1// Copyright (c) 2012 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef CRYPTO_OPENSSL_UTIL_H_
6#define CRYPTO_OPENSSL_UTIL_H_
7
8#include <stddef.h>
9
10#include "base/location.h"
11#include "base/macros.h"
12#include "crypto/crypto_export.h"
13
14namespace crypto {
15
16// Provides a buffer of at least MIN_SIZE bytes, for use when calling OpenSSL's
17// SHA256, HMAC, etc functions, adapting the buffer sizing rules to meet those
18// of our base wrapper APIs.
19// This allows the library to write directly to the caller's buffer if it is of
20// sufficient size, but if not it will write to temporary |min_sized_buffer_|
21// of required size and then its content is automatically copied out on
22// destruction, with truncation as appropriate.
23template<int MIN_SIZE>
24class ScopedOpenSSLSafeSizeBuffer {
25 public:
26  ScopedOpenSSLSafeSizeBuffer(unsigned char* output, size_t output_len)
27      : output_(output),
28        output_len_(output_len) {
29  }
30
31  ~ScopedOpenSSLSafeSizeBuffer() {
32    if (output_len_ < MIN_SIZE) {
33      // Copy the temporary buffer out, truncating as needed.
34      memcpy(output_, min_sized_buffer_, output_len_);
35    }
36    // else... any writing already happened directly into |output_|.
37  }
38
39  unsigned char* safe_buffer() {
40    return output_len_ < MIN_SIZE ? min_sized_buffer_ : output_;
41  }
42
43 private:
44  // Pointer to the caller's data area and its associated size, where data
45  // written via safe_buffer() will [eventually] end up.
46  unsigned char* output_;
47  size_t output_len_;
48
49  // Temporary buffer writen into in the case where the caller's
50  // buffer is not of sufficient size.
51  unsigned char min_sized_buffer_[MIN_SIZE];
52
53  DISALLOW_COPY_AND_ASSIGN(ScopedOpenSSLSafeSizeBuffer);
54};
55
56// Initialize OpenSSL if it isn't already initialized. This must be called
57// before any other OpenSSL functions though it is safe and cheap to call this
58// multiple times.
59// This function is thread-safe, and OpenSSL will only ever be initialized once.
60// OpenSSL will be properly shut down on program exit.
61CRYPTO_EXPORT void EnsureOpenSSLInit();
62
63// Drains the OpenSSL ERR_get_error stack. On a debug build the error codes
64// are send to VLOG(1), on a release build they are disregarded. In most
65// cases you should pass FROM_HERE as the |location|.
66CRYPTO_EXPORT void ClearOpenSSLERRStack(
67    const tracked_objects::Location& location);
68
69// Place an instance of this class on the call stack to automatically clear
70// the OpenSSL error stack on function exit.
71class OpenSSLErrStackTracer {
72 public:
73  // Pass FROM_HERE as |location|, to help track the source of OpenSSL error
74  // messages. Note any diagnostic emitted will be tagged with the location of
75  // the constructor call as it's not possible to trace a destructor's callsite.
76  explicit OpenSSLErrStackTracer(const tracked_objects::Location& location)
77      : location_(location) {
78    EnsureOpenSSLInit();
79  }
80  ~OpenSSLErrStackTracer() {
81    ClearOpenSSLERRStack(location_);
82  }
83
84 private:
85  const tracked_objects::Location location_;
86
87  DISALLOW_IMPLICIT_CONSTRUCTORS(OpenSSLErrStackTracer);
88};
89
90}  // namespace crypto
91
92#endif  // CRYPTO_OPENSSL_UTIL_H_
93