attempt to decode a value not in base64 char set

问题:

I am using the following code snippet to base64 encode and decode a string using Boost C++ library.

//Base64 Encode Implementation using Boost C++ library const std::string base64_padding[] = {"", "=", "=="};  std::string X_Privet_Token_Generator::base64_encode(const std::string & s) {   namespace bai = boost::archive::iterators;    std::stringstream os;    // convert binary values to base64 characters   typedef bai::base64_from_binary    // retrieve 6 bit integers from a sequence of 8 bit bytes   <:transform_width char=""> > base64_enc; // compose all the above operations in to a new iterator    std::copy(base64_enc(s.c_str()), base64_enc(s.c_str() + s.size()), std::ostream_iterator(os));    os  > base64_dec;    unsigned int size = s.size();    // Remove the padding characters, cf.   if (size && s[size - 1] == '=')   {       --size;       if (size && s[size - 1] == '=')           --size;   }    if (size == 0)       return std::string();    LOGINFO("Hash decoded token : %s", s.c_str());   std::copy(base64_dec(s.data()), base64_dec(s.data() + size), std::ostream_iterator(os));   std::cout

Encoding works well, however, while decoding I get the following error:

terminate called after throwing an instance of boost::archive::iterators::dataflow_exception

what(): attempt to decode a value not in base64 char set

Is it one of the padded characters that is causing this issue? Am I missing something here?

回答1:

The padding characters '=' are part of the b64 encoded data and should not be removed before decoding. b64 is encoded in blocks of 4 character, I suspect that while decoding it reads a '\0' instead of an expected '=' at the end of the string.

回答2:

Changing the

std::copy(base64_dec(s.data()), base64_dec(s.data() + size), std::ostream_iterator(os)) 

to

return std::string( base64_dec(s.c_str()), base64_dec(s.c_str() + size)) 

resolved the issue.

回答3:

A more efficient solution for base64 encoding and decoding is as follows:

#include  #include  #include  #include  #include  #include  #include  #include   std::string X_Privet_Token_Generator::base64_encode(std::string s) {     namespace bai = boost::archive::iterators;      std::stringstream os;      // convert binary values to base64 characters     typedef bai::base64_from_binary      // retrieve 6 bit integers from a sequence of 8 bit bytes     <:transform_width> > base64_enc; // compose all the above operations in to a new iterator      std::copy(base64_enc(s.c_str()), base64_enc(s.c_str() + s.size()), std::ostream_iterator(os));      os , 8, 6>       base64_dec;      unsigned int size = s.size();      // Remove the padding characters.     if(size && s[size - 1] == '=') {         --size;     if(size && s[size - 1] == '=')         --size;     }      if(size == 0) return std::string();      unsigned int paddChars = count(s.begin(), s.end(), '=');     std::replace(s.begin(),s.end(), '=', 'A');     std::string decoded_token(base64_dec(s.c_str()), base64_dec(s.c_str() + size));     decoded_token.erase(decoded_token.end()-paddChars,decoded_token.end());     return decoded_token;  } 

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