text: // Copyright (c) 2011 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.
  
  #ifndef CRYPTO_OPENSSL_UTIL_H_
  #define CRYPTO_OPENSSL_UTIL_H_
  #pragma once
  
  #include "base/basictypes.h"
  #include "base/tracked.h"
  
  namespace crypto {
  
  // A helper class that takes care of destroying OpenSSL objects when it goes out
  // of scope.
  template <typename T, void (*destructor)(T*)>
  class ScopedOpenSSL {
   public:
    ScopedOpenSSL() : ptr_(NULL) { }
    explicit ScopedOpenSSL(T* ptr) : ptr_(ptr) { }
    ~ScopedOpenSSL() {
      reset(NULL);
    }
  
    T* get() const { return ptr_; }
    void reset(T* ptr) {
      if (ptr != ptr_) {
        if (ptr_) (*destructor)(ptr_);
        ptr_ = ptr;
      }
    }
  
   private:
    T* ptr_;
  
    DISALLOW_COPY_AND_ASSIGN(ScopedOpenSSL);
  };
  
  // Provides a buffer of at least MIN_SIZE bytes, for use when calling OpenSSL's
  // SHA256, HMAC, etc functions, adapting the buffer sizing rules to meet those
  // of the our base wrapper APIs.
  // This allows the library to write directly to the caller's buffer if it is of
  // sufficient size, but if not it will write to temporary |min_sized_buffer_|
  // of required size and then its content is automatically copied out on
  // destruction, with truncation as appropriate.
  template<int MIN_SIZE>
  class ScopedOpenSSLSafeSizeBuffer {
   public:
    ScopedOpenSSLSafeSizeBuffer(unsigned char* output, size_t output_len)
        : output_(output),
          output_len_(output_len) {
    }
  
    ~ScopedOpenSSLSafeSizeBuffer() {
      if (output_len_ < MIN_SIZE) {
        // Copy the temporary buffer out, truncating as needed.
        memcpy(output_, min_sized_buffer_, output_len_);
      }
      // else... any writing already happened directly into |output_|.
    }
  
    unsigned char* safe_buffer() {
      return output_len_ < MIN_SIZE ? min_sized_buffer_ : output_;
    }
  
   private:
    // Pointer to the caller's data area and it's associated size, where data
    // written via safe_buffer() will [eventually] end up.
    unsigned char* output_;
    size_t output_len_;
  
    // Temporary buffer writen into in the case where the caller's
    // buffer is not of sufficient size.
    unsigned char min_sized_buffer_[MIN_SIZE];
  
    DISALLOW_COPY_AND_ASSIGN(ScopedOpenSSLSafeSizeBuffer);
  };
  
  // Initialize OpenSSL if it isn't already initialized. This must be called
  // before any other OpenSSL functions.
  // This function is thread-safe, and OpenSSL will only ever be initialized once.
  // OpenSSL will be properly shut down on program exit.
  void EnsureOpenSSLInit();
  
  // Drains the OpenSSL ERR_get_error stack. On a debug build the error codes
  // are send to VLOG(1), on a release build they are disregarded. In most
  // cases you should pass FROM_HERE as the |location|.
  void ClearOpenSSLERRStack(const tracked_objects::Location& location);
  
  // Place an instance of this class on the call stack to automatically clear
  // the OpenSSL error stack on function exit.
  class OpenSSLErrStackTracer {
   public:
    // Pass FROM_HERE as |location|, to help track the source of OpenSSL error
    // messages. Note any diagnostic emitted will be tagged with the location of
    // the constructor call as it's not possible to trace a destructor's callsite.
    explicit OpenSSLErrStackTracer(const tracked_objects::Location& location)
        : location_(location) {
      EnsureOpenSSLInit();
    }
    ~OpenSSLErrStackTracer() {
      ClearOpenSSLERRStack(location_);
    }
  
   private:
    const tracked_objects::Location location_;
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(OpenSSLErrStackTracer);
  };
  
  }  // namespace crypto
  
  #endif  // CRYPTO_OPENSSL_UTIL_H_
  