services/image_annotation/annotator.cc

// Copyright 2019 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 "services/image_annotation/annotator.h"

#include <algorithm>
#include <tuple>
#include <utility>

#include "base/base64.h"
#include "base/bind.h"
#include "base/feature_list.h"
#include "base/json/json_writer.h"
#include "base/location.h"
#include "base/logging.h"
#include "base/no_destructor.h"
#include "base/stl_util.h"
#include "base/strings/string_split.h"
#include "components/google/core/common/google_util.h"
#include "net/base/load_flags.h"
#include "net/base/net_errors.h"
#include "net/traffic_annotation/network_traffic_annotation.h"
#include "services/image_annotation/image_annotation_metrics.h"
#include "services/network/public/mojom/url_response_head.mojom.h"
#include "url/gurl.h"

namespace image_annotation {

namespace {

constexpr size_t kImageAnnotationMaxResponseSize = 1024 * 1024;  // 1MB.
constexpr size_t kServerLangsMaxResponseSize = 1024;             // 1KB.

// For a given source ID and requested description language, returns the unique
// image ID string that can be used to look up results from a server response.
std::string MakeImageId(const std::string& source_id,
                        const std::string& desc_lang_tag) {
  return source_id + (desc_lang_tag.empty() ? "" : " " + desc_lang_tag);
}

std::string NormalizeLanguageCode(std::string language) {
  // Remove anything after a comma, in case we got more than one language
  // like "de,de-DE".
  language = language.substr(0, language.find(','));

  // Split based on underscore or dash so that we catch both
  // "zh_CN" and "zh-CN".
  const std::vector<std::string> tokens = base::SplitString(
      language, "-_", base::KEEP_WHITESPACE, base::SPLIT_WANT_NONEMPTY);

  if (tokens.size() == 0)
    return "";

  // Normalize the language portion to lowercase.
  const std::string language_only = base::ToLowerASCII(tokens[0]);

  // For every language other than "zh" (Chinese), return only the language
  // and strip the locale. Image descriptions don't changed based on locale,
  // but zh-CN and zh-TW use different character sets.
  if (tokens.size() == 1 || language_only != "zh")
    return language_only;

  // Normalize the locale to uppercase.
  std::string locale_only = base::ToUpperASCII(tokens[1]);

  // Map several Chinese locales to the two most common ones used for
  // Simplified and Traditional.
  if (locale_only == "CN" || locale_only == "HANS" || locale_only == "SG") {
    return "zh-CN";
  } else if (locale_only == "TW" || locale_only == "HANT" ||
             locale_only == "MO" || locale_only == "HK") {
    return "zh-TW";
  }

  return "zh";
}

// The server returns separate OCR results for each region of the image; we
// naively concatenate these into one response string.
//
// Returns a null pointer if there is any unexpected structure to the
// annotations message.
mojom::AnnotationPtr ParseJsonOcrAnnotation(const base::Value& ocr_engine,
                                            const double min_ocr_confidence) {
  if (!ocr_engine.is_dict())
    return mojom::AnnotationPtr(nullptr);

  // No OCR regions is valid - it just means there is no text.
  const base::Value* const ocr_regions = ocr_engine.FindKey("ocrRegions");
  if (!ocr_regions) {
    ReportOcrAnnotation(1.0 /* confidence */, true /* empty */);
    return mojom::Annotation::New(mojom::AnnotationType::kOcr, 1.0 /* score */,
                                  std::string() /* text */);
  }

  if (!ocr_regions->is_list())
    return mojom::AnnotationPtr(nullptr);

  std::string all_ocr_text;
  int word_count = 0;
  double word_confidence_sum = 0.0;
  for (const base::Value& ocr_region : ocr_regions->GetList()) {
    if (!ocr_region.is_dict())
      continue;

    const base::Value* const words = ocr_region.FindKey("words");
    if (!words || !words->is_list())
      continue;

    std::string region_ocr_text;
    for (const base::Value& word : words->GetList()) {
      if (!word.is_dict())
        continue;

      const base::Value* const detected_text = word.FindKey("detectedText");
      if (!detected_text || !detected_text->is_string())
        continue;

      // A confidence value of 0 or 1 is interpreted as an int and not a double.
      const base::Value* const confidence = word.FindKey("confidenceScore");
      if (!confidence || (!confidence->is_double() && !confidence->is_int()) ||
          confidence->GetDouble() < 0.0 || confidence->GetDouble() > 1.0)
        continue;

      if (confidence->GetDouble() < min_ocr_confidence)
        continue;

      const std::string& detected_text_str = detected_text->GetString();

      if (detected_text_str.empty())
        continue;

      if (!region_ocr_text.empty())
        region_ocr_text += " ";

      region_ocr_text += detected_text_str;
      ++word_count;
      word_confidence_sum += confidence->GetDouble();
    }

    if (!all_ocr_text.empty() && !region_ocr_text.empty())
      all_ocr_text += "\n";
    all_ocr_text += region_ocr_text;
  }

  const double all_ocr_confidence =
      word_count == 0 ? 1.0 : word_confidence_sum / word_count;
  ReportOcrAnnotation(all_ocr_confidence, all_ocr_text.empty());
  return mojom::Annotation::New(mojom::AnnotationType::kOcr, all_ocr_confidence,
                                all_ocr_text);
}

// Extracts annotations from the given description engine result into the second
// element of the return tuple.
//
// The first element of the return tuple will be true if the image was
// classified as containing adult content.
std::tuple<bool, std::vector<mojom::AnnotationPtr>> ParseJsonDescAnnotations(
    const base::Value& desc_engine) {
  static const base::NoDestructor<std::map<std::string, mojom::AnnotationType>>
      kAnnotationTypes({{"OCR", mojom::AnnotationType::kOcr},
                        {"CAPTION", mojom::AnnotationType::kCaption},
                        {"LABEL", mojom::AnnotationType::kLabel}});

  bool adult = false;
  std::vector<mojom::AnnotationPtr> results;

  if (!desc_engine.is_dict())
    return {adult, std::move(results)};

  // If there is a failure reason, log it and track whether it is due to adult
  // content.
  const base::Value* const failure_reason_value =
      desc_engine.FindKey("failureReason");
  if (failure_reason_value && failure_reason_value->is_string()) {
    const DescFailureReason failure_reason =
        ParseDescFailureReason(failure_reason_value->GetString());
    ReportDescFailure(failure_reason);
    adult = failure_reason == DescFailureReason::kAdult;
  }

  const base::Value* const desc_list_dict =
      desc_engine.FindKey("descriptionList");
  if (!desc_list_dict || !desc_list_dict->is_dict())
    return {adult, std::move(results)};

  const base::Value* const desc_list = desc_list_dict->FindKey("descriptions");
  if (!desc_list || !desc_list->is_list())
    return {adult, std::move(results)};

  for (const base::Value& desc : desc_list->GetList()) {
    if (!desc.is_dict())
      continue;

    const base::Value* const type = desc.FindKey("type");
    if (!type || !type->is_string())
      continue;

    const auto type_lookup = kAnnotationTypes->find(type->GetString());
    if (type_lookup == kAnnotationTypes->end())
      continue;

    const base::Value* const score = desc.FindKey("score");
    if (!score || (!score->is_double() && !score->is_int()))
      continue;

    const base::Value* const text = desc.FindKey("text");
    if (!text || !text->is_string())
      continue;

    ReportDescAnnotation(type_lookup->second, score->GetDouble(),
                         text->GetString().empty());

    // For OCR, we allow empty text and unusual scores; at the time of writing,
    // a score of -1 is always returned for OCR.
    //
    // For other annotation types, we do not allow these cases.
    if (type_lookup->second != mojom::AnnotationType::kOcr &&
        (text->GetString().empty() || score->GetDouble() < 0.0 ||
         score->GetDouble() > 1.0))
      continue;

    results.push_back(mojom::Annotation::New(
        type_lookup->second, score->GetDouble(), text->GetString()));
  }

  return {adult, std::move(results)};
}

// Returns the integer status code for this engine, or -1 if no status can be
// extracted.
int ExtractStatusCode(const base::Value* const status_dict) {
  if (!status_dict || !status_dict->is_dict())
    return -1;

  const base::Value* const code_value = status_dict->FindKey("code");

  // A missing code is the same as a default (i.e. OK) code.
  if (!code_value)
    return 0;

  if (!code_value->is_int())
    return -1;
  const int code = code_value->GetInt();

#ifndef NDEBUG
  // Also log error status messages (which are helpful for debugging).
  const base::Value* const message = status_dict->FindKey("message");
  if (code != 0 && message && message->is_string())
    DVLOG(1) << "Engine failed with status " << code << " and message '"
             << message->GetString() << "'";
#endif

  return code;
}

// Attempts to extract annotation results from the server response, returning a
// map from each image ID to its annotations (if successfully extracted).
std::map<std::string, mojom::AnnotateImageResultPtr> UnpackJsonResponse(
    const base::Value& json_data,
    const double min_ocr_confidence) {
  if (!json_data.is_dict())
    return {};

  const base::Value* const results = json_data.FindKey("results");
  if (!results || !results->is_list())
    return {};

  std::map<std::string, mojom::AnnotateImageResultPtr> out;
  for (const base::Value& result : results->GetList()) {
    if (!result.is_dict())
      continue;

    const base::Value* const image_id = result.FindKey("imageId");
    if (!image_id || !image_id->is_string())
      continue;

    const base::Value* const engine_results = result.FindKey("engineResults");
    if (!engine_results || !engine_results->is_list())
      continue;

    // We expect the engine result list to have exactly two results: one for OCR
    // and one for image descriptions. However, we "robustly" handle missing
    // engines, unknown engines (by skipping them) and repetitions (by
    // overwriting data).
    bool adult = false;
    std::vector<mojom::AnnotationPtr> annotations;
    mojom::AnnotationPtr ocr_annotation;
    for (const base::Value& engine_result : engine_results->GetList()) {
      if (!engine_result.is_dict())
        continue;

      // A non-zero status code means the following:
      //  -1:                       The status dict could not be parsed. We
      //                            still try to parse an engine result in this
      //                            case to be robust.
      //  any other non-zero value: The status dict was parsed and contains a
      //                            known failure. We always report an error
      //                            in this case.
      const int status_code =
          ExtractStatusCode(engine_result.FindKey("status"));

      const base::Value* const desc_engine =
          engine_result.FindKey("descriptionEngine");
      const base::Value* const ocr_engine = engine_result.FindKey("ocrEngine");

      if (desc_engine) {
        // Add description annotations and update the adult image flag.
        ReportDescStatus(status_code);

        if (status_code <= 0) {
          std::tie(adult, annotations) = ParseJsonDescAnnotations(*desc_engine);
        }
      } else if (ocr_engine) {
        // Update the specialized OCR annotations.
        ReportOcrStatus(status_code);

        if (status_code <= 0) {
          ocr_annotation =
              ParseJsonOcrAnnotation(*ocr_engine, min_ocr_confidence);
        }
      }

      ReportEngineKnown(ocr_engine || desc_engine);
    }

    // Remove any description OCR data (which is lower quality) if we have
    // specialized OCR results.
    if (!ocr_annotation.is_null()) {
      base::EraseIf(annotations, [](const mojom::AnnotationPtr& a) {
        return a->type == mojom::AnnotationType::kOcr;
      });
      annotations.push_back(std::move(ocr_annotation));
    }

    if (adult) {
      out[image_id->GetString()] = mojom::AnnotateImageResult::NewErrorCode(
          mojom::AnnotateImageError::kAdult);
    } else if (!annotations.empty()) {
      out[image_id->GetString()] =
          mojom::AnnotateImageResult::NewAnnotations(std::move(annotations));
    }
  }

  return out;
}

}  // namespace

constexpr char Annotator::kGoogApiKeyHeader[];

static_assert(Annotator::kDescMinDimension > 0,
              "Description engine must accept images of some sizes.");
static_assert(Annotator::kDescMaxAspectRatio > 0.0,
              "Description engine must accept images of some aspect ratios.");

Annotator::ClientRequestInfo::ClientRequestInfo(
    mojo::PendingRemote<mojom::ImageProcessor> in_image_processor,
    AnnotateImageCallback in_callback)
    : image_processor(std::move(in_image_processor)),
      callback(std::move(in_callback)) {}

Annotator::ClientRequestInfo::~ClientRequestInfo() = default;

Annotator::ServerRequestInfo::ServerRequestInfo(
    const std::string& in_source_id,
    const bool in_desc_requested,
    const std::string& in_desc_lang_tag,
    const std::vector<uint8_t>& in_image_bytes)
    : source_id(in_source_id),
      desc_requested(in_desc_requested),
      desc_lang_tag(in_desc_lang_tag),
      image_bytes(in_image_bytes) {}

Annotator::ServerRequestInfo& Annotator::ServerRequestInfo::operator=(
    ServerRequestInfo&& other) = default;

Annotator::ServerRequestInfo::~ServerRequestInfo() = default;

Annotator::Annotator(
    GURL pixels_server_url,
    GURL langs_server_url,
    std::string api_key,
    const base::TimeDelta throttle,
    const int batch_size,
    const double min_ocr_confidence,
    scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory,
    std::unique_ptr<Client> client)
    : client_(std::move(client)),
      url_loader_factory_(std::move(url_loader_factory)),
      pixels_server_url_(std::move(pixels_server_url)),
      langs_server_url_(std::move(langs_server_url)),
      api_key_(std::move(api_key)),
      batch_size_(batch_size),
      min_ocr_confidence_(min_ocr_confidence),
      server_languages_({"de", "en", "es", "fr", "hi", "it"}) {
  server_request_timer_ = std::make_unique<base::RepeatingTimer>(
      FROM_HERE, throttle,
      base::BindRepeating(&Annotator::SendRequestBatchToServer,
                          weak_factory_.GetWeakPtr()));
  FetchServerLanguages();
}

Annotator::~Annotator() {
  // Report any clients still connected at service shutdown.
  for (const auto& request_info_kv : request_infos_) {
    for (const auto& unused : request_info_kv.second) {
      ReportClientResult(ClientResult::kShutdown);
      ANALYZER_ALLOW_UNUSED(unused);
    }
  }
}

void Annotator::BindReceiver(mojo::PendingReceiver<mojom::Annotator> receiver) {
  receivers_.Add(this, std::move(receiver));
}

void Annotator::AnnotateImage(
    const std::string& source_id,
    const std::string& page_language,
    mojo::PendingRemote<mojom::ImageProcessor> image_processor,
    AnnotateImageCallback callback) {
  // Compute the desired language for the description result, based on the
  // page language, the accept languages, the top languages, and the
  // server languages.
  const std::string preferred_language =
      ComputePreferredLanguage(page_language);
  client_->RecordLanguageMetrics(page_language, preferred_language);

  const RequestKey request_key(source_id, preferred_language);

  // Return cached results if they exist.
  const auto cache_lookup = cached_results_.find(request_key);
  ReportCacheHit(cache_lookup != cached_results_.end());
  if (cache_lookup != cached_results_.end()) {
    std::move(callback).Run(cache_lookup->second.Clone());
    return;
  }

  // Register the ImageProcessor and callback to be used for this request.
  std::list<ClientRequestInfo>& request_info_list = request_infos_[request_key];
  request_info_list.emplace_back(std::move(image_processor),
                                 std::move(callback));

  // If the image processor dies: automatically delete the request info and
  // reassign local processing (for other interested clients) if the dead image
  // processor was responsible for some ongoing work.
  request_info_list.back().image_processor.set_disconnect_handler(
      base::BindOnce(&Annotator::RemoveRequestInfo, weak_factory_.GetWeakPtr(),
                     request_key, --request_info_list.end(),
                     true /* canceled */));

  // Don't start local work if it would duplicate some already-ongoing work.
  if (base::Contains(local_processors_, request_key) ||
      base::Contains(pending_requests_, request_key))
    return;

  local_processors_.insert(
      {request_key, &request_info_list.back().image_processor});

  // TODO(crbug.com/916420): first query the public result cache by URL to
  // improve latency.

  request_info_list.back().image_processor->GetJpgImageData(base::BindOnce(
      &Annotator::OnJpgImageDataReceived, weak_factory_.GetWeakPtr(),
      request_key, --request_info_list.end()));
}

// static
bool Annotator::IsWithinDescPolicy(const int32_t width, const int32_t height) {
  if (width < kDescMinDimension || height < kDescMinDimension)
    return false;

  // Can't be 0 or inf because |kDescMinDimension| is guaranteed positive (via a
  // static_assert).
  const double aspect_ratio = static_cast<double>(width) / height;
  if (aspect_ratio < 1.0 / kDescMaxAspectRatio ||
      aspect_ratio > kDescMaxAspectRatio)
    return false;

  return true;
}

// static
std::string Annotator::FormatJsonRequest(
    const std::deque<ServerRequestInfo>::iterator begin,
    const std::deque<ServerRequestInfo>::iterator end) {
  base::Value image_request_list(base::Value::Type::LIST);
  for (std::deque<ServerRequestInfo>::iterator it = begin; it != end; ++it) {
    // Re-encode image bytes into base64, which can be represented in JSON.
    std::string base64_data;
    Base64Encode(
        base::StringPiece(reinterpret_cast<const char*>(it->image_bytes.data()),
                          it->image_bytes.size()),
        &base64_data);

    // TODO(crbug.com/916420): accept and propagate page language info to
    //                         improve OCR accuracy.
    base::Value ocr_engine_params(base::Value::Type::DICTIONARY);
    ocr_engine_params.SetKey("ocrParameters",
                             base::Value(base::Value::Type::DICTIONARY));

    base::Value engine_params_list(base::Value::Type::LIST);
    engine_params_list.Append(std::move(ocr_engine_params));

    // Also add a description annotations request if the image is within model
    // policy.
    if (it->desc_requested) {
      base::Value desc_params(base::Value::Type::DICTIONARY);

      // Add preferred description language if it has been specified.
      if (!it->desc_lang_tag.empty()) {
        base::Value desc_lang_list(base::Value::Type::LIST);
        desc_lang_list.Append(base::Value(it->desc_lang_tag));

        desc_params.SetKey("preferredLanguages", std::move(desc_lang_list));
      }

      base::Value engine_params(base::Value::Type::DICTIONARY);
      engine_params.SetKey("descriptionParameters", std::move(desc_params));

      engine_params_list.Append(std::move(engine_params));
    }
    ReportImageRequestIncludesDesc(it->desc_requested);

    base::Value image_request(base::Value::Type::DICTIONARY);
    image_request.SetKey(
        "imageId", base::Value(MakeImageId(it->source_id, it->desc_lang_tag)));
    image_request.SetKey("imageBytes", base::Value(std::move(base64_data)));
    image_request.SetKey("engineParameters", std::move(engine_params_list));

    image_request_list.Append(std::move(image_request));
  }

  base::Value request(base::Value::Type::DICTIONARY);
  request.SetKey("imageRequests", std::move(image_request_list));

  std::string json_request;
  base::JSONWriter::Write(request, &json_request);

  ReportServerRequestSizeKB(json_request.size() / 1024);

  return json_request;
}

// static
std::unique_ptr<network::SimpleURLLoader> Annotator::MakeRequestLoader(
    const GURL& server_url,
    const std::string& api_key) {
  auto resource_request = std::make_unique<network::ResourceRequest>();
  resource_request->method = "POST";

  resource_request->url = server_url;

  resource_request->credentials_mode = network::mojom::CredentialsMode::kOmit;

  // Put API key in request's header if a key exists, and the endpoint is
  // trusted by Google.
  if (!api_key.empty() && server_url.SchemeIs(url::kHttpsScheme) &&
      google_util::IsGoogleAssociatedDomainUrl(server_url)) {
    resource_request->headers.SetHeader(kGoogApiKeyHeader, api_key);
  }

  const net::NetworkTrafficAnnotationTag traffic_annotation =
      net::DefineNetworkTrafficAnnotation("image_annotation", R"(
        semantics {
          sender: "Get Image Descriptions from Google"
          description:
            "Chrome can provide image labels (which include detected objects, "
            "extracted text and generated captions) to screen readers (for "
            "visually-impaired users) by sending images to Google's servers. "
            "If image labeling is enabled for a page, Chrome will send the "
            "URLs and pixels of all images on the page to Google's servers, "
            "which will return labels for content identified inside the "
            "images. This content is made accessible to screen reading "
            "software. Chrome fetches the list of supported languages from "
            "the servers and uses that to determine what language to request "
            "descriptions in."
          trigger: "A page containing images is loaded for a user who has "
                   "automatic image labeling enabled. At most once per day, "
                   "Chrome fetches the list of supported languages as a "
                   "separate network request."
          data: "Image pixels and URLs. No user identifier is sent along with "
                "the data."
          destination: GOOGLE_OWNED_SERVICE
        }
        policy {
          cookies_allowed: NO
          setting:
            "You can enable or disable this feature via the context menu "
            "for images, or via 'Get Image Descriptions' in Chrome's "
            "settings under Accessibility. This feature is disabled by default."
          chrome_policy {
            AccessibilityImageLabelsEnabled {
              AccessibilityImageLabelsEnabled: false
            }
          }
        })");

  return network::SimpleURLLoader::Create(std::move(resource_request),
                                          traffic_annotation);
}

void Annotator::OnJpgImageDataReceived(
    const RequestKey& request_key,
    const std::list<ClientRequestInfo>::iterator request_info_it,
    const std::vector<uint8_t>& image_bytes,
    const int32_t width,
    const int32_t height) {
  const std::string& source_id = request_key.first;
  const std::string& request_language = request_key.second;

  ReportPixelFetchSuccess(!image_bytes.empty());

  // Failed to retrieve bytes from local processor; remove dead processor and
  // reschedule processing.
  if (image_bytes.empty()) {
    RemoveRequestInfo(request_key, request_info_it, false /* canceled */);
    return;
  }

  // Local processing is no longer ongoing.
  local_processors_.erase(request_key);

  // Schedule a server request for this image.
  server_request_queue_.emplace_front(source_id,
                                      IsWithinDescPolicy(width, height),
                                      request_language, image_bytes);
  pending_requests_.insert(request_key);

  // Start sending batches to the server.
  if (!server_request_timer_->IsRunning())
    server_request_timer_->Reset();
}

void Annotator::SendRequestBatchToServer() {
  if (server_request_queue_.empty()) {
    server_request_timer_->Stop();
    return;
  }

  // Take last n elements (or all elements if there are less than n).
  const auto begin =
      server_request_queue_.end() -
      std::min<size_t>(server_request_queue_.size(), batch_size_);
  const auto end = server_request_queue_.end();

  // The set of (source ID, desc lang) pairs relevant for this request.
  std::set<RequestKey> request_keys;
  for (std::deque<ServerRequestInfo>::iterator it = begin; it != end; it++) {
    request_keys.insert({it->source_id, it->desc_lang_tag});
  }

  // Kick off server communication.
  std::unique_ptr<network::SimpleURLLoader> url_loader =
      MakeRequestLoader(pixels_server_url_, api_key_);
  url_loader->AttachStringForUpload(FormatJsonRequest(begin, end),
                                    "application/json");
  ongoing_server_requests_.push_back(std::move(url_loader));
  ongoing_server_requests_.back()->DownloadToString(
      url_loader_factory_.get(),
      base::BindOnce(&Annotator::OnServerResponseReceived,
                     weak_factory_.GetWeakPtr(), request_keys,
                     --ongoing_server_requests_.end()),
      kImageAnnotationMaxResponseSize);

  server_request_queue_.erase(begin, end);
}

void Annotator::OnServerResponseReceived(
    const std::set<RequestKey>& request_keys,
    const UrlLoaderList::iterator server_request_it,
    const std::unique_ptr<std::string> json_response) {
  ReportServerNetError(server_request_it->get()->NetError());

  if (const network::mojom::URLResponseHead* const response_info =
          server_request_it->get()->ResponseInfo()) {
    ReportServerResponseCode(response_info->headers->response_code());
    ReportServerLatency(response_info->response_time -
                        response_info->request_time);
  }

  ongoing_server_requests_.erase(server_request_it);

  if (!json_response) {
    DVLOG(1) << "HTTP request to image annotation server failed.";
    ProcessResults(request_keys, {});
    return;
  }

  ReportServerResponseSizeBytes(json_response->size());

  // Send JSON string to a dedicated service for safe parsing.
  GetJsonParser()->Parse(
      *json_response, base::BindOnce(&Annotator::OnResponseJsonParsed,
                                     weak_factory_.GetWeakPtr(), request_keys));
}

void Annotator::OnResponseJsonParsed(
    const std::set<RequestKey>& request_keys,
    const base::Optional<base::Value> json_data,
    const base::Optional<std::string>& error) {
  const bool success = json_data.has_value() && !error.has_value();
  ReportJsonParseSuccess(success);

  // Extract annotation results for each request key with valid results.
  if (success) {
    ProcessResults(request_keys,
                   UnpackJsonResponse(*json_data, min_ocr_confidence_));
  } else {
    DVLOG(1) << "Parsing server response JSON failed with error: "
             << error.value_or("No reason reported.");
    ProcessResults(request_keys, {});
  }
}

void Annotator::ProcessResults(
    const std::set<RequestKey>& request_keys,
    const std::map<std::string, mojom::AnnotateImageResultPtr>& results) {
  // Process each request key for which we expect to have results.
  for (const RequestKey& request_key : request_keys) {
    pending_requests_.erase(request_key);

    // The lookup will be successful if there is a valid result (i.e. not an
    // error and not a malformed result) for this (source ID, desc lang) pair.
    const auto result_lookup =
        results.find(MakeImageId(request_key.first, request_key.second));

    // Populate the result struct for this image and copy it into the cache if
    // necessary.
    if (result_lookup != results.end())
      cached_results_.insert(
          std::make_pair(request_key, result_lookup->second.Clone()));

    // This should not happen, since only this method removes entries of
    // |request_infos_|, and this method should only execute once per request
    // key.
    const auto request_info_it = request_infos_.find(request_key);
    if (request_info_it == request_infos_.end()) {
      LOG(ERROR) << "Could not find request key in request_infos_: "
                 << request_key.first << "," << request_key.second;
      continue;
    }

    const auto image_result = result_lookup != results.end()
                                  ? result_lookup->second.Clone()
                                  : mojom::AnnotateImageResult::NewErrorCode(
                                        mojom::AnnotateImageError::kFailure);
    const auto client_result = result_lookup != results.end()
                                   ? ClientResult::kSucceeded
                                   : ClientResult::kFailed;

    // Notify clients of success or failure.
    // TODO(crbug.com/916420): explore server retry strategies.
    for (auto& info : request_info_it->second) {
      std::move(info.callback).Run(image_result.Clone());
      ReportClientResult(client_result);
    }
    request_infos_.erase(request_info_it);
  }
}

data_decoder::mojom::JsonParser* Annotator::GetJsonParser() {
  if (!json_parser_) {
    client_->BindJsonParser(json_parser_.BindNewPipeAndPassReceiver());
    json_parser_.reset_on_disconnect();
  }

  return json_parser_.get();
}

void Annotator::RemoveRequestInfo(
    const RequestKey& request_key,
    const std::list<ClientRequestInfo>::iterator request_info_it,
    const bool canceled) {
  // Check whether we are deleting the ImageProcessor responsible for current
  // local processing.
  auto local_processor_lookup = local_processors_.find(request_key);
  const bool should_reassign =
      local_processor_lookup != local_processors_.end() &&
      local_processor_lookup->second == &request_info_it->image_processor;

  // Notify client of cancellation / failure.
  ReportClientResult(canceled ? ClientResult::kCanceled
                              : ClientResult::kFailed);
  std::move(request_info_it->callback)
      .Run(mojom::AnnotateImageResult::NewErrorCode(
          canceled ? mojom::AnnotateImageError::kCanceled
                   : mojom::AnnotateImageError::kFailure));

  // Delete the specified ImageProcessor.
  std::list<ClientRequestInfo>& request_info_list = request_infos_[request_key];
  request_info_list.erase(request_info_it);

  // If necessary, reassign local processing.
  if (should_reassign) {
    if (request_info_list.empty()) {
      local_processors_.erase(local_processor_lookup);
    } else {
      local_processor_lookup->second =
          &request_info_list.front().image_processor;

      request_info_list.front().image_processor->GetJpgImageData(base::BindOnce(
          &Annotator::OnJpgImageDataReceived, weak_factory_.GetWeakPtr(),
          request_key, request_info_list.begin()));
    }
  }
}

std::string Annotator::ComputePreferredLanguage(
    const std::string& in_page_language) const {
  DCHECK(!server_languages_.empty());
  if (in_page_language.empty())
    return "";

  std::string page_language = NormalizeLanguageCode(in_page_language);
  std::vector<std::string> accept_languages = client_->GetAcceptLanguages();
  std::transform(accept_languages.begin(), accept_languages.end(),
                 accept_languages.begin(), NormalizeLanguageCode);
  std::vector<std::string> top_languages = client_->GetTopLanguages();
  std::transform(top_languages.begin(), top_languages.end(),
                 top_languages.begin(), NormalizeLanguageCode);

  // If the page language is a server language and it's in the list of accept
  // languages or top languages for this user, return that.
  if (base::Contains(server_languages_, page_language) &&
      (base::Contains(accept_languages, page_language) ||
       base::Contains(top_languages, page_language))) {
    return page_language;
  }

  // Otherwise, ignore the page language and compute the best language
  // for this user. The accept languages are the ones the user can
  // explicitly choose, so pick the first accept language that's a
  // top language and a server language.
  if (!top_languages.empty()) {
    for (const std::string& accept_language : accept_languages) {
      if (base::Contains(server_languages_, accept_language) &&
          base::Contains(top_languages, accept_language)) {
        return accept_language;
      }
    }
  }

  // Sometimes the top languages are empty. Try any accept language that's
  // a server language.
  for (const std::string& accept_language : accept_languages) {
    if (base::Contains(server_languages_, accept_language))
      return accept_language;
  }

  // If that still fails, try any top language that's a server language.
  for (const std::string& top_language : top_languages) {
    if (base::Contains(server_languages_, top_language))
      return top_language;
  }

  // If all else fails, return the first accept language. The server can
  // still do OCR and it can log this language request.
  if (!accept_languages.empty())
    return accept_languages[0];

  // If that fails, return the page language. The server can
  // still do OCR and it can log this language request.
  return page_language;
}

void Annotator::FetchServerLanguages() {
  if (langs_server_url_.is_empty())
    return;

  langs_url_loader_ = MakeRequestLoader(langs_server_url_, api_key_);
  langs_url_loader_->AttachStringForUpload("", "application/json");
  langs_url_loader_->DownloadToString(
      url_loader_factory_.get(),
      base::BindOnce(&Annotator::OnServerLangsResponseReceived,
                     weak_factory_.GetWeakPtr()),
      kServerLangsMaxResponseSize);
}

void Annotator::OnServerLangsResponseReceived(
    const std::unique_ptr<std::string> json_response) {
  if (!json_response) {
    DVLOG(1) << "Failed to get languages from the server.";
    return;
  }

  GetJsonParser()->Parse(
      *json_response,
      base::BindOnce(&Annotator::OnServerLangsResponseJsonParsed,
                     weak_factory_.GetWeakPtr()));
}

void Annotator::OnServerLangsResponseJsonParsed(
    base::Optional<base::Value> json_data,
    const base::Optional<std::string>& error) {
  if (!json_data.has_value() || error.has_value()) {
    DVLOG(1) << "Parsing server langs response JSON failed with error: "
             << error.value_or("No reason reported.");
    return;
  }

  const base::Value* const langs = json_data->FindKey("langs");
  if (!langs || !langs->is_list()) {
    DVLOG(1) << "No langs in response JSON";
    return;
  }

  std::vector<std::string> new_server_languages;
  for (const base::Value& lang : langs->GetList()) {
    if (!lang.is_string()) {
      DVLOG(1) << "Lang in response JSON is not a string";
      return;
    }
    new_server_languages.push_back(lang.GetString());
  }

  if (!base::Contains(new_server_languages, "en")) {
    DVLOG(1) << "Server langs don't even include 'en', rejecting";
    return;
  }

  // Only swap in the new languages at the end, if all of the other
  // checks passed.
  server_languages_.swap(new_server_languages);
}

}  // namespace image_annotation