Add RandomString() and its test, and use it everywhere it makes sense

util/misc/random_string_test.cc

+// Copyright 2015 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "util/misc/random_string.h"
+
+#include <set>
+
+#include "base/basictypes.h"
+#include "gtest/gtest.h"
+
+namespace crashpad {
+namespace test {
+namespace {
+
+TEST(RandomString, RandomString) {
+  // Explicitly list the allowed characters, rather than relying on a range.
+  // This prevents the test from having any dependency on the character set, so
+  // that the implementation is free to assume all uppercase letters are
+  // contiguous as in ASCII.
+  const std::string allowed_characters("ABCDEFGHIJKLMNOPQRSTUVWXYZ");
+
+  size_t character_counts[26] = {};
+  ASSERT_EQ(arraysize(character_counts), allowed_characters.size());
+
+  std::set<std::string> strings;
+
+  for (size_t i = 0; i < 256; ++i) {
+    const std::string random_string = RandomString();
+    EXPECT_EQ(16u, random_string.size());
+
+    // Make sure that the string is unique. It is possible, but extremely
+    // unlikely, for there to be collisions.
+    auto result = strings.insert(random_string);
+    EXPECT_TRUE(result.second) << random_string;
+
+    for (char c : random_string) {
+      size_t character_index = allowed_characters.find(c);
+
+      // Make sure that no unexpected characters appear.
+      EXPECT_NE(character_index, std::string::npos) << c;
+
+      if (character_index != std::string::npos) {
+        ++character_counts[character_index];
+      }
+    }
+  }
+
+  // Make sure every character appears at least once. It is possible, but
+  // extremely unlikely, for a character to not appear at all.
+  for (size_t character_index = 0;
+       character_index < arraysize(character_counts);
+       ++character_index) {
+    EXPECT_GT(character_counts[character_index], 0u)
+        << allowed_characters[character_index];
+  }
+}
+
+}  // namespace
+}  // namespace test
+}  // namespace crashpad