Refactor CRX verification in preparation to support CRX₃ files.

components/crx_file/crx2_file.h

+// Copyright 2017 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 COMPONENTS_CRX_FILE_CRX2_FILE_H_
+#define COMPONENTS_CRX_FILE_CRX2_FILE_H_
+
+#include <stddef.h>
+#include <stdint.h>
+#include <sys/types.h>
+
+#include <memory>
+#include <string>
+#include <vector>
+
+namespace crx_file {
+
+// The magic string embedded in the header.
+constexpr char kCrx2FileHeaderMagic[] = "Cr24";
+constexpr char kCrxDiffFileHeaderMagic[] = "CrOD";
+constexpr int kCrx2FileHeaderMagicSize = 4;
+
+// CRX files have a header that includes a magic key, version number, and
+// some signature sizing information. Use Crx2File object to validate whether
+// the header is valid or not.
+class Crx2File {
+ public:
+  // This header is the first data at the beginning of an extension. Its
+  // contents are purposely 32-bit aligned so that it can just be slurped into
+  // a struct without manual parsing.
+  struct Header {
+    char magic[kCrx2FileHeaderMagicSize];
+    uint32_t version;
+    uint32_t key_size;        // The size of the public key, in bytes.
+    uint32_t signature_size;  // The size of the signature, in bytes.
+    // An ASN.1-encoded PublicKeyInfo structure follows.
+    // The signature follows.
+  };
+
+  enum Error {
+    kWrongMagic,
+    kInvalidVersion,
+    kInvalidKeyTooLarge,
+    kInvalidKeyTooSmall,
+    kInvalidSignatureTooLarge,
+    kInvalidSignatureTooSmall,
+    kMaxValue,
+  };
+
+  // Construct a new header for the given key and signature sizes.
+  // Returns null if erroneous values of |key_size| and/or
+  // |signature_size| are provided. |error| contains an error code with
+  // additional information.
+  // Use this constructor and then .header() to obtain the Header
+  // for writing out to a CRX file.
+  static std::unique_ptr<Crx2File> Create(const uint32_t key_size,
+                                          const uint32_t signature_size,
+                                          Error* error);
+
+  // Returns the header structure for writing out to a CRX file.
+  const Header& header() const { return header_; }
+
+ private:
+  Header header_;
+
+  // Constructor is private. Clients should use static factory methods above.
+  explicit Crx2File(const Header& header);
+
+  // Checks the |header| for validity and returns true if the values are valid.
+  // If false is returned, more detailed error code is returned in |error|.
+  static bool HeaderIsValid(const Header& header, Error* error);
+};
+
+}  // namespace crx_file
+
+#endif  // COMPONENTS_CRX_FILE_CRX2_FILE_H_