base/openssl_util.h

   1 // Copyright (c) 2010 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 BASE_OPENSSL_UTIL_H_
   6 #define BASE_OPENSSL_UTIL_H_
   7 #pragma once
   8
   9 #include "base/basictypes.h"
  10 #include "base/tracked.h"
  11
  12 namespace base {
  13
  14 // A helper class that takes care of destroying OpenSSL objects when it goes out
  15 // of scope.
  16 template <typename T, void (*destructor)(T*)>
  17 class ScopedOpenSSL {
  18  public:
  19   ScopedOpenSSL() : ptr_(NULL) { }
  20   explicit ScopedOpenSSL(T* ptr) : ptr_(ptr) { }
  21   ~ScopedOpenSSL() {
  22     reset(NULL);
  23   }
  24
  25   T* get() const { return ptr_; }
  26   void reset(T* ptr) {
  27     if (ptr != ptr_) {
  28       if (ptr_) (*destructor)(ptr_);
  29       ptr_ = ptr;
  30     }
  31   }
  32
  33  private:
  34   T* ptr_;
  35
  36   DISALLOW_COPY_AND_ASSIGN(ScopedOpenSSL);
  37 };
  38
  39 // Provides a buffer of at least MIN_SIZE bytes, for use when calling OpenSSL's
  40 // SHA256, HMAC, etc functions, adapting the buffer sizing rules to meet those
  41 // of the our base wrapper APIs.
  42 // This allows the library to write directly to the caller's buffer if it is of
  43 // sufficient size, but if not it will write to temporary |min_sized_buffer_|
  44 // of required size and then its content is automatically copied out on
  45 // destruction, with truncation as appropriate.
  46 template<int MIN_SIZE>
  47 class ScopedOpenSSLSafeSizeBuffer {
  48  public:
  49   ScopedOpenSSLSafeSizeBuffer(unsigned char* output, size_t output_len)
  50       : output_(output),
  51         output_len_(output_len) {
  52   }
  53
  54   ~ScopedOpenSSLSafeSizeBuffer() {
  55     if (output_len_ < MIN_SIZE) {
  56       // Copy the temporary buffer out, truncating as needed.
  57       memcpy(output_, min_sized_buffer_, output_len_);
  58     }
  59     // else... any writing already happened directly into |output_|.
  60   }
  61
  62   unsigned char* safe_buffer() {
  63     return output_len_ < MIN_SIZE ? min_sized_buffer_ : output_;
  64   }
  65
  66  private:
  67   // Pointer to the caller's data area and it's associated size, where data
  68   // written via safe_buffer() will [eventually] end up.
  69   unsigned char* output_;
  70   size_t output_len_;
  71
  72   // Temporary buffer writen into in the case where the caller's
  73   // buffer is not of sufficient size.
  74   unsigned char min_sized_buffer_[MIN_SIZE];
  75
  76   DISALLOW_COPY_AND_ASSIGN(ScopedOpenSSLSafeSizeBuffer);
  77 };
  78
  79 // Initialize OpenSSL if it isn't already initialized. This must be called
  80 // before any other OpenSSL functions.
  81 // This function is thread-safe, and OpenSSL will only ever be initialized once.
  82 // OpenSSL will be properly shut down on program exit.
  83 void EnsureOpenSSLInit();
  84
  85 // Drains the OpenSSL ERR_get_error stack. On a debug build the error codes
  86 // are send to VLOG(1), on a release build they are disregarded. In most
  87 // cases you should pass FROM_HERE as the |location|.
  88 void ClearOpenSSLERRStack(const tracked_objects::Location& location);
  89
  90 // Place an instance of this class on the call stack to automatically clear
  91 // the OpenSSL error stack on function exit.
  92 class OpenSSLErrStackTracer {
  93  public:
  94   // Pass FROM_HERE as |location|, to help track the source of OpenSSL error
  95   // messages. Note any diagnostic emitted will be tagged with the location of
  96   // the constructor call as it's not possible to trace a destructor's callsite.
  97   explicit OpenSSLErrStackTracer(const tracked_objects::Location& location)
  98       : location_(location) {
  99     EnsureOpenSSLInit();
 100   }
 101   ~OpenSSLErrStackTracer() {
 102     ClearOpenSSLERRStack(location_);
 103   }
 104
 105  private:
 106   const tracked_objects::Location location_;
 107
 108   DISALLOW_IMPLICIT_CONSTRUCTORS(OpenSSLErrStackTracer);
 109 };
 110
 111 }  // namespace base
 112
 113 #endif  // BASE_OPENSSL_UTIL_H_