Add PPDProvider barebones implementation and associated cache skeleton.

chromeos/printing/ppd_provider.cc

Index: chromeos/printing/ppd_provider.cc
diff --git a/chromeos/printing/ppd_provider.cc b/chromeos/printing/ppd_provider.cc
new file mode 100644
index 0000000000000000000000000000000000000000..bd6f74c80510e3a44308f8701f585bcb80b25d0d
--- /dev/null
+++ b/chromeos/printing/ppd_provider.cc
@@ -0,0 +1,227 @@
+// 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 "chromeos/printing/ppd_provider.h"
+
+#include <utility>
+
+#include "base/files/file_util.h"
+#include "base/json/json_parser.h"
+#include "base/memory/ptr_util.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/string_util.h"
+#include "base/strings/stringprintf.h"
+#include "base/time/time.h"
+#include "base/values.h"
+#include "chromeos/printing/ppd_cache.h"
+#include "net/base/load_flags.h"
+#include "net/http/http_status_code.h"
+#include "net/url_request/url_fetcher.h"
+#include "net/url_request/url_fetcher_delegate.h"
+#include "net/url_request/url_request_context_getter.h"
+#include "url/gurl.h"
+
+using ::base::FilePath;
+using ::net::URLFetcher;
+using ::std::string;
+using ::std::unique_ptr;
+
+namespace chromeos {
+namespace printing {
+namespace {
+
+// Expected fields from the quirks server.
+const char kJSONPPDKey[] = "compressedPpd";
+const char kJSONLastUpdatedKey[] = "lastUpdatedTime";
+
+class PpdProviderImpl;
+
+// URLFetcherDelegate that just forwards the complete callback back to
+// the PpdProvider that owns the delegate.
+class ForwardingURLFetcherDelegate : public net::URLFetcherDelegate {
+ public:
+  explicit ForwardingURLFetcherDelegate(PpdProviderImpl* owner)
+      : owner_(owner) {}
+  ~ForwardingURLFetcherDelegate() override {}
+
+  // URLFetcherDelegate API method.  Defined below since we need the
+  // PpdProviderImpl definition first.
+  void OnURLFetchComplete(const URLFetcher* source) override;
+
+ private:
+  // owner of this delegate.
+  PpdProviderImpl* owner_;
+};
+
+class PpdProviderImpl : public PpdProvider {
+ public:
+  PpdProviderImpl(
+      const string& api_key,
+      scoped_refptr<net::URLRequestContextGetter> url_context_getter,
+      unique_ptr<PpdCache> cache,
+      const PpdProvider::Options& options)
+      : api_key_(api_key),
+        forwarding_delegate_(this),
+        url_context_getter_(url_context_getter),
+        cache_(std::move(cache)),
+        options_(options) {
+    CHECK_GT(options_.max_ppd_contents_size_, 0U);
+  }
+  ~PpdProviderImpl() override {}
+
+  void Resolve(const Printer::PpdReference& ppd_reference,
+               PpdProvider::ResolveCallback cb) override {
+    CHECK(fetcher_ == nullptr)
+        << "Can't have concurrent PpdProvider Resolve calls";
+
+    base::Optional<FilePath> tmp = cache_->Find(ppd_reference);
+    if (tmp) {
+      // Cache hit.  Schedule the callback right now.
+      url_context_getter_->GetNetworkTaskRunner()->PostTask(
+          FROM_HERE, base::Bind(cb, PpdProvider::SUCCESS, tmp.value()));
+      return;
+    }
+
+    // We don't have a way to automatically resolve user-supplied PPDs yet.  So
+    // if we have one specified, and it's not cached, we fail out rather than
+    // fall back to quirks-server based resolution.  The reasoning here is that
+    // if the user has specified a PPD when a quirks-server one exists, it
+    // probably means the quirks server one doesn't work for some reason, so we
+    // shouldn't silently use it.
+    if (!ppd_reference.user_supplied_ppd_url.empty()) {
+      // Cache hit.  Schedule the callback right now.
+      url_context_getter_->GetNetworkTaskRunner()->PostTask(

[skau, 2016/10/21 16:12:57]

Are we trying to post the callback to the network thread rather than the calling
thread?

[Carlson, 2016/10/24 17:32:33]

I thought I had seen that URLFetcher always invokes things on the network
thread, so I was trying to match that behavior.  However, I just found 

https://cs.chromium.org/chromium/src/net/url_request/url_fetcher.h?rcl=0&l=67

that says otherwise, so converted to just do the simpler
call-from-the-current-thread thing.

There's a reasonable argument that we should still post this as a task to the
current runner instead of running it directly, but I think it should be ok to
just run directly.

[skau, 2016/10/24 17:55:33]

Please continue to post the callback on the current thread.  It's easier to
program against the PpdProvider if callback always runs after the message loop
completes.  You can used SequencedTaskRunner::Get() to post a runnable on the
current task runner.

[Carlson, 2016/10/24 18:39:50]

My instincts definitely run the other way here.  I think code that does
something like

* Resolve()
* ...do other stuff needed to handle the callback correctly...
* return to message loop

is likely to be fragile in the future and so should be disallowed.  

But OK, done.

(Note we discussed offline that this means we don't have thread affinity, only
sequencing).

+          FROM_HERE, base::Bind(cb, PpdProvider::NOT_FOUND, base::FilePath()));
+      return;
+    }
+
+    active_reference_ = ppd_reference;
+    done_callback_ = cb;
+
+    fetcher_ = URLFetcher::Create(GetQuirksServerLookupURL(ppd_reference),
+                                  URLFetcher::GET, &forwarding_delegate_);
+    fetcher_->SetRequestContext(url_context_getter_.get());
+    fetcher_->SetLoadFlags(net::LOAD_BYPASS_CACHE | net::LOAD_DISABLE_CACHE |
+                           net::LOAD_DO_NOT_SAVE_COOKIES |
+                           net::LOAD_DO_NOT_SEND_COOKIES |
+                           net::LOAD_DO_NOT_SEND_AUTH_DATA);
+    fetcher_->Start();
+  };
+
+  void AbortResolve() override {
+    // UrlFetcher guarantees that when the object has been destroyed, no further
+    // callbacks will occur.
+    fetcher_.reset();
+  }
+
+  bool CachePpd(const Printer::PpdReference& ppd_reference,
+                const base::FilePath& ppd_path) override {
+    string buf;
+    if (!base::ReadFileToStringWithMaxSize(ppd_path, &buf,
+                                           options_.max_ppd_contents_size_)) {

[skau, 2016/10/21 16:12:57]

nit: {} is commonly excluded from single statements following an if in the
Chromium codebase.  It's just a style preference.

[Carlson, 2016/10/24 17:32:33]

Having been bitten one too many times by bugs of the form "let's add a statement
to this if oh crap it wasn't in the if because no braces", I'd rather leave this
as is.

+      return false;
+    }
+    return static_cast<bool>(cache_->Store(ppd_reference, buf));
+  }
+
+  // Called on the network thread when the fetcher completes its fetch.
+  void OnURLFetchComplete() {
+    // Scope the allocated |fetcher_| into this function so we clean it up when
+    // we're done here instead of leaving it around until the next Resolve call.
+    auto fetcher = std::move(fetcher_);
+    string contents;
+    if ((fetcher->GetStatus().status() != net::URLRequestStatus::SUCCESS) ||
+        (fetcher->GetResponseCode() != net::HTTP_OK) ||
+        !fetcher->GetResponseAsString(&contents)) {
+      // Something went wrong with the fetch.
+      done_callback_.Run(PpdProvider::SERVER_ERROR, FilePath());
+      return;
+    }
+
+    auto dict = base::DictionaryValue::From(base::JSONReader::Read(contents));
+    if (dict == nullptr) {
+      done_callback_.Run(PpdProvider::SERVER_ERROR, FilePath());
+      return;
+    }
+    string ppd_contents;
+    string last_updated_time_string;
+    uint64_t last_updated_time;
+    if (!(dict->GetString(kJSONPPDKey, &ppd_contents) &&
+          dict->GetString(kJSONLastUpdatedKey, &last_updated_time_string) &&
+          base::StringToUint64(last_updated_time_string, &last_updated_time))) {
+      // Malformed response.  TODO(justincarlson) - LOG something here?
+      done_callback_.Run(PpdProvider::SERVER_ERROR, FilePath());
+      return;
+    }
+
+    if (ppd_contents.size() > options_.max_ppd_contents_size_) {
+      // PPD is too big.
+      //
+      // Note -- if we ever add shared-ppd-sourcing, e.g. we may serve a ppd to
+      // a user that's not from an explicitly trusted source, we should also
+      // check *uncompressed* size here to head off zip-bombs (e.g. let's
+      // compress 1GBs of zeros into a 900kb file and see what cups does when it
+      // tries to expand that...)
+      done_callback_.Run(PpdProvider::SERVER_ERROR, FilePath());
+      return;
+    }
+
+    auto ppd_file = cache_->Store(active_reference_, ppd_contents);
+    if (!ppd_file) {
+      // Failed to store.
+      done_callback_.Run(PpdProvider::INTERNAL_ERROR, FilePath());
+      return;
+    }
+    done_callback_.Run(PpdProvider::SUCCESS, ppd_file.value());

[skau, 2016/10/21 16:12:56]

Can you double check that the callback can be invoked from the network thread?

[Carlson, 2016/10/24 17:32:33]

Don't think this is relevant now.

+  }
+
+ private:
+  // Generate a url to look up a manufacturer/model from the quirks server
+  GURL GetQuirksServerLookupURL(
+      const Printer::PpdReference& ppd_reference) const {
+    return GURL(base::StringPrintf(
+        "https://%s/v2/printer/manufacturers/%s/models/%s?key=%s",
+        options_.quirks_server.c_str(),
+        ppd_reference.effective_manufacturer.c_str(),
+        ppd_reference.effective_model.c_str(), api_key_.c_str()));
+  }
+
+  // API key for accessing quirks server.
+  const string api_key_;
+
+  // Reference we're currently trying to resolve.
+  Printer::PpdReference active_reference_;
+
+  ForwardingURLFetcherDelegate forwarding_delegate_;
+  scoped_refptr<net::URLRequestContextGetter> url_context_getter_;
+  unique_ptr<PpdCache> cache_;
+
+  PpdProvider::ResolveCallback done_callback_;
+
+  // Fetcher for the current resolve call, if any.
+  unique_ptr<URLFetcher> fetcher_;
+
+  // Construction-time options, immutable.
+  const PpdProvider::Options options_;
+};
+
+void ForwardingURLFetcherDelegate::OnURLFetchComplete(
+    const URLFetcher* source) {
+  owner_->OnURLFetchComplete();
+}
+
+}  // namespace
+
+// static
+unique_ptr<PpdProvider> PpdProvider::Create(
+    const string& api_key,
+    scoped_refptr<net::URLRequestContextGetter> url_context_getter,
+    unique_ptr<PpdCache> cache,
+    const PpdProvider::Options& options) {
+  return base::MakeUnique<PpdProviderImpl>(api_key, url_context_getter,
+                                           std::move(cache), options);
+}
+
+}  // namespace printing
+}  // namespace chromeos