bencode

A simple bencode parser which uses hash tables for dictionaries. Hash algorithm used is FNV-1a (32 bit). Also note that all string related data is read/returned as unsigned char* and not as char*.

NOTE: You need the openssl library installed so that info_hash can be calculated

decoding a bencoded torrent file

be_dict *dict = decode_file(const char *file);

This will return the outermost dictionary in the torrent file or NULL if an error occurs. Note that this does not differentiate between the cases where the file doesn't exist or a syntax error occurs.

decoding from buffer

unsigned char *buffer;
size_t len;
be_type type;
// ... Initialize the buffer and length
be_dict *dict = decode(&buffer, &len, &type);

This will return NULL only when a syntax error is present. This way, you can check for syntax errors and problems with reading files separately. But you will need to check the type manually.

freeing the created dictionary

Should always be done after the outermost dictionary is used. There's no need to free individual values or lists. Do this once after everything is done.

dict_destroy(dict);
dict = NULL;

DO NOT free, list_free or dict_destroy anything other than the outermost dictionary. It will cause double-freeing when freeing the outermost dictionary later. Set your outer dictionary to NULL after destroying it to prevent double-freeing as well.

getting the value of a key

be_type type;
void *val = dict_get(be_dict *dict, unsigned char *key, be_type *type);

Returns the value of the key or NULL if it doesn't exist. Stores the type of the value in the be_type pointer provided. You can cast the returned value depending on type.

lists

Linked lists are used for storing lists here. Iterating over a list which you got from a dictionary can be done by:

be_type type;
be_list *list = (be_list*)dict_get(dict, key, &type);
while(list != NULL) {
	be_node node = list->node;
	void *node_val = node.val;
	be_type type = node.type;
	list = list->next;
}

strings

Strings are stored in a struct that contain the string itself and the length of the string.

be_type type;
be_string *string = (be_string*)dict_get(dict, key, &type);
size_t len = string->len;
unsigned char *val = string->str;

integers

Integers are stored as long long int here.

be_type type;
long long int i = (long long int)dict_get(dict, key, &type);

info hash

The info hash of the torrent file is stored in the struct be_dict as an array of unsigned char. You can access it by dict->info_hash. Please check if dict->has_info_hash is set to 1 before doing anything with the actual hash to prevent undefined behaviour. You can dump the info hash (or any string, really) in hex form with the hex_dump method.

running the tests

test.c is more of a demonstration file. You should have a look to see how some things work. You can compile and run it by:

make && make test

Using valgrind to detect any memory leaks is recommended (makefile already uses valgrind). Please report if you find any.

note

Be sure to check all returned values for NULL and confirm the types before actually using the values further. You could also store the returned void*, check the type and then cast it.

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Please read bencode.h for documentation on other functions (which you may or may not need).