nbt.h

/*
 * -----------------------------------------------------------------------------
 * "THE BEER-WARE LICENSE" (Revision 42):
 * Lukas Niederbremer <webmaster@flippeh.de> and Clark Gaebel <cg.wowus.cg@gmail.com>
 * wrote this file. As long as you retain this notice you can do whatever you
 * want with this stuff. If we meet some day, and you think this stuff is worth
 * it, you can buy us a beer in return.
 * -----------------------------------------------------------------------------
 */

#ifndef NBT_H
#define NBT_H

#ifdef __cplusplus
extern "C" {
#endif

#include <stdbool.h>
#include <stddef.h> /* for size_t */
#include <stdint.h>
#include <stdio.h>  /* for FILE* */

#include "buffer.h" /* for struct buffer */
#include "list.h"   /* For struct list_entry etc. */

typedef enum {
    NBT_OK   =  0, /* No error. */
    NBT_ERR  = -1, /* Generic error, most likely of the parsing variety. */
    NBT_EMEM = -2, /* Out of memory. */
    NBT_EIO  = -3, /* IO error. */
    NBT_EZ   = -4  /* Zlib compression/decompression error. */
} nbt_status;

typedef enum {
    TAG_INVALID    = 0, /* tag_end, but we don't use it in the in-memory representation. */
    TAG_BYTE       = 1, /* char, 8 bits, signed */
    TAG_SHORT      = 2, /* short, 16 bits, signed */
    TAG_INT        = 3, /* long, 32 bits, signed */
    TAG_LONG       = 4, /* long long, 64 bits, signed */
    TAG_FLOAT      = 5, /* float, 32 bits, signed */
    TAG_DOUBLE     = 6, /* double, 64 bits, signed */
    TAG_BYTE_ARRAY = 7, /* char *, 8 bits, unsigned, TAG_INT length */
    TAG_STRING     = 8, /* char *, 8 bits, signed, TAG_SHORT length */
    TAG_LIST       = 9, /* X *, X bits, TAG_INT length, no names inside */
    TAG_COMPOUND   = 10 /* nbt_tag * */

} nbt_type;

typedef enum {
    STRAT_GZIP,   /* Use a gzip header. Use this if you want your data to be
                     compressed like level.dat */

    STRAT_INFLATE /* Use a zlib header. Use this if you want your data to be
                     compressed like a chunk. */
} nbt_compression_strategy;

/*
 * Represents a single node in the tree. You should switch on `type' and ONLY
 * access the union member it signifies. tag_compound and tag_list contain
 * recursive nbt_node entries, so those will have to be switched on too. I
 * recommended being VERY comfortable with recursion before traversing this
 * beast, or at least sticking to the library routines provided.
 */
typedef struct nbt_node {
    nbt_type type;
    char* name; /* This may be NULL. Check your damn pointers. */

    union { /* payload */

        /* tag_end has no payload */
        int8_t  tag_byte;
        int16_t tag_short;
        int32_t tag_int;
        int64_t tag_long;
        float   tag_float;
        double  tag_double;

        struct nbt_byte_array {
            unsigned char* data;
            int32_t length;
        } tag_byte_array;

        char* tag_string; /* TODO: technically, this should be a UTF-8 string */

        /*
         * Design addendum: we make tag_list a linked list instead of an array
         * so that nbt_node can be a true recursive data structure. If we used
         * an array, it would be incorrect to call free() on any element except
         * the first one. By using a linked list, the context of the node is
         * irrelevant. One tradeoff of this design is that we don't get tight
         * list packing when memory is a concern and huge lists are created.
         *
         * For more information on using the linked list, see `list.h'. The API
         * is well documented.
         */
        struct tag_list {
            struct nbt_node* data; /* A single node's data. */
            struct list_head entry;
        } *tag_list, /* The only difference between a list and a compound is its name */
          *tag_compound;

    } payload;
} nbt_node;

               /***** High Level Loading/Saving Functions *****/

/*
 * Loads a NBT tree from a compressed file. The file must have been opened with
 * a mode of "rb". If an error occurs, NULL will be returned and errno will be
 * set to the appropriate nbt_status. Check your danm pointers.
 */
nbt_node* nbt_parse_file(FILE* fp);

static inline nbt_node* nbt_parse_path(const char* filename)
{
    FILE* fp = fopen(filename, "rb");

    if(fp == NULL)
    {
        errno = NBT_EIO;
        return NULL;
    }

    nbt_node* r = nbt_parse_file(fp);
    fclose(fp);
    return r;
}

/*
 * Loads a NBT tree from a compressed block of memory (such as a chunk or a
 * pre-loaded level.dat). If an error occurs, NULL will be returned and errno
 * will be set to the appropriate nbt_status. Check your damn pointers.
 *
 * PROTIP: Memory map each individual region file, then call
 *         nbt_parse_compressed for chunks as needed.
 */
nbt_node* nbt_parse_compressed(const void* chunk_start, size_t length);

/*
 * Dumps a tree into a file. Check your damn error codes. This function should
 * return NBT_OK.
 *
 * @see nbt_compression_strategy
 */
nbt_status nbt_dump_file(const nbt_node* tree,
                         FILE* fp, nbt_compression_strategy);

/*
 * Dumps a tree into a block of memory. If an error occurs, a buffer with a NULL
 * `data' pointer will be returned, and errno will be set.
 *
 * 1) Check your damn pointers.
 * 2) Don't forget to free buf->data. Memory leaks are bad, mkay?
 *
 * @see nbt_compression_strategy
 */
struct buffer nbt_dump_compressed(const nbt_node* tree,
                                  nbt_compression_strategy);

                /***** Low Level Loading/Saving Functions *****/

/*
 * Loads a NBT tree from memory. The tree MUST NOT be compressed. If an error
 * occurs, NULL will be returned, and errno will be set to the appropriate
 * nbt_status. Please check your damn pointers.
 */
nbt_node* nbt_parse(const void* memory, size_t length);

/*
 * Returns a NULL-terminated string as the ascii representation of the tree. If
 * an error occurs, NULL will be returned and errno will be set.
 *
 * 1) Check your damn pointers.
 * 2) Don't forget to free the returned pointer. Memory leaks are bad, mkay?
 */
char* nbt_dump_ascii(const nbt_node* tree);

/*
 * Returns a buffer representing the uncompressed tree in Notch's official
 * binary format. Trees dumped with this function can be regenerated with
 * nbt_parse. If an error occurs, a buffer with a NULL `data' pointer will be
 * returned, and errno will be set.
 *
 * 1) Check your damn pointers.
 * 2) Don't forget to free buf->data. Memory leaks are bad, mkay?
 */
struct buffer nbt_dump_binary(const nbt_node* tree);

                   /***** Tree Manipulation Functions *****/

/*
 * Clones an existing tree. Returns NULL on memory errors.
 */
nbt_node* nbt_clone(nbt_node*);

/*
 * Recursively deallocates a node and all its children. If this is used on a an
 * entire tree, no memory will be leaked.
 */
void nbt_free(nbt_node*);

/*
 * Recursively frees all the elements of a list, and then frees the list itself.
 */
void nbt_free_list(struct tag_list*);

/*
 * A visitor function to traverse the tree. Return true to keep going, false to
 * stop. `aux' is an optional parameter which will be passed to your visitor
 * from the parent function.
 */
typedef bool (*nbt_visitor_t)(nbt_node* node, void* aux);

/*
 * A function which directs the overall algorithm with its return type.
 * `aux' is an optional parameter which will be passed to your predicate from
 * the parent function.
 */
typedef bool (*nbt_predicate_t)(const nbt_node* node, void* aux);

/*
 * Traverses the tree until a visitor says stop or all elements are exhausted.
 * Returns false if it was terminated by a visitor, true otherwise. In most
 * cases this can be ignored.
 *
 * TODO: Is there a way to do this without expensive function pointers? Maybe
 * something like list_for_each?
 */
bool nbt_map(nbt_node* tree, nbt_visitor_t, void* aux);

/*
 * Returns a new tree, consisting of a copy of all the nodes the predicate
 * returned `true' for. If the new tree is empty, this function will return
 * NULL. If an out of memory error occured, errno will be set to NBT_EMEM.
 *
 * TODO: What if I want to keep a tree and all of its children? Do I need to
 * augment nbt_node with parent pointers?
 */
nbt_node* nbt_filter(const nbt_node* tree, nbt_predicate_t, void* aux);

/*
 * The exact same as nbt_filter, except instead of returning a new tree, the
 * existing tree is modified in place, and then returned for convenience.
 */
nbt_node* nbt_filter_inplace(nbt_node* tree, nbt_predicate_t, void* aux);

/*
 * Returns the first node which causes the predicate to return true. If all
 * nodes are rejected, NULL is returned. If you want to find every instance of
 * something, consider using nbt_map with a visitor that keeps track.
 *
 * Since const-ing `tree' would require me const-ing the return value, you'll
 * just have to take my word for it that nbt_find DOES NOT modify the tree.
 * Feel free to cast as necessary.
 */
nbt_node* nbt_find(nbt_node* tree, nbt_predicate_t, void* aux);

/*
 * Returns the first node with the name `name'. If no node with that name is in
 * the tree, returns NULL.
 *
 * If `name' is NULL, this function will find the first unnamed node.
 *
 * Since const-ing `tree' would require me const-ing the return value, you'll
 * just have to take my word for it that nbt_find DOES NOT modify the tree.
 * Feel free to cast as necessary.
 */
nbt_node* nbt_find_by_name(nbt_node* tree, const char* name);

/* Returns the number of nodes in the tree. */
size_t nbt_size(const nbt_node* tree);

/* TODO: More utilities as requests are made and patches contributed. */

                      /***** Utility Functions *****/

/* Returns true if the trees are identical. */
bool nbt_eq(const nbt_node* restrict a, const nbt_node* restrict b);

/*
 * Converts a type to a print-friendly string. The string is statically
 * allocated, and therefore does not have to be freed by the user.
*/
const char* nbt_type_to_string(nbt_type);

/*
 * Converts an error code into a print-friendly string. The string is statically
 * allocated, and therefore does not have to be freed by the user.
 */
const char* nbt_error_to_string(nbt_status);

#ifdef __cplusplus
}
#endif

#endif