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