Add --only-cached/-C command line flag

src/bin/tectonic.rs

@@ -101,13 +101,17 @@ fn inner(args: ArgMatches, config: PersistentConfig, status: &mut TermcolorStatu
         }
     }
 
+    let only_cached = args.is_present("only_cached");
+    if only_cached {
+        tt_note!(status, "using only cached resource files");
+    }
     if let Some(p) = args.value_of("bundle") {
         let zb = ctry!(ZipBundle::<File>::open(Path::new(&p)); "error opening bundle");
         sess_builder.bundle(Box::new(zb));
     } else if let Some(u) = args.value_of("web_bundle") {
-        sess_builder.bundle(Box::new(config.make_cached_url_provider(&u, status)?));
+        sess_builder.bundle(Box::new(config.make_cached_url_provider(&u, only_cached, status)?));
     } else {
-        sess_builder.bundle(config.default_bundle(status)?);
+        sess_builder.bundle(config.default_bundle(only_cached, status)?);
     }
 
     let mut sess = sess_builder.create(status)?;
@@ -149,6 +153,10 @@ fn main() {
              .value_name("URL")
              .help("Use this URL find resource files instead of the default")
              .takes_value(true))
+        .arg(Arg::with_name("only_cached")
+             .short("C")
+             .long("only-cached")
+             .help("Use only resource files cached locally"))
         .arg(Arg::with_name("outfmt")
              .long("outfmt")
              .value_name("FORMAT")

src/config.rs

@@ -74,7 +74,7 @@ impl PersistentConfig {
         Ok(config)
     }
 
-    pub fn make_cached_url_provider(&self, url: &str, status: &mut StatusBackend) -> Result<LocalCache<ITarBundle<HttpITarIoFactory>>> {
+    pub fn make_cached_url_provider(&self, url: &str, only_cached: bool, status: &mut StatusBackend) -> Result<LocalCache<ITarBundle<HttpITarIoFactory>>> {
         let itb = ITarBundle::<HttpITarIoFactory>::new(url);
 
         let mut url2digest_path = app_dir(AppDataType::UserCache, &::APP_INFO, "urls")?;
@@ -85,16 +85,17 @@ impl PersistentConfig {
             &url2digest_path,
             &app_dir(AppDataType::UserCache, &::APP_INFO, "manifests")?,
             &app_dir(AppDataType::UserCache, &::APP_INFO, "files")?,
+            only_cached,
             status
         )
     }
 
-    pub fn default_bundle(&self, status: &mut StatusBackend) -> Result<Box<Bundle>> {
+    pub fn default_bundle(&self, only_cached: bool, status: &mut StatusBackend) -> Result<Box<Bundle>> {
         if self.default_bundles.len() != 1 {
             return Err(ErrorKind::Msg("exactly one default_bundle item must be specified (for now)".to_owned()).into());
         }
 
-        Ok(Box::new(self.make_cached_url_provider(&self.default_bundles[0].url, status)?))
+        Ok(Box::new(self.make_cached_url_provider(&self.default_bundles[0].url, only_cached, status)?))
     }
 
     pub fn format_cache_path(&self) -> Result<PathBuf> {

src/io/local_cache.rs

@@ -31,13 +31,14 @@ pub struct LocalCache<B: Bundle> {
     manifest_path: PathBuf,
     data_path: PathBuf,
     contents: HashMap<OsString,LocalCacheItem>,
+    only_cached: bool,
 }
 
 
 impl<B: Bundle> LocalCache<B> {
     pub fn new(
         mut backend: B, digest: &Path, manifest_base: &Path,
-        data: &Path, status: &mut StatusBackend
+        data: &Path, only_cached: bool, status: &mut StatusBackend
     ) -> Result<LocalCache<B>> {
         // If the `digest` file exists, we assume that it is valid; this is
         // *essential* so that we can use a URL as our default IoProvider
@@ -142,7 +143,8 @@ impl<B: Bundle> LocalCache<B> {
             checked_digest: checked_digest,
             manifest_path: manifest_path,
             data_path: data.to_owned(),
-            contents: contents
+            contents: contents,
+            only_cached: only_cached,
         })
     }
 
@@ -225,6 +227,11 @@ impl<B: Bundle> LocalCache<B> {
             };
         }
 
+        // The file is not in the cache and we are asked not to try to fetch it.
+        if self.only_cached {
+            return OpenResult::NotAvailable;
+        }
+
         // Bummer, we haven't seen this file before. We need to (try to) fetch
         // the item from the backend, saving it to disk and calculating its
         // digest ourselves, then enter it in the cache and in our manifest.