net/filter/sdch_policy_delegate.cc - chromium/src - Git at Google

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #include "net/filter/sdch_policy_delegate.h"

 #include "base/metrics/histogram_macros.h"
 #include "base/strings/string_util.h"
 #include "base/values.h"
 #include "net/base/sdch_problem_codes.h"
 #include "net/log/net_log.h"
 #include "net/log/net_log_event_type.h"
 #include "net/url_request/url_request_http_job.h"

 namespace net {

 namespace {

 const char kRefreshHtml[] =
     "<head><META HTTP-EQUIV=\"Refresh\" CONTENT=\"0\"></head>";
 // Mime types:
 const char kTextHtml[] = "text/html";

 // Disambiguate various types of responses that trigger a meta-refresh,
 // failure, or fallback to pass-through.
 enum ResponseCorruptionDetectionCause {
   RESPONSE_NONE,

   // 404 Http Response Code
   RESPONSE_404 = 1,

   // Not a 200 Http Response Code
   RESPONSE_NOT_200 = 2,

   // Cached before dictionary retrieved.
   RESPONSE_OLD_UNENCODED = 3,

   // Speculative but incorrect SDCH filtering was added added.
   RESPONSE_TENTATIVE_SDCH = 4,

   // Missing correct dict for decoding.
   RESPONSE_NO_DICTIONARY = 5,

   // Not an SDCH response but should be.
   RESPONSE_CORRUPT_SDCH = 6,

   // No dictionary was advertised with the request, the server claims
   // to have encoded with SDCH anyway, but it isn't an SDCH response.
   RESPONSE_ENCODING_LIE = 7,

   RESPONSE_MAX,
 };

 const char* ResponseCorruptionDetectionCauseToString(
     ResponseCorruptionDetectionCause cause) {
   const char* cause_string = "<unknown>";
   switch (cause) {
     case RESPONSE_NONE:
       cause_string = "NONE";
       break;
     case RESPONSE_404:
       cause_string = "404";
       break;
     case RESPONSE_NOT_200:
       cause_string = "NOT_200";
       break;
     case RESPONSE_OLD_UNENCODED:
       cause_string = "OLD_UNENCODED";
       break;
     case RESPONSE_TENTATIVE_SDCH:
       cause_string = "TENTATIVE_SDCH";
       break;
     case RESPONSE_NO_DICTIONARY:
       cause_string = "NO_DICTIONARY";
       break;
     case RESPONSE_CORRUPT_SDCH:
       cause_string = "CORRUPT_SDCH";
       break;
     case RESPONSE_ENCODING_LIE:
       cause_string = "ENCODING_LIE";
       break;
     case RESPONSE_MAX:
       cause_string = "<Error: max enum value>";
       break;
   }
   return cause_string;
 }

 std::unique_ptr<base::Value> NetLogResponseCorruptionDetectionCallback(
     ResponseCorruptionDetectionCause cause,
     bool cached,
     NetLogCaptureMode capture_mode) {
   std::unique_ptr<base::DictionaryValue> dict(new base::DictionaryValue());
   dict->SetString("cause", ResponseCorruptionDetectionCauseToString(cause));
   dict->SetBoolean("cached", cached);
   return std::move(dict);
 }

 void LogCorruptionDetection(const NetLogWithSource& net_log,
                             bool is_cached_content,
                             ResponseCorruptionDetectionCause cause) {
   // Use if statement rather than ?: because UMA_HISTOGRAM_ENUMERATION
   // caches the histogram name based on the call site.
   if (is_cached_content) {
     UMA_HISTOGRAM_ENUMERATION("Sdch3.ResponseCorruptionDetection.Cached", cause,
                               RESPONSE_MAX);
   } else {
     UMA_HISTOGRAM_ENUMERATION("Sdch3.ResponseCorruptionDetection.Uncached",
                               cause, RESPONSE_MAX);
   }
   net_log.AddEvent(NetLogEventType::SDCH_RESPONSE_CORRUPTION_DETECTION,
                    base::Bind(&NetLogResponseCorruptionDetectionCallback, cause,
                               is_cached_content));
 }

 }  // namespace

 SdchPolicyDelegate::SdchPolicyDelegate(
     bool possible_pass_through,
     URLRequestHttpJob* job,
     std::string mime_type,
     const GURL& url,
     bool is_cached_content,
     SdchManager* sdch_manager,
     std::unique_ptr<SdchManager::DictionarySet> dictionary_set,
     int response_code,
     const NetLogWithSource& net_log)
     : possible_pass_through_(possible_pass_through),
       job_(job),
       mime_type_(mime_type),
       url_(url),
       is_cached_content_(is_cached_content),
       sdch_manager_(sdch_manager),
       dictionary_set_(std::move(dictionary_set)),
       response_code_(response_code),
       net_log_(net_log) {
   DCHECK(sdch_manager_);
 }

 SdchPolicyDelegate::~SdchPolicyDelegate() {}

 // static
 void SdchPolicyDelegate::FixUpSdchContentEncodings(
     const NetLogWithSource& net_log,
     const std::string& mime_type,
     SdchManager::DictionarySet* dictionary_set,
     std::vector<SourceStream::SourceType>* types) {
   if (!dictionary_set) {
     // If sdch dictionary is advertised, we might need to add some decoding, as
     // some proxies strip encoding completely.
     // It was not an SDCH request, so we'll just record stats.
     if (1 < types->size()) {
       // Multiple filters were intended to only be used for SDCH (thus far!)
       SdchManager::LogSdchProblem(net_log,
                                   SDCH_MULTIENCODING_FOR_NON_SDCH_REQUEST);
     }
     if ((1 == types->size()) && (SourceStream::TYPE_SDCH == types->front())) {
       SdchManager::LogSdchProblem(
           net_log, SDCH_SDCH_CONTENT_ENCODE_FOR_NON_SDCH_REQUEST);
     }
     return;
   }
   // If content encoding included SDCH, then everything is "relatively" fine.
   if (!types->empty() && types->front() == SourceStream::TYPE_SDCH) {
     // Some proxies (found currently in Argentina) strip the Content-Encoding
     // text from "sdch,gzip" to a mere "sdch" without modifying the compressed
     // payload.  To handle this gracefully, we simulate the "probably" deleted
     // ",gzip" by appending a tentative gzip decode, which will default to a
     // no-op pass through filter if it doesn't get gzip headers where
     // expected.
     if (1 == types->size()) {
       types->push_back(SourceStream::TYPE_GZIP_FALLBACK);
       SdchManager::LogSdchProblem(net_log, SDCH_OPTIONAL_GUNZIP_ENCODING_ADDED);
     }
     return;
   }

   // There are now several cases to handle for an SDCH request. Foremost, if
   // the outbound request was stripped so as not to advertise support for
   // encodings, we might get back content with no encoding, or (for example)
   // just gzip. We have to be sure that any changes we make allow for such
   // minimal coding to work. That issue is why we use POSSIBLE_SDCH filters,
   // as those filters sniff the content, and act as pass-through filters if
   // headers are not found. TODO(xunjieli): Currently POSSIBLE_SDCH filters
   // issue meta-refresh instead of pass-throughs to match old code. Change it
   // to do pass-throughs.

   // If the outbound GET is not modified, then the server will generally try to
   // send us SDCH encoded content. As that content returns, there are several
   // corruptions of the header "content-encoding" that proxies may perform (and
   // have been detected in the wild). We already dealt with the a honest
   // content encoding of "sdch,gzip" being corrupted into "sdch" with no change
   // of the actual content. Another common corruption is to either discard
   // the accurate content encoding, or to replace it with gzip only (again, with
   // no change in actual content). The last observed corruption it to actually
   // change the content, such as by re-gzipping it, and that may happen along
   // with corruption of the stated content encoding (wow!).

   // The one unresolved failure mode comes when we advertise a dictionary, and
   // the server tries to *send* a gzipped file (not gzip encode content), and
   // then we could do a gzip decode :-(.
   // We will gather a lot of stats as we perform the fixups.
   if (base::StartsWith(mime_type, kTextHtml,
                        base::CompareCase::INSENSITIVE_ASCII)) {
     // Suspicious case: Advertised dictionary, but server didn't use sdch, and
     // we're HTML tagged.
     if (types->empty()) {
       SdchManager::LogSdchProblem(net_log, SDCH_ADDED_CONTENT_ENCODING);
     } else if (1 == types->size()) {
       SdchManager::LogSdchProblem(net_log, SDCH_FIXED_CONTENT_ENCODING);
     } else {
       SdchManager::LogSdchProblem(net_log, SDCH_FIXED_CONTENT_ENCODINGS);
     }
   } else {
     // Remarkable case!?!  We advertised an SDCH dictionary, content-encoding
     // was not marked for SDCH processing: Why did the server suggest an SDCH
     // dictionary in the first place??. Also, the content isn't
     // tagged as HTML, despite the fact that SDCH encoding is mostly likely
     // for HTML: Did some anti-virus system strip this tag (sometimes they
     // strip accept-encoding headers on the request)??  Does the content
     // encoding not start with "text/html" for some other reason??  We'll
     // report this as a fixup to a binary file, but it probably really is
     // text/html (some how).
     if (types->empty()) {
       SdchManager::LogSdchProblem(net_log, SDCH_BINARY_ADDED_CONTENT_ENCODING);
     } else if (1 == types->size()) {
       SdchManager::LogSdchProblem(net_log, SDCH_BINARY_FIXED_CONTENT_ENCODING);
     } else {
       SdchManager::LogSdchProblem(net_log, SDCH_BINARY_FIXED_CONTENT_ENCODINGS);
     }
   }

   // Leave the existing encoding type to be processed first, and add our
   // tentative decodings to be done afterwards. Vodaphone UK reportedly will
   // perform a second layer of gzip encoding atop the server's sdch,gzip
   // encoding, and then claim that the content encoding is a mere gzip. As a
   // result we'll need (in that case) to do the gunzip, plus our tentative
   // gunzip and tentative SDCH decoding. This approach nicely handles the
   // empty() list as well, and should work with other (as yet undiscovered)
   // proxies the choose to re-compressed with some other encoding (such as
   // bzip2, etc.).
   types->insert(types->begin(), SourceStream::TYPE_GZIP_FALLBACK);
   types->insert(types->begin(), SourceStream::TYPE_SDCH_POSSIBLE);
 }

 // Dictionary id errors are often the first indication that the SDCH stream has
 // become corrupt. There are many possible causes: non-200 response codes, a
 // cached non-SDCH-ified reply, or a response that claims to be SDCH but isn't
 // actually. These are handled here by issuing a meta-refresh or swapping to the
 // "passthrough" mode if appropriate, or failing the request if the error is
 // unrecoverable.
 SdchPolicyDelegate::ErrorRecovery SdchPolicyDelegate::OnDictionaryIdError(
     std::string* replace_output) {
   if (possible_pass_through_) {
     LogCorruptionDetection(net_log_, is_cached_content_,
                            RESPONSE_TENTATIVE_SDCH);
     // Ideally we should return PASS_THROUGH here, but this is done to match
     // the old behavior in sdch_filter.cc.
   }
   // HTTP 404 might be an unencoded error page, so if decoding failed, pass it
   // through. TODO(xunjieli): Remove this. crbug.com/516773.
   if (response_code_ == 404) {
     SdchManager::LogSdchProblem(net_log_, SDCH_PASS_THROUGH_404_CODE);
     LogCorruptionDetection(net_log_, is_cached_content_, RESPONSE_404);
     return PASS_THROUGH;
   }

   // HTTP !200 gets a meta-refresh for HTML.
   // TODO(xunjieli): remove this. crbug.com/654393.
   if (response_code_ != 200) {
     LogCorruptionDetection(net_log_, is_cached_content_, RESPONSE_NOT_200);
     return IssueMetaRefreshIfPossible(replace_output);
   }

   // If this is a cached result and the source hasn't requested a dictionary, it
   // probably never had a dictionary to begin and is an unencoded response from
   // earlier.
   if (is_cached_content_) {
     SdchManager::LogSdchProblem(net_log_, SDCH_PASS_THROUGH_OLD_CACHED);
     LogCorruptionDetection(net_log_, is_cached_content_,
                            RESPONSE_OLD_UNENCODED);
     return PASS_THROUGH;
   }

   // The original request didn't advertise any dictionaries, but the
   // response claimed to be SDCH. There is no way to repair this situation: the
   // original request already didn't advertise any dictionaries, and retrying it
   // would likely have the/ same result. Blacklist the domain and try passing
   // through.
   if (!dictionary_set_) {
     sdch_manager_->BlacklistDomain(url_, SDCH_PASSING_THROUGH_NON_SDCH);
     LogCorruptionDetection(net_log_, is_cached_content_, RESPONSE_ENCODING_LIE);
     return PASS_THROUGH;
   }
   // Since SDCH dictionaries are advertised, this is a corrupt SDCH response.
   LogCorruptionDetection(net_log_, is_cached_content_, RESPONSE_CORRUPT_SDCH);
   return IssueMetaRefreshIfPossible(replace_output);
 }

 // Dictionary fails to load when we have a plausible dictionay id. There are
 // many possible causes: a cached SDCH-ified reply for which the SdchManager did
 // not have the dictionary or a corrupted response. These are handled here by
 // issuing a meta-refresh except the case where response code is 404.
 SdchPolicyDelegate::ErrorRecovery SdchPolicyDelegate::OnGetDictionaryError(
     std::string* replace_output) {
   if (possible_pass_through_) {
     LogCorruptionDetection(net_log_, is_cached_content_,
                            RESPONSE_TENTATIVE_SDCH);
     // Ideally we should return PASS_THROUGH here, but this is done to match
     // the old behavior in sdch_filter.cc.
   }
   // HTTP 404 might be an unencoded error page, so if decoding failed, pass it
   // through. TODO(xunjieli): Remove this case crbug.com/516773.
   if (response_code_ == 404) {
     SdchManager::LogSdchProblem(net_log_, SDCH_PASS_THROUGH_404_CODE);
     LogCorruptionDetection(net_log_, is_cached_content_, RESPONSE_404);
     return PASS_THROUGH;
   }
   SdchManager::LogSdchProblem(net_log_, SDCH_DICTIONARY_HASH_NOT_FOUND);
   LogCorruptionDetection(net_log_, is_cached_content_, RESPONSE_NO_DICTIONARY);
   return IssueMetaRefreshIfPossible(replace_output);
 }

 SdchPolicyDelegate::ErrorRecovery SdchPolicyDelegate::OnDecodingError(
     std::string* replace_output) {
   // A decoding error, as opposed to a dictionary error, indicates a
   // decompression failure partway through the payload of the SDCH stream,
   // which means that the filter already witnessed a valid dictionary ID and
   // successfully retrieved a dictionary for it. Decoding errors are not
   // recoverable and it is not appropriate to stop decoding, so there are
   // relatively few error cases here.
   //
   // In particular, a decoding error for an HTML payload is recoverable by
   // issuing a meta-refresh, but to avoid having that happen too often, this
   // class also temporarily blacklists the domain. A decoding error for a
   // non-HTML payload is unrecoverable, so such an error gets a permanent
   // blacklist entry. If the content was cached, no blacklisting is needed.
   // TODO(xunjieli): This case should be removed. crbug.com/651821.
   return IssueMetaRefreshIfPossible(replace_output);
 }

 bool SdchPolicyDelegate::OnGetDictionary(const std::string& server_id,
                                          const std::string** text) {
   if (dictionary_set_) {
     *text = dictionary_set_->GetDictionaryText(server_id);
     if (*text) {
       server_id_ = server_id;
       return true;
     }
   }
   // This is a hack. Naively, the dictionaries available for
   // decoding should be only the ones advertised. However, there are
   // cases, specifically resources encoded with old dictionaries living
   // in the cache, that mean the full set of dictionaries should be made
   // available for decoding. It's not known how often this happens;
   // if it happens rarely enough, this code can be removed.
   //
   // TODO(rdsmith): Long-term, a better solution is necessary, since
   // an entry in the cache being encoded with the dictionary doesn't
   // guarantee that the dictionary is present. That solution probably
   // involves storing unencoded resources in the cache, but might
   // involve evicting encoded resources on dictionary removal.
   // See http://crbug.com/383405.
   SdchProblemCode rv = SDCH_OK;
   unexpected_dictionary_set_ =
       sdch_manager_->GetDictionarySetByHash(url_, server_id, &rv);
   if (unexpected_dictionary_set_) {
     *text = unexpected_dictionary_set_->GetDictionaryText(server_id);
     SdchManager::LogSdchProblem(
         net_log_, is_cached_content_ ? SDCH_UNADVERTISED_DICTIONARY_USED_CACHED
                                      : SDCH_UNADVERTISED_DICTIONARY_USED);
     if (*text) {
       server_id_ = server_id;
       return true;
     }
   }
   return false;
 }

 void SdchPolicyDelegate::OnStreamDestroyed(
     SdchSourceStream::InputState input_state,
     bool buffered_output_present,
     bool decoding_not_finished) {
   if (decoding_not_finished) {
     SdchManager::LogSdchProblem(net_log_, SDCH_INCOMPLETE_SDCH_CONTENT);
     // Make it possible for the user to hit reload, and get non-sdch content.
     // Note this will "wear off" quickly enough, and is just meant to assure
     // in some rare case that the user is not stuck.
     sdch_manager_->BlacklistDomain(url_, SDCH_INCOMPLETE_SDCH_CONTENT);
   }
   // Filter chaining error, or premature teardown.
   if (buffered_output_present)
     SdchManager::LogSdchProblem(net_log_, SDCH_UNFLUSHED_CONTENT);

   // Only record packet stats for non-cached content.
   if (is_cached_content_) {
     // Not a real error, but it is useful to have this tally.
     // TODO(jar): Remove this stat after SDCH stability is validated.
     SdchManager::LogSdchProblem(net_log_, SDCH_CACHE_DECODED);
     return;  // We don't need timing stats, and we aready got ratios.
   }
   switch (input_state) {
     case SdchSourceStream::STATE_DECODE: {
       job_->RecordPacketStats(StatisticSelector::SDCH_DECODE);
       // Allow latency experiments to proceed.
       sdch_manager_->SetAllowLatencyExperiment(url_, true);

       // Notify successful dictionary usage.
       DCHECK(!server_id_.empty());
       sdch_manager_->OnDictionaryUsed(server_id_);
       return;
     }
     case SdchSourceStream::STATE_LOAD_DICTIONARY:
       SdchManager::LogSdchProblem(net_log_, SDCH_PRIOR_TO_DICTIONARY);
       return;
     case SdchSourceStream::STATE_PASS_THROUGH:
       job_->RecordPacketStats(StatisticSelector::SDCH_PASSTHROUGH);
       return;
     case SdchSourceStream::STATE_OUTPUT_REPLACE:
       // This is meta refresh case. Already accounted for when set.
       return;
   }  // end of switch.
 }

 // TODO(xunjieli): Remove meta refresh. crbug.com/651821.
 SdchPolicyDelegate::ErrorRecovery
 SdchPolicyDelegate::IssueMetaRefreshIfPossible(std::string* replace_output) {
   // Errors for non-HTML payloads are unrecoverable and get the domain
   // blacklisted indefinitely.
   if (mime_type_.npos == mime_type_.find("text/html")) {
     SdchProblemCode problem =
         (is_cached_content_ ? SDCH_CACHED_META_REFRESH_UNSUPPORTED
                             : SDCH_META_REFRESH_UNSUPPORTED);
     sdch_manager_->BlacklistDomainForever(url_, problem);
     SdchManager::LogSdchProblem(net_log_, problem);
     return NONE;
   }

   if (is_cached_content_) {
     // Cached content is a probably startup tab, so just get the fresh content
     // and try again, without disabling SDCH.
     SdchManager::LogSdchProblem(net_log_, SDCH_META_REFRESH_CACHED_RECOVERY);
   } else {
     // Since it wasn't in the cache, blacklist for some period to get the
     // correct content.
     sdch_manager_->BlacklistDomain(url_, SDCH_META_REFRESH_RECOVERY);
     SdchManager::LogSdchProblem(net_log_, SDCH_META_REFRESH_RECOVERY);
   }

   *replace_output = std::string(kRefreshHtml, strlen(kRefreshHtml));
   return REPLACE_OUTPUT;
 }

 }  // namespace net
	// Copyright 2016 The Chromium Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#include "net/filter/sdch_policy_delegate.h"

	#include "base/metrics/histogram_macros.h"
	#include "base/strings/string_util.h"
	#include "base/values.h"
	#include "net/base/sdch_problem_codes.h"
	#include "net/log/net_log.h"
	#include "net/log/net_log_event_type.h"
	#include "net/url_request/url_request_http_job.h"

	namespace net {

	namespace {

	const char kRefreshHtml[] =
	"<head><META HTTP-EQUIV=\"Refresh\" CONTENT=\"0\"></head>";
	// Mime types:
	const char kTextHtml[] = "text/html";

	// Disambiguate various types of responses that trigger a meta-refresh,
	// failure, or fallback to pass-through.
	enum ResponseCorruptionDetectionCause {
	RESPONSE_NONE,

	// 404 Http Response Code
	RESPONSE_404 = 1,

	// Not a 200 Http Response Code
	RESPONSE_NOT_200 = 2,

	// Cached before dictionary retrieved.
	RESPONSE_OLD_UNENCODED = 3,

	// Speculative but incorrect SDCH filtering was added added.
	RESPONSE_TENTATIVE_SDCH = 4,

	// Missing correct dict for decoding.
	RESPONSE_NO_DICTIONARY = 5,

	// Not an SDCH response but should be.
	RESPONSE_CORRUPT_SDCH = 6,

	// No dictionary was advertised with the request, the server claims
	// to have encoded with SDCH anyway, but it isn't an SDCH response.
	RESPONSE_ENCODING_LIE = 7,

	RESPONSE_MAX,
	};

	const char* ResponseCorruptionDetectionCauseToString(
	ResponseCorruptionDetectionCause cause) {
	const char* cause_string = "<unknown>";
	switch (cause) {
	case RESPONSE_NONE:
	cause_string = "NONE";
	break;
	case RESPONSE_404:
	cause_string = "404";
	break;
	case RESPONSE_NOT_200:
	cause_string = "NOT_200";
	break;
	case RESPONSE_OLD_UNENCODED:
	cause_string = "OLD_UNENCODED";
	break;
	case RESPONSE_TENTATIVE_SDCH:
	cause_string = "TENTATIVE_SDCH";
	break;
	case RESPONSE_NO_DICTIONARY:
	cause_string = "NO_DICTIONARY";
	break;
	case RESPONSE_CORRUPT_SDCH:
	cause_string = "CORRUPT_SDCH";
	break;
	case RESPONSE_ENCODING_LIE:
	cause_string = "ENCODING_LIE";
	break;
	case RESPONSE_MAX:
	cause_string = "<Error: max enum value>";
	break;
	}
	return cause_string;
	}

	std::unique_ptr<base::Value> NetLogResponseCorruptionDetectionCallback(
	ResponseCorruptionDetectionCause cause,
	bool cached,
	NetLogCaptureMode capture_mode) {
	std::unique_ptr<base::DictionaryValue> dict(new base::DictionaryValue());
	dict->SetString("cause", ResponseCorruptionDetectionCauseToString(cause));
	dict->SetBoolean("cached", cached);
	return std::move(dict);
	}

	void LogCorruptionDetection(const NetLogWithSource& net_log,
	bool is_cached_content,
	ResponseCorruptionDetectionCause cause) {
	// Use if statement rather than ?: because UMA_HISTOGRAM_ENUMERATION
	// caches the histogram name based on the call site.
	if (is_cached_content) {
	UMA_HISTOGRAM_ENUMERATION("Sdch3.ResponseCorruptionDetection.Cached", cause,
	RESPONSE_MAX);
	} else {
	UMA_HISTOGRAM_ENUMERATION("Sdch3.ResponseCorruptionDetection.Uncached",
	cause, RESPONSE_MAX);
	}
	net_log.AddEvent(NetLogEventType::SDCH_RESPONSE_CORRUPTION_DETECTION,
	base::Bind(&NetLogResponseCorruptionDetectionCallback, cause,
	is_cached_content));
	}

	} // namespace

	SdchPolicyDelegate::SdchPolicyDelegate(
	bool possible_pass_through,
	URLRequestHttpJob* job,
	std::string mime_type,
	const GURL& url,
	bool is_cached_content,
	SdchManager* sdch_manager,
	std::unique_ptr<SdchManager::DictionarySet> dictionary_set,
	int response_code,
	const NetLogWithSource& net_log)
	: possible_pass_through_(possible_pass_through),
	job_(job),
	mime_type_(mime_type),
	url_(url),
	is_cached_content_(is_cached_content),
	sdch_manager_(sdch_manager),
	dictionary_set_(std::move(dictionary_set)),
	response_code_(response_code),
	net_log_(net_log) {
	DCHECK(sdch_manager_);
	}

	SdchPolicyDelegate::~SdchPolicyDelegate() {}

	// static
	void SdchPolicyDelegate::FixUpSdchContentEncodings(
	const NetLogWithSource& net_log,
	const std::string& mime_type,
	SdchManager::DictionarySet* dictionary_set,
	std::vector<SourceStream::SourceType>* types) {
	if (!dictionary_set) {
	// If sdch dictionary is advertised, we might need to add some decoding, as
	// some proxies strip encoding completely.
	// It was not an SDCH request, so we'll just record stats.
	if (1 < types->size()) {
	// Multiple filters were intended to only be used for SDCH (thus far!)
	SdchManager::LogSdchProblem(net_log,
	SDCH_MULTIENCODING_FOR_NON_SDCH_REQUEST);
	}
	if ((1 == types->size()) && (SourceStream::TYPE_SDCH == types->front())) {
	SdchManager::LogSdchProblem(
	net_log, SDCH_SDCH_CONTENT_ENCODE_FOR_NON_SDCH_REQUEST);
	}
	return;
	}
	// If content encoding included SDCH, then everything is "relatively" fine.
	if (!types->empty() && types->front() == SourceStream::TYPE_SDCH) {
	// Some proxies (found currently in Argentina) strip the Content-Encoding
	// text from "sdch,gzip" to a mere "sdch" without modifying the compressed
	// payload. To handle this gracefully, we simulate the "probably" deleted
	// ",gzip" by appending a tentative gzip decode, which will default to a
	// no-op pass through filter if it doesn't get gzip headers where
	// expected.
	if (1 == types->size()) {
	types->push_back(SourceStream::TYPE_GZIP_FALLBACK);
	SdchManager::LogSdchProblem(net_log, SDCH_OPTIONAL_GUNZIP_ENCODING_ADDED);
	}
	return;
	}

	// There are now several cases to handle for an SDCH request. Foremost, if
	// the outbound request was stripped so as not to advertise support for
	// encodings, we might get back content with no encoding, or (for example)
	// just gzip. We have to be sure that any changes we make allow for such
	// minimal coding to work. That issue is why we use POSSIBLE_SDCH filters,
	// as those filters sniff the content, and act as pass-through filters if
	// headers are not found. TODO(xunjieli): Currently POSSIBLE_SDCH filters
	// issue meta-refresh instead of pass-throughs to match old code. Change it
	// to do pass-throughs.

	// If the outbound GET is not modified, then the server will generally try to
	// send us SDCH encoded content. As that content returns, there are several
	// corruptions of the header "content-encoding" that proxies may perform (and
	// have been detected in the wild). We already dealt with the a honest
	// content encoding of "sdch,gzip" being corrupted into "sdch" with no change
	// of the actual content. Another common corruption is to either discard
	// the accurate content encoding, or to replace it with gzip only (again, with
	// no change in actual content). The last observed corruption it to actually
	// change the content, such as by re-gzipping it, and that may happen along
	// with corruption of the stated content encoding (wow!).

	// The one unresolved failure mode comes when we advertise a dictionary, and
	// the server tries to send a gzipped file (not gzip encode content), and
	// then we could do a gzip decode :-(.
	// We will gather a lot of stats as we perform the fixups.
	if (base::StartsWith(mime_type, kTextHtml,
	base::CompareCase::INSENSITIVE_ASCII)) {
	// Suspicious case: Advertised dictionary, but server didn't use sdch, and
	// we're HTML tagged.
	if (types->empty()) {
	SdchManager::LogSdchProblem(net_log, SDCH_ADDED_CONTENT_ENCODING);
	} else if (1 == types->size()) {
	SdchManager::LogSdchProblem(net_log, SDCH_FIXED_CONTENT_ENCODING);
	} else {
	SdchManager::LogSdchProblem(net_log, SDCH_FIXED_CONTENT_ENCODINGS);
	}
	} else {
	// Remarkable case!?! We advertised an SDCH dictionary, content-encoding
	// was not marked for SDCH processing: Why did the server suggest an SDCH
	// dictionary in the first place??. Also, the content isn't
	// tagged as HTML, despite the fact that SDCH encoding is mostly likely
	// for HTML: Did some anti-virus system strip this tag (sometimes they
	// strip accept-encoding headers on the request)?? Does the content
	// encoding not start with "text/html" for some other reason?? We'll
	// report this as a fixup to a binary file, but it probably really is
	// text/html (some how).
	if (types->empty()) {
	SdchManager::LogSdchProblem(net_log, SDCH_BINARY_ADDED_CONTENT_ENCODING);
	} else if (1 == types->size()) {
	SdchManager::LogSdchProblem(net_log, SDCH_BINARY_FIXED_CONTENT_ENCODING);
	} else {
	SdchManager::LogSdchProblem(net_log, SDCH_BINARY_FIXED_CONTENT_ENCODINGS);
	}
	}

	// Leave the existing encoding type to be processed first, and add our
	// tentative decodings to be done afterwards. Vodaphone UK reportedly will
	// perform a second layer of gzip encoding atop the server's sdch,gzip
	// encoding, and then claim that the content encoding is a mere gzip. As a
	// result we'll need (in that case) to do the gunzip, plus our tentative
	// gunzip and tentative SDCH decoding. This approach nicely handles the
	// empty() list as well, and should work with other (as yet undiscovered)
	// proxies the choose to re-compressed with some other encoding (such as
	// bzip2, etc.).
	types->insert(types->begin(), SourceStream::TYPE_GZIP_FALLBACK);
	types->insert(types->begin(), SourceStream::TYPE_SDCH_POSSIBLE);
	}

	// Dictionary id errors are often the first indication that the SDCH stream has
	// become corrupt. There are many possible causes: non-200 response codes, a
	// cached non-SDCH-ified reply, or a response that claims to be SDCH but isn't
	// actually. These are handled here by issuing a meta-refresh or swapping to the
	// "passthrough" mode if appropriate, or failing the request if the error is
	// unrecoverable.
	SdchPolicyDelegate::ErrorRecovery SdchPolicyDelegate::OnDictionaryIdError(
	std::string* replace_output) {
	if (possible_pass_through_) {
	LogCorruptionDetection(net_log_, is_cached_content_,
	RESPONSE_TENTATIVE_SDCH);
	// Ideally we should return PASS_THROUGH here, but this is done to match
	// the old behavior in sdch_filter.cc.
	}
	// HTTP 404 might be an unencoded error page, so if decoding failed, pass it
	// through. TODO(xunjieli): Remove this. crbug.com/516773.
	if (response_code_ == 404) {
	SdchManager::LogSdchProblem(net_log_, SDCH_PASS_THROUGH_404_CODE);
	LogCorruptionDetection(net_log_, is_cached_content_, RESPONSE_404);
	return PASS_THROUGH;
	}

	// HTTP !200 gets a meta-refresh for HTML.
	// TODO(xunjieli): remove this. crbug.com/654393.
	if (response_code_ != 200) {
	LogCorruptionDetection(net_log_, is_cached_content_, RESPONSE_NOT_200);
	return IssueMetaRefreshIfPossible(replace_output);
	}

	// If this is a cached result and the source hasn't requested a dictionary, it
	// probably never had a dictionary to begin and is an unencoded response from
	// earlier.
	if (is_cached_content_) {
	SdchManager::LogSdchProblem(net_log_, SDCH_PASS_THROUGH_OLD_CACHED);
	LogCorruptionDetection(net_log_, is_cached_content_,
	RESPONSE_OLD_UNENCODED);
	return PASS_THROUGH;
	}

	// The original request didn't advertise any dictionaries, but the
	// response claimed to be SDCH. There is no way to repair this situation: the
	// original request already didn't advertise any dictionaries, and retrying it
	// would likely have the/ same result. Blacklist the domain and try passing
	// through.
	if (!dictionary_set_) {
	sdch_manager_->BlacklistDomain(url_, SDCH_PASSING_THROUGH_NON_SDCH);
	LogCorruptionDetection(net_log_, is_cached_content_, RESPONSE_ENCODING_LIE);
	return PASS_THROUGH;
	}
	// Since SDCH dictionaries are advertised, this is a corrupt SDCH response.
	LogCorruptionDetection(net_log_, is_cached_content_, RESPONSE_CORRUPT_SDCH);
	return IssueMetaRefreshIfPossible(replace_output);
	}

	// Dictionary fails to load when we have a plausible dictionay id. There are
	// many possible causes: a cached SDCH-ified reply for which the SdchManager did
	// not have the dictionary or a corrupted response. These are handled here by
	// issuing a meta-refresh except the case where response code is 404.
	SdchPolicyDelegate::ErrorRecovery SdchPolicyDelegate::OnGetDictionaryError(
	std::string* replace_output) {
	if (possible_pass_through_) {
	LogCorruptionDetection(net_log_, is_cached_content_,
	RESPONSE_TENTATIVE_SDCH);
	// Ideally we should return PASS_THROUGH here, but this is done to match
	// the old behavior in sdch_filter.cc.
	}
	// HTTP 404 might be an unencoded error page, so if decoding failed, pass it
	// through. TODO(xunjieli): Remove this case crbug.com/516773.
	if (response_code_ == 404) {
	SdchManager::LogSdchProblem(net_log_, SDCH_PASS_THROUGH_404_CODE);
	LogCorruptionDetection(net_log_, is_cached_content_, RESPONSE_404);
	return PASS_THROUGH;
	}
	SdchManager::LogSdchProblem(net_log_, SDCH_DICTIONARY_HASH_NOT_FOUND);
	LogCorruptionDetection(net_log_, is_cached_content_, RESPONSE_NO_DICTIONARY);
	return IssueMetaRefreshIfPossible(replace_output);
	}

	SdchPolicyDelegate::ErrorRecovery SdchPolicyDelegate::OnDecodingError(
	std::string* replace_output) {
	// A decoding error, as opposed to a dictionary error, indicates a
	// decompression failure partway through the payload of the SDCH stream,
	// which means that the filter already witnessed a valid dictionary ID and
	// successfully retrieved a dictionary for it. Decoding errors are not
	// recoverable and it is not appropriate to stop decoding, so there are
	// relatively few error cases here.
	//
	// In particular, a decoding error for an HTML payload is recoverable by
	// issuing a meta-refresh, but to avoid having that happen too often, this
	// class also temporarily blacklists the domain. A decoding error for a
	// non-HTML payload is unrecoverable, so such an error gets a permanent
	// blacklist entry. If the content was cached, no blacklisting is needed.
	// TODO(xunjieli): This case should be removed. crbug.com/651821.
	return IssueMetaRefreshIfPossible(replace_output);
	}

	bool SdchPolicyDelegate::OnGetDictionary(const std::string& server_id,
	const std::string** text) {
	if (dictionary_set_) {
	*text = dictionary_set_->GetDictionaryText(server_id);
	if (*text) {
	server_id_ = server_id;
	return true;
	}
	}
	// This is a hack. Naively, the dictionaries available for
	// decoding should be only the ones advertised. However, there are
	// cases, specifically resources encoded with old dictionaries living
	// in the cache, that mean the full set of dictionaries should be made
	// available for decoding. It's not known how often this happens;
	// if it happens rarely enough, this code can be removed.
	//
	// TODO(rdsmith): Long-term, a better solution is necessary, since
	// an entry in the cache being encoded with the dictionary doesn't
	// guarantee that the dictionary is present. That solution probably
	// involves storing unencoded resources in the cache, but might
	// involve evicting encoded resources on dictionary removal.
	// See http://crbug.com/383405.
	SdchProblemCode rv = SDCH_OK;
	unexpected_dictionary_set_ =
	sdch_manager_->GetDictionarySetByHash(url_, server_id, &rv);
	if (unexpected_dictionary_set_) {
	*text = unexpected_dictionary_set_->GetDictionaryText(server_id);
	SdchManager::LogSdchProblem(
	net_log_, is_cached_content_ ? SDCH_UNADVERTISED_DICTIONARY_USED_CACHED
	: SDCH_UNADVERTISED_DICTIONARY_USED);
	if (*text) {
	server_id_ = server_id;
	return true;
	}
	}
	return false;
	}

	void SdchPolicyDelegate::OnStreamDestroyed(
	SdchSourceStream::InputState input_state,
	bool buffered_output_present,
	bool decoding_not_finished) {
	if (decoding_not_finished) {
	SdchManager::LogSdchProblem(net_log_, SDCH_INCOMPLETE_SDCH_CONTENT);
	// Make it possible for the user to hit reload, and get non-sdch content.
	// Note this will "wear off" quickly enough, and is just meant to assure
	// in some rare case that the user is not stuck.
	sdch_manager_->BlacklistDomain(url_, SDCH_INCOMPLETE_SDCH_CONTENT);
	}
	// Filter chaining error, or premature teardown.
	if (buffered_output_present)
	SdchManager::LogSdchProblem(net_log_, SDCH_UNFLUSHED_CONTENT);

	// Only record packet stats for non-cached content.
	if (is_cached_content_) {
	// Not a real error, but it is useful to have this tally.
	// TODO(jar): Remove this stat after SDCH stability is validated.
	SdchManager::LogSdchProblem(net_log_, SDCH_CACHE_DECODED);
	return; // We don't need timing stats, and we aready got ratios.
	}
	switch (input_state) {
	case SdchSourceStream::STATE_DECODE: {
	job_->RecordPacketStats(StatisticSelector::SDCH_DECODE);
	// Allow latency experiments to proceed.
	sdch_manager_->SetAllowLatencyExperiment(url_, true);

	// Notify successful dictionary usage.
	DCHECK(!server_id_.empty());
	sdch_manager_->OnDictionaryUsed(server_id_);
	return;
	}
	case SdchSourceStream::STATE_LOAD_DICTIONARY:
	SdchManager::LogSdchProblem(net_log_, SDCH_PRIOR_TO_DICTIONARY);
	return;
	case SdchSourceStream::STATE_PASS_THROUGH:
	job_->RecordPacketStats(StatisticSelector::SDCH_PASSTHROUGH);
	return;
	case SdchSourceStream::STATE_OUTPUT_REPLACE:
	// This is meta refresh case. Already accounted for when set.
	return;
	} // end of switch.
	}

	// TODO(xunjieli): Remove meta refresh. crbug.com/651821.
	SdchPolicyDelegate::ErrorRecovery
	SdchPolicyDelegate::IssueMetaRefreshIfPossible(std::string* replace_output) {
	// Errors for non-HTML payloads are unrecoverable and get the domain
	// blacklisted indefinitely.
	if (mime_type_.npos == mime_type_.find("text/html")) {
	SdchProblemCode problem =
	(is_cached_content_ ? SDCH_CACHED_META_REFRESH_UNSUPPORTED
	: SDCH_META_REFRESH_UNSUPPORTED);
	sdch_manager_->BlacklistDomainForever(url_, problem);
	SdchManager::LogSdchProblem(net_log_, problem);
	return NONE;
	}

	if (is_cached_content_) {
	// Cached content is a probably startup tab, so just get the fresh content
	// and try again, without disabling SDCH.
	SdchManager::LogSdchProblem(net_log_, SDCH_META_REFRESH_CACHED_RECOVERY);
	} else {
	// Since it wasn't in the cache, blacklist for some period to get the
	// correct content.
	sdch_manager_->BlacklistDomain(url_, SDCH_META_REFRESH_RECOVERY);
	SdchManager::LogSdchProblem(net_log_, SDCH_META_REFRESH_RECOVERY);
	}

	*replace_output = std::string(kRefreshHtml, strlen(kRefreshHtml));
	return REPLACE_OUTPUT;
	}

	} // namespace net