adler32: Add tests from the standard library

1 files changed, 231 insertions, 0 deletions

diff --git a/internal/adler32/testhash.go b/internal/adler32/testhash.go
new file mode 100644
index 00000000..cadf8748
--- /dev/null
+++ b/internal/adler32/testhash.go
@@ -0,0 +1,231 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package adler32
+
+import (
+	"bytes"
+	"hash"
+	"io"
+	"math/rand"
+	"testing"
+	"time"
+)
+
+type MakeHash func() hash.Hash
+
+// TestHash performs a set of tests on hash.Hash implementations, checking the
+// documented requirements of Write, Sum, Reset, Size, and BlockSize.
+func TestHash(t *testing.T, mh MakeHash) {
+	TestHashWithoutClone(t, mh)
+
+	// Test whether the results after cloning are consistent.
+	t.Run("Clone", func(t *testing.T) {
+		h, ok := mh().(hash.Cloner)
+		if !ok {
+			t.Fatalf("%T does not implement hash.Cloner", mh)
+		}
+		h3, err := h.Clone()
+		if err != nil {
+			t.Fatalf("Clone failed: %v", err)
+		}
+		prefix := []byte("tmp")
+		writeToHash(t, h, prefix)
+		h2, err := h.Clone()
+		if err != nil {
+			t.Fatalf("Clone failed: %v", err)
+		}
+		prefixSum := h.Sum(nil)
+		if !bytes.Equal(prefixSum, h2.Sum(nil)) {
+			t.Fatalf("%T Clone results are inconsistent", h)
+		}
+		suffix := []byte("tmp2")
+		writeToHash(t, h, suffix)
+		writeToHash(t, h3, append(prefix, suffix...))
+		compositeSum := h3.Sum(nil)
+		if !bytes.Equal(h.Sum(nil), compositeSum) {
+			t.Fatalf("%T Clone results are inconsistent", h)
+		}
+		if !bytes.Equal(h2.Sum(nil), prefixSum) {
+			t.Fatalf("%T Clone results are inconsistent", h)
+		}
+		writeToHash(t, h2, suffix)
+		if !bytes.Equal(h.Sum(nil), compositeSum) {
+			t.Fatalf("%T Clone results are inconsistent", h)
+		}
+		if !bytes.Equal(h2.Sum(nil), compositeSum) {
+			t.Fatalf("%T Clone results are inconsistent", h)
+		}
+	})
+}
+
+func TestHashWithoutClone(t *testing.T, mh MakeHash) {
+	// Test that Sum returns an appended digest matching output of Size
+	t.Run("SumAppend", func(t *testing.T) {
+		h := mh()
+		rng := newRandReader(t)
+
+		emptyBuff := []byte("")
+		shortBuff := []byte("a")
+		longBuff := make([]byte, h.BlockSize()+1)
+		rng.Read(longBuff)
+
+		// Set of example strings to append digest to
+		prefixes := [][]byte{nil, emptyBuff, shortBuff, longBuff}
+
+		// Go to each string and check digest gets appended to and is correct size.
+		for _, prefix := range prefixes {
+			h.Reset()
+
+			sum := getSum(t, h, prefix) // Append new digest to prefix
+
+			// Check that Sum didn't alter the prefix
+			if !bytes.Equal(sum[:len(prefix)], prefix) {
+				t.Errorf("Sum alters passed buffer instead of appending; got %x, want %x", sum[:len(prefix)], prefix)
+			}
+
+			// Check that the appended sum wasn't affected by the prefix
+			if expectedSum := getSum(t, h, nil); !bytes.Equal(sum[len(prefix):], expectedSum) {
+				t.Errorf("Sum behavior affected by data in the input buffer; got %x, want %x", sum[len(prefix):], expectedSum)
+			}
+
+			// Check size of append
+			if got, want := len(sum)-len(prefix), h.Size(); got != want {
+				t.Errorf("Sum appends number of bytes != Size; got %v , want %v", got, want)
+			}
+		}
+	})
+
+	// Test that Hash.Write never returns error.
+	t.Run("WriteWithoutError", func(t *testing.T) {
+		h := mh()
+		rng := newRandReader(t)
+
+		emptySlice := []byte("")
+		shortSlice := []byte("a")
+		longSlice := make([]byte, h.BlockSize()+1)
+		rng.Read(longSlice)
+
+		// Set of example strings to append digest to
+		slices := [][]byte{emptySlice, shortSlice, longSlice}
+
+		for _, slice := range slices {
+			writeToHash(t, h, slice) // Writes and checks Write doesn't error
+		}
+	})
+
+	t.Run("ResetState", func(t *testing.T) {
+		h := mh()
+		rng := newRandReader(t)
+
+		emptySum := getSum(t, h, nil)
+
+		// Write to hash and then Reset it and see if Sum is same as emptySum
+		writeEx := make([]byte, h.BlockSize())
+		rng.Read(writeEx)
+		writeToHash(t, h, writeEx)
+		h.Reset()
+		resetSum := getSum(t, h, nil)
+
+		if !bytes.Equal(emptySum, resetSum) {
+			t.Errorf("Reset hash yields different Sum than new hash; got %x, want %x", emptySum, resetSum)
+		}
+	})
+
+	// Check that Write isn't reading from beyond input slice's bounds
+	t.Run("OutOfBoundsRead", func(t *testing.T) {
+		h := mh()
+		blockSize := h.BlockSize()
+		rng := newRandReader(t)
+
+		msg := make([]byte, blockSize)
+		rng.Read(msg)
+		writeToHash(t, h, msg)
+		expectedDigest := getSum(t, h, nil) // Record control digest
+
+		h.Reset()
+
+		// Make a buffer with msg in the middle and data on either end
+		buff := make([]byte, blockSize*3)
+		endOfPrefix, startOfSuffix := blockSize, blockSize*2
+
+		copy(buff[endOfPrefix:startOfSuffix], msg)
+		rng.Read(buff[:endOfPrefix])
+		rng.Read(buff[startOfSuffix:])
+
+		writeToHash(t, h, buff[endOfPrefix:startOfSuffix])
+		testDigest := getSum(t, h, nil)
+
+		if !bytes.Equal(testDigest, expectedDigest) {
+			t.Errorf("Write affected by data outside of input slice bounds; got %x, want %x", testDigest, expectedDigest)
+		}
+	})
+
+	// Test that multiple calls to Write is stateful
+	t.Run("StatefulWrite", func(t *testing.T) {
+		h := mh()
+		rng := newRandReader(t)
+
+		prefix, suffix := make([]byte, h.BlockSize()), make([]byte, h.BlockSize())
+		rng.Read(prefix)
+		rng.Read(suffix)
+
+		// Write prefix then suffix sequentially and record resulting hash
+		writeToHash(t, h, prefix)
+		writeToHash(t, h, suffix)
+		serialSum := getSum(t, h, nil)
+
+		h.Reset()
+
+		// Write prefix and suffix at the same time and record resulting hash
+		writeToHash(t, h, append(prefix, suffix...))
+		compositeSum := getSum(t, h, nil)
+
+		// Check that sequential writing results in the same as writing all at once
+		if !bytes.Equal(compositeSum, serialSum) {
+			t.Errorf("two successive Write calls resulted in a different Sum than a single one; got %x, want %x", compositeSum, serialSum)
+		}
+	})
+}
+
+// Helper function for writing. Verifies that Write does not error.
+func writeToHash(t *testing.T, h hash.Hash, p []byte) {
+	t.Helper()
+
+	before := make([]byte, len(p))
+	copy(before, p)
+
+	n, err := h.Write(p)
+	if err != nil || n != len(p) {
+		t.Errorf("Write returned error; got (%v, %v), want (nil, %v)", err, n, len(p))
+	}
+
+	if !bytes.Equal(p, before) {
+		t.Errorf("Write modified input slice; got %x, want %x", p, before)
+	}
+}
+
+// Helper function for getting Sum. Checks that Sum doesn't change hash state.
+func getSum(t *testing.T, h hash.Hash, buff []byte) []byte {
+	t.Helper()
+
+	testBuff := make([]byte, len(buff))
+	copy(testBuff, buff)
+
+	sum := h.Sum(buff)
+	testSum := h.Sum(testBuff)
+
+	// Check that Sum doesn't change underlying hash state
+	if !bytes.Equal(sum, testSum) {
+		t.Errorf("successive calls to Sum yield different results; got %x, want %x", sum, testSum)
+	}
+
+	return sum
+}
+
+func newRandReader(t *testing.T) io.Reader {
+	seed := time.Now().UnixNano()
+	t.Logf("Deterministic RNG seed: 0x%x", seed)
+	return rand.New(rand.NewSource(seed))
+}