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
use base64::Engine;
use log::{debug, trace, warn};
use serde::{Deserialize, Serialize};
use sha2::{Digest, Sha256};
use std::hash::Hash;
use std::hash::Hasher;
use std::io::Write;
use std::path::{Path, PathBuf};
use std::{fs, io};

#[macro_use] // for tests
mod config;
mod worker;

pub use config::{create_new_config, CacheConfig};
use worker::Worker;

/// Module level cache entry.
pub struct ModuleCacheEntry<'config>(Option<ModuleCacheEntryInner<'config>>);

struct ModuleCacheEntryInner<'config> {
    root_path: PathBuf,
    cache_config: &'config CacheConfig,
}

struct Sha256Hasher(Sha256);

impl<'config> ModuleCacheEntry<'config> {
    /// Create the cache entry.
    pub fn new<'data>(compiler_name: &str, cache_config: &'config CacheConfig) -> Self {
        if cache_config.enabled() {
            Self(Some(ModuleCacheEntryInner::new(
                compiler_name,
                cache_config,
            )))
        } else {
            Self(None)
        }
    }

    #[cfg(test)]
    fn from_inner(inner: ModuleCacheEntryInner<'config>) -> Self {
        Self(Some(inner))
    }

    /// Gets cached data if state matches, otherwise calls `compute`.
    ///
    /// Data is automatically serialized/deserialized with `bincode`.
    pub fn get_data<T, U, E>(&self, state: T, compute: fn(&T) -> Result<U, E>) -> Result<U, E>
    where
        T: Hash,
        U: Serialize + for<'a> Deserialize<'a>,
    {
        self.get_data_raw(
            &state,
            compute,
            |_state, data| bincode::serialize(data).ok(),
            |_state, data| bincode::deserialize(&data).ok(),
        )
    }

    /// Gets cached data if state matches, otherwise calls `compute`.
    ///
    /// If the cache is disabled or no cached data is found then `compute` is
    /// called to calculate the data. If the data was found in cache it is
    /// passed to `deserialize`, which if successful will be the returned value.
    /// When computed the `serialize` function is used to generate the bytes
    /// from the returned value.
    pub fn get_data_raw<T, U, E>(
        &self,
        state: &T,
        // NOTE: These are function pointers instead of closures so that they
        // don't accidentally close over something not accounted in the cache.
        compute: fn(&T) -> Result<U, E>,
        serialize: fn(&T, &U) -> Option<Vec<u8>>,
        deserialize: fn(&T, Vec<u8>) -> Option<U>,
    ) -> Result<U, E>
    where
        T: Hash,
    {
        let inner = match &self.0 {
            Some(inner) => inner,
            None => return compute(state),
        };

        let mut hasher = Sha256Hasher(Sha256::new());
        state.hash(&mut hasher);
        let hash: [u8; 32] = hasher.0.finalize().into();
        // standard encoding uses '/' which can't be used for filename
        let hash = base64::engine::general_purpose::URL_SAFE_NO_PAD.encode(&hash);

        if let Some(cached_val) = inner.get_data(&hash) {
            if let Some(val) = deserialize(state, cached_val) {
                let mod_cache_path = inner.root_path.join(&hash);
                inner.cache_config.on_cache_get_async(&mod_cache_path); // call on success
                return Ok(val);
            }
        }
        let val_to_cache = compute(state)?;
        if let Some(bytes) = serialize(state, &val_to_cache) {
            if inner.update_data(&hash, &bytes).is_some() {
                let mod_cache_path = inner.root_path.join(&hash);
                inner.cache_config.on_cache_update_async(&mod_cache_path); // call on success
            }
        }
        Ok(val_to_cache)
    }
}

impl<'config> ModuleCacheEntryInner<'config> {
    fn new<'data>(compiler_name: &str, cache_config: &'config CacheConfig) -> Self {
        // If debug assertions are enabled then assume that we're some sort of
        // local build. We don't want local builds to stomp over caches between
        // builds, so just use a separate cache directory based on the mtime of
        // our executable, which should roughly correlate with "you changed the
        // source code so you get a different directory".
        //
        // Otherwise if this is a release build we use the `GIT_REV` env var
        // which is either the git rev if installed from git or the crate
        // version if installed from crates.io.
        let compiler_dir = if cfg!(debug_assertions) {
            fn self_mtime() -> Option<String> {
                let path = std::env::current_exe().ok()?;
                let metadata = path.metadata().ok()?;
                let mtime = metadata.modified().ok()?;
                Some(match mtime.duration_since(std::time::UNIX_EPOCH) {
                    Ok(dur) => format!("{}", dur.as_millis()),
                    Err(err) => format!("m{}", err.duration().as_millis()),
                })
            }
            let self_mtime = self_mtime().unwrap_or("no-mtime".to_string());
            format!(
                "{comp_name}-{comp_ver}-{comp_mtime}",
                comp_name = compiler_name,
                comp_ver = env!("GIT_REV"),
                comp_mtime = self_mtime,
            )
        } else {
            format!(
                "{comp_name}-{comp_ver}",
                comp_name = compiler_name,
                comp_ver = env!("GIT_REV"),
            )
        };
        let root_path = cache_config.directory().join("modules").join(compiler_dir);

        Self {
            root_path,
            cache_config,
        }
    }

    fn get_data(&self, hash: &str) -> Option<Vec<u8>> {
        let mod_cache_path = self.root_path.join(hash);
        trace!("get_data() for path: {}", mod_cache_path.display());
        let compressed_cache_bytes = fs::read(&mod_cache_path).ok()?;
        let cache_bytes = zstd::decode_all(&compressed_cache_bytes[..])
            .map_err(|err| warn!("Failed to decompress cached code: {}", err))
            .ok()?;
        Some(cache_bytes)
    }

    fn update_data(&self, hash: &str, serialized_data: &[u8]) -> Option<()> {
        let mod_cache_path = self.root_path.join(hash);
        trace!("update_data() for path: {}", mod_cache_path.display());
        let compressed_data = zstd::encode_all(
            &serialized_data[..],
            self.cache_config.baseline_compression_level(),
        )
        .map_err(|err| warn!("Failed to compress cached code: {}", err))
        .ok()?;

        // Optimize syscalls: first, try writing to disk. It should succeed in most cases.
        // Otherwise, try creating the cache directory and retry writing to the file.
        if fs_write_atomic(&mod_cache_path, "mod", &compressed_data).is_ok() {
            return Some(());
        }

        debug!(
            "Attempting to create the cache directory, because \
             failed to write cached code to disk, path: {}",
            mod_cache_path.display(),
        );

        let cache_dir = mod_cache_path.parent().unwrap();
        fs::create_dir_all(cache_dir)
            .map_err(|err| {
                warn!(
                    "Failed to create cache directory, path: {}, message: {}",
                    cache_dir.display(),
                    err
                )
            })
            .ok()?;

        match fs_write_atomic(&mod_cache_path, "mod", &compressed_data) {
            Ok(_) => Some(()),
            Err(err) => {
                warn!(
                    "Failed to write file with rename, target path: {}, err: {}",
                    mod_cache_path.display(),
                    err
                );
                None
            }
        }
    }
}

impl Hasher for Sha256Hasher {
    fn finish(&self) -> u64 {
        panic!("Sha256Hasher doesn't support finish!");
    }

    fn write(&mut self, bytes: &[u8]) {
        self.0.update(bytes);
    }
}

// Assumption: path inside cache directory.
// Then, we don't have to use sound OS-specific exclusive file access.
// Note: there's no need to remove temporary file here - cleanup task will do it later.
fn fs_write_atomic(path: &Path, reason: &str, contents: &[u8]) -> io::Result<()> {
    let lock_path = path.with_extension(format!("wip-atomic-write-{}", reason));
    fs::OpenOptions::new()
        .create_new(true) // atomic file creation (assumption: no one will open it without this flag)
        .write(true)
        .open(&lock_path)
        .and_then(|mut file| file.write_all(contents))
        // file should go out of scope and be closed at this point
        .and_then(|()| fs::rename(&lock_path, &path)) // atomic file rename
}

#[cfg(test)]
mod tests;