4 files changed, 64 insertions, 1 deletions
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7d6962a..b02936a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 #### [Unreleased]
 
 - BREAKING CHANGE: Support Dhall v19.0.0
+- Support reading a CBOR-encoded binary file (https://github.com/Nadrieril/dhall-rust/issues/199)
 
 #### [0.8.0] - 2020-10-28
 
diff --git a/serde_dhall/src/lib.rs b/serde_dhall/src/lib.rs
index 9f8539f..2af445c 100644
--- a/serde_dhall/src/lib.rs
+++ b/serde_dhall/src/lib.rs
@@ -274,7 +274,7 @@ pub use dhall_proc_macros::StaticType;
 pub use deserialize::{from_simple_value, FromDhall};
 pub(crate) use error::ErrorKind;
 pub use error::{Error, Result};
-pub use options::de::{from_file, from_str, Deserializer};
+pub use options::de::{from_binary_file, from_file, from_str, Deserializer};
 pub use options::ser::{serialize, Serializer};
 pub use serialize::ToDhall;
 pub use static_type::StaticType;
diff --git a/serde_dhall/src/options/de.rs b/serde_dhall/src/options/de.rs
index e4f3456..22fa7ba 100644
--- a/serde_dhall/src/options/de.rs
+++ b/serde_dhall/src/options/de.rs
@@ -10,6 +10,7 @@ use crate::{Error, ErrorKind, FromDhall, Result, Value};
 enum Source<'a> {
     Str(&'a str),
     File(PathBuf),
+    BinaryFile(PathBuf),
     // Url(&'a str),
 }
 
@@ -80,6 +81,9 @@ impl<'a> Deserializer<'a, NoAnnot> {
     fn from_file<P: AsRef<Path>>(path: P) -> Self {
         Self::default_with_source(Source::File(path.as_ref().to_owned()))
     }
+    fn from_binary_file<P: AsRef<Path>>(path: P) -> Self {
+        Self::default_with_source(Source::BinaryFile(path.as_ref().to_owned()))
+    }
     // fn from_url(url: &'a str) -> Self {
     //     Self::default_with_source(Source::Url(url))
     // }
@@ -233,6 +237,7 @@ impl<'a, A> Deserializer<'a, A> {
         let parsed = match &self.source {
             Source::Str(s) => Parsed::parse_str(s)?,
             Source::File(p) => Parsed::parse_file(p.as_ref())?,
+            Source::BinaryFile(p) => Parsed::parse_binary_file(p.as_ref())?,
         };
         let resolved = if self.allow_imports {
             parsed.resolve()?
@@ -344,6 +349,42 @@ pub fn from_file<'a, P: AsRef<Path>>(path: P) -> Deserializer<'a, NoAnnot> {
     Deserializer::from_file(path)
 }
 
+/// Deserialize a value from a CBOR-encoded Dhall binary file. The binary format is specified by
+/// the Dhall standard specification and is mostly used for caching expressions. Using the format
+/// is not recommended because errors won't have a file to refer to and thus will be hard to fix.
+///
+/// This returns a [`Deserializer`] object. Call the [`parse`] method to get the deserialized
+/// value, or use other [`Deserializer`] methods to control the deserialization process.
+///
+/// Imports will be resolved relative to the provided file's path.
+///
+/// # Example
+///
+/// ```no_run
+/// # fn main() -> serde_dhall::Result<()> {
+/// use serde::Deserialize;
+///
+/// // We use serde's derive feature
+/// #[derive(Deserialize)]
+/// struct Point {
+///     x: u64,
+///     y: u64,
+/// }
+///
+/// // Parse the Dhall file as a Point.
+/// let point: Point = serde_dhall::from_binary_file("foo.dhallb").parse()?;
+/// # Ok(())
+/// # }
+/// ```
+///
+/// [`Deserializer`]: struct.Deserializer.html
+/// [`parse`]: struct.Deserializer.html#method.parse
+pub fn from_binary_file<'a, P: AsRef<Path>>(
+    path: P,
+) -> Deserializer<'a, NoAnnot> {
+    Deserializer::from_binary_file(path)
+}
+
 // pub fn from_url(url: &str) -> Deserializer<'_, NoAnnot> {
 //     Deserializer::from_url(url)
 // }
diff --git a/serde_dhall/tests/serde.rs b/serde_dhall/tests/serde.rs
index 4c184e7..1181f72 100644
--- a/serde_dhall/tests/serde.rs
+++ b/serde_dhall/tests/serde.rs
@@ -205,6 +205,27 @@ mod serde {
         assert!(from_str("List/length [True, 42]").parse::<bool>().is_err());
     }
 
+    #[test]
+    fn test_file() {
+        assert_eq!(
+            serde_dhall::from_file(
+                "../dhall-lang/tests/parser/success/unit/BoolLitTrueA.dhall"
+            )
+            .static_type_annotation()
+            .parse::<bool>()
+            .map_err(|e| e.to_string()),
+            Ok(true)
+        );
+        assert_eq!(
+            serde_dhall::from_binary_file(
+                "../dhall-lang/tests/parser/success/unit/BoolLitTrueB.dhallb"
+            )
+            .static_type_annotation()
+            .parse::<bool>()
+            .map_err(|e| e.to_string()),
+            Ok(true)
+        );
+    }
     // TODO: test various builder configurations
     // In particular test cloning and reusing builder
 }