feat: Hash and Multihash arbitrary (#51)

Both for internal purposes and for use by other crates

Author: rklaehn

Cargo.toml

@@ -18,11 +18,16 @@ sha-1 = { version = "0.8", default-features = false }
 sha2 = { version = "0.8", default-features = false }
 sha3 = { version = "0.8", default-features = false }
 unsigned-varint = "0.3"
+quickcheck = { version = "0.9.2", optional = true }
+rand = { version = "0.7.3", optional = true }
 
 [dev-dependencies]
 criterion = "0.3"
-rand = "0.7"
 quickcheck = "0.9.2"
+rand = "0.7.3"
+
+[features]
+test = ["quickcheck", "rand"]
 
 [[bench]]
 name = "multihash"

src/arb.rs

@@ -0,0 +1,31 @@
+use crate::{Code, Code::*, Multihash};
+use quickcheck::{Arbitrary, Gen};
+use rand::seq::SliceRandom;
+
+const HASHES: [Code; 16] = [
+    Identity, Sha1, Sha2_256, Sha2_512, Sha3_512, Sha3_384, Sha3_256, Sha3_224, Keccak224,
+    Keccak256, Keccak384, Keccak512, Blake2b256, Blake2b512, Blake2s128, Blake2s256,
+];
+
+/// Generates a random hash algorithm.
+///
+/// The more exotic ones will be generated just as frequently as the common ones.
+impl Arbitrary for Code {
+    fn arbitrary<G: Gen>(g: &mut G) -> Self {
+        *HASHES.choose(g).unwrap()
+    }
+}
+
+/// Generates a random valid multihash.
+///
+/// This is done by encoding a random piece of data.
+impl Arbitrary for Multihash {
+    fn arbitrary<G: Gen>(g: &mut G) -> Self {
+        let code: Code = Arbitrary::arbitrary(g);
+        let data: Vec<u8> = Arbitrary::arbitrary(g);
+        // encoding an actual random piece of data might be better than just choosing
+        // random numbers of the appropriate size, since some hash algos might produce
+        // a limited set of values
+        code.hasher().unwrap().digest(&data)
+    }
+}

src/lib.rs

@@ -13,6 +13,9 @@ mod errors;
 mod hashes;
 mod storage;
 
+#[cfg(any(test, feature = "test"))]
+mod arb;
+
 pub use digests::{wrap, Multihash, MultihashDigest, MultihashRef};
 pub use errors::{DecodeError, DecodeOwnedError, EncodeError};
 pub use hashes::*;