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缘由：

学习、提高需要

正文：

参考解答：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>

#include <openssl/ssl.h>
#include <openssl/bio.h>
#include <openssl/err.h>


//base64_encode
int base64_encode(const char *input, int input_size, int with_new_line, char *buff, int buff_size)
{
	if (input == NULL || input_size <= 0 || buff == NULL || buff_size <= 0) {
		return -1;
	}

	BIO *bmem = NULL;
	BUF_MEM *bptr = NULL;
	BIO *b64 = NULL;
	b64 = BIO_new(BIO_f_base64());  
	if(!with_new_line) {  
		BIO_set_flags(b64, BIO_FLAGS_BASE64_NO_NL);  
	}  
	bmem = BIO_new(BIO_s_mem());  
	b64 = BIO_push(b64, bmem);  
	BIO_write(b64, input, input_size);  
	BIO_flush(b64);  
	BIO_get_mem_ptr(b64, &bptr);  

	if (buff_size < (bptr->length + 1)) {
		fprintf(stderr, "base64_encode output buff too small, need %ld, now %d\n", bptr->length + 1, buff_size);
		BIO_free_all(b64);
		return -1;
	}
	// char *buff = (char *)malloc(bptr->length + 1);  
	memcpy(buff, bptr->data, bptr->length);  
	buff[bptr->length] = 0;  

	BIO_free_all(b64);  

	return 0;  
}  

//base64_decode
int base64_decode(char *input, int input_size, int with_new_line, char *buff, int buff_size)
{
	if (input == NULL || input_size <= 0 || buff == NULL || buff_size <= 0) {
		return -1;
	}
	memset(buff, 0, buff_size);  

	BIO *bmem = NULL;
	BIO *b64 = NULL;
	b64 = BIO_new(BIO_f_base64());  
	if(!with_new_line) {  
		BIO_set_flags(b64, BIO_FLAGS_BASE64_NO_NL);  
	}  
	bmem = BIO_new_mem_buf(input, input_size);  
	bmem = BIO_push(b64, bmem);  
	BIO_read(bmem, buff, input_size);  

	BIO_free_all(bmem);  
	CRYPTO_cleanup_all_ex_data();	//free crypto_malloc

	return 0;  
}

// int base64_encode(const char *input, int input_size, int with_new_line, char *buff, int buff_size);
// int base64_decode(char *input, int input_size, int with_new_line, char *buff, int buff_size);
// $ gcc openssl_base64.c -lcrypto
int main(int argc, char const *argv[])
{
	if (argc < 2) {
		printf("Usage:\n\t%s str_to_be_base64_encode\n\n", argv[0]);
		return 0;
	}

	char buff[1024] = "\0";
	int ret = -1;
	ret = base64_encode(argv[1], strlen(argv[1]), 0, buff, sizeof(buff));
	if (ret == 0) {
		printf("input = %s\n", argv[1]);
		printf("base64_encode = %s\n", buff);
	}

	char buff_decode[1024] = "\0";
	ret = base64_decode(buff, strlen(buff), 0, buff_decode, sizeof(buff_decode));
	if (ret == 0) {
		printf("input = %s\n", buff);
		printf("buff_decode = %s\n", buff_decode);
	}

    return 0;
}

参考链接：

• http://www.cnblogs.com/hancq/p/5535869.html
• https://shanetully.com/2013/08/working-with-binary-data-in-c-and-openssl/
• https://gist.github.com/barrysteyn/7308212
• https://gist.github.com/barrysteyn/4409525
• http://doctrina.org/Base64-With-OpenSSL-C-API.html
• https://journal.missiondata.com/how-to-base64-encode-with-c-c-and-openssl-acccb1045c42
• https://devenix.wordpress.com/2008/01/18/howto-base64-encode-and-decode-with-c-and-openssl-2/

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