log/kv/
source.rs

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1//! Sources for key-values.
2//!
3//! This module defines the [`Source`] type and supporting APIs for
4//! working with collections of key-values.
5
6use crate::kv::{Error, Key, ToKey, ToValue, Value};
7use std::fmt;
8
9/// A source of key-values.
10///
11/// The source may be a single pair, a set of pairs, or a filter over a set of pairs.
12/// Use the [`VisitSource`](trait.VisitSource.html) trait to inspect the structured data
13/// in a source.
14///
15/// A source is like an iterator over its key-values, except with a push-based API
16/// instead of a pull-based one.
17///
18/// # Examples
19///
20/// Enumerating the key-values in a source:
21///
22/// ```
23/// # fn main() -> Result<(), log::kv::Error> {
24/// use log::kv::{self, Source, Key, Value, VisitSource};
25///
26/// // A `VisitSource` that prints all key-values
27/// // VisitSources are fed the key-value pairs of each key-values
28/// struct Printer;
29///
30/// impl<'kvs> VisitSource<'kvs> for Printer {
31///     fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), kv::Error> {
32///         println!("{key}: {value}");
33///
34///         Ok(())
35///     }
36/// }
37///
38/// // A source with 3 key-values
39/// // Common collection types implement the `Source` trait
40/// let source = &[
41///     ("a", 1),
42///     ("b", 2),
43///     ("c", 3),
44/// ];
45///
46/// // Pass an instance of the `VisitSource` to a `Source` to visit it
47/// source.visit(&mut Printer)?;
48/// # Ok(())
49/// # }
50/// ```
51pub trait Source {
52    /// Visit key-values.
53    ///
54    /// A source doesn't have to guarantee any ordering or uniqueness of key-values.
55    /// If the given visitor returns an error then the source may early-return with it,
56    /// even if there are more key-values.
57    ///
58    /// # Implementation notes
59    ///
60    /// A source should yield the same key-values to a subsequent visitor unless
61    /// that visitor itself fails.
62    fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error>;
63
64    /// Get the value for a given key.
65    ///
66    /// If the key appears multiple times in the source then which key is returned
67    /// is implementation specific.
68    ///
69    /// # Implementation notes
70    ///
71    /// A source that can provide a more efficient implementation of this method
72    /// should override it.
73    fn get(&self, key: Key) -> Option<Value<'_>> {
74        get_default(self, key)
75    }
76
77    /// Count the number of key-values that can be visited.
78    ///
79    /// # Implementation notes
80    ///
81    /// A source that knows the number of key-values upfront may provide a more
82    /// efficient implementation.
83    ///
84    /// A subsequent call to `visit` should yield the same number of key-values.
85    fn count(&self) -> usize {
86        count_default(self)
87    }
88}
89
90/// The default implementation of `Source::get`
91fn get_default<'v>(source: &'v (impl Source + ?Sized), key: Key) -> Option<Value<'v>> {
92    struct Get<'k, 'v> {
93        key: Key<'k>,
94        found: Option<Value<'v>>,
95    }
96
97    impl<'k, 'kvs> VisitSource<'kvs> for Get<'k, 'kvs> {
98        fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error> {
99            if self.key == key {
100                self.found = Some(value);
101            }
102
103            Ok(())
104        }
105    }
106
107    let mut get = Get { key, found: None };
108
109    let _ = source.visit(&mut get);
110    get.found
111}
112
113/// The default implementation of `Source::count`.
114fn count_default(source: impl Source) -> usize {
115    struct Count(usize);
116
117    impl<'kvs> VisitSource<'kvs> for Count {
118        fn visit_pair(&mut self, _: Key<'kvs>, _: Value<'kvs>) -> Result<(), Error> {
119            self.0 += 1;
120
121            Ok(())
122        }
123    }
124
125    let mut count = Count(0);
126    let _ = source.visit(&mut count);
127    count.0
128}
129
130impl<'a, T> Source for &'a T
131where
132    T: Source + ?Sized,
133{
134    fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
135        Source::visit(&**self, visitor)
136    }
137
138    fn get(&self, key: Key) -> Option<Value<'_>> {
139        Source::get(&**self, key)
140    }
141
142    fn count(&self) -> usize {
143        Source::count(&**self)
144    }
145}
146
147impl<K, V> Source for (K, V)
148where
149    K: ToKey,
150    V: ToValue,
151{
152    fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
153        visitor.visit_pair(self.0.to_key(), self.1.to_value())
154    }
155
156    fn get(&self, key: Key) -> Option<Value<'_>> {
157        if self.0.to_key() == key {
158            Some(self.1.to_value())
159        } else {
160            None
161        }
162    }
163
164    fn count(&self) -> usize {
165        1
166    }
167}
168
169impl<S> Source for [S]
170where
171    S: Source,
172{
173    fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
174        for source in self {
175            source.visit(visitor)?;
176        }
177
178        Ok(())
179    }
180
181    fn get(&self, key: Key) -> Option<Value<'_>> {
182        for source in self {
183            if let Some(found) = source.get(key.clone()) {
184                return Some(found);
185            }
186        }
187
188        None
189    }
190
191    fn count(&self) -> usize {
192        self.iter().map(Source::count).sum()
193    }
194}
195
196impl<const N: usize, S> Source for [S; N]
197where
198    S: Source,
199{
200    fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
201        Source::visit(self as &[_], visitor)
202    }
203
204    fn get(&self, key: Key) -> Option<Value<'_>> {
205        Source::get(self as &[_], key)
206    }
207
208    fn count(&self) -> usize {
209        Source::count(self as &[_])
210    }
211}
212
213impl<S> Source for Option<S>
214where
215    S: Source,
216{
217    fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
218        if let Some(source) = self {
219            source.visit(visitor)?;
220        }
221
222        Ok(())
223    }
224
225    fn get(&self, key: Key) -> Option<Value<'_>> {
226        self.as_ref().and_then(|s| s.get(key))
227    }
228
229    fn count(&self) -> usize {
230        self.as_ref().map_or(0, Source::count)
231    }
232}
233
234/// A visitor for the key-value pairs in a [`Source`](trait.Source.html).
235pub trait VisitSource<'kvs> {
236    /// Visit a key-value pair.
237    fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error>;
238}
239
240impl<'a, 'kvs, T> VisitSource<'kvs> for &'a mut T
241where
242    T: VisitSource<'kvs> + ?Sized,
243{
244    fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error> {
245        (**self).visit_pair(key, value)
246    }
247}
248
249impl<'a, 'b: 'a, 'kvs> VisitSource<'kvs> for fmt::DebugMap<'a, 'b> {
250    fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error> {
251        self.entry(&key, &value);
252        Ok(())
253    }
254}
255
256impl<'a, 'b: 'a, 'kvs> VisitSource<'kvs> for fmt::DebugList<'a, 'b> {
257    fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error> {
258        self.entry(&(key, value));
259        Ok(())
260    }
261}
262
263impl<'a, 'b: 'a, 'kvs> VisitSource<'kvs> for fmt::DebugSet<'a, 'b> {
264    fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error> {
265        self.entry(&(key, value));
266        Ok(())
267    }
268}
269
270impl<'a, 'b: 'a, 'kvs> VisitSource<'kvs> for fmt::DebugTuple<'a, 'b> {
271    fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error> {
272        self.field(&key);
273        self.field(&value);
274        Ok(())
275    }
276}
277
278#[cfg(feature = "std")]
279mod std_support {
280    use super::*;
281    use std::borrow::Borrow;
282    use std::collections::{BTreeMap, HashMap};
283    use std::hash::{BuildHasher, Hash};
284    use std::rc::Rc;
285    use std::sync::Arc;
286
287    impl<S> Source for Box<S>
288    where
289        S: Source + ?Sized,
290    {
291        fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
292            Source::visit(&**self, visitor)
293        }
294
295        fn get(&self, key: Key) -> Option<Value<'_>> {
296            Source::get(&**self, key)
297        }
298
299        fn count(&self) -> usize {
300            Source::count(&**self)
301        }
302    }
303
304    impl<S> Source for Arc<S>
305    where
306        S: Source + ?Sized,
307    {
308        fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
309            Source::visit(&**self, visitor)
310        }
311
312        fn get(&self, key: Key) -> Option<Value<'_>> {
313            Source::get(&**self, key)
314        }
315
316        fn count(&self) -> usize {
317            Source::count(&**self)
318        }
319    }
320
321    impl<S> Source for Rc<S>
322    where
323        S: Source + ?Sized,
324    {
325        fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
326            Source::visit(&**self, visitor)
327        }
328
329        fn get(&self, key: Key) -> Option<Value<'_>> {
330            Source::get(&**self, key)
331        }
332
333        fn count(&self) -> usize {
334            Source::count(&**self)
335        }
336    }
337
338    impl<S> Source for Vec<S>
339    where
340        S: Source,
341    {
342        fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
343            Source::visit(&**self, visitor)
344        }
345
346        fn get(&self, key: Key) -> Option<Value<'_>> {
347            Source::get(&**self, key)
348        }
349
350        fn count(&self) -> usize {
351            Source::count(&**self)
352        }
353    }
354
355    impl<'kvs, V> VisitSource<'kvs> for Box<V>
356    where
357        V: VisitSource<'kvs> + ?Sized,
358    {
359        fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error> {
360            (**self).visit_pair(key, value)
361        }
362    }
363
364    impl<K, V, S> Source for HashMap<K, V, S>
365    where
366        K: ToKey + Borrow<str> + Eq + Hash,
367        V: ToValue,
368        S: BuildHasher,
369    {
370        fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
371            for (key, value) in self {
372                visitor.visit_pair(key.to_key(), value.to_value())?;
373            }
374            Ok(())
375        }
376
377        fn get(&self, key: Key) -> Option<Value<'_>> {
378            HashMap::get(self, key.as_str()).map(|v| v.to_value())
379        }
380
381        fn count(&self) -> usize {
382            self.len()
383        }
384    }
385
386    impl<K, V> Source for BTreeMap<K, V>
387    where
388        K: ToKey + Borrow<str> + Ord,
389        V: ToValue,
390    {
391        fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
392            for (key, value) in self {
393                visitor.visit_pair(key.to_key(), value.to_value())?;
394            }
395            Ok(())
396        }
397
398        fn get(&self, key: Key) -> Option<Value<'_>> {
399            BTreeMap::get(self, key.as_str()).map(|v| v.to_value())
400        }
401
402        fn count(&self) -> usize {
403            self.len()
404        }
405    }
406
407    #[cfg(test)]
408    mod tests {
409        use crate::kv::value;
410
411        use super::*;
412
413        #[test]
414        fn count() {
415            assert_eq!(1, Source::count(&Box::new(("a", 1))));
416            assert_eq!(2, Source::count(&vec![("a", 1), ("b", 2)]));
417        }
418
419        #[test]
420        fn get() {
421            let source = vec![("a", 1), ("b", 2), ("a", 1)];
422            assert_eq!(
423                value::inner::Token::I64(1),
424                Source::get(&source, Key::from_str("a")).unwrap().to_token()
425            );
426
427            let source = Box::new(None::<(&str, i32)>);
428            assert!(Source::get(&source, Key::from_str("a")).is_none());
429        }
430
431        #[test]
432        fn hash_map() {
433            let mut map = HashMap::new();
434            map.insert("a", 1);
435            map.insert("b", 2);
436
437            assert_eq!(2, Source::count(&map));
438            assert_eq!(
439                value::inner::Token::I64(1),
440                Source::get(&map, Key::from_str("a")).unwrap().to_token()
441            );
442        }
443
444        #[test]
445        fn btree_map() {
446            let mut map = BTreeMap::new();
447            map.insert("a", 1);
448            map.insert("b", 2);
449
450            assert_eq!(2, Source::count(&map));
451            assert_eq!(
452                value::inner::Token::I64(1),
453                Source::get(&map, Key::from_str("a")).unwrap().to_token()
454            );
455        }
456    }
457}
458
459// NOTE: Deprecated; but aliases can't carry this attribute
460#[cfg(feature = "kv_unstable")]
461pub use VisitSource as Visitor;
462
463#[cfg(test)]
464mod tests {
465    use crate::kv::value;
466
467    use super::*;
468
469    #[test]
470    fn source_is_object_safe() {
471        fn _check(_: &dyn Source) {}
472    }
473
474    #[test]
475    fn visitor_is_object_safe() {
476        fn _check(_: &dyn VisitSource) {}
477    }
478
479    #[test]
480    fn count() {
481        struct OnePair {
482            key: &'static str,
483            value: i32,
484        }
485
486        impl Source for OnePair {
487            fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
488                visitor.visit_pair(self.key.to_key(), self.value.to_value())
489            }
490        }
491
492        assert_eq!(1, Source::count(&("a", 1)));
493        assert_eq!(2, Source::count(&[("a", 1), ("b", 2)] as &[_]));
494        assert_eq!(0, Source::count(&None::<(&str, i32)>));
495        assert_eq!(1, Source::count(&OnePair { key: "a", value: 1 }));
496    }
497
498    #[test]
499    fn get() {
500        let source = &[("a", 1), ("b", 2), ("a", 1)] as &[_];
501        assert_eq!(
502            value::inner::Token::I64(1),
503            Source::get(source, Key::from_str("a")).unwrap().to_token()
504        );
505        assert_eq!(
506            value::inner::Token::I64(2),
507            Source::get(source, Key::from_str("b")).unwrap().to_token()
508        );
509        assert!(Source::get(&source, Key::from_str("c")).is_none());
510
511        let source = None::<(&str, i32)>;
512        assert!(Source::get(&source, Key::from_str("a")).is_none());
513    }
514}
log/kv/source.rs

log/kv/
source.rs
