cranpose_services/
app_update.rs

1//! Typed application update discovery, verification, and platform installation.
2//!
3//! An update is the one download an application performs that can replace the
4//! application, so what arrives is checked against what was promised before it
5//! reaches a platform installer. The check lives here, once, rather than in each
6//! platform's installer: a digest computed four different ways is four chances
7//! to compute it wrongly, and one of them will be the one nobody tested.
8
9use std::sync::{
10    Arc, Mutex, OnceLock,
11    atomic::{AtomicU64, Ordering},
12};
13
14use sha2::{Digest, Sha256};
15
16use crate::registry::ServiceRegistry;
17
18/// How a package's bytes are checked against what the release promised.
19#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Hash)]
20pub enum DigestAlgorithm {
21    /// SHA-256, which is what release feeds publish.
22    #[default]
23    Sha256,
24}
25
26impl DigestAlgorithm {
27    /// The name a release feed writes, and the name a platform's own digest API
28    /// answers to.
29    pub fn name(self) -> &'static str {
30        match self {
31            DigestAlgorithm::Sha256 => "sha256",
32        }
33    }
34
35    /// Reads an algorithm a release feed named, or `None` for one this
36    /// framework cannot compute — which is refused rather than skipped, because
37    /// a digest nobody checks is worse than no digest at all.
38    pub fn parse(name: &str) -> Option<Self> {
39        match name.trim().to_ascii_lowercase().as_str() {
40            "sha256" | "sha-256" => Some(DigestAlgorithm::Sha256),
41            _ => None,
42        }
43    }
44}
45
46/// The digest a downloaded package must match.
47#[derive(Clone, Debug, PartialEq, Eq, Hash)]
48pub struct PackageDigest {
49    pub algorithm: DigestAlgorithm,
50    /// Lower-case hexadecimal.
51    pub value: String,
52}
53
54impl PackageDigest {
55    /// A SHA-256 digest, from hexadecimal in either case.
56    pub fn sha256(value: impl AsRef<str>) -> Self {
57        Self {
58            algorithm: DigestAlgorithm::Sha256,
59            value: value.as_ref().trim().to_ascii_lowercase(),
60        }
61    }
62
63    /// Reads the `sha256:<hex>` form release feeds publish.
64    pub fn parse(value: &str) -> Option<Self> {
65        let (algorithm, digest) = value.split_once(':')?;
66        let algorithm = DigestAlgorithm::parse(algorithm)?;
67        let digest = digest.trim().to_ascii_lowercase();
68        (!digest.is_empty()).then_some(Self {
69            algorithm,
70            value: digest,
71        })
72    }
73
74    /// Whether this digest could be one: the right length, and hexadecimal.
75    ///
76    /// A malformed digest is refused before a download starts rather than after
77    /// it, so nobody waits for two hundred megabytes to learn the release feed
78    /// was misconfigured.
79    pub fn is_well_formed(&self) -> bool {
80        let expected = match self.algorithm {
81            DigestAlgorithm::Sha256 => 64,
82        };
83        self.value.len() == expected && self.value.bytes().all(|byte| byte.is_ascii_hexdigit())
84    }
85
86    /// The `sha256:<hex>` form.
87    pub fn to_feed_string(&self) -> String {
88        format!("{}:{}", self.algorithm.name(), self.value)
89    }
90}
91
92/// The SHA-256 of `bytes`, as lower-case hexadecimal.
93pub fn sha256_hex(bytes: &[u8]) -> String {
94    let mut hasher = Sha256::new();
95    hasher.update(bytes);
96    hex(&hasher.finalize())
97}
98
99fn hex(bytes: &[u8]) -> String {
100    let mut out = String::with_capacity(bytes.len() * 2);
101    for byte in bytes {
102        out.push(char::from_digit((byte >> 4) as u32, 16).unwrap_or('0'));
103        out.push(char::from_digit((byte & 0x0f) as u32, 16).unwrap_or('0'));
104    }
105    out
106}
107
108/// Checks a package as it is read, so a package too large to hold in memory is
109/// still checked.
110///
111/// An installer feeds every chunk it writes through this and calls
112/// [`DigestVerifier::finish`] before committing; nothing installs a package
113/// whose bytes were never seen in full.
114pub struct DigestVerifier {
115    expected: PackageDigest,
116    hasher: Sha256,
117    len: u64,
118}
119
120impl DigestVerifier {
121    /// A verifier for `expected`, or an error when the digest is malformed.
122    pub fn new(expected: PackageDigest) -> Result<Self, AppUpdateError> {
123        if !expected.is_well_formed() {
124            return Err(AppUpdateError::MalformedDigest(expected.to_feed_string()));
125        }
126        Ok(Self {
127            expected,
128            hasher: Sha256::new(),
129            len: 0,
130        })
131    }
132
133    /// Feeds the next chunk of the package.
134    pub fn update(&mut self, chunk: &[u8]) {
135        self.hasher.update(chunk);
136        self.len += chunk.len() as u64;
137    }
138
139    /// How many bytes have been read so far.
140    pub fn len(&self) -> u64 {
141        self.len
142    }
143
144    /// Whether nothing has been read yet.
145    pub fn is_empty(&self) -> bool {
146        self.len == 0
147    }
148
149    /// Checks what was read against what was promised.
150    pub fn finish(self) -> Result<(), AppUpdateError> {
151        let actual = hex(&self.hasher.finalize());
152        if actual == self.expected.value {
153            Ok(())
154        } else {
155            Err(AppUpdateError::VerificationFailed {
156                expected: self.expected.value,
157                actual,
158            })
159        }
160    }
161}
162
163/// Checks a package held in memory against `digest`.
164pub fn verify_package(bytes: &[u8], digest: &PackageDigest) -> Result<(), AppUpdateError> {
165    let mut verifier = DigestVerifier::new(digest.clone())?;
166    verifier.update(bytes);
167    verifier.finish()
168}
169
170/// A package an update would install.
171#[derive(Clone, Debug, Default, PartialEq, Eq, Hash)]
172pub struct UpdatePackage {
173    /// The version this package installs.
174    pub version: String,
175    /// Where the package is downloaded from.
176    pub download_url: String,
177    /// How large it is, when the release feed says.
178    pub size: Option<u64>,
179    /// What its bytes must hash to.
180    ///
181    /// `None` means the release feed published none, and
182    /// [`install_app_update`] refuses such a package: the platform's own
183    /// signature check catches a package signed by someone else, but not one
184    /// that arrived corrupted, and this is the one download that replaces the
185    /// application. A feed with no digest is a feed to fix.
186    pub digest: Option<PackageDigest>,
187    /// Release notes, when the feed carries them.
188    pub notes: Option<String>,
189}
190
191impl UpdatePackage {
192    /// A package at `download_url` installing `version`.
193    pub fn new(version: impl Into<String>, download_url: impl Into<String>) -> Self {
194        Self {
195            version: version.into(),
196            download_url: download_url.into(),
197            ..Self::default()
198        }
199    }
200
201    pub fn with_size(mut self, size: u64) -> Self {
202        self.size = Some(size);
203        self
204    }
205
206    pub fn with_digest(mut self, digest: PackageDigest) -> Self {
207        self.digest = Some(digest);
208        self
209    }
210
211    pub fn with_notes(mut self, notes: impl Into<String>) -> Self {
212        self.notes = Some(notes.into());
213        self
214    }
215
216    /// Whether this package can be checked against what the feed promised.
217    pub fn is_verifiable(&self) -> bool {
218        self.digest
219            .as_ref()
220            .is_some_and(PackageDigest::is_well_formed)
221    }
222}
223
224/// A GitHub release feed used to discover an application package.
225#[derive(Clone, Debug, PartialEq, Eq, Hash)]
226pub struct GitHubReleaseUpdate {
227    /// Repository in `owner/name` form.
228    pub repository: String,
229    /// Version of the running application.
230    pub current_version: String,
231    /// File-name suffix selected from the release assets, such as `.apk`.
232    pub asset_suffix: String,
233}
234
235impl GitHubReleaseUpdate {
236    /// Creates a GitHub release request.
237    pub fn new(
238        repository: impl Into<String>,
239        current_version: impl Into<String>,
240        asset_suffix: impl Into<String>,
241    ) -> Self {
242        Self {
243            repository: repository.into(),
244            current_version: current_version.into(),
245            asset_suffix: asset_suffix.into(),
246        }
247    }
248}
249
250/// Observable state of the application update flow.
251#[derive(Clone, Debug, Default, PartialEq, Eq)]
252pub enum AppUpdateStatus {
253    /// No operation has started.
254    #[default]
255    Idle,
256    /// The release feed is being queried.
257    Checking,
258    /// The running application is current.
259    UpToDate,
260    /// A package can be installed.
261    Available {
262        /// What the release feed offers, including its size and digest when it
263        /// published them.
264        package: UpdatePackage,
265    },
266    /// A package is being transferred to the platform installer.
267    Downloading {
268        /// Bytes transferred so far.
269        downloaded: u64,
270        /// Total bytes when supplied by the server.
271        total: Option<u64>,
272    },
273    /// The transfer finished and the package is being checked against the
274    /// digest the release feed published.
275    Verifying,
276    /// The platform is asking the user to approve installation.
277    AwaitingConfirmation,
278    /// The platform installer accepted the package.
279    Installing,
280    /// The operation could not continue.
281    Error(String),
282}
283
284/// Failure to start an update operation.
285#[derive(Clone, Debug, thiserror::Error, PartialEq, Eq)]
286pub enum AppUpdateError {
287    /// This platform has no registered installer.
288    #[error("application updates are unavailable on this platform")]
289    Unsupported,
290    /// The platform rejected the request before work started.
291    #[error("application update request failed: {0}")]
292    Request(String),
293    /// The release feed published no digest for this package.
294    ///
295    /// Refused rather than installed: this is an application replacing itself
296    /// with bytes off the network, and bytes nobody checked are bytes nobody
297    /// checked whether or not the feed mentioned it. A feed that publishes no
298    /// digest is a feed to fix, not a check to skip.
299    #[error("the release feed published no digest for this package, so it cannot be checked")]
300    Unverifiable,
301    /// The release feed published a digest this framework cannot check.
302    ///
303    /// Refused rather than ignored: a digest nobody checks reads as a package
304    /// that was verified.
305    #[error("the release feed published a digest that cannot be checked: {0}")]
306    MalformedDigest(String),
307    /// What arrived is not what the release feed promised.
308    #[error("the downloaded package does not match its digest (expected {expected}, got {actual})")]
309    VerificationFailed {
310        /// The digest the release feed published.
311        expected: String,
312        /// The digest the bytes that arrived actually have.
313        actual: String,
314    },
315}
316
317/// Platform implementation for update discovery and package installation.
318pub trait AppUpdater: Send + Sync {
319    /// What this backend can do.
320    ///
321    /// Defaults to neither, so a backend states what it can do rather than
322    /// inheriting a claim: the two entry points below refuse a half a backend
323    /// has not claimed, and a backend that forgot to declare one is refused
324    /// rather than allowed to fail at the platform boundary.
325    fn capabilities(&self) -> AppUpdateCapabilities {
326        AppUpdateCapabilities::default()
327    }
328
329    /// Starts release discovery. Progress is published through
330    /// [`set_app_update_status`].
331    fn check(&self, source: &GitHubReleaseUpdate) -> Result<(), AppUpdateError> {
332        let _ = source;
333        Err(AppUpdateError::Unsupported)
334    }
335
336    /// Transfers a package to the platform installer.
337    ///
338    /// An implementation checks the package against
339    /// [`UpdatePackage::digest`] before committing it — nothing is installed
340    /// whose bytes were not the ones the release feed promised.
341    fn install(&self, package: &UpdatePackage) -> Result<(), AppUpdateError> {
342        let _ = package;
343        Err(AppUpdateError::Unsupported)
344    }
345}
346
347/// What an update backend can do on this platform.
348///
349/// The two halves are separate because a platform can genuinely have one
350/// without the other: an iOS application may discover that a newer version
351/// exists and send the reader to the store, while installing a replacement
352/// binary is something the platform does not allow it to do at all. Reporting
353/// one flag for both would make `check` look unavailable where it works, or
354/// make `install` look available where it can only fail.
355#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
356pub struct AppUpdateCapabilities {
357    /// Whether this platform can discover a newer release.
358    pub check: bool,
359    /// Whether this platform can install one.
360    pub install: bool,
361}
362
363/// Shared updater service.
364pub type AppUpdaterRef = Arc<dyn AppUpdater>;
365
366static PLATFORM_UPDATER: ServiceRegistry<dyn AppUpdater> = ServiceRegistry::new();
367
368/// Installs the platform updater.
369pub fn set_platform_app_updater(updater: AppUpdaterRef) {
370    PLATFORM_UPDATER.set(updater);
371}
372
373/// Removes the platform updater.
374pub fn clear_platform_app_updater() {
375    PLATFORM_UPDATER.clear();
376}
377
378/// What this host can do about application updates.
379pub fn app_update_capabilities() -> AppUpdateCapabilities {
380    PLATFORM_UPDATER
381        .get()
382        .map(|updater| updater.capabilities())
383        .unwrap_or_default()
384}
385
386/// Returns whether this host can install application updates.
387pub fn app_updates_supported() -> bool {
388    app_update_capabilities().install
389}
390
391/// Returns whether this host can discover a newer release.
392///
393/// A host may answer yes here and no to [`app_updates_supported`]: knowing an
394/// update exists is what lets an application point at the store it cannot
395/// install from itself.
396pub fn app_update_checks_supported() -> bool {
397    app_update_capabilities().check
398}
399
400fn publish_failure(error: AppUpdateError) -> Result<(), AppUpdateError> {
401    set_app_update_status(AppUpdateStatus::Error(error.to_string()));
402    Err(error)
403}
404
405/// Starts update discovery and publishes the initial state.
406pub fn check_for_app_update(source: &GitHubReleaseUpdate) -> Result<(), AppUpdateError> {
407    let Some(updater) = PLATFORM_UPDATER.get() else {
408        return publish_failure(AppUpdateError::Unsupported);
409    };
410    if !updater.capabilities().check {
411        return publish_failure(AppUpdateError::Unsupported);
412    }
413    set_app_update_status(AppUpdateStatus::Checking);
414    updater.check(source).inspect_err(|error| {
415        set_app_update_status(AppUpdateStatus::Error(error.to_string()));
416    })
417}
418
419/// Starts package installation and publishes the initial transfer state.
420///
421/// A digest the release feed published but this framework cannot check is
422/// refused here, before anything is downloaded: nobody waits for two hundred
423/// megabytes to learn the feed was misconfigured, and nothing reaches an
424/// installer unchecked because its digest was unreadable.
425pub fn install_app_update(package: &UpdatePackage) -> Result<(), AppUpdateError> {
426    let Some(updater) = PLATFORM_UPDATER.get() else {
427        return publish_failure(AppUpdateError::Unsupported);
428    };
429    if !updater.capabilities().install {
430        return publish_failure(AppUpdateError::Unsupported);
431    }
432    let error = match &package.digest {
433        None => Some(AppUpdateError::Unverifiable),
434        Some(digest) if !digest.is_well_formed() => {
435            Some(AppUpdateError::MalformedDigest(digest.to_feed_string()))
436        }
437        Some(_) => None,
438    };
439    if let Some(error) = error {
440        return publish_failure(error);
441    }
442    set_app_update_status(AppUpdateStatus::Downloading {
443        downloaded: 0,
444        total: package.size,
445    });
446    updater.install(package).inspect_err(|error| {
447        set_app_update_status(AppUpdateStatus::Error(error.to_string()));
448    })
449}
450
451fn status_slot() -> &'static Mutex<AppUpdateStatus> {
452    static STATUS: OnceLock<Mutex<AppUpdateStatus>> = OnceLock::new();
453    STATUS.get_or_init(|| Mutex::new(AppUpdateStatus::Idle))
454}
455
456/// Returns the latest update state.
457pub fn app_update_status() -> AppUpdateStatus {
458    status_slot().lock().map_or_else(
459        |poisoned| poisoned.into_inner().clone(),
460        |status| status.clone(),
461    )
462}
463
464#[cfg(not(target_arch = "wasm32"))]
465type Observer = Arc<dyn Fn(AppUpdateStatus) + Send + Sync>;
466#[cfg(target_arch = "wasm32")]
467type Observer = std::rc::Rc<dyn Fn(AppUpdateStatus)>;
468
469#[cfg(not(target_arch = "wasm32"))]
470fn observers() -> &'static Mutex<Vec<(u64, Observer)>> {
471    static OBSERVERS: OnceLock<Mutex<Vec<(u64, Observer)>>> = OnceLock::new();
472    OBSERVERS.get_or_init(|| Mutex::new(Vec::new()))
473}
474
475#[cfg(target_arch = "wasm32")]
476thread_local! {
477    static OBSERVERS: std::cell::RefCell<Vec<(u64, Observer)>> = const { std::cell::RefCell::new(Vec::new()) };
478}
479
480static NEXT_OBSERVER_ID: AtomicU64 = AtomicU64::new(1);
481
482/// Registration returned by [`observe_app_update_status`].
483pub struct AppUpdateObserver {
484    id: u64,
485}
486
487impl Drop for AppUpdateObserver {
488    fn drop(&mut self) {
489        #[cfg(not(target_arch = "wasm32"))]
490        if let Ok(mut observers) = observers().lock() {
491            observers.retain(|(id, _)| *id != self.id);
492        }
493        #[cfg(target_arch = "wasm32")]
494        OBSERVERS.with(|observers| observers.borrow_mut().retain(|(id, _)| *id != self.id));
495    }
496}
497
498/// Observes update state changes. The current state is delivered immediately.
499#[cfg(not(target_arch = "wasm32"))]
500pub fn observe_app_update_status(
501    observer: impl Fn(AppUpdateStatus) + Send + Sync + 'static,
502) -> AppUpdateObserver {
503    let id = NEXT_OBSERVER_ID.fetch_add(1, Ordering::Relaxed);
504    let observer: Observer = Arc::new(observer);
505    if let Ok(mut observers) = observers().lock() {
506        observers.push((id, Arc::clone(&observer)));
507    }
508    observer(app_update_status());
509    AppUpdateObserver { id }
510}
511
512/// Observes update state changes. The current state is delivered immediately.
513#[cfg(target_arch = "wasm32")]
514pub fn observe_app_update_status(
515    observer: impl Fn(AppUpdateStatus) + 'static,
516) -> AppUpdateObserver {
517    let id = NEXT_OBSERVER_ID.fetch_add(1, Ordering::Relaxed);
518    let observer: Observer = std::rc::Rc::new(observer);
519    OBSERVERS.with(|observers| {
520        observers
521            .borrow_mut()
522            .push((id, std::rc::Rc::clone(&observer)));
523    });
524    observer(app_update_status());
525    AppUpdateObserver { id }
526}
527
528/// Publishes state from a platform updater.
529pub fn set_app_update_status(status: AppUpdateStatus) {
530    if let Ok(mut current) = status_slot().lock() {
531        if *current == status {
532            return;
533        }
534        *current = status.clone();
535    }
536    #[cfg(not(target_arch = "wasm32"))]
537    let observers = observers()
538        .lock()
539        .map(|observers| {
540            observers
541                .iter()
542                .map(|(_, observer)| Arc::clone(observer))
543                .collect::<Vec<_>>()
544        })
545        .unwrap_or_default();
546    #[cfg(target_arch = "wasm32")]
547    let observers = OBSERVERS.with(|observers| {
548        observers
549            .borrow()
550            .iter()
551            .map(|(_, observer)| std::rc::Rc::clone(observer))
552            .collect::<Vec<_>>()
553    });
554    for observer in observers {
555        observer(status.clone());
556    }
557}
558
559#[cfg(test)]
560#[path = "tests/app_update_tests.rs"]
561mod tests;
cranpose_services/app_update.rs

cranpose_services/
app_update.rs
