Re: [PATCH v5 4/9] lib: introduce json_path_cmp routine

[Vladimir Davydov <vdavydov.dev@gmail.com>]

On Mon, Nov 26, 2018 at 01:49:38PM +0300, Kirill Shcherbatov wrote:
> diff --git a/src/lib/json/json.h b/src/lib/json/json.h
> index dd09f5a..7d46601 100644
> --- a/src/lib/json/json.h
> +++ b/src/lib/json/json.h
> @@ -137,6 +137,17 @@ json_lexer_create(struct json_lexer *lexer, const char *src, int src_len)
>  int
>  json_lexer_next_token(struct json_lexer *lexer, struct json_token *token);
>  
> +/**
> + * Compare two JSON paths using Lexer class.
> + * - @a path must be valid
> + * - at the case of paths that have same token-sequence prefix,
> + *   the path having more tokens is assumed to be greater
> + * - when @b path contains an error, the path "a" is assumed to
> + *   be greater
> + */
> +int
> +json_path_cmp(const char *a, uint32_t a_len, const char *b, uint32_t b_len);
> +

One typically expects cmp(a, b) to be equivalent to -cmp(b, a).
Can't we make json_path_cmp satisfy this property, for example, by
requiring both strings to be valid json paths with an assertion?

>  /** Create a JSON tree object to manage data relations. */
>  int
>  json_tree_create(struct json_tree *tree);
> diff --git a/test/unit/json_path.c b/test/unit/json_path.c
> index f6b0472..35c2164 100644
> --- a/test/unit/json_path.c
> +++ b/test/unit/json_path.c
> @@ -352,15 +352,44 @@ test_tree()
>  	footer();
>  }
>  
> +void
> +test_path_cmp()
> +{
> +	const char *a = "Data[1][\"FIO\"].fname";
> +	uint32_t a_len = strlen(a);
> +	const struct path_and_errpos rc[] = {
> +		{a, 0},
> +		{"[\"Data\"][1].FIO[\"fname\"]", 0},
> +		{"Data[[1][\"FIO\"].fname", 6},
> +		{"Data[1]", 1},
> +		{"Data[1][\"FIO\"].fname[1]", -2},
> +		{"Data[1][\"Info\"].fname[1]", -1},

Should we reorder values of json_token_type enum, and we would have to
fix the test. Let's please rewrite the test so that it doesn't depend on
the json_lexer implementation, in other words just check that the sign
of the return value is correct.

> +	};
> +	header();
> +	plan(lengthof(rc));
> +
> +	for (size_t i = 0; i < lengthof(rc); ++i) {
> +		const char *path = rc[i].path;
> +		int errpos = rc[i].errpos;
> +		int rc = json_path_cmp(a, a_len, path, strlen(path));
> +		is(rc, errpos, "path cmp result \"%s\" with \"%s\": "
> +		   "have %d, expected %d", a, path, rc, errpos);
> +	}
> +
> +	check_plan();
> +	footer();
> +}