Add PPDProvider barebones implementation and associated cache skeleton.

chromeos/printing/ppd_provider.h

Index: chromeos/printing/ppd_provider.h
diff --git a/chromeos/printing/ppd_provider.h b/chromeos/printing/ppd_provider.h
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index 0000000000000000000000000000000000000000..076bb6167b61e2db02e009cca8cf940a20e2fa09
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+++ b/chromeos/printing/ppd_provider.h
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+// 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.
+
+#ifndef CHROMEOS_PRINTING_PPD_PROVIDER_H_
+#define CHROMEOS_PRINTING_PPD_PROVIDER_H_
+
+#include <memory>
+#include <string>
+
+#include "base/callback.h"
+#include "chromeos/printing/printer_configuration.h"
+
+namespace net {
+class URLRequestContextGetter;
+}
+
+namespace chromeos {
+namespace printing {
+
+class PPDCache;
+
+// PPDProvider is responsible for mapping printer descriptions
+// to CUPS-PostScript Printer Description (PPD) files.  The
+// provider is a caching client to
+class CHROMEOS_EXPORT PPDProvider {
+ public:
+  // Possible results of a Lookup call.
+  enum LookupResult {
+    // Found a PPD
+    SUCCESS,
+
+    // TODO(justincarlson) - Should we have a "FALLBACK" result here indicating
+    // we found a ppd that we think will work, but wasn't an exact match?

[skau, 2016/09/17 00:59:59]

What would provide the "FALLBACK" signal?  I think if we ask the server it'll
give us a binary response even if the PPD doesn't explicitly support the given
printer.

[Carlson, 2016/10/06 15:56:05]

I'm just speculating here that there may be some user-visible feedback we want
to give at some point of the form "we don't *really* know what this printer is,
but we think this driver will work." 

As for who tells us, presumably the quirks-server would for a server-provided
ppd.  If we use any of the mechanisms to generate ppds, there might be other
sources, too.

+
+    // Looked for a ppd for this configuration, but couldn't find a match.
+    NOT_FOUND,
+
+    // Failed to contact the Quirks server to look for a PPD.
+    SERVER_ERROR,
+  };
+
+  typedef ::base::Callback<void(LookupResult, Printer::PPDFile)> LookupCallback;

[skau, 2016/09/17 00:59:59]

Chromium is moving away from typedef in favor of using aliases. i.e. using foo =
bar;

[Carlson, 2016/10/06 15:56:05]

I keep forgetting you can do that, done.

+
+  // Construction-time options.  Everything in this structure should have
+  // a sane default.
+  struct Options {
+    // hostname of quirks server to query.  Default is
+    // "chromeosquirksserver-pa.googleapis.com".
+    ::std::string quirks_server;
+
+    // API key for accessing quirks server.
+    ::std::string api_key;
+
+    // TODO(justincarlson) - Add a limit to the size of data we'll download for
+    // a single printer.  There doesn't seem to actually be a simple way to
+    // enforce this, though? See
+    // https://groups.google.com/a/chromium.org/d/topic/chromium-dev/niK2rVMoMuo/discussion
+  };
+
+  // Return a sane set of default options.
+  static Options Defaults();
+
+  // Create and return a new PPDProvider with the given cache and options.
+  static std::unique_ptr<PPDProvider> Create(
+      scoped_refptr<net::URLRequestContextGetter> url_context_getter,
+      std::unique_ptr<PPDCache> cache,
+      const Options& options);
+
+  // Convenience overload to create a provider with default options.
+  static std::unique_ptr<PPDProvider> Create(
+      scoped_refptr<net::URLRequestContextGetter> url_context_getter,
+      std::unique_ptr<PPDCache> cache);
+
+  virtual ~PPDProvider() {}
+
+  // Given a manufacturer name and model name, attempt to get a PPD file for
+  // that printer.  Will invoke cb with the result of the lookup.  If the
+  // function returns SUCCESS, the second argument to the callback gives the
+  // found file, otherwise the PPDFile argument is invalid and should not be
+  // used.
+  virtual void Lookup(const std::string& manufacturer,
+                      const std::string& model,
+                      LookupCallback cb) = 0;
+};
+
+}  // namespace printing
+}  // namespace chromeos
+
+#endif  // CHROMEOS_PRINTING_PPD_PROVIDER_H_