Add support for hashing from a reader

fixes #141

Author: Stebalien

derive/Cargo.toml

@@ -25,4 +25,4 @@ std = []
 
 [dev-dependencies]
 pretty_assertions = "1.0.0"
-multihash = { path = "..", default-features = false, features = ["derive", "sha2"] }
+multihash = { path = "..", default-features = false, features = ["derive", "sha2", "std"] }

derive/src/lib.rs

@@ -22,7 +22,7 @@
 //! use multihash::MultihashDigest;
 //!
 //! #[derive(Clone, Copy, Debug, Eq, Multihash, PartialEq)]
-//! #[mh(alloc_size = 64)]
+//! #[mh(alloc_size = 64, io_path = ::std::io)]
 //! pub enum Code {
 //!     #[mh(code = 0x01, hasher = multihash::Sha2_256)]
 //!     Foo,

derive/src/multihash.rs

@@ -17,6 +17,7 @@ mod kw {
     custom_keyword!(hasher);
     custom_keyword!(mh);
     custom_keyword!(alloc_size);
+    custom_keyword!(io_path);
 }
 
 /// Attributes for the enum items.
@@ -42,12 +43,15 @@ impl Parse for MhAttr {
 #[derive(Debug)]
 enum DeriveAttr {
     AllocSize(utils::Attr<kw::alloc_size, syn::LitInt>),
+    IoPath(utils::Attr<kw::io_path, syn::Path>),
 }
 
 impl Parse for DeriveAttr {
     fn parse(input: ParseStream) -> syn::Result<Self> {
         if input.peek(kw::alloc_size) {
             Ok(Self::AllocSize(input.parse()?))
+        } else if input.peek(kw::io_path) {
+            Ok(Self::IoPath(input.parse()?))
         } else {
             Err(syn::Error::new(input.span(), "unknown attribute"))
         }
@@ -89,6 +93,17 @@ impl Hash {
             Multihash::wrap(#code, hasher.finalize()).unwrap()
         })
     }
+
+    fn code_reader(&self) -> TokenStream {
+        let ident = &self.ident;
+        let hasher = &self.hasher;
+        let code = &self.code;
+        quote!(Self::#ident => {
+            let mut hasher = #hasher::default();
+            io::copy(reader, &mut hasher)?;
+            Ok(Multihash::wrap(#code, hasher.finalize()).unwrap())
+        })
+    }
 }
 
 impl<'a> From<&'a VariantInfo<'a>> for Hash {
@@ -134,9 +149,11 @@ impl<'a> From<&'a VariantInfo<'a>> for Hash {
 ///
 /// Returns the `alloc_size` and whether errors regarding to `alloc_size` should be reported or not.
 #[allow(dead_code)] // TODO
-fn parse_code_enum_attrs(ast: &syn::DeriveInput) -> syn::LitInt {
+fn parse_code_enum_attrs(ast: &syn::DeriveInput) -> (syn::LitInt, syn::Path) {
     let mut alloc_size = None;
 
+    let mut io_path = syn::parse_quote!(::std::io);
+
     for attr in &ast.attrs {
         let derive_attrs: Result<utils::Attrs<DeriveAttr>, _> = syn::parse2(attr.tokens.clone());
         if let Ok(derive_attrs) = derive_attrs {
@@ -145,12 +162,15 @@ fn parse_code_enum_attrs(ast: &syn::DeriveInput) -> syn::LitInt {
                     DeriveAttr::AllocSize(alloc_size_attr) => {
                         alloc_size = Some(alloc_size_attr.value)
                     }
+                    DeriveAttr::IoPath(io_path_attr) => {
+                        io_path = io_path_attr.value;
+                    }
                 }
             }
         }
     }
     match alloc_size {
-        Some(alloc_size) => alloc_size,
+        Some(alloc_size) => (alloc_size, io_path),
         None => {
             let msg = "enum is missing `alloc_size` attribute: e.g. #[mh(alloc_size = 64)]";
             #[cfg(test)]
@@ -206,7 +226,7 @@ pub fn multihash(s: Structure) -> TokenStream {
         }
     };
     let code_enum = &s.ast().ident;
-    let alloc_size = parse_code_enum_attrs(s.ast());
+    let (alloc_size, io_path) = parse_code_enum_attrs(s.ast());
     let hashes: Vec<_> = s.variants().iter().map(Hash::from).collect();
 
     error_code_duplicates(&hashes);
@@ -218,6 +238,7 @@ pub fn multihash(s: Structure) -> TokenStream {
     let code_into_u64 = hashes.iter().map(|h| h.code_into_u64(&params));
     let code_from_u64 = hashes.iter().map(|h| h.code_from_u64());
     let code_digest = hashes.iter().map(|h| h.code_digest());
+    let code_reader = hashes.iter().map(|h| h.code_reader());
 
     quote! {
         /// A Multihash with the same allocated size as the Multihashes produces by this derive.
@@ -232,6 +253,15 @@ pub fn multihash(s: Structure) -> TokenStream {
                 }
             }
 
+            fn digest_reader<R: #io_path::Read>(&self, reader: &mut R) -> #io_path::Result<Multihash> {
+                use #io_path;
+                use #mh_crate::Hasher;
+                match self {
+                    #(#code_reader,)*
+                    _ => unreachable!(),
+                }
+            }
+
             fn wrap(&self, digest: &[u8]) -> Result<Multihash, #mh_crate::Error> {
                 Multihash::wrap((*self).into(), digest)
             }
@@ -298,9 +328,27 @@ mod tests {
                    }
                }
 
-               fn wrap(&self, digest: &[u8]) -> Result<Multihash, multihash::Error> {
-                Multihash::wrap((*self).into(), digest)
+               fn digest_reader<R: ::std::io::Read>(&self, reader: &mut R) -> ::std::io::Result<Multihash> {
+                   use ::std::io;
+                   use multihash::Hasher;
+                   match self {
+                       Self::Identity256 => {
+                           let mut hasher = multihash::Identity256::default();
+                           io::copy(reader, &mut hasher)?;
+                           Ok(Multihash::wrap(multihash::IDENTITY, hasher.finalize()).unwrap())
+                       },
+                       Self::Strobe256 => {
+                           let mut hasher = multihash::Strobe256::default();
+                           io::copy(reader, &mut hasher)?;
+                           Ok(Multihash::wrap(0x38b64f, hasher.finalize()).unwrap())
+                       },
+                       _ => unreachable!(),
+                   }
                }
+
+                fn wrap(&self, digest: &[u8]) -> Result<Multihash, multihash::Error> {
+                    Multihash::wrap((*self).into(), digest)
+                }
             }
 
             impl From<Code> for u64 {

derive/src/utils.rs

@@ -4,7 +4,7 @@ use syn::parse::{Parse, ParseStream};
 use syn::punctuated::Punctuated;
 use syn::Error;
 
-pub fn use_crate(name: &str) -> Result<syn::Ident, Error> {
+pub(crate) fn use_crate(name: &str) -> Result<syn::Ident, Error> {
     match crate_name(name) {
         Ok(FoundCrate::Name(krate)) => Ok(syn::Ident::new(&krate, Span::call_site())),
         Ok(FoundCrate::Itself) => Ok(syn::Ident::new("crate", Span::call_site())),

examples/custom_table.rs

@@ -3,6 +3,12 @@ use std::convert::TryFrom;
 use multihash::derive::Multihash;
 use multihash::{Error, Hasher, MultihashDigest, MultihashGeneric, Sha2_256};
 
+#[cfg(feature = "std")]
+use std::io;
+
+#[cfg(not(feature = "std"))]
+use core2::io;
+
 // You can implement a custom hasher. This is a SHA2 256-bit hasher that returns a hash that is
 // truncated to 160 bits.
 #[derive(Default, Debug)]
@@ -19,6 +25,15 @@ impl Hasher for Sha2_256Truncated20 {
     }
 }
 
+impl io::Write for Sha2_256Truncated20 {
+    fn write(&mut self, input: &[u8]) -> io::Result<usize> {
+        self.0.write(input)
+    }
+    fn flush(&mut self) -> io::Result<()> {
+        Ok(())
+    }
+}
+
 #[derive(Clone, Copy, Debug, Eq, Multihash, PartialEq)]
 #[mh(alloc_size = 64)]
 pub enum Code {

src/hasher.rs

@@ -1,5 +1,11 @@
+#[cfg(feature = "std")]
+use std::io;
+
+#[cfg(not(feature = "std"))]
+use core2::io;
+
 /// Trait implemented by a hash function implementation.
-pub trait Hasher {
+pub trait Hasher: io::Write {
     /// Consume input and update internal state.
     fn update(&mut self, input: &[u8]);
 

src/multihash.rs

@@ -35,7 +35,27 @@ pub trait MultihashDigest<const S: usize>:
     /// let hash = Code::Sha3_256.digest(b"Hello world!");
     /// println!("{:02x?}", hash);
     /// ```
-    fn digest(&self, input: &[u8]) -> Multihash<S>;
+    fn digest(&self, input: &[u8]) -> Multihash<S> {
+        let mut input = input;
+        self.digest_reader(&mut input).unwrap()
+    }
+
+    /// Calculate the hash of some input stream.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// // `Code` implements `MultihashDigest`
+    /// use multihash::{Code, MultihashDigest};
+    ///
+    /// let mut data = std::io::Cursor::new(b"Hello world!");
+    ///
+    /// let hash = Code::Sha3_256.digest_reader(&mut data).unwrap();
+    /// println!("{:02x?}", hash);
+    /// ```
+    fn digest_reader<R: io::Read>(&self, input: &mut R) -> io::Result<Multihash<S>>
+    where
+        Self: Sized;
 
     /// Create a multihash from an existing multihash digest.
     ///
@@ -49,7 +69,9 @@ pub trait MultihashDigest<const S: usize>:
     /// let hash = Code::Sha3_256.wrap(&hasher.finalize()).unwrap();
     /// println!("{:02x?}", hash);
     /// ```
-    fn wrap(&self, digest: &[u8]) -> Result<Multihash<S>, Error>;
+    fn wrap(&self, digest: &[u8]) -> Result<Multihash<S>, Error> {
+        Multihash::wrap((*self).into(), digest)
+    }
 }
 
 /// A Multihash instance that only supports the basic functionality and no hashing.

src/multihash_impl.rs

@@ -7,7 +7,8 @@ pub use multihash_derive::Multihash;
 ///
 /// [`Multihash` derive]: crate::derive
 #[derive(Copy, Clone, Debug, Eq, Multihash, PartialEq)]
-#[mh(alloc_size = 64)]
+#[cfg_attr(feature = "std", mh(alloc_size = 64, io_path = ::std::io))]
+#[cfg_attr(not(feature = "std"), mh(alloc_size = 64, io_path = ::core2::io))]
 pub enum Code {
     /// SHA-256 (32-byte hash size)
     #[cfg(feature = "sha2")]

tests/lib.rs

@@ -70,6 +70,13 @@ macro_rules! assert_encode {
                expected,
                "{:?} encodes correctly (from hasher)", stringify!($alg)
            );
+
+           // From a reader.
+           assert_eq!(
+               $code.digest_reader(&mut Cursor::new($data)).unwrap().to_bytes(),
+               expected,
+               "{:?} encodes correctly (from hasher)", stringify!($alg)
+           );
        )*
    }
 }