diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..dbd6f91
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,6 @@
+# VSCodium
+.cache/
+
+# Meson
+build/
+debug/
diff --git a/gcovr.cfg b/gcovr.cfg
new file mode 100644
index 0000000..f6c4ea7
--- /dev/null
+++ b/gcovr.cfg
@@ -0,0 +1 @@
+exclude = .*tests/.+
diff --git a/include/ksr/arrays.h b/include/ksr/arrays.h
new file mode 100644
index 0000000..a8c69cd
--- /dev/null
+++ b/include/ksr/arrays.h
@@ -0,0 +1,92 @@
+#pragma once
+
+#include <jemalloc/jemalloc.h>
+#include <stddef.h>
+
+/*
+ *  KSRARRAY DEFAULT SIZES.
+ */
+
+#define KSRARRAY_TINY_SIZE 2
+#define KSRARRAY_SMALL_SIZE 8
+#define KSRARRAY_BASIC_SIZE 16
+#define KSRARRAY_BIG_SIZE 64
+#define KSRARRAY_HUGE_SIZE 128
+
+/**
+ * ksrarray structure.
+ */
+typedef struct {
+	void **data; // array data.
+	size_t length; // currently used size.
+
+	size_t _allocated_size; // currently allocated size.
+} ksrarray;
+
+/**
+ * Create a ksrarray with the given start size.
+ * @param start_size - the allocated size at start.
+ */
+ksrarray* ksrarray_new(const size_t start_size);
+/**
+ * Create a tiny sized ksrarray.
+ */
+static inline ksrarray* ksrarray_new_tiny()
+{ return ksrarray_new(KSRARRAY_TINY_SIZE); }
+/**
+ * Create a small sized ksrarray.
+ */
+static inline ksrarray* ksrarray_new_small()
+{ return ksrarray_new(KSRARRAY_SMALL_SIZE); }
+/**
+ * Create a normal sized ksrarray.
+ */
+static inline ksrarray* ksrarray_new_basic()
+{ return ksrarray_new(KSRARRAY_BASIC_SIZE); }
+/**
+ * Create a big sized ksrarray.
+ */
+static inline ksrarray* ksrarray_new_big()
+{ return ksrarray_new(KSRARRAY_BIG_SIZE); }
+/**
+ * Create a huge sized ksrarray.
+ */
+static inline ksrarray* ksrarray_new_huge()
+{ return ksrarray_new(KSRARRAY_HUGE_SIZE); }
+
+/**
+ * Push a new element at the end of a ksrarray.
+ * @param array - the ksrarray in which to push.
+ * @param element - the element to push.
+ */
+void ksrarray_push(ksrarray *array, void *element);
+
+/**
+ * Remove an element from a ksrarray.
+ * @param array - the ksrarray in which to remove.
+ * @param index - the index of the element to remove.
+ */
+bool ksrarray_remove(ksrarray *array, const size_t index);
+
+/**
+ * Free a ksrarray.
+ * /!\ This will NOT free the elements, just the container and its internal data.
+ */
+static inline void ksrarray_free(ksrarray *array)
+{
+	free(array->data);
+	free(array);
+}
+
+/**
+ * Get the iterator variable name, used in ksrarray_foreach.
+ */
+#define _ksrarray_get_iter_name(a, b) b ## _iter
+/**
+ * For each element of the given ksrarray, do...
+ */
+#define ksrarray_foreach(ksrarray, element) \
+        for(size_t _ksrarray_get_iter_name(ksrarray, element) = 0; \
+        	(element = ksrarray.data[_ksrarray_get_iter_name(ksrarray, element)]) || true, \
+        		_ksrarray_get_iter_name(ksrarray, element) < ksrarray.length; \
+        	_ksrarray_get_iter_name(ksrarray, element)++)
diff --git a/include/ksr/buffers.h b/include/ksr/buffers.h
new file mode 100644
index 0000000..2bed038
--- /dev/null
+++ b/include/ksr/buffers.h
@@ -0,0 +1,44 @@
+#pragma once
+
+#include <jemalloc/jemalloc.h>
+#include <stdio.h>
+
+/**
+ * ksrbuffer structure.
+ */
+typedef struct {
+	char *bytes;
+	size_t length;
+} ksrbuffer;
+
+/**
+ * Create a buffer of given size.
+ */
+ksrbuffer* ksrbuffer_new(const size_t buffer_size);
+
+/**
+ * Create a buffer of given size.
+ */
+ksrbuffer* ksrbuffer_new_empty(const size_t buffer_size);
+
+/**
+ * Create a buffer from given size and content.
+ */
+ksrbuffer* ksrbuffer_new_from_content(const size_t buffer_size, const char *buffer_content);
+
+/**
+ * Create a buffer of default buffer size.
+ */
+static inline ksrbuffer* ksrbuffer_new_default()
+{
+	return ksrbuffer_new(BUFSIZ);
+}
+
+/**
+ * Free a ksrbuffer and its content.
+ */
+static inline void ksrbuffer_free(ksrbuffer *buffer)
+{
+	free(buffer->bytes);
+	free(buffer);
+}
diff --git a/include/ksr/files.h b/include/ksr/files.h
new file mode 100644
index 0000000..f18a4b8
--- /dev/null
+++ b/include/ksr/files.h
@@ -0,0 +1,38 @@
+#pragma once
+
+#include <ksr/buffers.h>
+#include <stdbool.h>
+#include <sys/types.h>
+
+/**
+ * Expand the path in parameter.
+ * If the path expands to multiple paths, return the first one.
+ */
+char* path_exp_simple(const char* path);
+
+/**
+ * Make all directories to the file in argument.
+ * @param path - will create the directories for this path.
+ * @param mode - permissions of created directories.
+ */
+int mkpath(const char *path, const mode_t mode);
+
+/**
+ * Read the file.
+ * @param file - the opened file stream.
+ * @return - the buffer of the read file.
+ */
+ksrbuffer* read_file(FILE *file);
+/**
+ * Read the file from its path.
+ * @param file_path - path of the file to read.
+ * @return - the buffer of the read file.
+ */
+ksrbuffer* read_file_from_path(const char *file_path);
+
+/**
+ * Write a buffer into a file.
+ * @param file_path - path of the file to read.
+ * @return - true if the writing is successful, false otherwise.
+ */
+bool write_file(const char *file_path, const ksrbuffer *buffer);
diff --git a/include/ksr/logging.h b/include/ksr/logging.h
new file mode 100644
index 0000000..d0a308e
--- /dev/null
+++ b/include/ksr/logging.h
@@ -0,0 +1,11 @@
+#pragma once
+
+#define TERMSTYLE_RESET   "\033[0m"
+#define TERMSTYLE_BLACK   "\033[30m"
+#define TERMSTYLE_RED     "\033[31m"
+#define TERMSTYLE_GREEN   "\033[32m"
+#define TERMSTYLE_YELLOW  "\033[33m"
+#define TERMSTYLE_BLUE    "\033[34m"
+#define TERMSTYLE_MAGENTA "\033[35m"
+#define TERMSTYLE_CYAN    "\033[36m"
+#define TERMSTYLE_WHITE   "\033[37m"
diff --git a/include/ksr/promises.h b/include/ksr/promises.h
new file mode 100644
index 0000000..2211fca
--- /dev/null
+++ b/include/ksr/promises.h
@@ -0,0 +1,114 @@
+#pragma once
+
+#include <jemalloc/jemalloc.h>
+#include <pthread.h>
+#include <ksr/arrays.h>
+
+// sleep delay of promise await function, in µs.
+#define KSRPROMISES_AWAIT_SLEEP_DELAY 50*1000
+
+/**
+ * KSR promise.
+ */
+typedef struct {
+	pthread_t thread;
+	ksrarray *then_callbacks; // array of then callbacks.
+	ksrarray *catch_callbacks; // array of catch callbacks.
+
+	bool successful; // determine if the promise has been fulfilled or not.
+	void *result; // the promised result.
+
+	int error_code;
+	const char *error_message;
+} ksrpromise;
+
+// type of promise execution function.
+typedef void (*ksrpromise_execution_f)(ksrpromise *promise, void *userdata);
+// type of then callback.
+typedef void (*ksrpromise_then_callback_f)(void *result, void *userdata);
+// type of catch callback.
+typedef void (*ksrpromise_catch_callback_f)(int code, const char *message, void *userdata);
+
+/**
+ * Create a new promise.
+ * @param exec - promise execution function.
+ * @param data - custom user data.
+ * @return - the new promise.
+ */
+ksrpromise* ksrpromise_new(ksrpromise_execution_f exec, void *userdata);
+
+/**
+ * Resolve the given promise.
+ * @param promise - the promise to resolve.
+ * @param result - the promised result.
+ */
+void ksrpromise_resolve(ksrpromise *promise, void *result);
+
+/**
+ * Reject the given promise.
+ * @param promise - the promise to resolve.
+ * @param code - the error code.
+ * @param message - the error message.
+ */
+void ksrpromise_reject(ksrpromise *promise, int code, const char *message);
+
+/**
+ * Await a given promise.
+ * @param promise - the promise to await.
+ * @return - the promised result.
+ */
+void* ksrpromise_await(ksrpromise *promise);
+
+/**
+ * Set a new callback to call on promise resolution.
+ * @param promise - the promise for which to set a resolution callback.
+ * @param callback - the callback to set.
+ */
+void ksrpromise_then(ksrpromise *promise, ksrpromise_then_callback_f, void *userdata);
+
+/**
+ * Set a new callback to call on promise rejection.
+ * @param promise - the promise for which to set a rejection callback.
+ * @param callback - a callback to set.
+ */
+void ksrpromise_catch(ksrpromise *promise, ksrpromise_catch_callback_f, void *userdata);
+
+/**
+ * Determine if the given promise is successful or not.
+ * @param - the promise to check.
+ */
+static inline bool ksrpromise_is_successful(const ksrpromise *promise)
+{
+	return promise->successful;
+}
+/**
+ * Determine if the given promise is failed or not.
+ * @param - the promise to check.
+ */
+static inline bool ksrpromise_is_failed(const ksrpromise *promise)
+{
+	return !!promise->error_code;
+}
+/**
+ * Determine if the given promise is running or not.
+ * @param - the promise to check.
+ */
+static inline bool ksrpromise_is_running(const ksrpromise *promise)
+{
+	return !ksrpromise_is_successful(promise) && !ksrpromise_is_failed(promise);
+}
+
+/**
+ * Free the promise.
+ * /!\ The promise is freed automatically on rejection or resolution.
+ * @param promise - the promise to free.
+ */
+static inline void ksrpromise_free(ksrpromise *promise)
+{
+	// free arrays of callbacks.
+	ksrarray_free(promise->then_callbacks);
+	ksrarray_free(promise->catch_callbacks);
+	
+	// free promise data.
+	free(promise);
+}
diff --git a/include/ksr/regex.h b/include/ksr/regex.h
new file mode 100644
index 0000000..4665252
--- /dev/null
+++ b/include/ksr/regex.h
@@ -0,0 +1,63 @@
+#pragma once
+
+#include <jemalloc/jemalloc.h>
+#include <regex.h>
+
+/**
+ * Regex structure.
+ */
+typedef struct {
+	regex_t expr;
+	unsigned nmatches;
+	char **matches;
+} ksregex;
+
+/**
+ * Create a ksregex from an expression.
+ * @param expression - the expression to compile.
+ * @param nmatches - the number of matches groups to get, 0 if you want none.
+ * @param flags - regex flags.
+ * @return - the created regex, NULL if an error happen.
+ */
+ksregex* ksregex_new(const char *expression, unsigned nmatches, int flags);
+/**
+ * Create a ksregex from an expression with 0 match group.
+ * @param expression - the expression to compile.
+ * @param flags - regex flags.
+ */
+static inline ksregex* ksregex_new_nogroup(const char *expression, int flags)
+{ return ksregex_new(expression, 0, flags); }
+
+/**
+ * Try to match the regex with a tested string.
+ * @param regex - the regex to match.
+ * @param tested - the string that should match the regex.
+ * @return - true if the string matches, false otherwise.
+ */
+bool ksregex_matches(ksregex *regex, const char *tested);
+
+/**
+ * Free ksregex matches.
+ */
+static inline void _ksregex_free_matches(ksregex *regex)
+{
+	if (regex->matches)
+	{
+		// free all matches.
+		for (unsigned i = 0; i < regex->nmatches; i++) free(regex->matches[i]);
+		// free matches array.
+		free(regex->matches);
+		regex->matches = NULL;
+	}
+}
+
+/**
+ * Free a ksregex.
+ */
+static inline void ksregex_free(ksregex *regex)
+{
+	// free matches groups.
+	_ksregex_free_matches(regex);
+
+	free(regex); // free regex data.
+}
diff --git a/include/ksr/string.h b/include/ksr/string.h
new file mode 100644
index 0000000..e52a530
--- /dev/null
+++ b/include/ksr/string.h
@@ -0,0 +1,17 @@
+#pragma once
+
+#include <string.h>
+#include <stdbool.h>
+
+/**
+ * Check if two strings are equal.
+ * @param a - the first string to check.
+ * @param b - the second string to check.
+ */
+static inline bool str_equals(const char *a, const char *b)
+{ return 0 == strcmp(a, b); }
+
+/**
+ * Convert a string to lowercase.
+ */
+char* to_lowercase(const char* str);
diff --git a/meson.build b/meson.build
new file mode 100644
index 0000000..b6ee5ce
--- /dev/null
+++ b/meson.build
@@ -0,0 +1,42 @@
+project('ksr', 'c', version : '0.1', default_options : ['warning_level=3'])
+c = meson.get_compiler('c')
+
+# declare the dependencies of the library.
+deps = [ dependency('jemalloc') ]
+# add pthread dependency
+deps += c.find_library('pthread')
+
+# includes
+include_dirs = [ 'include' ]
+
+# source files.
+libsrc = [
+	'src/arrays.c',
+	'src/buffers.c',
+	'src/promises.c',
+	'src/regex.c',
+	'src/files.c',
+	'src/string.c',
+]
+
+# library target.
+libksr = library('ksr', libsrc, dependencies : deps, include_directories : include_dirs, install : true)
+
+# add the library to the dependencies of the executables.
+deps += declare_dependency(link_with : libksr)
+
+# test executables.
+test_ksrarrays = executable('test_ksrarrays', [ 'tests/ksrarrays.c' ], dependencies : deps, include_directories : include_dirs, install : false)
+test_ksrbuffers = executable('test_ksrbuffers', [ 'tests/ksrbuffers.c' ], dependencies : deps, include_directories : include_dirs, install : false)
+test_ksrpromises = executable('test_ksrpromises', [ 'tests/ksrpromises.c' ], dependencies : deps, include_directories : include_dirs, install : false)
+test_ksregex = executable('test_ksregex', [ 'tests/ksregex.c' ], dependencies : deps, include_directories : include_dirs, install : false)
+test_ksrstring = executable('test_ksrstring', [ 'tests/ksrstring.c' ], dependencies : deps, include_directories : include_dirs, install : false)
+test_ksrfiles = executable('test_ksrfiles', [ 'tests/ksrfiles.c' ], dependencies : deps, include_directories : include_dirs, install : false)
+
+# tests.
+test('ksrarrays', test_ksrarrays)
+test('ksrbuffers', test_ksrbuffers)
+test('ksrpromises', test_ksrpromises)
+test('ksregex', test_ksregex)
+test('ksrfiles', test_ksrfiles)
+test('ksrstring', test_ksrstring)
diff --git a/src/arrays.c b/src/arrays.c
new file mode 100644
index 0000000..58087b7
--- /dev/null
+++ b/src/arrays.c
@@ -0,0 +1,41 @@
+#include <ksr/arrays.h>
+
+ksrarray* ksrarray_new(const size_t start_size)
+{
+	// allocate array.
+	ksrarray *array = malloc(sizeof(ksrarray));
+
+	// initialize array fields.
+	array->_allocated_size = start_size;
+	array->length = 0;
+	// allocate array from start size.
+	array->data = malloc(sizeof(void*) * array->_allocated_size);
+
+	return array; // return initialized array.
+}
+
+void ksrarray_push(ksrarray *array, void *element)
+{
+	if (array->length == array->_allocated_size)
+	{ // cannot add a new element without allocating more memory.
+		array->_allocated_size *= 2; // allocate two times bigger space.
+		array->data = realloc(array->data, sizeof(void*) * array->_allocated_size); // reallocate array.
+	}
+
+	// push the element at the end of the array.
+	array->data[array->length++] = element;
+}
+
+bool ksrarray_remove(ksrarray *array, const size_t index)
+{
+	if (index >= array->length)
+		// the index is not associated with a value, cannot delete it.
+		return false;
+
+	array->length--; // length is decreasing because we are removing a value.
+	for (size_t i = index; i < array->length; i++)
+		// moving each value left.
+		array->data[i] = array->data[i+1];
+
+	return true;
+}
diff --git a/src/buffers.c b/src/buffers.c
new file mode 100644
index 0000000..a7caddb
--- /dev/null
+++ b/src/buffers.c
@@ -0,0 +1,36 @@
+#include <ksr/buffers.h>
+#include <string.h>
+
+ksrbuffer* ksrbuffer_new(const size_t buffer_size)
+{
+	// allocate buffer.
+	ksrbuffer *buffer = malloc(sizeof(ksrbuffer));
+
+	buffer->length = buffer_size;
+	// allocate buffer bytes.
+	buffer->bytes = malloc(buffer->length);
+
+	return buffer; // return allocated buffer.
+}
+
+ksrbuffer* ksrbuffer_new_empty(const size_t buffer_size)
+{
+	// create buffer.
+	ksrbuffer *buffer = ksrbuffer_new(buffer_size);
+
+	// cleanup allocated memory.
+	memset(buffer->bytes, 0, buffer->length);
+
+	return buffer; // return created buffer.
+}
+
+ksrbuffer* ksrbuffer_new_from_content(const size_t buffer_size, const char *buffer_content)
+{
+	// create buffer.
+	ksrbuffer *buffer = ksrbuffer_new(buffer_size);
+
+	// cleanup allocated memory.
+	memcpy(buffer->bytes, buffer_content, buffer->length);
+
+	return buffer; // return created buffer.
+}
diff --git a/src/files.c b/src/files.c
new file mode 100644
index 0000000..28ac17d
--- /dev/null
+++ b/src/files.c
@@ -0,0 +1,115 @@
+#include "ksr/buffers.h"
+#include <ksr/files.h>
+
+#include <string.h>
+#include <wordexp.h>
+#include <dirent.h>
+#include <libgen.h>
+#include <sys/stat.h>
+#include <errno.h>
+
+char* path_exp_simple(const char* path)
+{
+	// expanding the path.
+	wordexp_t exp;
+	wordexp(path, &exp, 0);
+	// copying the first expanded path.
+	char *expanded_path = strdup(exp.we_wordv[0]);
+	wordfree(&exp); // freeing the path expansion.
+
+	return expanded_path; // returning the first expanded path.
+}
+
+int mkpath(const char *path, const mode_t mode)
+{
+	// getting the current directory path to create.
+	char *fullpath = strdup(path);
+	char *dirpath = dirname(fullpath);
+
+	int res; // result of mkpath / mkdir.
+	DIR *dir = opendir(dirpath); // trying to open the directory, to see if it exists.
+	if (dir) // the parent directory exists, closing it.
+		closedir(dir);
+	else
+	{ // the parent directory does not exist, creating it recursively.
+		res = mkpath(dirpath, mode);
+		if (res != 0) goto err; // returning the error instantly if there is one.
+	}
+
+	// creating the current directory.
+	res = mkdir(dirpath, mode);
+	if (errno == EEXIST)
+		// the directory exists, everything have been created correctly.
+		res = 0;
+
+	err:
+	free(fullpath);
+	return res; // if an error happened while creating, returning it.
+}
+
+ksrbuffer* read_file(FILE *file)
+{
+	if (file)
+	{ // the file stream is open.
+		// searching the end of the file.
+		fseek(file, 0, SEEK_END);
+		long filesize = ftell(file); // getting file size.
+		// getting back to the beginning of the file.
+		fseek(file, 0, SEEK_SET);
+
+		// allocating a buffer corresponding to the file size, plus the end of string char.
+		ksrbuffer *buffer = ksrbuffer_new(filesize + 1);
+
+		// reading the file into the buffer.
+		fread(buffer->bytes, 1, buffer->length, file);
+		buffer->bytes[buffer->length - 1] = 0; // 0-terminated string.
+
+		return buffer; // returning allocated buffer.
+	}
+	else // the file is not readable, just returning NULL as we cannot read it.
+		return NULL;
+}
+ksrbuffer* read_file_from_path(const char *file_path)
+{
+	// expanding the file path.
+	char *fullpath = path_exp_simple(file_path);
+
+	// opening file.
+	FILE *file = fopen(fullpath, "r");
+	
+	free(fullpath); // freeing used full path.
+
+	if (file)
+	{ // the file is readable.
+		// reading file stream.
+		ksrbuffer *buffer = read_file(file);
+		fclose(file); // closing the read file.
+
+		return buffer; // returning allocated buffer.
+	}
+	else // the file is not readable, just returning NULL as we cannot read it.
+		return NULL;
+}
+
+bool write_file(const char *file_path, const ksrbuffer *buffer)
+{
+	// expanding the file path.
+	char *fullpath = path_exp_simple(file_path);
+
+	// creating directories if it is necessary.
+	mkpath(fullpath, 0755);
+	// opening file.
+	FILE *file = fopen(fullpath, "w");
+
+	free(fullpath); // free full path to file.
+
+	if (file)
+	{ // the file is writable.
+		// write buffer bytes to the file.
+		fwrite(buffer->bytes, 1, buffer->length, file);
+		fclose(file); // closing file stream.
+		return true; // returning true because the file have been written.
+	}
+	else
+		return false; // returning false because the file could not be written.
+}
diff --git a/src/promises.c b/src/promises.c
new file mode 100644
index 0000000..b76ce1f
--- /dev/null
+++ b/src/promises.c
@@ -0,0 +1,168 @@
+#include "ksr/arrays.h"
+#include <ksr/promises.h>
+#include <signal.h>
+#include <unistd.h>
+
+// global variable indicating if the program has been interrupted or not.
+bool interrupted = false;
+
+/**
+ * Function launched on signal reception.
+ * @param signal - the received signal.
+ */
+void onsigint(/*int signal*/)
+{
+	//if (signal == SIGINT)
+	// the program is now interrupted.
+	interrupted = true;
+}
+
+/**
+ * Promise thread structure.
+ */
+typedef struct {
+	ksrpromise *promise;
+	ksrpromise_execution_f exec;
+	void *data;
+} promise_thread_data;
+
+/**
+ * Promise then user callback.
+ */
+typedef struct {
+	ksrpromise_then_callback_f callback;
+	void *userdata;
+} promise_then_user_callback;
+/**
+ * Promise catch user callback.
+ */
+typedef struct {
+	ksrpromise_catch_callback_f callback;
+	void *userdata;
+} promise_catch_user_callback;
+
+/**
+ * The main promise thread function.
+ * @param data - thread data.
+ */
+void* promise_thread(void *data)
+{
+	// reading thread data.
+	promise_thread_data *thread_data = data;
+
+	// executing the promise.
+	thread_data->exec(thread_data->promise, thread_data->data);
+
+	return NULL; // this thread has no result.
+}
+
+ksrpromise* ksrpromise_new(ksrpromise_execution_f exec, void *data)
+{
+	// allocate the promise.
+	ksrpromise *promise = malloc(sizeof(ksrpromise));
+	promise->then_callbacks = ksrarray_new_tiny();
+	promise->catch_callbacks = ksrarray_new_tiny();
+	promise->successful = false;
+	promise->result = NULL;
+	promise->error_code = 0;
+	promise->error_message = NULL;
+
+	// allocate thread data.
+	promise_thread_data *thread_data = malloc(sizeof(promise_thread_data));
+	// assign thread data.
+	thread_data->promise = promise;
+	thread_data->exec = exec;
+	thread_data->data = data;
+
+	// initialize and run a new thread.
+	pthread_create(&promise->thread, NULL, promise_thread, thread_data);
+
+	return promise; // returning the created promise.
+}
+
+/**
+ * Run then callbacks for the given promise.
+ * @param promise - the promise for which to run then callbacks.
+ */
+void ksrpromise_run_then_callbacks(ksrpromise *promise)
+{
+	promise_then_user_callback *user_callback; // initialize user callback pointer.
+	for (size_t i = 0; i < promise->then_callbacks->length; i++)
+	{ // for each then callback, execute it.
+		user_callback = promise->then_callbacks->data[i]; // getting callback.
+		(user_callback->callback)(promise->result, user_callback->userdata); // executing callback with promised result.
+	}
+}
+
+void ksrpromise_resolve(ksrpromise *promise, void *result)
+{
+	// save success and result.
+	promise->successful = true;
+	promise->result = result;
+
+	// running then callbacks.
+	ksrpromise_run_then_callbacks(promise);
+}
+
+/**
+ * Run reject callbacks for the given promise.
+ * @param promise - the promise for which to run reject callbacks.
+ */
+void ksrpromise_run_catch_callbacks(ksrpromise *promise)
+{
+	promise_catch_user_callback *user_callback; // initialize user callback pointer.
+	for (size_t i = 0; i < promise->catch_callbacks->length; i++)
+	{ // for each catch callback, execute it.
+		user_callback = promise->catch_callbacks->data[i]; // getting callback.
+		(user_callback->callback)(promise->error_code, promise->error_message, user_callback->userdata); // executing callback with the promise error.
+	}
+}
+
+void ksrpromise_reject(ksrpromise *promise, int code, const char *message)
+{
+	// save error details.
+	promise->error_code = code;
+	promise->error_message = message;
+
+	// running catch callbacks.
+	ksrpromise_run_catch_callbacks(promise);
+}
+
+void* ksrpromise_await(ksrpromise *promise)
+{
+	// register signal reception callback.
+	signal(SIGINT, onsigint);
+
+	while (!interrupted)
+	{ // infinite loop, waiting for promise end or interruption.
+		if (!ksrpromise_is_running(promise))
+			// promise is not running anymore, returning result if there is one.
+			return promise->result;
+		
+		usleep(KSRPROMISES_AWAIT_SLEEP_DELAY); // sleeping a bit...
+	}
+
+	return NULL; // the promise have been interrupted before the result was found.
+}
+
+void ksrpromise_then(ksrpromise *promise, ksrpromise_then_callback_f callback, void *userdata)
+{
+	// allocate user callback.
+	promise_then_user_callback *user_callback = malloc(sizeof(promise_then_user_callback));
+	user_callback->callback = callback;
+	user_callback->userdata = userdata;
+
+	// we use a pointer of the given function pointer as a workaround for generic arrays (see https://stackoverflow.com/a/16682718/7496951).
+	ksrarray_push(promise->then_callbacks, user_callback);
+}
+
+void ksrpromise_catch(ksrpromise *promise, ksrpromise_catch_callback_f callback, void *userdata)
+{
+	// allocate user callback.
+	promise_catch_user_callback *user_callback = malloc(sizeof(promise_catch_user_callback));
+	user_callback->callback = callback;
+	user_callback->userdata = userdata;
+
+	// we use a pointer of the given function pointer as a workaround for generic arrays (see https://stackoverflow.com/a/16682718/7496951).
+	ksrarray_push(promise->catch_callbacks, user_callback);
+}
diff --git a/src/regex.c b/src/regex.c
new file mode 100644
index 0000000..fca4d18
--- /dev/null
+++ b/src/regex.c
@@ -0,0 +1,58 @@
+#include <ksr/regex.h>
+#include <regex.h>
+#include <string.h>
+
+ksregex* ksregex_new(const char *expression, unsigned nmatches, int flags)
+{
+	ksregex *regex = malloc(sizeof(ksregex));
+	regex->nmatches = nmatches;
+	regex->matches = NULL;
+
+	if (regcomp(&regex->expr, expression, // compile expression in regex.
+			flags | REG_EXTENDED | (nmatches == 0 ? REG_NOSUB : 0)) != 0)
+		return NULL; // an error happened, returning NULL.
+
+	return regex; // return created regex.
+}
+
+void ksregex_save_string_matches(ksregex *regex, regmatch_t *raw_matches, const char *source)
+{
+	// allocate string matches array.
+	regex->matches = malloc(sizeof(char *) * regex->nmatches);
+
+	// save full string match.
+	regex->matches[0] = strdup(source);
+
+	for(unsigned i = 1; i < regex->nmatches; i++)
+	{ // for each group match, converting it to an independent string.
+		regoff_t current_match_length = raw_matches[i].rm_eo - raw_matches[i].rm_so;
+		regex->matches[i] = malloc(current_match_length + 1); // allocate the current group match string.
+		// copying the string part from source to the current match string.
+		strncpy(regex->matches[i], &source[raw_matches[i].rm_so], current_match_length);
+		regex->matches[i][current_match_length] = 0; // set end of string.
+	}
+}
+
+bool ksregex_matches(ksregex *regex, const char *tested)
+{
+	// if there was matches, free them.
+	_ksregex_free_matches(regex);
+
+	// allocate raw matches array.
+	regmatch_t *raw_matches = malloc(sizeof(regmatch_t) * regex->nmatches);
+
+	if (regexec(&regex->expr, tested, regex->nmatches, raw_matches, 0) != 0)
+	{ // an error happened, freeing results then returning NULL.
+		free(raw_matches); // free raw groups matches.
+		return false;
+	}
+
+	if (regex->nmatches > 0)
+	{ // there are matches, getting them.
+		ksregex_save_string_matches(regex, raw_matches, tested);
+	}
+
+	free(raw_matches); // free raw groups matches.
+
+	return true; // no error, return true.
+}
diff --git a/src/string.c b/src/string.c
new file mode 100644
index 0000000..e74c277
--- /dev/null
+++ b/src/string.c
@@ -0,0 +1,15 @@
+#include <ksr/string.h>
+#include <ctype.h>
+
+char* to_lowercase(const char* src)
+{
+	// duplicate the string.
+	char *lowercased = strdup(src);
+	char *ret = lowercased; // store the first pointer to return it at the end of the conversion.
+	
+	for (;*lowercased; lowercased++)
+		// for each character, convert it to lowercase.
+		*lowercased = tolower(*lowercased);
+
+	return ret; // returning the first string pointer.
+}
diff --git a/tests/ksrarrays.c b/tests/ksrarrays.c
new file mode 100644
index 0000000..196d609
--- /dev/null
+++ b/tests/ksrarrays.c
@@ -0,0 +1,58 @@
+#include <ksr/arrays.h>
+#include <assert.h>
+#include <string.h>
+
+int main(/*int argc, char *argv[]*/)
+{
+	// try to create arrays.
+	ksrarray *array_tiny = ksrarray_new_tiny();
+	ksrarray *array_small = ksrarray_new_small();
+	ksrarray *array_basic = ksrarray_new_basic();
+	ksrarray *array_big = ksrarray_new_big();
+	ksrarray *array_huge = ksrarray_new_huge();
+
+	// try to push things in arrays.
+	ksrarray_push(array_tiny, "hello");
+	ksrarray_push(array_tiny, "world");
+
+	// check that things have been inserted properly.
+	assert(strcmp(array_tiny->data[0], "hello") == 0);
+	assert(strcmp(array_tiny->data[1], "world") == 0);
+	assert(array_tiny->_allocated_size == KSRARRAY_TINY_SIZE);
+	assert(array_tiny->length == 2);
+
+	// try to remove something.
+	ksrarray_remove(array_tiny, 0);
+	// try to remove something that does not exists.
+	ksrarray_remove(array_tiny, 3);
+
+	// check that the removal produces a good result.
+	assert(strcmp(array_tiny->data[0], "world") == 0);
+	assert(array_tiny->_allocated_size == KSRARRAY_TINY_SIZE);
+	assert(array_tiny->length == 1);
+
+	// insert more things.
+	ksrarray_push(array_tiny, "hello");
+	ksrarray_push(array_tiny, "you");
+	ksrarray_push(array_tiny, "!");
+
+	// check that the allocated size has increased.
+	assert(array_tiny->length == 4);
+	assert(array_tiny->_allocated_size == 2*KSRARRAY_TINY_SIZE);
+
+	// check that foreach is working.
+	char *element;
+	ksrarray_foreach((*array_tiny), element)
+	{
+		assert(element);
+	}
+
+	// free arrays.
+	ksrarray_free(array_tiny);
+	ksrarray_free(array_small);
+	ksrarray_free(array_basic);
+	ksrarray_free(array_big);
+	ksrarray_free(array_huge);
+
+	return 0;
+}
diff --git a/tests/ksrbuffers.c b/tests/ksrbuffers.c
new file mode 100644
index 0000000..6c10171
--- /dev/null
+++ b/tests/ksrbuffers.c
@@ -0,0 +1,49 @@
+#include <assert.h>
+#include <ksr/buffers.h>
+
+int main(/*int argc, char *argv[]*/)
+{
+	// create an empty buffer and check that it is properly instantiated.
+	ksrbuffer *empty_buffer = ksrbuffer_new_empty(30);
+	assert(empty_buffer->bytes[0] == 0);
+	assert(empty_buffer->bytes[10] == 0);
+	assert(empty_buffer->bytes[20] == 0);
+	assert(empty_buffer->bytes[29] == 0);
+
+	// create a buffer and set some bytes.
+	ksrbuffer *buffer = ksrbuffer_new(20);
+
+	buffer->bytes[0] = 12;
+	buffer->bytes[5] = 3;
+	buffer->bytes[10] = 44;
+	buffer->bytes[15] = 54;
+	buffer->bytes[19] = 8;
+
+	// create a buffer from existing content, taking raw content from the previous buffer.
+	ksrbuffer *copied_buffer = ksrbuffer_new_from_content(buffer->length, buffer->bytes);
+
+	// checking that content has been properly copied.
+	assert(buffer->bytes[0] == copied_buffer->bytes[0]);
+	assert(buffer->bytes[5] == copied_buffer->bytes[5]);
+	assert(buffer->bytes[10] == copied_buffer->bytes[10]);
+	assert(buffer->bytes[15] == copied_buffer->bytes[15]);
+	assert(buffer->bytes[19] == copied_buffer->bytes[19]);
+
+	assert(copied_buffer->bytes[0] == 12);
+	assert(copied_buffer->bytes[5] == 3);
+	assert(copied_buffer->bytes[10] == 44);
+	assert(copied_buffer->bytes[15] == 54);
+	assert(copied_buffer->bytes[19] == 8);
+
+	// try to create a default buffer.
+	ksrbuffer *default_buffer = ksrbuffer_new_default();
+	assert(default_buffer->length == BUFSIZ);
+
+	// free buffers.
+	ksrbuffer_free(empty_buffer);
+	ksrbuffer_free(buffer);
+	ksrbuffer_free(copied_buffer);
+	ksrbuffer_free(default_buffer);
+
+	return 0;
+}
diff --git a/tests/ksregex.c b/tests/ksregex.c
new file mode 100644
index 0000000..cf1f4f8
--- /dev/null
+++ b/tests/ksregex.c
@@ -0,0 +1,45 @@
+#include <assert.h>
+#include <ksr/regex.h>
+#include <ksr/string.h>
+
+int main(/*int argc, char *argv[]*/)
+{
+	// try a simple regex and check that it matches properly.
+	ksregex *reg1 = ksregex_new_nogroup("^[0-9]+$", 0);
+	assert(ksregex_matches(reg1, "12") == true);
+	assert(reg1->matches == NULL);
+
+	// try a more complex regex with matches groups.
+	ksregex *reg2 = ksregex_new("^([0-9])([a-z])$", 3, REG_ICASE);
+	assert(ksregex_matches(reg2, "1a"));
+	assert(!ksregex_matches(reg2, "H8"));
+	assert(!ksregex_matches(reg2, "4MM"));
+	assert(!ksregex_matches(reg2, "4_"));
+	assert(ksregex_matches(reg2, "3F"));
+
+	// check that groups have been extracted properly.
+	assert(str_equals("3F", reg2->matches[0]));
+	assert(str_equals("3", reg2->matches[1]));
+	assert(str_equals("F", reg2->matches[2]));
+
+	// check that groups are properly extracted even in more complex cases.
+	ksregex *reg3 = ksregex_new("^([0-9]+)([a-z]?)$", 3, 0);
+	assert(ksregex_matches(reg3, "123545"));
+	assert(str_equals("123545", reg3->matches[0]));
+	assert(str_equals("123545", reg3->matches[1]));
+	assert(str_equals("", reg3->matches[2]));
+
+	// check that matches are empty when matching fail.
+	assert(!ksregex_matches(reg3, "123bA"));
+	assert(reg3->matches == NULL);
+
+	// try to create an invalid regex.
+	assert(ksregex_new_nogroup("^(123$", 0) == NULL);
+
+	// try to free instantiated regex.
+	ksregex_free(reg1);
+	ksregex_free(reg2);
+	ksregex_free(reg3);
+
+	return 0;
+}
diff --git a/tests/ksrfiles.c b/tests/ksrfiles.c
new file mode 100644
index 0000000..4751302
--- /dev/null
+++ b/tests/ksrfiles.c
@@ -0,0 +1,33 @@
+#include <ksr/files.h>
+#include <assert.h>
+
+int main(/*int argc, char *argv[]*/)
+{
+	// delete test directory if it exists.
+	system("rm -Rf ksrtesttesttmp");
+
+	// create a new buffer and write it in a file.
+	ksrbuffer *buffer = ksrbuffer_new_from_content(12, "Hello World!");
+	write_file("ksrtesttesttmp/tmp/test.tmp", buffer);
+
+	// try to read the previously written file, and checking that the buffer has been read properly.
+	ksrbuffer *read_buffer = read_file_from_path("test.tmp");
+	assert(read_buffer->length == 13);
+	assert(read_buffer->bytes[0] == 'H');
+	assert(read_buffer->bytes[3] == 'l');
+	assert(read_buffer->bytes[7] == 'o');
+	assert(read_buffer->bytes[11] == '!');
+	assert(read_buffer->bytes[12] == 0);
+
+	// delete test directory.
+	system("rm -Rf ksrtesttesttmp");
+
+	// try to write a file where it is not writable.
+	assert(write_file("/dev/test/test.tmp", buffer) == false);
+	// try to read a non-existing file.
+	assert(read_file_from_path("/dev/test.tmp") == NULL);
+	// try to read a NULL file.
+	assert(read_file(NULL) == NULL);
+
+	return 0;
+}
diff --git a/tests/ksrpromises.c b/tests/ksrpromises.c
new file mode 100644
index 0000000..fc69eb1
--- /dev/null
+++ b/tests/ksrpromises.c
@@ -0,0 +1,69 @@
+#include <assert.h>
+#include <ksr/promises.h>
+#include <ksr/string.h>
+#include <unistd.h>
+#include <signal.h>
+
+void promise_execution_ok(ksrpromise *promise, void *data)
+{
+	// checking that user data has been properly transfered.
+	assert(data == NULL);
+
+	sleep(1);
+	// try to resolve the promise.
+	ksrpromise_resolve(promise, "OK");
+}
+
+void promise_execution_sigint(/*ksrpromise *promise, void *data*/)
+{
+	// raise a signal to interrupt await.
+	raise(SIGINT);
+}
+
+void promise_execution_error(ksrpromise *promise, void *data)
+{
+	// try to read the error details from user data ; the content will be checked in the catch callback.
+	const char* error = data;
+	sleep(1);
+	// try to reject the promise with an error.
+	ksrpromise_reject(promise, 124, error);
+}
+
+void on_promise_ok(void *result, void *userdata)
+{
+	// checking that result and user data have been properly transfered.
+	assert(str_equals("OK", result));
+	assert(userdata == NULL);
+}
+
+void on_promise_failed(int error_code, const char *error_message, void *userdata)
+{
+	// checking that error details and user data have been properly transfered.
+	assert(error_code == 124);
+	assert(str_equals("hello", error_message));
+	assert(str_equals("blabla", userdata));
+}
+
+int main(/*int argc, char *argv[]*/)
+{
+	// try to create a promise.
+	ksrpromise *promise = ksrpromise_new(promise_execution_ok, NULL);
+	// checking that then is properly launched.
+	ksrpromise_then(promise, on_promise_ok, NULL);
+	// checking that await is working properly on a successful promise.
+	assert(str_equals("OK", ksrpromise_await(promise)));
+
+	// try to create a promise which fails.
+	ksrpromise *promise_fail = ksrpromise_new(promise_execution_error, "hello");
+	// checking that catch is properly launched.
+	ksrpromise_catch(promise_fail, on_promise_failed, "blabla");
+	// checking that await is working properly on a promise which fails.
+	assert(ksrpromise_await(promise_fail) == NULL);
+
+	// try to create a promise that will be interrupted.
+	ksrpromise *interrupted_promise = ksrpromise_new(promise_execution_sigint, NULL);
+	// checking that interruption is handled properly in an await.
+	assert(NULL == ksrpromise_await(interrupted_promise));
+
+	return 0;
+}
diff --git a/tests/ksrstring.c b/tests/ksrstring.c
new file mode 100644
index 0000000..3f42c8d
--- /dev/null
+++ b/tests/ksrstring.c
@@ -0,0 +1,15 @@
+#include "ksr/string.h"
+#include <assert.h>
+#include <ksr/buffers.h>
+
+int main(/*int argc, char *argv[]*/)
+{
+	assert(str_equals("hello", to_lowercase("heLLo")));
+	assert(str_equals("hello", to_lowercase("HELLO")));
+	assert(str_equals("hello", to_lowercase("Hello")));
+	assert(str_equals("hello", to_lowercase("hellO")));
+
+	assert(!str_equals("heLLo", to_lowercase("heLLo")));
+
+	return 0;
+}