Generalize a base64url implementation in //base.

We currently have eight different base64url implementations living in
Chrome. This CL generalizes them to a single implementation in //base.

Uses will be updated after this CL lands on a per-feature basis with the
appropriate OWNERS.

BUG=536745

Review URL: https://codereview.chromium.org/1399363008

Cr-Commit-Position: refs/heads/master@{#356812}

1 files changed, 98 insertions, 0 deletions

diff --git a/base/base64url.cc b/base/base64url.cc
new file mode 100644
index 0000000..106bba9
--- /dev/null
+++ b/base/base64url.cc
@@ -0,0 +1,98 @@
+// Copyright 2015 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 "base/base64url.h"
+
+#include "base/base64.h"
+#include "base/numerics/safe_math.h"
+#include "base/strings/string_util.h"
+#include "third_party/modp_b64/modp_b64.h"
+
+namespace base {
+
+const char kPaddingChar = '=';
+
+// Base64url maps {+, /} to {-, _} in order for the encoded content to be safe
+// to use in a URL. These characters will be translated by this implementation.
+const char kBase64Chars[] = "+/";
+const char kBase64UrlSafeChars[] = "-_";
+
+void Base64UrlEncode(const StringPiece& input,
+                     Base64UrlEncodePolicy policy,
+                     std::string* output) {
+  Base64Encode(input, output);
+
+  ReplaceChars(*output, "+", "-", output);
+  ReplaceChars(*output, "/", "_", output);
+
+  switch (policy) {
+    case Base64UrlEncodePolicy::INCLUDE_PADDING:
+      // The padding included in |*output| will not be amended.
+      break;
+    case Base64UrlEncodePolicy::OMIT_PADDING:
+      // The padding included in |*output| will be removed.
+      const size_t last_non_padding_pos =
+          output->find_last_not_of(kPaddingChar);
+      if (last_non_padding_pos != std::string::npos)
+        output->resize(last_non_padding_pos + 1);
+
+      break;
+  }
+}
+
+bool Base64UrlDecode(const StringPiece& input,
+                     Base64UrlDecodePolicy policy,
+                     std::string* output) {
+  // Characters outside of the base64url alphabet are disallowed, which includes
+  // the {+, /} characters found in the conventional base64 alphabet.
+  if (input.find_first_of(kBase64Chars) != std::string::npos)
+    return false;
+
+  const size_t required_padding_characters = input.size() % 4;
+  const bool needs_replacement =
+      input.find_first_of(kBase64UrlSafeChars) != std::string::npos;
+
+  switch (policy) {
+    case Base64UrlDecodePolicy::REQUIRE_PADDING:
+      // Fail if the required padding is not included in |input|.
+      if (required_padding_characters > 0)
+        return false;
+      break;
+    case Base64UrlDecodePolicy::IGNORE_PADDING:
+      // Missing padding will be silently appended.
+      break;
+    case Base64UrlDecodePolicy::DISALLOW_PADDING:
+      // Fail if padding characters are included in |input|.
+      if (input.find_first_of(kPaddingChar) != std::string::npos)
+        return false;
+      break;
+  }
+
+  // If the string either needs replacement of URL-safe characters to normal
+  // base64 ones, or additional padding, a copy of |input| needs to be made in
+  // order to make these adjustments without side effects.
+  if (required_padding_characters > 0 || needs_replacement) {
+    std::string base64_input;
+
+    CheckedNumeric<size_t> base64_input_size = input.size();
+    if (required_padding_characters > 0)
+      base64_input_size += 4 - required_padding_characters;
+
+    base64_input.reserve(base64_input_size.ValueOrDie());
+    input.AppendToString(&base64_input);
+
+    // Substitute the base64url URL-safe characters to their base64 equivalents.
+    ReplaceChars(base64_input, "-", "+", &base64_input);
+    ReplaceChars(base64_input, "_", "/", &base64_input);
+
+    // Append the necessary padding characters.
+    base64_input.resize(base64_input_size.ValueOrDie(), '=');
+
+    return Base64Decode(base64_input, output);
+  }
+
+  return Base64Decode(input, output);
+}
+
+}  // namespace base