[C] fix decode funtion (OpenAPITools#5642)

* fix function names and add parameter to return decoded bytes length from base64decode function

* format base64decode function to avoid unnecessary malloc and fix wrong length assigning

* update the pointer assigning

for some reason var++ / *var++ cannot be done on int *var, hence making a local variable which is incremented and at the end it is assigned to the pointer.

Author: zhemant

modules/openapi-generator/src/main/resources/C-libcurl/apiClient.c.mustache

@@ -578,7 +578,7 @@ char *strReplace(char *orig, char *rep, char *with) {
     return result;
 }
 
-char *sbi_base64encode (const void *b64_encode_this, int encode_this_many_bytes){
+char *base64encode (const void *b64_encode_this, int encode_this_many_bytes){
 #ifdef OPENSSL
     BIO *b64_bio, *mem_bio;      //Declares two OpenSSL BIOs: a base64 filter and a memory BIO.
     BUF_MEM *mem_bio_mem_ptr;    //Pointer to a "memory BIO" structure holding our base64 data.
@@ -597,7 +597,7 @@ char *sbi_base64encode (const void *b64_encode_this, int encode_this_many_bytes)
 #endif
 }
 
-char *sbi_base64decode (const void *b64_decode_this, int decode_this_many_bytes){
+char *base64decode (const void *b64_decode_this, int decode_this_many_bytes, int *decoded_bytes){
 #ifdef OPENSSL
     BIO *b64_bio, *mem_bio;      //Declares two OpenSSL BIOs: a base64 filter and a memory BIO.
     char *base64_decoded = calloc( (decode_this_many_bytes*3)/4+1, sizeof(char) ); //+1 = null.
@@ -611,6 +611,7 @@ char *sbi_base64decode (const void *b64_decode_this, int decode_this_many_bytes)
         decoded_byte_index++; //Increment the index until read of BIO decoded data is complete.
     } //Once we're done reading decoded data, BIO_read returns -1 even though there's no error.
     BIO_free_all(b64_bio);  //Destroys all BIOs in chain, starting with b64 (i.e. the 1st one).
+    *decoded_bytes = decoded_byte_index;
     return base64_decoded;        //Returns base-64 decoded data with trailing null terminator.
 #endif
 }

modules/openapi-generator/src/main/resources/C-libcurl/model-body.mustache

@@ -540,13 +540,10 @@ fail:
     {
     goto end; //Binary
     }
-    char* decoded = base64decode({{{name}}}->valuestring, strlen({{{name}}}->valuestring));
-    decoded_str_{{{name}}}->data = malloc(strlen(decoded) - 1);
+    decoded_str_{{{name}}}->data = base64decode({{{name}}}->valuestring, strlen({{{name}}}->valuestring), &decoded_str_{{{name}}}->len);
     if (!decoded_str_{{{name}}}->data) {
         goto end;
     }
-    memcpy(decoded_str_{{{name}}}->data,decoded,(strlen(decoded)-1));
-    decoded_str_{{{name}}}->len = strlen(decoded) - 1;
     {{/isBinary}}
     {{#isDate}}
     {{^required}}if ({{{name}}}) { {{/required}}