
 574  * pstream_accept_block() blocks until a connection is ready or until an error
 575  * occurs.  It will not return EAGAIN. */
 576 int
 577 pstream_accept_block(struct pstream *pstream, struct stream **new_stream)
 578 {
 579     int error;
 580
 581     fatal_signal_run();
 582     while ((error = pstream_accept(pstream, new_stream)) == EAGAIN) {
 583         pstream_wait(pstream);
 584         poll_block();
 585     }
 586     if (error) {
 587         *new_stream = NULL;
 588     }
 589     return error;
 590 }
 591
 592 void
 593 pstream_wait(struct pstream *pstream)
 594 {
 595     (pstream->class->wait)(pstream);
 596 }
 597 \f
 598 /* Initializes 'stream' as a new stream named 'name', implemented via 'class'.
 599  * The initial connection status, supplied as 'connect_status', is interpreted
 600  * as follows:
 601  *
 602  *      - 0: 'stream' is connected.  Its 'send' and 'recv' functions may be
 603  *        called in the normal fashion.
 604  *
 605  *      - EAGAIN: 'stream' is trying to complete a connection.  Its 'connect'
 606  *        function should be called to complete the connection.
 607  *
 608  *      - Other positive errno values indicate that the connection failed with
 609  *        the specified error.
 610  *
 611  * After calling this function, stream_close() must be used to destroy
 612  * 'stream', otherwise resources will be leaked.
 613  *
 614  * The caller retains ownership of 'name'. */
 615 void
 616 stream_init(struct stream *stream, struct stream_class *class,
 617             int connect_status, const char *name)
 618 {
 619     stream->class = class;
 620     stream->state = (connect_status == EAGAIN ? SCS_CONNECTING
 621                     : !connect_status ? SCS_CONNECTED
 622                     : SCS_DISCONNECTED);
 623     stream->error = connect_status;
 624     stream->name = xstrdup(name);
 625     assert(stream->state != SCS_CONNECTING || class->connect);
 626 }
 627
 628 void
 629 stream_set_remote_ip(struct stream *stream, ovs_be32 ip)
 630 {
 631     stream->remote_ip = ip;
 632 }
 633
 634 void
 635 stream_set_remote_port(struct stream *stream, ovs_be16 port)
 636 {
 637     stream->remote_port = port;
 638 }
 639
 640 void
 641 stream_set_local_ip(struct stream *stream, ovs_be32 ip)
 642 {
 643     stream->local_ip = ip;
 644 }
 645
 646 void
 647 stream_set_local_port(struct stream *stream, ovs_be16 port)
 648 {
 649     stream->local_port = port;
 650 }
 651
 652 void
 653 pstream_init(struct pstream *pstream, struct pstream_class *class,
 654             const char *name)
 655 {
 656     pstream->class = class;
 657     pstream->name = xstrdup(name);
 658 }
 659 \f
 660 static int
 661 count_fields(const char *s_)
 662 {
 663     char *s, *field, *save_ptr;
 664     int n = 0;
 665
 666     save_ptr = NULL;
 667     s = xstrdup(s_);
 668     for (field = strtok_r(s, ":", &save_ptr); field != NULL;
 669          field = strtok_r(NULL, ":", &save_ptr)) {
 670         n++;
 671     }
 672     free(s);
 673
 674     return n;
 675 }
 676
 677 /* Like stream_open(), but for tcp streams the port defaults to
 678  * 'default_tcp_port' if no port number is given and for SSL streams the port
 679  * defaults to 'default_ssl_port' if no port number is given. */
 680 int
 681 stream_open_with_default_ports(const char *name_,
 682                                uint16_t default_tcp_port,
 683                                uint16_t default_ssl_port,
 684                                struct stream **streamp)
 685 {
 686     char *name;
 687     int error;
 688
 689     if (!strncmp(name_, "tcp:", 4) && count_fields(name_) < 3) {
 690         name = xasprintf("%s:%d", name_, default_tcp_port);
 691     } else if (!strncmp(name_, "ssl:", 4) && count_fields(name_) < 3) {
 692         name = xasprintf("%s:%d", name_, default_ssl_port);
 693     } else {
 694         name = xstrdup(name_);
 695     }
 696     error = stream_open(name, streamp);
 697     free(name);
 698
 699     return error;
 700 }
 701
 702 /* Like pstream_open(), but for ptcp streams the port defaults to
 703  * 'default_ptcp_port' if no port number is given and for passive SSL streams
 704  * the port defaults to 'default_pssl_port' if no port number is given. */
 705 int
 706 pstream_open_with_default_ports(const char *name_,
 707                                 uint16_t default_ptcp_port,
 708                                 uint16_t default_pssl_port,
 709                                 struct pstream **pstreamp)
 710 {
 711     char *name;
 712     int error;
 713
 714     if (!strncmp(name_, "ptcp:", 5) && count_fields(name_) < 2) {
 715         name = xasprintf("%s%d", name_, default_ptcp_port);
 716     } else if (!strncmp(name_, "pssl:", 5) && count_fields(name_) < 2) {
 717         name = xasprintf("%s%d", name_, default_pssl_port);
 718     } else {
 719         name = xstrdup(name_);
 720     }
 721     error = pstream_open(name, pstreamp);
 722     free(name);
 723
 724     return error;
 725 }
 726 \f
 727 /* Attempts to guess the content type of a stream whose first few bytes were
 728  * the 'size' bytes of 'data'. */
 729 static enum stream_content_type
 730 stream_guess_content(const uint8_t *data, size_t size)
 731 {
 732     if (size >= 2) {
 733 #define PAIR(A, B) (((A) << 8) | (B))
 734         switch (PAIR(data[0], data[1])) {
 735         case PAIR(0x16, 0x03):  /* Handshake, version 3. */
 736             return STREAM_SSL;
 737         case PAIR('{', '"'):
 738             return STREAM_JSONRPC;
 739         case PAIR(OFP_VERSION, OFPT_HELLO):
 740             return STREAM_OPENFLOW;
 741         }
 742     }
 743
 744     return STREAM_UNKNOWN;
 745 }
 746
 747 /* Returns a string represenation of 'type'. */
 748 static const char *
 749 stream_content_type_to_string(enum stream_content_type type)
 750 {
 751     switch (type) {
 752     case STREAM_UNKNOWN:
 753     default:
 754         return "unknown";
 755
 756     case STREAM_JSONRPC:
 757         return "JSON-RPC";
 758
 759     case STREAM_OPENFLOW:
 760         return "OpenFlow";
 761
 762     case STREAM_SSL:
 763         return "SSL";
 764     }
 765 }
 766
 767 /* Attempts to guess the content type of a stream whose first few bytes were
 768  * the 'size' bytes of 'data'.  If this is done successfully, and the guessed
 769  * content type is other than 'expected_type', then log a message in vlog
 770  * module 'module', naming 'stream_name' as the source, explaining what
 771  * content was expected and what was actually received. */
 772 void
 773 stream_report_content(const void *data, size_t size,
 774                       enum stream_content_type expected_type,
 775                       struct vlog_module *module, const char *stream_name)
 776 {
 777     static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(5, 5);
 778     enum stream_content_type actual_type;
 779
 780     actual_type = stream_guess_content(data, size);
 781     if (actual_type != expected_type && actual_type != STREAM_UNKNOWN) {
 782         vlog_rate_limit(module, VLL_WARN, &rl,
 783                         "%s: received %s data on %s channel",
 784                         stream_name,
 785                         stream_content_type_to_string(actual_type),
 786                         stream_content_type_to_string(expected_type));
 787     }
 788 }