EVP_EncodeFinal
EVP_EncodeFinal(ctx->base64, ctx->buf, &(ctx->buf_len));
EVP_EncodeFinal(ctx, buf, &outl);
EVP_EncodeFinal(ctx, (unsigned char *)dst + outl, &outl2);
void EVP_EncodeFinal(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl);
EVP_EncodeFinal(encode_ctx, encode_out + output_len, &chunk_len);