launchdarkly_server_sdk_evaluation/contexts/
attribute_reference.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
use serde::{Deserialize, Serialize, Serializer};
use std::fmt::Display;

#[derive(Clone, Hash, PartialEq, Eq, Debug, Serialize)]
enum Error {
    Empty,
    InvalidEscapeSequence,
    DoubleOrTrailingSlash,
}

impl Display for Error {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        match self {
            Error::Empty => write!(f, "Reference cannot be empty"),
            Error::InvalidEscapeSequence => write!(f, "Reference contains invalid escape sequence"),
            Error::DoubleOrTrailingSlash => {
                write!(f, "Reference contains double or trailing slash")
            }
        }
    }
}

/// Represents an attribute name or path expression identifying a value within a [crate::Context].
///
/// This can be used to retrieve a value with [crate::Context::get_value], or to identify an attribute or
/// nested value that should be considered private with
/// [crate::ContextBuilder::add_private_attribute] (the SDK configuration can also have a list of
/// private attribute references).
///
/// This is represented as a separate type, rather than just a string, so that validation and parsing can
/// be done ahead of time if an attribute reference will be used repeatedly later (such as in flag
/// evaluations).
///
/// If the string starts with '/', then this is treated as a slash-delimited path reference where the
/// first component is the name of an attribute, and subsequent components are the names of nested JSON
/// object properties. In this syntax, the escape sequences "~0" and "~1" represent '~' and '/'
/// respectively within a path component.
///
/// If the string does not start with '/', then it is treated as the literal name of an attribute.
///
/// # Example
/// ```
/// # use crate::launchdarkly_server_sdk_evaluation::{ContextBuilder, Context, Reference, AttributeValue};
/// # use serde_json::json;
/// # let context: Context = serde_json::from_value(json!(
/// // Given the following JSON representation of a context:
/// {
///   "kind": "user",
///   "key": "123",
///   "name": "xyz",
///   "address": {
///     "street": "99 Main St.",
///     "city": "Westview"
///   },
///   "a/b": "ok"
/// }
/// # )).unwrap();
///
/// assert_eq!(context.get_value(&Reference::new("name")),
///     Some(AttributeValue::String("xyz".to_owned())));
/// assert_eq!(context.get_value(&Reference::new("/address/street")),
///     Some(AttributeValue::String("99 Main St.".to_owned())));
/// assert_eq!(context.get_value(&Reference::new("a/b")),
///     Some(AttributeValue::String("ok".to_owned())));
/// assert_eq!(context.get_value(&Reference::new("/a~1b")),
///     Some(AttributeValue::String("ok".to_owned())));
/// ```
#[derive(Clone, Hash, PartialEq, Eq, Debug)]
pub struct Reference {
    variant: Variant,
    input: String,
}

#[derive(Clone, Hash, PartialEq, Eq, Debug)]
enum Variant {
    /// Represents a plain, top-level attribute name; does not start with a '/'.
    PlainName,
    /// Represents an attribute pointer; starts with a '/'.
    Pointer(Vec<String>),
    /// Represents an invalid input string.
    Error(Error),
}

impl Serialize for Reference {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_str(&self.input)
    }
}

impl<'de> Deserialize<'de> for Reference {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        let s = String::deserialize(deserializer)?;
        Ok(Reference::new(s))
    }
}

impl Reference {
    /// Construct a new context attribute reference.
    ///
    /// This constructor always returns a reference that preserves the original string, even if
    /// validation fails, so that serializing the reference to JSON will produce the original
    /// string.
    pub fn new<S: AsRef<str>>(value: S) -> Self {
        let value = value.as_ref();

        if value.is_empty() || value == "/" {
            return Self {
                variant: Variant::Error(Error::Empty),
                input: value.to_owned(),
            };
        }

        if !value.starts_with('/') {
            return Self {
                variant: Variant::PlainName,
                input: value.to_owned(),
            };
        }

        let component_result = value[1..]
            .split('/')
            .into_iter()
            .map(|part| {
                if part.is_empty() {
                    return Err(Error::DoubleOrTrailingSlash);
                }
                Reference::unescape_path(part)
            })
            .collect::<Result<Vec<String>, Error>>();

        match component_result {
            Ok(components) => Self {
                variant: Variant::Pointer(components),
                input: value.to_owned(),
            },
            Err(e) => Self {
                variant: Variant::Error(e),
                input: value.to_owned(),
            },
        }
    }

    /// Returns true if the reference is valid.
    pub fn is_valid(&self) -> bool {
        !matches!(&self.variant, Variant::Error(_))
    }

    /// If the reference is invalid, this method returns an error description; otherwise, it
    /// returns an empty string.
    pub fn error(&self) -> String {
        match &self.variant {
            Variant::Error(e) => e.to_string(),
            _ => "".to_owned(),
        }
    }

    /// Returns the number of path components in the reference.
    ///
    /// For a simple attribute reference such as "name" with no leading slash, this returns 1.
    ///
    /// For an attribute reference with a leading slash, it is the number of slash-delimited path
    /// components after the initial slash.
    /// # Example
    /// ```
    /// # use crate::launchdarkly_server_sdk_evaluation::Reference;
    /// assert_eq!(Reference::new("a").depth(), 1);
    /// assert_eq!(Reference::new("/a/b").depth(), 2);
    /// ```
    pub fn depth(&self) -> usize {
        match &self.variant {
            Variant::Pointer(components) => components.len(),
            Variant::PlainName => 1,
            _ => 0,
        }
    }

    /// Retrieves a single path component from the attribute reference.
    ///
    /// Returns the attribute name for a simple attribute reference such as "name" with no leading slash, if index is zero.
    ///
    /// Returns the specified path component if index is less than [Reference::depth], and the reference begins with a slash.
    ///
    /// If index is out of range, it returns None.
    ///
    /// # Examples
    /// ```
    /// # use launchdarkly_server_sdk_evaluation::Reference;
    /// assert_eq!(Reference::new("a").component(0), Some("a"));
    /// assert_eq!(Reference::new("/a/b").component(1), Some("b"));
    /// assert_eq!(Reference::new("/a/b").component(2), None);
    /// ```
    pub fn component(&self, index: usize) -> Option<&str> {
        match (&self.variant, index) {
            (Variant::Pointer(components), _) => components.get(index).map(|c| c.as_str()),
            (Variant::PlainName, 0) => Some(&self.input),
            _ => None,
        }
    }

    // Checks if the Reference resolves to a Context's 'kind' attribute.
    pub(crate) fn is_kind(&self) -> bool {
        matches!((self.depth(), self.component(0)), (1, Some(comp)) if comp == "kind")
    }

    fn unescape_path(path: &str) -> Result<String, Error> {
        // If there are no tildes then there's definitely nothing to do
        if !path.contains('~') {
            return Ok(path.to_string());
        }

        let mut out = String::new();

        let mut iter = path.chars().peekable();
        while let Some(c) = iter.next() {
            if c != '~' {
                out.push(c);
                continue;
            }
            if iter.peek().is_none() {
                return Err(Error::InvalidEscapeSequence);
            }

            let unescaped = match iter.next().unwrap() {
                '0' => '~',
                '1' => '/',
                _ => return Err(Error::InvalidEscapeSequence),
            };
            out.push(unescaped);
        }

        Ok(out)
    }
}

impl Default for Reference {
    /// A default [Reference] is empty and invalid.
    fn default() -> Self {
        Reference::new("")
    }
}

/// Displays the input string used to construct the [Reference].
impl Display for Reference {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
        write!(f, "{}", self.input)
    }
}

impl<S> From<S> for Reference
where
    S: AsRef<str>,
{
    fn from(reference: S) -> Self {
        Reference::new(reference)
    }
}

impl From<Reference> for String {
    fn from(r: Reference) -> Self {
        r.input
    }
}

#[derive(Debug, Deserialize, PartialEq)]
#[serde(transparent)]
/// Represents an attribute name, found in pre-Context data.
/// AttributeNames are incapable of referring to nested values, and instead only
/// refer to top-level attributes.  
pub(crate) struct AttributeName(String);

impl AttributeName {
    /// Constructs an AttributeName, which can be converted into an equivalent [Reference].
    #[cfg(test)]
    pub(crate) fn new(s: String) -> Self {
        Self(s)
    }
}

impl Default for AttributeName {
    fn default() -> Self {
        Self("".to_owned())
    }
}

impl From<AttributeName> for Reference {
    /// AttributeNames are converted into References based on the presence or
    /// absence of a leading '/'.
    ///
    /// Although References are able to represent plain, top-level attribute
    /// names, they cannot represent those that begin with a leading '/' because that signifies
    /// the pointer syntax.
    ///
    /// Therefore, if the first character is a '/' the string must be escaped.
    ///
    /// This results in the equivalent [Reference] representation of that [AttributeName].
    ///
    /// Note that References constructed from an AttributeName will serialize to the
    /// string passed into the Reference constructor, not the original AttributeName. This
    /// is desirable since data should be "upgraded" into the new format as it is encountered.
    fn from(name: AttributeName) -> Self {
        if !name.0.starts_with('/') {
            return Self::new(name.0);
        }
        let mut escaped = name.0.replace('~', "~0").replace('/', "~1");
        escaped.insert(0, '/');
        Self::new(escaped)
    }
}

#[cfg(test)]
pub(crate) mod proptest_generators {
    use super::{AttributeName, Reference};
    use proptest::prelude::*;

    // This regular expression is meant to match our spec for an acceptable attribute string,
    // both those representing attribute references, and those representing literal attribute
    // names.
    // A. Plain attribute names are handled by the first alternative (not beginning with '/')
    // B. Attribute references are handled by the second alternative.
    //    1) Starts with a slash
    //    2) Followed by any character that isn't a / or ~ (they must be escaped with ~1 and ~0)
    //    3) Or, an occurrence of ~1 or ~0
    //    4) At least one of 2) or 3) is required.
    //    The path component can repeat one or more times.
    prop_compose! {
        // Generate any string that could represent a valid reference, either using
        // JSON-pointer-like syntax, or plain attribute name. Will not return an empty string.
        pub(crate) fn any_valid_ref_string()(s in "([^/].*|(/([^/~]|~[01])+)+)") -> String {
            s
        }

    }

    prop_compose! {
         pub(crate) fn any_valid_plain_name()(s in "([^/].*)") -> String {
            s
         }
    }

    prop_compose! {
         pub(crate) fn any_attribute_name()(s in any_valid_ref_string()) -> AttributeName {
            AttributeName::new(s)
         }
    }

    prop_compose! {
        // Generate any valid reference.
        pub(crate) fn any_valid_ref()(s in any_valid_ref_string()) -> Reference {
            Reference::new(s)
        }
    }

    prop_compose! {
        // Generate any reference, invalid or not. May generate empty strings.
        pub(crate) fn any_ref()(s in any::<String>()) -> Reference {
            Reference::new(s)
        }
    }

    prop_compose! {
        pub(crate) fn any_valid_ref_transformed_from_attribute_name()(s in any_valid_ref_string()) -> Reference {
            Reference::from(AttributeName::new(s))
        }
    }

    prop_compose! {
        // Generate any literal reference, valid or not. May generate empty strings.
        pub(crate) fn any_ref_transformed_from_attribute_name()(s in any::<String>()) -> Reference {
            Reference::from(AttributeName::new(s))
        }
    }

    prop_compose! {
        pub(crate) fn any_valid_plain_ref()(s in any_valid_plain_name()) -> Reference {
            Reference::new(s)
        }
    }
}

#[cfg(test)]
mod tests {
    use super::{AttributeName, Error, Reference};
    use crate::proptest_generators::*;
    use proptest::prelude::*;
    use test_case::test_case;

    proptest! {
        #[test]
        fn regex_creates_valid_references(reference in any_valid_ref()) {
            prop_assert!(reference.is_valid());
        }
    }

    proptest! {
        // Although this should be a subset of the previous test, it's still useful to
        // assert that it obeys the property of generating valid references on its own.
        #[test]
        fn regex_creates_valid_plain_references(reference in any_valid_plain_ref()) {
            prop_assert!(reference.is_valid());
        }
    }

    proptest! {
        #[test]
        fn plain_references_have_single_component(reference in any_valid_plain_ref()) {
            prop_assert_eq!(reference.depth(), 1);
        }
    }

    proptest! {
        #[test]
        fn attribute_names_are_valid_references(reference in any_valid_ref_transformed_from_attribute_name()) {
            prop_assert!(reference.is_valid());
            prop_assert_eq!(reference.depth(), 1);
        }
    }

    proptest! {
        #[test]
        fn attribute_name_references_have_single_component(reference in any_valid_ref_transformed_from_attribute_name()) {
            prop_assert_eq!(reference.depth(), 1);
            let component = reference.component(0);
            prop_assert!(component.is_some(), "component 0 should exist");
        }
    }

    proptest! {
        #[test]
        fn raw_returns_input_unmodified(s in any::<String>()) {
            let a = Reference::new(s.clone());
            prop_assert_eq!(a.to_string(), s);
        }
    }

    #[test]
    fn default_reference_is_invalid() {
        assert!(!Reference::default().is_valid());
    }

    #[test_case("", Error::Empty; "Empty reference")]
    #[test_case("/", Error::Empty; "Single slash")]
    #[test_case("//", Error::DoubleOrTrailingSlash; "Double slash")]
    #[test_case("/a//b", Error::DoubleOrTrailingSlash; "Double slash in middle")]
    #[test_case("/a/b/", Error::DoubleOrTrailingSlash; "Trailing slash")]
    #[test_case("/~3", Error::InvalidEscapeSequence; "Tilde must be followed by 0 or 1 only")]
    #[test_case("/testing~something", Error::InvalidEscapeSequence; "Tilde cannot be alone")]
    #[test_case("/m~~0", Error::InvalidEscapeSequence; "Extra tilde before valid escape")]
    #[test_case("/a~", Error::InvalidEscapeSequence; "Tilde cannot be followed by nothing")]
    fn invalid_references(input: &str, error: Error) {
        let reference = Reference::new(input);
        assert!(!reference.is_valid());
        assert_eq!(error.to_string(), reference.error());
    }

    #[test_case("key")]
    #[test_case("kind")]
    #[test_case("name")]
    #[test_case("name/with/slashes")]
    #[test_case("name~0~1with-what-looks-like-escape-sequences")]
    fn plain_reference_syntax(input: &str) {
        let reference = Reference::new(input);
        assert!(reference.is_valid());
        assert_eq!(input, reference.to_string());
        assert_eq!(
            input,
            reference
                .component(0)
                .expect("Failed to get first component")
        );
        assert_eq!(1, reference.depth());
    }

    #[test_case("/key", "key")]
    #[test_case("/kind", "kind")]
    #[test_case("/name", "name")]
    #[test_case("/custom", "custom")]
    fn pointer_syntax(input: &str, path: &str) {
        let reference = Reference::new(input);
        assert!(reference.is_valid());
        assert_eq!(input, reference.to_string());
        assert_eq!(
            path,
            reference
                .component(0)
                .expect("Failed to get first component")
        );
        assert_eq!(1, reference.depth())
    }

    #[test_case("/a/b", 2, 0, "a")]
    #[test_case("/a/b", 2, 1, "b")]
    #[test_case("/a~1b/c", 2, 0, "a/b")]
    #[test_case("/a~1b/c", 2, 1, "c")]
    #[test_case("/a/10/20/30x", 4, 1, "10")]
    #[test_case("/a/10/20/30x", 4, 2, "20")]
    #[test_case("/a/10/20/30x", 4, 3, "30x")]
    fn handles_subcomponents(input: &str, len: usize, index: usize, expected_name: &str) {
        let reference = Reference::new(input);
        assert!(reference.is_valid());
        assert_eq!(input, reference.input);
        assert_eq!(len, reference.depth());
        assert_eq!(expected_name, reference.component(index).unwrap());
    }

    #[test]
    fn can_handle_invalid_index_requests() {
        let reference = Reference::new("/a/b/c");
        assert!(reference.is_valid());
        assert!(reference.component(0).is_some());
        assert!(reference.component(1).is_some());
        assert!(reference.component(2).is_some());
        assert!(reference.component(3).is_none());
    }

    #[test_case("/a/b", "/~1a~1b")]
    #[test_case("a", "a")]
    #[test_case("a~1b", "a~1b")]
    #[test_case("/a~1b", "/~1a~01b")]
    #[test_case("/a~0b", "/~1a~00b")]
    #[test_case("", "")]
    #[test_case("/", "/~1")]
    fn attribute_name_equality(name: &str, reference: &str) {
        let as_name = AttributeName::new(name.to_owned());
        let reference = Reference::new(reference);
        assert_eq!(Reference::from(as_name), reference);
    }

    #[test]
    fn is_kind() {
        assert!(Reference::new("/kind").is_kind());
        assert!(Reference::new("kind").is_kind());
        assert!(Reference::from(AttributeName::new("kind".to_owned())).is_kind());

        assert!(!Reference::from(AttributeName::new("/kind".to_owned())).is_kind());
        assert!(!Reference::new("foo").is_kind());
    }
}