Welcome to hipack-c’s documentation!

Contents:

Quickstart

This guide will walk you through the usage of the hipack-c C library.

Note

All the examples in this guide need a compiler which supports C99.

Reading (deserialization)

Let’s start by parsing some data from the file which contains a HiPack message like the following:

title: "Quickstart"
is-documentation? True

First of all, we need to include the hipack.h header in the source of our program, and then use a hipack_read() to parse it. In this example we use the hipack_stdio_getchar() function included in the library which is used to read data from a FILE*:

#include <hipack.h>
#include <stdio.h>   /* Needed for FILE* streams */

static void handle_message (hipack_dict_t *message);

int main (int argc, const char *argv[]) {
    hipack_reader_t reader = {
        .getchar_data = fopen ("input.hipack", "rb"),
        .getchar = hipack_stdio_getchar,
    };
    hipack_dict_t *message = hipack_read (&reader);
    fclose (reader.getchar_data);

    handle_message (message); /* Use "message". */

    hipack_dict_free (message);
    return 0;
}

Once the message was parsed, a dictionary (hipack_dict_t) is returned. The Dictionary Functions can be used to inspect the message. For example, adding the following as the handle_message() function prints the value of the title element:

void handle_message (hipack_dict_t *message) {
    hipack_string_t *key = hipack_string_new_from_string ("title");
    hipack_value_t *value = hipack_dict_get (message, key);

    printf ("Title is '%s'\n", hipack_value_get_string (value));

    hipack_string_free (key); // Free memory used by "key".
}

Note how objects cretated by us, like the key string, have to be freed by us. In general, the user of the library is responsible for freeing any objects created by them. On the other hand, objects allocated by the library are freed by library functions.

In our example, the memory area which contains the value is owned by the message (more precisely: by the dictionary that represents the message), and the call to hipack_value_get() returns a pointer to the memory area owned by the message. The same happens with the call to hipack_value_get_string(): it returns a pointer to a memory area containing the bytes of the string value, which is owned by the hipack_value_t structure. This means that we must not free the value structure or the string, because when the whole message is freed —by calling hipack_dict_free() at the end of our main() function— the memory areas used by the value structure and the string will be freed as well.

Values

Objects of hipack_value_t represent a single value of those supported by HiPack: an integer number, a floating point number, a boolean, a list, or a dictionary. Creating an object if a “basic” value, that is all except lists and dictionary, can be done using the C99 designated initializer syntax. For example, to create a floating point number value:

hipack_value_t flt_val = {
    .type = HIPACK_FLOAT,
    .v_float = 4.5e-1
};

Alternatively, it is also possible to use provided utility functions to create values. The example above is equivalent to:

hipack_value_t flt_val = hipack_float (4.5e-1);

When using the C99 initializer syntax directly, the name of the field containing the value depends on the type. The following table summarizes the equivalence between types, the field to use in hipack_value_t, and the utility function for constructing values:

Type	Field	Macro
HIPACK_INTEGER	.v_integer	hipack_integer()
HIPACK_FLOAT	.v_float	hipack_float()
HIPACK_BOOL	.v_bool	hipack_bool()
HIPACK_STRING	.v_string	hipack_string()
HIPACK_LIST	.v_list	hipack_list()
HIPACK_DICT	.v_dict	hipack_dict()

Note that strings, lists, and dictionaries may have additional memory allocated. When wrapping them into a hipack_value_t only the pointer is stored, and it is still your responsibility to make sure the memory is freed when the values are not used anymore:

hipack_string_t *str = hipack_string_new_from_string ("spam");
hipack_value_t str_val = hipack_string (str);
assert (str == hipack_value_get_string (&str_val)); // Always true

For convenience, a hipack_value_free() function which will ensure the memory allocated by values referenced by a hipack_value_t will be freed properly. This way, one can write code in which the the value objects (hipack_value_t) are considered to be the owners of the memory which has been dynamically allocated:

// Ownership of the hipack_string_t is passed to "str_val"
hipack_value_t str_val =
    hipack_string (hipack_string_new_from_string ("spam"));
// ...
hipack_value_free (&str_val);  // Free memory.

This behaviour is particularly handy when assembling complex values: all items contained in lists and dictionaries can be just added to them, and when freeing the container, all the values in them will be freed as well. Consider the following function which creates a HiPack message with a few fields:

/*
 * Creates a message which would serialize as:
 *
 *    street: "Infinite Loop"
 *    lat: 37.332
 *    lon: -122.03
 *    number: 1
 */
hipack_dict_t* make_address_message (void) {
    hipack_dict_t *message = hipack_dict_new ();
    hipack_dict_set_adopt_key (message,
        hipack_string_new_from_string ("lat"),
        hipack_float (37.332));
    hipack_dict_set_adopt_key (message,
        hipack_string_new_from_string ("lon"),
        hipack_float (-122.03));
    hipack_dict_set_adopt_key (message,
        hipack_string_new_from_string ("street"),
        hipack_string (
            hipack_string_new_from_string ("Infinite Loop")));
    hipack_dict_set_adopt_key (message,
        hipack_string_new_from_string ("number"),
        hipack_integer (1));
    return message;
}

Note how it is not needed to free any of the values because they are “owned” by the dictionary, which gets returned from the function. Also, we use hipack_dict_set_adopt_key() (instead of hipack_dict_set()) to pass ownership of the keys to the dictionary as well and, at the same time, avoiding creating copies of the strings. The caller of this function would be the owner of the memory allocated by the returned dictionary and all its contained values.

Writing (serialization)

In order to serialize messages, we need a dictionary containing the values which we want to have serialized — remember that any dictionary can be considered a HiPack message. In order to serialize a message, we use hipack_write(), and in particular using hipack_stdio_putchar() we can directly write to a FILE* stream. Given the make_address_message() function from the previous section:

int main (int argc, char *argv[]) {
    hipack_dict_t *message = make_address_message ();
    hipack_writer_t writer = {
        .putchar_data = fopen ("address.hipack", "wb"),
        .putchar = hipack_stdio_putchar,
    };
    hipack_write (&writer, message);
    hipack_dict_free (message);
    return 0;
}

The resulting address.hipack file will have the following contents (the order of the elements may vary):

number: 1
street: "Infinite Loop"
lat: 37.332
lon: -122.03

API Reference

Types

hipack_type_t

Type of a value. This enumeration takes one of the following values:

• HIPACK_INTEGER: Integer value.
• HIPACK_FLOAT: Floating point value.
• HIPACK_BOOL: Boolean value.
• HIPACK_STRING: String value.
• HIPACK_LIST: List value.
• HIPACK_DICT: Dictionary value.

hipack_value_t

Represent any valid HiPack value.

• hipack_value_type() obtains the type of a value.

hipack_string_t

String value.

hipack_list_t

List value.

hipack_dict_t

Dictionary value.

Memory Allocation

How hipack-c allocates memory can be customized by setting hipack_alloc to a custom allocation function.

hipack_alloc

Allocation function. By default it is set to hipack_alloc_stdlib(), which uses the implementations of malloc(), realloc(), and free() provided by the C library.

Allocation functions always have the following prototype:

void* func (void *oldptr, size_t size);

The behavior must be as follows:

• When invoked with oldptr set to NULL, and a non-zero size, the function behaves like malloc(): a memory block of at least size bytes is allocated and a pointer to it returned.
• When oldptr is non-NULL, and a non-zero size, the function behaves like realloc(): the memory area pointed to by oldptr is resized to be at least size bytes, or its contents moved to a new memory area of at least size bytes. The returned pointer may either be oldptr, or a pointer to the new memory area if the data was relocated.
• When oldptr is non-NULL, and size is zero, the function behaves like free().

void* hipack_alloc_stdlib(void*, size_t)

Default allocation function. It uses malloc(), realloc(), and free() from the C library. By default hipack_alloc is set to use this function.

void* hipack_alloc_array_extra(void *oldptr, size_t nmemb, size_t size, size_t extra)

Allocates (if oldptr is NULL) or reallocates (if oldptr is non-NULL) memory for an array which contains nmemb elements, each one of size bytes, plus an arbitrary amount of extra bytes.

This function is used internally by the HiPack parser, and it is not likely to be needed by client code.

void* hipack_alloc_array(void *optr, size_t nmemb, size_t size)

Same as hipack_alloc_array_extra(), without allowing to specify the amount of extra bytes. The following calls are both equivalent:

void *a = hipack_alloc_array_extra (NULL, 10, 4, 0);
void *b = hipack_alloc_array (NULL, 10, 4);

See hipack_alloc_array_extra() for details.

void* hipack_alloc_bzero(size_t size)

Allocates an area of memory of size bytes, and initializes it to zeroes.

void hipack_alloc_free(void *pointer)

Frees the memory area referenced by the given pointer.

String Functions

The following functions are provided as a convenience to operate on values of type hipack_string_t.

Note

The hash function used by hipack_string_hash() is not guaranteed to be cryptographically safe. Please do avoid exposing values returned by this function to the attack surface of your applications, in particular do not expose them to the network.

hipack_string_t* hipack_string_copy(const hipack_string_t *hstr)

Returns a new copy of a string.

The returned value must be freed using hipack_string_free().

hipack_string_t* hipack_string_new_from_string(const char *str)

Creates a new string from a C-style zero terminated string.

The returned value must be freed using hipack_string_free().

hipack_string_t* hipack_string_new_from_lstring(const char *str, uint32_t len)

Creates a new string from a memory area and its length.

The returned value must be freed using hipack_string_free().

uint32_t hipack_string_hash(const hipack_string_t *hstr)

Calculates a hash value for a string.

bool hipack_string_equal(const hipack_string_t *hstr1, const hipack_string_t *hstr2)

Compares two strings to check whether their contents are the same.

void hipack_string_free(hipack_string_t *hstr)

Frees the memory used by a string.

List Functions

hipack_list_t* hipack_list_new(uint32_t size)

Creates a new list for size elements.

void hipack_list_free(hipack_list_t *list)

Frees the memory used by a list.

bool hipack_list_equal(const hipack_list_t *a, const hipack_list_t *b)

Checks whether two lists contains the same values.

uint32_t hipack_list_size(const hipack_list_t *list)

Obtains the number of elements in a list.

HIPACK_LIST_AT(list, index)

Obtains a pointer to the element at a given index of a list.

Dictionary Functions

uint32_t hipack_dict_size(const hipack_dict_t *dict)

Obtains the number of elements in a dictionary.

hipack_dict_t* hipack_dict_new(void)

Creates a new, empty dictionary.

void hipack_dict_free(hipack_dict_t *dict)

Frees the memory used by a dictionary.

bool hipack_dict_equal(const hipack_dict_t *a, const hipack_dict_t *b)

Checks whether two dictinaries contain the same keys, and their associated values in each of the dictionaries are equal.

void hipack_dict_set(hipack_dict_t *dict, const hipack_string_t *key, const hipack_value_t *value)

Adds an association of a key to a value.

Note that this function will copy the key. If you are not planning to continue reusing the key, it is recommended to use hipack_dict_set_adopt_key() instead.

void hipack_dict_set_adopt_key(hipack_dict_t *dict, hipack_string_t **key, const hipack_value_t *value)

Adds an association of a key to a value, passing ownership of the memory using by the key to the dictionary (i.e. the string used as key will be freed by the dictionary).

Use this function instead of hipack_dict_set() when the key is not going to be used further afterwards.

void hipack_dict_del(hipack_dict_t *dict, const hipack_string_t *key)

Removes the element from a dictionary associated to a key.

hipack_value_t* hipack_dict_get(const hipack_dict_t *dict, const hipack_string_t *key)

Obtains the value associated to a key from a dictionary.

The returned value points to memory owned by the dictionary. The value can be modified in-place, but it shall not be freed.

hipack_value_t* hipack_dict_first(const hipack_dict_t *dict, const hipack_string_t **key)

Obtains an a (key, value) pair, which is considered the first in iteration order. This can be used in combination with hipack_dict_next() to enumerate all the (key, value) pairs stored in the dictionary:

hipack_dict_t *d = get_dictionary ();
hipack_value_t *v;
hipack_string_t *k;

for (v = hipack_dict_first (d, &k);
     v != NULL;
     v = hipack_dict_next (v, &k)) {
    // Use "k" and "v" normally.
}

As a shorthand, consider using HIPACK_DICT_FOREACH() instead.

hipack_value_t* hipack_dict_next(hipack_value_t *value, const hipack_string_t **key)

Iterates to the next (key, value) pair of a dictionary. For usage details, see hipack_dict_first().

HIPACK_DICT_FOREACH(dict, key, value)

Convenience macro used to iterate over the (key, value) pairs contained in a dictionary. Internally this uses hipack_dict_first() and hipack_dict_next().

hipack_dict_t *d = get_dictionary ();
hipack_string_t *k;
hipack_value_t *v;
HIPACK_DICT_FOREACH (d, k, v) {
    // Use "k" and "v"
}

Using this macro is the recommended way of writing a loop to enumerate elements from a dictionary.

Value Functions

hipack_type_t hipack_value_type(const hipack_value_t *value)

Obtains the type of a value.

hipack_value_t hipack_integer(int32_t value)

Creates a new integer value.

hipack_value_t hipack_float(double value)

Creates a new floating point value.

hipack_value_t hipack_bool(bool value)

Creates a new boolean value.

hipack_value_t hipack_string(hipack_string_t *value)

Creates a new string value.

hipack_value_t hipack_list(hipack_list_t *value)

Creates a new list value.

hipack_value_t hipack_dict(hipack_dict_t *value)

Creates a new dictionary value.

bool hipack_value_is_integer(const hipack_value_t *value)

Checks whether a value is an integer.

bool hipack_value_is_float(const hipack_value_t *value)

Checks whether a value is a floating point number.

bool hipack_value_is_bool(const hipack_value_t *value)

Checks whether a value is a boolean.

bool hipack_value_is_string(const hipack_value_t *value)

Checks whether a value is a string.

bool hipack_value_is_list(const hipack_value_t *value)

Checks whether a value is a list.

bool hipack_value_is_dict(const hipack_value_t *value)

Checks whether a value is a dictionary.

const int32_t hipack_value_get_integer(const hipack_value_t *value)

Obtains a numeric value as an int32_t.

const double hipack_value_get_float(const hipack_value_t *value)

Obtains a floating point value as a double.

const bool hipack_value_get_bool(const hipack_value_t *value)

Obtains a boolean value as a bool.

const hipack_string_t* hipack_value_get_string(const hipack_value_t *value)

Obtains a numeric value as a hipack_string_t.

const hipack_list_t* hipack_value_get_list(const hipack_value_t *value)

Obtains a numeric value as a hipack_list_t.

const hipack_dict_t* hipack_value_get_dict(const hipack_value_t *value)

Obtains a numeric value as a hipack_dict_t.

bool hipack_value_equal(const hipack_value_t *a, const hipack_value_t *b)

Checks whether two values are equal.

void hipack_value_free(hipack_value_t *value)

Frees the memory used by a value.

void hipack_value_add_annot(hipack_value_t *value, const char *annot)

Adds an annotation to a value. If the value already had the annotation, this function is a no-op.

bool hipack_value_has_annot(const hipack_value_t *value, const char *annot)

Checks whether a value has a given annotation.

void hipack_value_del_annot(hipack_value_t *value, const char *annot)

Removes an annotation from a value. If the annotation was not present, this function is a no-op.

Reader Interface

hipack_reader_t

Allows communicating with the parser, instructing it how to read text input data, and provides a way for the parser to report errors back.

The following members of the structure are to be used by client code:

int (*getchar)(void *data)

Reader callback function. The function will be called every time the next character of input is needed. It must return it as an integer, HIPACK_IO_EOF when trying to read pas the end of the input, or HIPACK_IO_ERROR if an input error occurs.

const char *error

On error, a string describing the issue, suitable to be displayed to the user.

unsigned error_line

On error, the line number where parsing was stopped.

unsigned error_column

On error, the column where parsing was stopped.

HIPACK_IO_EOF

Constant returned by reader functions when trying to read past the end of the input.

HIPACK_IO_ERROR

Constant returned by reader functions on input errors.

HIPACK_READ_ERROR

Constant value used to signal an underlying input error.

The error field of hipack_reader_t is set to this value when the reader function returns HIPACK_IO_ERROR. This is provided to allow client code to detect this condition and further query for the nature of the input error.

hipack_dict_t* hipack_read(hipack_reader_t *reader)

Reads a HiPack message from a stream reader and returns a dictionary.

On error, NULL is returned, and the members error, error_line, and error_column (see hipack_reader_t) are set accordingly in the reader.

int hipack_stdio_getchar(void* fp)

Reader function which uses FILE* objects from the standard C library.

To use this function to read from a FILE*, first open a file, and then create a reader using this function and the open file as data to be passed to it, and then use hipack_read():

FILE* stream = fopen (HIPACK_FILE_PATH, "rb")
hipack_reader_t reader = {
    .getchar = hipack_stdio_getchar,
    .getchar_data = stream,
};
hipack_dict_t *message = hipack_read (&reader);

The user is responsible for closing the FILE* after using it.

Writer Interface

hipack_writer_t

Allows specifying how to write text output data, and configuring how the produced HiPack output looks like.

The following members of the structure are to be used by client code:

int (*putchar)(void *data, int ch)

Writer callback function. The function will be called every time a character is produced as output. It must return HIPACK_IO_ERROR if an output error occurs, and it is invalid for the callback to return HIPACK_IO_EOF. Any other value is interpreted as indication of success.

void* putchar_data

Data passed to the writer callback function.

int32_t indent

Either HIPACK_WRITER_COMPACT or HIPACK_WRITER_INDENTED.

HIPACK_WRITER_COMPACT

Flag to generate output HiPack messages in their compact representation.

HIPACK_WRITER_INDENTED

Flag to generate output HiPack messages in “indented” (pretty-printed) representation.

bool hipack_write(hipack_writer_t *writer, const hipack_dict_t *message)

Writes a HiPack message to a stream writer, and returns whether writing the message was successful.

int hipack_stdio_putchar(void* data, int ch)

Writer function which uses FILE* objects from the standard C library.

To use this function to write a message to a FILE*, first open a file, then create a writer using this function, and then use hipack_write():

FILE* stream = fopen (HIPACK_FILE_PATH, "wb");
hipack_writer_t writer = {
    .putchar = hipack_stdio_putchar,
    .putchar_data = stream,
};
hipack_write (&writer, message);

The user is responsible for closing the FILE* after using it.

Indices and tables

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