Due 3/25

JSON 2: parse strings

Learning goals

You will learn or practice how to:

Parse strings
Apply test-driven development (TDD).
Use union and enum types.
Write programs that use dynamic memory (malloc(…))
Debug code that uses dynamic memory (malloc(…))
Practice writing programs with linked lists.
Write programs using more complex data structures (beyond the cannonical linked list and BST).

Overview

This is part 2 of a 3-part sequence in which you will create a decoder for the JSON data format.

JSON is a file format for exchanging hierarchical data between programs, often written in different programming languages and/or on different computers. In web programming, this allows a server application written in any language (e.g., Python or even C) to pass complex structures of information to the user's browser, which then renders it.

A JSON string may represent a number, a string, or a list. In this context, when we say “list”, we mean a linked list. (Linked lists are a data structure which we will cover in class soon.) Here are some examples:

type	json	data
number	10	10
string	"ten"	"ten"
list	[2, 6, 4]

Linked lists

As in C, whitespace is ignored (except within a string). Thus, the following are all equivalent.

type	json	data
list	[2, 6, 4]
list	[2, 6, "four"]
list	[2, [3, "+", 3], "four"]

Getting Started on HW11

Use 264get HW11 to fetch the starter code.
you@ecegrid-thin1 ~/ $cd 264

you@ecegrid-thin1 ~/264/ $264get hw11
Copy your miniunit.h, clog.h, and Makefile from HW09.
you@ecegrid-thin1 ~/264/ $mv hw09/miniunit.h hw09/clog.h -v -t hw11/

you@ecegrid-thin1 ~/264/ $cd hw11

you@ecegrid-thin1 ~/264/hw11 $
Implement parse_int(…).
1. Create a trivial test (e.g., 0).
2. Implement just enough of parse_int(…) so that it passes your trivial test. At this point, it should fail most other tests.
3. Submit.
4. Add another simple trivial test (e.g., 9).
5. Implement just enough to pass your two tests so far.
6. Submit.
7. Add another test (e.g., 15).
8. Implement just enough to pass your three tests so far.
9. Submit.
10. Add another test (e.g., -15).
11. … and so on, until parse_int(…) is finished.
Test your parse_int(…) completely, using miniunit.h. Get parse_int(…) completely finished and tested to perfection—including error handling—before you do anything else. Seriously… do not do anything else until this is done.
Submit.

Implement parse_element(…) just enough to support integers.

Add a test for a plain integer. Be sure to call it from main(…).

static int _test_parse_element_int_plain() {
  mu_start();
  //────────────────────
  Element element; // will be initialized by parse_element(…)
  char const* input = "1";
  char const* pos = input;
  bool is_success = parse_element(&element, &pos);
  mu_check(is_success);
  mu_check(element.as_int == 1);
  mu_check(element.type == ELEMENT_INT);
  mu_check(pos == input + 1);  // pos should now refer to the byte just after the '1' at input.
  mu_check(*pos == '\0');      // That byte should be the null terminator.
  //────────────────────
  mu_end();
}

Add just enough code to parse_element(…) to make this test pass. Expect to add about 2−4 lines of code inside parse_element(…).
Test.
Submit.

Extend the test function above to test for negative numbers.

// negative number
input = "-2";
pos = input;
is_success = parse_element(&element, &pos);
mu_check(is_success);
mu_check(element.as_int == -2);
mu_check(element.type == ELEMENT_INT);
mu_check(pos == input + 2);  // pos should now refer to the byte just after the '2'.
mu_check(*pos == '\0');      // That byte should be the null terminator.

Test.
Submit.

Add a test for a integer with leading whitespace. Be sure to call it from main(…).

static int _test_parse_element_with_leading_whitespace() {
  mu_start();
  //────────────────────
  Element element; // will be initialized by parse_element(…)
  char const* input = "  1";
  char const* pos = input;
  bool is_success = parse_element(&element, &pos);
  mu_check(is_success);
  mu_check(element.as_int == 1);
  mu_check(element.type == ELEMENT_INT);
  mu_check(pos == input + 3);  // pos should now refer to the byte just after the '1' at input.
  mu_check(*pos == '\0');      // That byte should be the null terminator.
  //────────────────────
  mu_end();
}

Add just enough code to parse_element(…) to make this test pass. Expect to add about 1−3 lines of code inside parse_element(…).
Test.
Submit.

Add a test function for some more cases involving integers. Here is a start. This is not adequate. You need to extend this with your own test cases.

static int _test_parse_element_int_oddballs() {
  mu_start();
  //────────────────────
  Element element; // will be initialized by parse_element(…)
  char const* input = " 4 A";
  char const* pos = input;
  bool is_success = parse_element(&element, &pos);
  mu_check(is_success);
  mu_check(element.as_int == 4);
  mu_check(element.type == ELEMENT_INT);
  mu_check(pos == input + 2);  // pos should now refer to the byte just after the '1' at input.
  mu_check(*pos == ' ');    // That byte contains a space.

  // TODO: Add more tests here based on your ideas for tests.

  //────────────────────
  mu_end();
}

You may or may not not need to add any code to make these tests pass.
Test.
Submit.

Add a test function for strings that contain integers but are not valid JSON because they are preceded by junk characters (not whitespace).

static int _test_parse_element_invalid() {
  mu_start();
  //────────────────────
  Element element; // will be initialized by parse_element(…)
  char const* input = "--4";
  char const* pos = input;
  bool is_success = parse_element(&element, &pos);
  mu_check(! is_success);
  mu_check(pos == input + 1);  // pos should now refer to second '-' since that is the
                               // character where we learn that this is not a valid JSON
                               // expression for an int.
  mu_check(*pos == '-'); // That byte contains a '-'.

  // TODO: Add more tests here based on your ideas for tests.

  //────────────────────
  mu_end();
}

You may or may not not need to add any code to make these tests pass.
Test.
Submit.

Implement parse_string(…).

Create a test function for a valid JSON expression representing an empty string.

static int _test_parse_string_valid_empty() {
  mu_start();
  //──────────────────────────────────────────────────────
  char* result;
  char const* input = "\"\"";
  char const* pos = input;
  bool is_success = parse_string(&result, &pos);
  mu_check(is_success);   // because the input is valid
  mu_check_strings_equal("", result);
  mu_check(pos == input + 2);
  mu_check(*pos == '\0');
  free(result);
  //──────────────────────────────────────────────────────
  mu_end();
}

Implement just enough of parse_string(…) to make this test pass.
Test.
Submit.

Create a test function for a valid JSON expression representing a string of size one.

static int _test_parse_string_valid_one_char() {
  mu_start();
  //──────────────────────────────────────────────────────
  char* result;
  char const* input = "\"A\"";
  char const* pos = input;
  bool is_success = parse_string(&result, &pos);
  mu_check(is_success);   // because the input is valid
  mu_check_strings_equal("A", result);
  mu_check(pos == input + 3);
  mu_check(*pos == '\0');
  free(result);
  //──────────────────────────────────────────────────────
  mu_end();
}

Implement just enough of parse_string(…) to make this test pass.
Test.
Submit.

Create a test function for a valid JSON expression representing a string containing multiple characters.

static int _test_parse_string_valid_multiple_chars() {
  mu_start();
  //──────────────────────────────────────────────────────
  char* result;
  char const* input = "\"ABC\"";
  char const* pos = input;
  bool is_success = parse_string(&result, &pos);
  mu_check(is_success);   // because the input is valid
  mu_check_strings_equal("ABC", result);
  mu_check(pos == input + 5);
  mu_check(*pos == '\0');
  free(result);
  //──────────────────────────────────────────────────────
  mu_end();
}

Implement just enough of parse_string(…) to make this test pass.
Test.
Submit.

Add test function(s) to check strings that contain double quotation marks but are not valid JSON. Here is a start. You will need to add more of your own.

static int _test_parse_string_invalid() {
  mu_start();
  //──────────────────────────────────────────────────────
  char* result;
  char const* input = "\"A";
  char const* pos = input;
  bool is_success = parse_string(&result, &pos);
  mu_check(! is_success);   // because the input is valid
  mu_check(pos == input + 2);
  mu_check(*pos == '\0');
  // We do not call free(…) if the string was invalid.

  input = "\"A\nB\"";
  pos = input;
  is_success = parse_string(&result, &pos);
  mu_check(! is_success);   // because the input is valid
  mu_check(pos == input + 2);
  mu_check(*pos == '\n');

  // TODO: Add more tests of your own.

  //──────────────────────────────────────────────────────
  mu_end();
}

Extend parse_element(…) to support strings. You will need to implement free_element(…) in the same step.

Add a test for a plain string containing multiple characters. Be sure to call it from main(…).

static int _test_parse_element_string() {
  mu_start();
  //────────────────────
  Element element; // will be initialized by parse_element(…)
  char const* input = "\"ABC\"";
  char const* pos = input;
  bool is_success = parse_element(&element, &pos);
  mu_check(is_success);
  mu_check_strings_equal("ABC", element.as_string);
  mu_check(element.type == ELEMENT_STRING);
  mu_check(pos == input + 5);  // pos should now refer to the byte just after the second double quote.
  mu_check(*pos == '\0');      // That byte should be the null terminator.
  free_element(element);
  //────────────────────
  mu_end();
}

Add just enough code to parse_element(…) to make this test pass. Expect to add about 4 lines of code inside parse_element(…) and 1−3 lines inside free_element(…).
Test.
Submit.
Add additional tests as needed to ensure that parse_element(…) works for JSON expressions representing strings and integers.
Test.
Submit.

Implement print_element(…) so that it supports integers and strings.

Add a test for Element objects that contain an integer. This will not use Miniunit. Since this is simple, you an use visual inspection (just look).

static void _test_print_element() {
  Element element; // will be initialized by parse_element(…)
  char const* input = "123";
  bool is_success = parse_element(&element, &input);
  printf("Testing parse_element(&element, \"123\")\n");
  printf(" - Expected: 123\n");
  printf(" - Actual:   ");
  print_element(element);
  fputc('\n', stdout);
  free_element(element);
}

Add just enough code to print_element(…) to make this test pass. Expect to add about 1―3 lines of code inside print_element(…).
Test.
Submit.

Add a test for Element objects that contain an string. Again, this will not use Miniunit.

static int _test_print_element() {
  mu_start();
  //──────────────────────────────────────────────────────
  // This uses diff testing to check print_element(…).
  Element element; // will be initialized by parse_element(…)
  char const* input = "\"ABC\"";
  bool is_success = parse_element(&element, &input);
  printf("Testing parse_element(&element, \"\\\"ABC\\\"\")\n");
  printf(" - Expected: \"ABC\"\n");
  printf(" - Actual:   ");
  print_element(element);
  fputc('\n', stdout);
  free_element(element);
  //──────────────────────────────────────────────────────
  mu_end();
}

Add just enough code to print_element(…) to make this test pass. Expect to add about 3―5 lines of code inside print_element(…).
Test.
Submit.

Implement parse_list(…).
1. Create a trivial test (e.g., []).
2. Implement just enough of parse_list(…) so that it passes your trivial test (functionality only). It should fail all other tests with linked lists.
3. Extend free_element(…) so that your parse_list(…) tests work without any memory leaks (e.g., passes Valgrind).
4. Add another simple test (e.g., [0]).
5. Implement just enough to pass your two list tests so far.
6. Add another simple test (e.g., ["a"]).
7. Implement just enough to pass your three list tests so far.
8. Add a test with multiple integers as list items (e.g., [1, 2]).
9. Implement just enough to pass your tests so far.
10. Add a test with multiple strings as list items (e.g., ["A", "B"]).
11. You shouldn't need to add any code for this, but make sure it works 100% before you proceed.
12. Add a test with an empty list as a list item (e.g., [[]]).
13. Implement just enough to pass your tests so far.
14. Add a test with a non-empty list as a list item (e.g., [[1]]).
15. Implement just enough to pass your tests so far.
16. Add a few more tests with gradually increasing complexity (e.g., [[1, 2]], [1, [2, 3], 4], [[1, 2], [3, 4], []]).
17. Test as needed. Get things perfect—including memory (Valgrind) and test coverage (gcov)—and submit at every stage.
Test error cases. Make sure parse_int(…), parse_string(…), and parse_element(…) return false for incorrect input.
Test that there are no memory leaks, even for incorrect input.

How much work is this?

You must be disciplined in your development appraoch. If you try to build this all at once, success is extremely unlikely.

HW10: Instructor's solution for parse_int(…) only is 18 sloc (14 sloc in the body of parse_int(…)).

HW11: Instructor's solution for parse_int(…), parse_string(…), and parse_element(…) only is 75 sloc.

HW13: Instructor's solution for parse_int(…), parse_string(…), parse_list(…), and parse_element(…) is 127 sloc.

SLOC means “source lines of code” and does not lines that are blank or contain only comments. The figures above do not count test_json.c. Also, those figures are based on a tight—but defensible—solution that meets code quality standards and uses no methods or language features we have not yet covered.

Bonus opportunities

2 bonus point for handling the following escape sequences: \", \\, \/, \b, \f, \n, \r, \t, \u00▒▒. Interpret these the same as in C. (You may need to search for more information.) These correspond to the nine escape sequences listsed at json.org. For \u00▒▒, you only need to handle \u0020 to \u007e. You can ignore any unicode-specific details, and just treat these as ASCII values (e.g., \u0041 for 'A', etc.). Add #define BONUS_JSON_ESCAPE_SEQUENCES to your json.h if you believe you have finished this.

2 bonus point for handling the constants null, true, and false. Add ELEMENT_NULL and ELEMENT_BOOL to the enum in json.h, and add void* as_null and bool as_bool to the union. Add #define BONUS_JSON_CONSTANTS to your json.h if you believe you have finished this.

4 points – Support JSON “objects” with BSTs. For the BST node, you will have typedef struct _BSTNode { struct _BSTNode* left; struct _BSTNode* right; Element element; char* key; } BSTNode;. For the parse function: bool parse_object(BSTNode** a_root, char const** a_pos) { … }. This note may be amended and/or replaced later, but the above details should be sufficient. Refer to the JSON standard

Bonus options must be submitted with ~~HW12~~ HW13. There will be no partial credit for the bonus options. You may be required to come and explain in person. We'll let you know if that is necessary.

Requirements

Your submission must contain each of the following files, as specified:

file	contents
json.c	functions	`parse int(int✶ a value, char const✶✶ a pos)` → return type: bool Set `a_value` to whatever integer value is found at `a_pos`. `a_pos` is initially the address of the first character of the integer literal in the input string. `a_value` is the (already allocated) location where the parsed int should be stored. Return `true` if a properly formed integer literal was found at `a_pos`. `a_pos` should refer to the next character in the input string, i.e., after the last digit of the integer literal. Ex: `parse_int(…)` should return `true` for `9`, `-99`, and `123AAA`. Return `false` if an integer literal was not found. `a_pos` should refer to the unexpected character that indicated a problem. Ex: `parse_int(…)` should return `false` for `A`, `AAA123`, `-A`, `-A9`, and `-`. ⚠ Calling `parse_int(…)` should not result in any calls to `malloc(…)`. You do not need to parse hexadecimal, octal, scientific notation, floating point values, or anything other than integers in decimal notation (positive or negative). Whenever `parse_int(…)` returns `false`, `a_value` should not be modified.
		`parse string(char✶✶ a string, char const✶✶ a pos)` → return type: bool Set `a_string` to a copy of the string literal at `a_pos`. Caller is responsible for freeing the memory. A string literal must be surrounded by double quotation marks, and may not contain a newline. In addition, we make two simplifications: Strings may not contain double quotation marks. Backslash is not special. Do not parse escape codes (i.e., `"\▒"`) in the input. Calling `parse_string(…)` should result in exactly one call to `malloc(…)`. Return `true` if a properly formed string literal was found. `a_pos` should be set to the next character in the input string, i.e., after* the ending double quotation mark. Ex: `parse_string(…)` should return `true` for `"abc"`, `"abc\"`, and `"abc\z"`. Return `false` if a string literal was not found. `a_pos` should refer to the unexpected character that indicated a problem (e.g., newline or null terminator in the input). Ex: `parse_string(…)` should return `false` for `"abc` and `"abc def"`. Whenever `parse_string(…)` returns `false`, do not modify `a_string`, and no heap memory should be allocated.
		`parse list(Node✶✶ a head, char const✶✶ a pos)` → return type: bool Set `a_head` to the head of a linked list of `Element` objects. Caller is responsible for freeing the memory if `parse_list(…)` returns `true`. Linked list consists of a `'['`, followed by 0 or more JSON-encoded elements (integers, strings, or lists) separated by commas, and finally a `']'`. See the examples above. (There will be no HBB on this definition, unless there is something truly wrong and/or grossly unclear.) There may be any number/amount of whitespace characters (`' '`, `'\n'`, or `'\t'`), before/after any of the elements. Return `true` if a properly formed list was found. `a_pos` should be set to the next character in the input string, after the list that was just parsed. Ex: `parse_list(…)` should return `true` for `[]`, `[1,2]`, `[1,"A"]`, `[1,[2]]`, and `[1]A`. Return `false` if a list was not found (i.e., syntax error in the input string). `*a_pos` should refer to the unexpected character that indicated a problem. Ex: `parse_list(…)` should return `false` for `A[]`, `[1,,2]`, `[[`, `1,2`, and `,2]`.
		`parse element(Element✶ a element, char const✶✶ a pos)` → return type: bool First, eat any whitespace at `a_pos`. “Eat whitespace” just means to skip over any whitespace characters (i.e., increment `a_pos` until `isspace(a_pos)==false`). Next, decide what kind of element this is. If it's a digit (`isdigit(a_pos)`) or hyphen (`'-'`), set the element's `type` to `ELEMENT_INT` and call `parse int(&(a element -> as int), a pos)`. If it's a string (`a_pos=='"'`), then set the element's `type` to `ELEMENT_STRING` and call `parse string(&(a element -> as string), a pos)`. If it's a list (`a_pos == '['`), then set the element's `type` to `ELEMENT_LIST` and call: `parse list(&(a element -> as list), a pos)`. Return whatever was returned by `parse_int(…)` `parse_string(…)` or `parse_list(…)`. If none of those functions was called—i.e., if the next character was neither digit, `'-'`, `'"'`, nor `'['`—then return `false`. Do not modify `a_pos` directly in `parse_element(…)`, except for eating whitespace. `a_pos` can—and should—be modified in `parse_int(…)` and `parse_string(…)` and and `parse_list(…)` Caller is responsible for freeing memory by calling `free_element(…)` whenever `parse_element(…)` returns `true`. Whenever `parse_element(…)` returns `false`, do not modify `*element` , and free any heap memory that was allocated prior to discovery of the error.
		`print element(Element element)` → return type: void Given an `Element` object, print it in JSON notation. Spacing is up to you, as long as it is valid JSON. If element is an integer, print it ~~(with double-quotes)~~ using `printf(…)`. If element is a string, then print it (with double-quotes) using `printf(…)`.
		`free element(Element element)` → return type: void Free the contents of the `Element`, as needed. If it contains a string, free the string. If it contains a linked list, free the list, including all elements. ⚠ Do not attempt to free the `Element` object itself. `free_element(element)` only frees dynamic memory that `element` refers to.
test_json.c	functions	`main(int argc, char✶ argv[])` → return type: int Test your all of the above functions using your `miniunit.h.`. This should consist primarily of calls to `mu_run(_test_▒▒▒)`. 100% code coverage is required. Your `main(…)` must return EXIT_SUCCESS.

You may ignore any trailing characters in the input string, as long as it starts with a well-formed JSON element.
- Acceptable: 123AAA, [1,2]AAA, [1,2][, "12"AAA, "12",[,
You only need to support the specific features of JSON that are explicitly required in this assignment description. You do not need to support unicode (e.g., "萬國碼", "يونيكود", "യൂണികോഡ്"), objects/dictionaries (e.g., {"a":1, "b":2}), backslash escapes (e.g., "\n"), embedded quotes (e.g., "He said, \"Roar!\""), floating point numbers (e.g., 3.1415), non-decimal notations (e.g., 0xdeadbeef, 0600), null, false)
Do not modify json.h except as explicitly directed.
There may be no memory faults (e.g., leaks, invalid read/write, etc.), even when parse_▒▒▒(…) return false.

The following external header files, functions, and symbols are allowed.

header	functions/symbols	allowed in…
stdbool.h	`bool`, `true`, `false`	`json.c`, `test_json.c`
stdio.h	`printf`, `fprintf`, `fputs`, `stdout`, `fflush`	`json.c`, `test_json.c`
assert.h	`assert`	`json.c`, `test_json.c`
ctype.h	`isdigit`, `isspace`	`json.c`, `test_json.c`
stdlib.h	`EXIT_SUCCESS`, `abs`, `malloc`, `free`, `size_t`	`json.c`, `test_json.c`
string.h	`strncpy`, `strchr`, `strlen`, `strcmp`	`json.c`, `test_json.c`
limits.h	`INT_MIN`, `INT_MAX`	`json.c`, `test_json.c`
miniunit.h	`anything`	`test_json.c`
clog.h	`anything`	`json.c`, `test_json.c`

For miniunit.h and clog.h, you can use anything from HW05. You are welcome to change them to your liking, and/or add more in the same spirit. All others are prohibited unless approved by the instructor. Feel free to ask if there is something you would like to use.

Submissions must meet the code quality standards and the course policies on homework and academic integrity.

Submit

To submit HW11 from within your hw11 directory, type 264submit HW11 json.c json.h test_json.c miniunit.h clog.h Makefile

If your code does not depend on miniunit.h or clog.h, those may be omitted. Your json.h will most likely be identical to the starter. Makefile will not be checked, but including it may help in case we need to do any troubleshooting.

In general, to submit any assignment for this course, you will use the following command:

264submit ASSIGNMENT FILES…

Submit often and early, even well before you are finished. Doing so creates a backup that you can retrieve in case of a problem (e.g., accidentally deleted your files).

To retrieve your most recent submission, type 264get --restore ASSIGNMENT (e.g., 264get --restore hw11).

To retrieve an earlier submission, first type 264get --list ASSIGNMENT to view your past submissions and find the timestamp of the one you want to retrieve. Then, type 264get --restore -t TIMESTAMP ASSIGNMENT.

Scores will be posted to the Scores page after the deadline for each assignment.

Pre-tester ●

The pre-tester for HW11 has been released and is ready to use.

Using the pretester

The pretester is a tool for checking your work after you believe you are done, and before we have scored it. It is not a substitute for your own checking, but it may help you avoid big surprises by letting you know if your checking was not adequate. To use the pre-tester, first submit your code. Then, type the following command. (Do this only after you have submitted, and only after you believe your submission is perfect.)

264test hw11

Do not ask TAs or instructors which tests you failed.

Keep in mind:

Pre-testing is intended only for those who believe they are done and believe their submission is perfect.
The pre-tester is not part of the requirements of this or any other assignment.
You are responsible for reading the assignment carefully, and ensuring that your code meets all requirements.
Feedback is limited, to ensure that everyone learns to test their own code.
If your code is failing some tests, review your tests and make sure they are comprehensive enough to catch any bugs (deviations from requirements). Follow the tips given by the pre-tester.
Code quality issues are not reported by the pre-tester; writing clean code is something you must learn to do from the start, not a clean-up step to do at the end.

Logistics:

If we discover that we have not checked some significant part of the assignment requirements, we may add additional tests at any time up to the point when scores are released.
The pre-tester will only be enabled after much of the class has submitted the assignment, and at least a few people have submitted perfect submissions. This is to allow us to test the pre-tester.
The pre-tester checks your most recent submission. You must submit first.
You may be limited to running the pre-tester ≤24 times in a 24-hour period. (This is not implemented yet but will be added.)

Q&A

How can I structure my tests?

Here's a start. (We may add to this at some point.)

// OK TO COPY / ADAPT this snippet---but ONLY if you understand it completely.
// ⚠ Do not copy blindly.
// 
// This test is nowhere near adequate on its own.  It is provided to illustrate how to
// use helper functions to streamline your test code.

#include <stdio.h>
#include <stdlib.h>
#include "json.h"
#include "miniunit.h"

static int _test_parse_int_valid() {
  mu_start();
  //──────────────────────────────────────────────────────
  int   result;  // will be initialized in parse_int(…)
  char* input = "0";
  char const* pos = input;
  bool is_success = parse_int(&result, &pos);
  mu_check(is_success);   // because the input is valid
  mu_check(pos == input + 1);
  mu_check(result == 0);
  //──────────────────────────────────────────────────────
  mu_end();
}

static int _test_parse_int_invalid() {
  mu_start();
  //──────────────────────────────────────────────────────
  int   result;  // will be initialized in parse_int(…)
  char* input = "A";
  char const* pos = input;
  bool is_success = parse_int(&result, &pos);
  mu_check(!is_success);  // because the input is valid
  mu_check(pos == input); // failure should be at the first character in the input
  //──────────────────────────────────────────────────────
  mu_end();
}

int main(int argc, char* argv[]) {
  mu_run(_test_parse_int_valid);
  mu_run(_test_parse_int_invalid);
  return EXIT_SUCCESS;
}

That's a lot of duplication! Can we make our tests more concise?

You could use a helper function and a struct type just for testing. You may copy/adapt this code—but only if you understand it completely. ⚠ Do not copy blindly.

// FANCY way of testing, using a helper function and struct type just for testing.
//
// Okay to copy/adapt, but ONLY IF YOU UNDERSTAND THIS CODE COMPLETELY.
// ⚠ Do not copy blindly.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "json.h"
#include "miniunit.h"

typedef struct {
    bool is_success;
    union {  // anonymous union (C11)
        Element element;
        long int error_idx;
    };
} ParseResult;

static ParseResult _parse_json(char* s) {
    Element element;  // Not initialized because parse_element(…) *must* do so.
    char const* pos = s;
    bool is_success = parse_element(&element, &pos);
    if(is_success) {
        return (ParseResult) { .is_success = is_success, .element = element };
    }
    else {
        return (ParseResult) { .is_success = is_success, .error_idx = pos - s };
    }
}

static int _test_int() {
    mu_start();
    //────────────────────
    ParseResult result = _parse_json("0");
    mu_check(result.is_success);
    if(result.is_success) {
        mu_check(result.element.type == ELEMENT_INT);
        mu_check(result.element.as_int == 0);
        free_element(result.element);  // should do nothing
    }
    //────────────────────
    mu_end();
}


static int _test_string() {
    mu_start();
    //────────────────────
    result = _parse_json("\"abc\"");
    mu_check(result.is_success);
    if(result.is_success) {
        mu_check(result.element.type == ELEMENT_STRING);
        mu_check(strcmp(result.element.as_string, "abc") == 0);
        mu_check(strlen(result.element.as_string) == 3);
        free_element(result.element);
    }
    //────────────────────
    mu_end();
}

static int _test_list_of_ints() {
    mu_start();
    //────────────────────
    ParseResult result = _parse_json("[1, 2]");
    mu_check(result.is_success);
    if(result.is_success) {
        mu_check(result.element.type == ELEMENT_LIST);
        mu_check(result.element.as_list != NULL);
        mu_check(result.element.as_list -> element.as_int == 1);
        mu_check(result.element.as_list -> element.type == ELEMENT_INT);
        mu_check(result.element.as_list -> next != NULL);
        mu_check(result.element.as_list -> next -> element.type == ELEMENT_INT);
        mu_check(result.element.as_list -> next -> element.as_int == 2);
        free_element(result.element);
    }
    //────────────────────
    mu_end();
}

int main(int argc, char* argv[]) {
    mu_run(_test_int);
    mu_run(_test_string);
    mu_run(_test_list_of_ints);
    return EXIT_SUCCESS;
}

⚠ If you do not understand this code, do not use it.

The code above covers all parts of this assignment. If you choose to use it, you will likely need to select only the parts relevant to the part you are doing right now.

What should be the value of `*a_pos` after `parse_▒▒▒(…)` returns?

_____________________________________________
# EXAMPLE #1

INPUT:

    123

BEFORE we call parse_int(…):

    123
    ↑
    *a_pos

RETURN value from parse_int(…):

    true

After parse_int(…) returns:

    123
       ↑
       *a_pos refers to null terminator just
        after the integer literal.

    element.type   == ELEMENT_INT
    element.as_int == 123

_____________________________________________
# EXAMPLE #2

INPUT:

    123ABC

BEFORE we call parse_int(…):

    123ABC
    ↑
    *a_pos

RETURN value from parse_int(…):

    true

After parse_int(…) returns:

    123ABC
       ↑
       *a_pos refers to the non-digit character
        after the integer literal.

    element.type   == ELEMENT_INT
    element.as_int == 123

_____________________________________________
# EXAMPLE #3

INPUT:

    -A1

BEFORE we call parse_int(…):

    -A1
    ↑
    *a_pos

RETURN value from parse_int(…):

    false

After parse_int(…) returns:

    -A1
     ↑
     *a_pos refers first character that informed
      us this cannot be an integer literal.

    element.type   == (don't care)
    element.as_int == (don't care)

What does the output of print_element(…) look like?

It's just the inverse operation to parse_element(…).

parse_element(…) takes JSON as input.

print_element(…) prints JSON as output.

If you were to parse the output of print_element(…) with parse_element(…) you should get an equivalent object.

If you parse a JSON string and then print it again, you should get an equivalent string.

If you're looking for concrete examples, just look at any example of input to parse_element(…) (except for the trailing characters). There are several at the top of this assignment description page.

The specification says we don't have to handle escape sequences, but then it mentions escape sequences. Do we parse escape sequences or don't we? How do we handle backslash?

We use C escape codes to make C string literals containing certain characters (e.g., double-quote, newline, etc.) in our C code.

You don't have to parse JSON escape codes. Unless you are doing the escape sequence bonus, just treat a backslash like any other character.

Here's an example to illustrate the distinction:

#include <stdlib.h>
#include <assert.h>
#include <string.h>
#include <stdio.h>
#include "json.h"

int main(int argc, char* argv[]) {
    Element element;   // 'element' will be initialized inside parse_element(…)

    // C escape codes used to create a C string literal containing double quotes
    char* json_input = "\"A\""; // same as: {'\"', 'A', '\"'}
    char const* pos = json_input;
    assert(strlen(json_input) == 3);
    parse_element(&element, &pos);
    printf(">>>|%s|<<<\n", element.as_string);
    // Output:
    // >>>|A|<<<

    // JSON escape codes
    json_input = "\"A\\nB\"";  // same as: {'\"', 'A', '\\', 'n', 'B', '\"'}
    assert(strlen(json_input) == 5);
    pos  = json_input;
    parse_element(&element, &pos);
    printf(">>>|%s|<<<\n", element.as_string);
    // Output:
    // >>>|A\nB|<<<

    // Output: (with escape code bonus)
    // >>>|A
    // B|<<<

    // Note: strlen(…) does not count the null terminator

    return EXIT_SUCCESS;
}

Should the double quotes be stored in memory?

No. The double quotes are part of the JSON syntax.
This is just like how in C, when you define a string like this:
```
char s[] = "abc";
```
… the double quotes are not stored in memory.
How much code should I end up with?
Here's a screenshot of the instructor's solution. The parts that had to be added to support lists (i.e., HW11) are highlighted in yellow.

Updates

3/11/2022	Do not submit expected.txt for HW10.
3/22/2022	Changed json.h and assignment description to declare `pos` and `a_pos` using `const`. `char* pos` → `char const* pos` `char a_pos` → `char const a_pos` Run `264get hw11` to get the updated json.h.

Advanced C Programming

Spring 2022 ECE 264 :: Purdue University

JSON 2: parse strings

Learning goals

Overview

Linked lists

Getting Started on HW11

How much work is this?

Requirements

Submit

Pre-tester ●

Q&A

How can I structure my tests?

That's a lot of duplication! Can we make our tests more concise?

What should be the value of `*a_pos` after `parse_▒▒▒(…)` returns?

What does the output of `print_element(…)` look like?

The specification says we don't have to handle escape sequences, but then it mentions escape sequences. Do we parse escape sequences or don't we? How do we handle backslash?

Should the double quotes be stored in memory?

How much code should I end up with?

Updates

Advanced C Programming

Spring 2022 ECE 264 :: Purdue University

JSON 2: parse strings

Learning goals

Overview

Linked lists

Getting Started on HW11

How much work is this?

Requirements

Submit

Pre-tester ●

Q&A

How can I structure my tests?

That's a lot of duplication! Can we make our tests more concise?

What should be the value of *a_pos after parse_▒▒▒(…) returns?

What does the output of print_element(…) look like?

The specification says we don't have to handle escape sequences, but then it mentions escape sequences. Do we parse escape sequences or don't we? How do we handle backslash?

Should the double quotes be stored in memory?

How much code should I end up with?

Updates

What should be the value of `*a_pos` after `parse_▒▒▒(…)` returns?

What does the output of `print_element(…)` look like?