Fix ReadFrom over-read

`bufio.NewReader` usually reads ahead. Limit the input to the expected size.

Return `io.ErrUnexpectedEOF` when stream is unexpectedly truncated.

Add regression tests (and apparently some Go 1.19 formatting)

Fixes #108

bitset.go

@@ -33,7 +33,6 @@ Example use:
 
 As an alternative to BitSets, one should check out the 'big' package,
 which provides a (less set-theoretical) view of bitsets.
-
 */
 package bitset
 
@@ -434,21 +433,20 @@ func (b *BitSet) NextSet(i uint) (uint, bool) {
 // including possibly the current index and up to cap(buffer).
 // If the returned slice has len zero, then no more set bits were found
 //
-//    buffer := make([]uint, 256) // this should be reused
-//    j := uint(0)
-//    j, buffer = bitmap.NextSetMany(j, buffer)
-//    for ; len(buffer) > 0; j, buffer = bitmap.NextSetMany(j,buffer) {
-//     for k := range buffer {
-//      do something with buffer[k]
-//     }
-//     j += 1
-//    }
-//
+//	buffer := make([]uint, 256) // this should be reused
+//	j := uint(0)
+//	j, buffer = bitmap.NextSetMany(j, buffer)
+//	for ; len(buffer) > 0; j, buffer = bitmap.NextSetMany(j,buffer) {
+//	 for k := range buffer {
+//	  do something with buffer[k]
+//	 }
+//	 j += 1
+//	}
 //
 // It is possible to retrieve all set bits as follow:
 //
-//    indices := make([]uint, bitmap.Count())
-//    bitmap.NextSetMany(0, indices)
+//	indices := make([]uint, bitmap.Count())
+//	bitmap.NextSetMany(0, indices)
 //
 // However if bitmap.Count() is large, it might be preferable to
 // use several calls to NextSetMany, for performance reasons.
@@ -932,6 +930,9 @@ func (b *BitSet) ReadFrom(stream io.Reader) (int64, error) {
 	// Read length first
 	err := binary.Read(stream, binaryOrder, &length)
 	if err != nil {
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
 		return 0, err
 	}
 	newset := New(uint(length))
@@ -940,17 +941,17 @@ func (b *BitSet) ReadFrom(stream io.Reader) (int64, error) {
 		return 0, errors.New("unmarshalling error: type mismatch")
 	}
 
-	// Read remaining bytes as set
-	// current implementation bufio.Reader is more memory efficient than
-	// binary.Read for large set
-	reader := bufio.NewReader(stream)
-	var item = make([]byte, binary.Size(uint64(0))) // one uint64
-	nWords := uint64(wordsNeeded(uint(length)))
-	for i := uint64(0); i < nWords; i++ {
-		if _, err := reader.Read(item); err != nil {
+	var item [8]byte
+	nWords := wordsNeeded(uint(length))
+	reader := bufio.NewReader(io.LimitReader(stream, 8*int64(nWords)))
+	for i := 0; i < nWords; i++ {
+		if _, err := reader.Read(item[:]); err != nil {
+			if err == io.EOF {
+				err = io.ErrUnexpectedEOF
+			}
 			return 0, err
 		}
-		newset.set[i] = binaryOrder.Uint64(item)
+		newset.set[i] = binaryOrder.Uint64(item[:])
 	}
 
 	*b = *newset

bitset_test.go

@@ -7,9 +7,14 @@
 package bitset
 
 import (
+	"bytes"
+	"compress/gzip"
 	"encoding"
+	"encoding/base64"
 	"encoding/json"
+	"errors"
 	"fmt"
+	"io"
 	"math"
 	"strconv"
 	"testing"
@@ -1279,7 +1284,7 @@ func TestMarshalUnmarshalJSONWithTrailingData(t *testing.T) {
 	}
 
 	// appending some noise
-	data = data[:len(data) - 3] // remove "
+	data = data[:len(data)-3] // remove "
 	data = append(data, []byte(`AAAAAAAAAA"`)...)
 
 	b := new(BitSet)
@@ -1644,3 +1649,145 @@ func TestDeleteWithBitSetInstance(t *testing.T) {
 
 	}
 }
+
+func TestWriteTo(t *testing.T) {
+	const length = 9585
+	const oneEvery = 97
+	addBuf := []byte(`12345678`)
+	bs := New(length)
+	// Add some bits
+	for i := uint(0); i < length; i += oneEvery {
+		bs = bs.Set(i)
+	}
+
+	var buf bytes.Buffer
+	n, err := bs.WriteTo(&buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	wantSz := buf.Len() // Size of the serialized data in bytes.
+	if n != int64(wantSz) {
+		t.Errorf("want write size to be %d, got %d", wantSz, n)
+	}
+	buf.Write(addBuf) // Add additional data on stream.
+
+	// Generate test input for regression tests:
+	if false {
+		gzout := bytes.NewBuffer(nil)
+		gz, err := gzip.NewWriterLevel(gzout, 9)
+		if err != nil {
+			t.Fatal(err)
+		}
+		gz.Write(buf.Bytes())
+		gz.Close()
+		t.Log("Encoded:", base64.StdEncoding.EncodeToString(gzout.Bytes()))
+	}
+
+	// Read back.
+	bs = New(length)
+	n, err = bs.ReadFrom(&buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != int64(wantSz) {
+		t.Errorf("want read size to be %d, got %d", wantSz, n)
+	}
+	// Check bits
+	for i := uint(0); i < length; i += oneEvery {
+		if !bs.Test(i) {
+			t.Errorf("bit %d was not set", i)
+		}
+	}
+
+	more, err := io.ReadAll(&buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(more, addBuf) {
+		t.Fatalf("extra mismatch. got %v, want %v", more, addBuf)
+	}
+}
+
+func TestReadFrom(t *testing.T) {
+	addBuf := []byte(`12345678`) // Bytes after stream
+	tests := []struct {
+		length   uint
+		oneEvery uint
+		input    string // base64+gzipped
+		wantErr  error
+	}{
+		{
+			length:   9585,
+			oneEvery: 97,
+			input:    "H4sIAAAAAAAC/2IAA9VCCM3AyMDAwMSACVgYGBg4sIgLMDAwKGARd2BgYGjAFB41noDx6IAJajw64IAajw4UoMajg4ZR4/EaP5pQh1g+MDQyNjE1M7cABAAA//9W5OoOwAQAAA==",
+		},
+		{
+			length:   1337,
+			oneEvery: 42,
+			input:    "H4sIAAAAAAAC/2IAA1ZLBgYWEIPRAUQKgJkMcCZYisEBzkSSYkSTYqCxAYZGxiamZuYWgAAAAP//D0wyWbgAAAA=",
+		},
+		{
+			length:   1337, // Truncated input.
+			oneEvery: 42,
+			input:    "H4sIAAAAAAAC/2IAA9VCCM3AyMDAwARmAQIAAP//vR3xdRkAAAA=",
+			wantErr:  io.ErrUnexpectedEOF,
+		},
+		{
+			length:   1337, // Empty input.
+			oneEvery: 42,
+			input:    "H4sIAAAAAAAC/wEAAP//AAAAAAAAAAA=",
+			wantErr:  io.ErrUnexpectedEOF,
+		},
+	}
+
+	for i, test := range tests {
+		t.Run(fmt.Sprint(i), func(t *testing.T) {
+			fatalErr := func(err error) {
+				t.Helper()
+				if err != nil {
+					t.Fatal(err)
+				}
+			}
+
+			var buf bytes.Buffer
+			b, err := base64.StdEncoding.DecodeString(test.input)
+			fatalErr(err)
+			gz, err := gzip.NewReader(bytes.NewBuffer(b))
+			fatalErr(err)
+			_, err = io.Copy(&buf, gz)
+			fatalErr(err)
+			fatalErr(gz.Close())
+
+			bs := New(test.length)
+			_, err = bs.ReadFrom(&buf)
+			if err != nil {
+				if errors.Is(err, test.wantErr) {
+					// Correct, nothing more we can test.
+					return
+				}
+				t.Fatalf("did not get expected error %v, got %v", test.wantErr, err)
+			} else {
+				if test.wantErr != nil {
+					t.Fatalf("did not get expected error %v", test.wantErr)
+				}
+			}
+			fatalErr(err)
+
+			// Test if correct bits are set.
+			for i := uint(0); i < test.length; i++ {
+				want := i%test.oneEvery == 0
+				got := bs.Test(i)
+				if want != got {
+					t.Errorf("bit %d was %v, should be %v", i, got, want)
+				}
+			}
+
+			more, err := io.ReadAll(&buf)
+			fatalErr(err)
+
+			if !bytes.Equal(more, addBuf) {
+				t.Errorf("extra mismatch. got %v, want %v", more, addBuf)
+			}
+		})
+	}
+}