minimal json parser for generated data

Makefile

@@ -1,12 +1,17 @@
-CFLAGS=-g -Wall
+CFLAGS=-lm -g -Wall -Walloc-size-larger-than=-1
 
-.PHONY := gen_data
+.PHONY := gen_data main
 
-gen_data: build/gen_data.exe
+gen_data: build/gen_data
+main: build/main
 
-build/gen_data.exe: src/gen_data.c
+build/gen_data: src/gen_data.c
 	mkdir -p build
-	gcc -o build/gen_data.exe src/gen_data.c $(CFLAGS) -O2
+	gcc -o build/gen_data src/gen_data.c $(CFLAGS) -O2
+
+build/main: src/main.c src/json_parser.c
+	mkdir -p build
+	gcc -o build/main src/main.c $(CFLAGS) -O2
 
 clean:
 	rm -r build

src/json_parser.c

@@ -0,0 +1,393 @@
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <assert.h>
+#include <stdlib.h>
+
+#include "json_parser.h"
+
+#define ARRAY_LEN(x) (sizeof(x)/sizeof(x[0]))
+
+typedef uint8_t u8;
+
+void free_json_object(struct json_object *object)
+{
+	if (object == NULL) return;
+
+	for (int i = 0; i < object->count; i++) {
+		free_json_string(object->keys[i]);
+		free_json_value(object->values[i]);
+	}
+	free(object->keys);
+	free(object->values);
+	free(object);
+}
+
+void free_json_value(struct json_value *value)
+{
+	if (value == NULL) return;
+
+	if (value->type == JSON_TYPE_OBJECT) {
+		free_json_object(value->object);
+	} else if (value->type == JSON_TYPE_ARRAY) {
+		free_json_array(value->array);
+	} else if (value->type == JSON_TYPE_STRING) {
+		free_json_string(value->string);
+	}
+	free(value);
+}
+
+void free_json_string(struct json_string *string)
+{
+	if (string == NULL) return;
+	free(string->str);
+	free(string);
+}
+
+void free_json_array(struct json_array *array)
+{
+	if (array == NULL) return;
+	for (int i = 0; i < array->count; i++) {
+		free_json_value(array->values[i]);
+	}
+	free(array->values);
+	free(array);
+}
+
+static size_t inc_cursor(char **data, size_t *data_size, size_t amount)
+{
+	size_t bytes_parsed = 0;
+	if (amount > *data_size) {
+		bytes_parsed = *data_size;
+		(*data) += *data_size;
+		(*data_size) = 0;
+	} else {
+		bytes_parsed = amount;
+		(*data) += amount;
+		(*data_size) -= amount;
+	}
+	return bytes_parsed;
+}
+
+static bool is_whitespace(char c)
+{
+	return c == ' ' || c == '\t' || c == '\n' || c == '\r' || c == '\0';
+}
+
+static size_t skip_ws(char **data, size_t *data_size)
+{
+	size_t ws_count = 0;
+	while (data_size > 0) {
+		if (!is_whitespace(**data)) break;
+		inc_cursor(data, data_size, 1);
+		ws_count++;
+	}
+	return ws_count;
+}
+
+static size_t get_json_string_size(char *data, size_t data_size)
+{
+	if (data_size == 0) return -1;
+
+	assert(data[0] == '"');
+	for (int i = 1; i < data_size; i++) {
+		bool is_escaped = false;
+		if (i > 2) {
+			is_escaped = data[i-1] == '\\' && data[i-2] != '\\';
+		} else {
+			is_escaped = data[i-1] == '\\';
+		}
+
+		if (data[i] == '"' && !is_escaped) return i+1;
+	}
+	return -1;
+}
+
+static u8 decode_hex(char hex)
+{
+	if ('a' <= hex && hex <= 'f') {
+		return hex - 'a' + 10;
+	} else if ('A' <= hex && hex <= 'F') {
+		return hex - 'A' + 10;
+	} else if ('0' <= hex && hex <= '9') {
+		return hex - '0';
+	} else {
+		abort();
+	}
+}
+
+static char read_hex_symbol(char *data)
+{
+	u8 byte1 = decode_hex(data[0]);
+	u8 byte2 = decode_hex(data[1]);
+	u8 byte3 = decode_hex(data[2]);
+	u8 byte4 = decode_hex(data[3]);
+	return (byte1 << 24) | (byte2 << 16) | (byte3 << 8) | (byte4 << 0);
+}
+
+static bool expect_char(char *data, size_t data_size, char expected)
+{
+	if (data_size == 0) return false;
+	return data[0] == expected;
+}
+
+static bool is_number_char(char c)
+{
+	char number_chars[] = "0123456789.-";
+	for (size_t i = 0; i < ARRAY_LEN(number_chars)-1; i++) {
+		if (number_chars[i] == c) return true;
+	}
+	return false;
+}
+
+static bool expect_number_char(char *data, size_t data_size)
+{
+	if (data_size == 0) return false;
+	return is_number_char(data[0]);
+}
+
+int parse_json_value(struct json_value *result, char *data, size_t data_size)
+{
+	size_t bytes_parsed = 0;
+	bytes_parsed += skip_ws(&data, &data_size);
+
+	if (expect_char(data, data_size, '{')) {
+		result->type = JSON_TYPE_OBJECT;
+		result->object = malloc(sizeof(struct json_object));
+		int object_size = parse_json_object(result->object, data, data_size);
+		assert(object_size >= 0);
+		bytes_parsed += object_size;
+	} else if (expect_char(data, data_size, '[')) {
+		result->type = JSON_TYPE_ARRAY;
+		result->object = malloc(sizeof(struct json_array));
+		int array_size = parse_json_array(result->array, data, data_size);
+		assert(array_size >= 0);
+		bytes_parsed += array_size;
+	} else if (expect_number_char(data, data_size)) {
+		result->type = JSON_TYPE_NUMBER;
+		int number_size = parse_json_number(&result->number, data, data_size);
+		assert(number_size >= 0);
+		bytes_parsed += number_size;
+	} else {
+		// TODO: number, null, boolean, string
+		assert(false && "todo");
+	}
+
+	return bytes_parsed;
+}
+
+int parse_json_object(struct json_object *result, char *data, size_t data_size)
+{
+	assert(expect_char(data, data_size, '{'));
+	size_t bytes_parsed = 0;
+	bytes_parsed += inc_cursor(&data, &data_size, 1);
+	bytes_parsed += skip_ws(&data, &data_size);
+
+	result->count = 0;
+	result->keys = NULL;
+	result->values = NULL;
+
+	if (expect_char(data, data_size, '}')) { // Empty object
+		return bytes_parsed + 1;
+	}
+
+	while (data_size > 0) {
+		int idx = result->count;
+		result->count++;
+		result->keys   = realloc(result->keys, result->count*sizeof(struct json_string*));
+		result->values = realloc(result->values, result->count*sizeof(struct json_value*));
+		result->keys[idx] = malloc(sizeof(struct json_string));
+		result->values[idx] = malloc(sizeof(struct json_value));
+
+		int key_size = parse_json_string(result->keys[idx], data, data_size);
+		assert(key_size >= 0);
+
+		bytes_parsed += inc_cursor(&data, &data_size, key_size);
+		bytes_parsed += skip_ws(&data, &data_size);
+		assert(expect_char(data, data_size, ':'));
+		bytes_parsed += inc_cursor(&data, &data_size, 1);
+		bytes_parsed += skip_ws(&data, &data_size);
+
+		int value_size = parse_json_value(result->values[idx], data, data_size);
+		assert(value_size >= 0);
+
+		bytes_parsed += inc_cursor(&data, &data_size, value_size);
+		bytes_parsed += skip_ws(&data, &data_size);
+
+		if (!expect_char(data, data_size, ',')) {
+			break;
+		}
+
+		bytes_parsed += inc_cursor(&data, &data_size, 1);
+		bytes_parsed += skip_ws(&data, &data_size);
+	}
+
+	assert(expect_char(data, data_size, '}'));
+
+	return bytes_parsed+1;
+}
+
+int parse_json_array(struct json_array *result, char *data, size_t data_size)
+{
+	assert(expect_char(data, data_size, '['));
+	size_t bytes_parsed = 0;
+	bytes_parsed += inc_cursor(&data, &data_size, 1);
+	bytes_parsed += skip_ws(&data, &data_size);
+
+	result->count = 0;
+	result->values = NULL;
+
+	if (expect_char(data, data_size, ']')) { // Empty object
+		return bytes_parsed + 1;
+	}
+
+	while (data_size > 0) {
+		int idx = result->count;
+		result->count++;
+		result->values = realloc(result->values, result->count*sizeof(struct json_value*));
+		result->values[idx] = malloc(sizeof(struct json_value));
+
+		int value_size = parse_json_value(result->values[idx], data, data_size);
+		assert(value_size >= 0);
+
+		bytes_parsed += inc_cursor(&data, &data_size, value_size);
+		bytes_parsed += skip_ws(&data, &data_size);
+
+		if (!expect_char(data, data_size, ',')) {
+			break;
+		}
+
+		bytes_parsed += inc_cursor(&data, &data_size, 1);
+		bytes_parsed += skip_ws(&data, &data_size);
+	}
+
+	assert(expect_char(data, data_size, ']'));
+
+	return bytes_parsed+1;
+}
+
+int parse_json_number(f64 *result, char *data, size_t data_size)
+{
+	int bytes_parsed = 0;
+	for (int i = 0; i < data_size; i++) {
+		if (!is_number_char(data[i])) break;
+		bytes_parsed++;
+	}
+
+	// TODO: `strtod` until first non number character
+	// Use alternative parsing, so `data_size` can be enforced
+	*result = strtod(data, NULL);
+
+	return bytes_parsed;
+}
+
+int parse_json_string(struct json_string *result, char *data, size_t data_size)
+{
+	assert(expect_char(data, data_size, '"'));
+
+	int json_string_size = get_json_string_size(data, data_size);
+
+	result->str = malloc((json_string_size-2)*sizeof(char));
+	result->size = 0;
+
+	for (size_t i = 1; i < data_size-1; i++) {
+		size_t str_idx = result->size;
+		if (data[i] == '"') {
+			break;
+		} else if (data[i] == '\\') {
+			if (data[i+1] == '\\') {
+				result->str[str_idx] = '\\';
+			} else if (data[i+1] == '"') {
+				result->str[str_idx] = '"';
+			} else if (data[i+1] == '/') {
+				result->str[str_idx] = '/';
+			} else if (data[i+1] == 'b') {
+				result->str[str_idx] = '\b';
+			} else if (data[i+1] == 'f') {
+				result->str[str_idx] = '\f';
+			} else if (data[i+1] == 'n') {
+				result->str[str_idx] = '\n';
+			} else if (data[i+1] == 'r') {
+				result->str[str_idx] = '\r';
+			} else if (data[i+1] == 't') {
+				result->str[str_idx] = '\t';
+			} else if (data[i+1] == 'u') {
+				result->str[str_idx] = read_hex_symbol(data + i + 2);
+				i+=4;
+			} else {
+				abort(); // Unknown escape sequence
+			}
+			i++;
+		} else {
+			result->str[str_idx] = data[i];
+		}
+		result->size++;
+	}
+
+	result->str = realloc(result->str, result->size*sizeof(char));
+
+	return json_string_size;
+}
+
+int parse_json_null(char *data, size_t data_size)
+{
+	return 0; // TODO:
+}
+
+int parse_json_bool(bool *result, char *data, size_t data_size)
+{
+	return 0; // TODO:
+}
+
+
+void printf_json_array(struct json_array *array)
+{
+	printf("[");
+	for (int i = 0; i < array->count; i++) {
+		printf_json_value(array->values[i]);
+		if (i < array->count-1) printf(",");
+	}
+	printf("]");
+}
+
+void printf_json_object(struct json_object *object)
+{
+	printf("{");
+	for (int i = 0; i < object->count; i++) {
+		printf_json_string(object->keys[i]);
+		printf(":");
+		printf_json_value(object->values[i]);
+		if (i < object->count-1) printf(",");
+	}
+	printf("}");
+}
+
+void printf_json_string(struct json_string *string)
+{
+	// TODO: Support to display escaped sequences
+	printf("\"%.*s\"", (int)string->size, string->str);
+}
+
+void printf_json_value(struct json_value *value)
+{
+	switch(value->type) {
+	case JSON_TYPE_NULL:
+		printf("null");
+		break;
+	case JSON_TYPE_OBJECT:
+		printf_json_object(value->object);
+		break;
+	case JSON_TYPE_ARRAY:
+		printf_json_array(value->array);
+		break;
+	case JSON_TYPE_STRING:
+		printf_json_string(value->string);
+		break;
+	case JSON_TYPE_NUMBER:
+		printf("%.16f", value->number);
+		break;
+	case JSON_TYPE_BOOLEAN:
+		printf("%s", value->boolean ? "true" : "false");
+		break;
+	}
+}

src/json_parser.h

@@ -0,0 +1,58 @@
+#include <stdbool.h>
+#include <stddef.h>
+
+typedef double f64;
+
+enum json_type {
+	JSON_TYPE_NULL,
+	JSON_TYPE_OBJECT,
+	JSON_TYPE_ARRAY,
+	JSON_TYPE_STRING,
+	JSON_TYPE_NUMBER,
+	JSON_TYPE_BOOLEAN,
+};
+
+struct json_string {
+	char *str;
+	size_t size;
+};
+
+struct json_array {
+	struct json_value **values;
+	size_t count;
+};
+
+struct json_object {
+	struct json_string **keys;
+	struct json_value **values;
+	size_t count;
+};
+
+struct json_value {
+	enum json_type type;
+	union {
+		bool boolean;
+		f64 number;
+		struct json_string *string;
+		struct json_array *array;
+		struct json_object *object;
+	};
+};
+
+void free_json_value(struct json_value *value);
+void free_json_array(struct json_array *array);
+void free_json_string(struct json_string *string);
+void free_json_object(struct json_object *object);
+
+int parse_json_null(char *data, size_t data_size);
+int parse_json_bool(bool *result, char *data, size_t data_size);
+int parse_json_number(f64 *result, char *data, size_t data_size);
+int parse_json_value(struct json_value *result, char *data, size_t data_size);
+int parse_json_object(struct json_object *result, char *data, size_t data_size);
+int parse_json_array(struct json_array *result, char *data, size_t data_size);
+int parse_json_string(struct json_string *result, char *data, size_t data_size);
+
+void printf_json_value(struct json_value *result);
+void printf_json_string(struct json_string *string);
+void printf_json_object(struct json_object *object);
+void printf_json_array(struct json_array *array);

src/main.c

@@ -0,0 +1,53 @@
+#include <stdio.h>
+#include <inttypes.h>
+#include <inttypes.h>
+
+#include "json_parser.c"
+
+void print_usage(char *program)
+{
+	printf("Usage: %s <json-file> [test-bin-file]\n", program);
+}
+
+size_t get_file_size(FILE *f)
+{
+	fseek(f, 0, SEEK_END);
+	size_t size = ftell(f);
+	fseek(f, 0, SEEK_SET);
+	return size;
+}
+
+int main(int argc, char **argv)
+{
+	if (argc < 2) {
+		print_usage(argv[0]);
+		return -1;
+	}
+
+	char *json_filename = argv[1];
+
+	FILE *f = fopen(json_filename, "r");
+	if (f == NULL) {
+		printf("Failed to open: %s\n", json_filename);
+		return -1;
+	}
+
+	size_t json_size = get_file_size(f);
+	char json_data[json_size];
+	size_t bytes_read = fread(json_data, 1, json_size, f);
+	if (bytes_read != json_size) {
+		printf("Failed to read all contents of file\n");
+		return -1;
+	}
+	fclose(f);
+
+	struct json_value *parsed = malloc(sizeof(struct json_value));
+	int bytes_parsed = parse_json_value(parsed, json_data, json_size);
+
+	printf_json_value(parsed);
+	printf("\n");
+
+	free_json_value(parsed);
+
+	return 0;
+}