Simplify data verification with HashReader. (#5071)

Verify() was being called by caller after the data
has been successfully read after io.EOF. This disconnection
opens a race under concurrent access to such an object.
Verification is not necessary outside of Read() call,
we can simply just do checksum verification right inside
Read() call at io.EOF.

This approach simplifies the usage.

pkg/hash/reader_test.go

@@ -0,0 +1,152 @@
+/*
+ * Minio Cloud Storage, (C) 2017 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package hash
+
+import (
+	"bytes"
+	"encoding/hex"
+	"io"
+	"io/ioutil"
+	"testing"
+)
+
+// Tests functions like Size(), MD5*(), SHA256*()
+func TestHashReaderHelperMethods(t *testing.T) {
+	r, err := NewReader(bytes.NewReader([]byte("abcd")), 4, "e2fc714c4727ee9395f324cd2e7f331f", "88d4266fd4e6338d13b845fcf289579d209c897823b9217da3e161936f031589")
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = io.Copy(ioutil.Discard, r)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if r.MD5HexString() != "e2fc714c4727ee9395f324cd2e7f331f" {
+		t.Errorf("Expected md5hex \"e2fc714c4727ee9395f324cd2e7f331f\", got %s", r.MD5HexString())
+	}
+	if r.SHA256HexString() != "88d4266fd4e6338d13b845fcf289579d209c897823b9217da3e161936f031589" {
+		t.Errorf("Expected sha256hex \"88d4266fd4e6338d13b845fcf289579d209c897823b9217da3e161936f031589\", got %s", r.SHA256HexString())
+	}
+	if r.Size() != 4 {
+		t.Errorf("Expected size 4, got %d", r.Size())
+	}
+	expectedMD5, err := hex.DecodeString("e2fc714c4727ee9395f324cd2e7f331f")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(r.MD5(), expectedMD5) {
+		t.Errorf("Expected md5hex \"e2fc714c4727ee9395f324cd2e7f331f\", got %s", r.MD5HexString())
+	}
+	expectedSHA256, err := hex.DecodeString("88d4266fd4e6338d13b845fcf289579d209c897823b9217da3e161936f031589")
+	if !bytes.Equal(r.SHA256(), expectedSHA256) {
+		t.Errorf("Expected md5hex \"88d4266fd4e6338d13b845fcf289579d209c897823b9217da3e161936f031589\", got %s", r.SHA256HexString())
+	}
+}
+
+// Tests hash reader checksum verification.
+func TestHashReaderVerification(t *testing.T) {
+	testCases := []struct {
+		src               io.Reader
+		size              int64
+		md5hex, sha256hex string
+		err               error
+	}{
+		// Success, no checksum verification provided.
+		{
+			src:  bytes.NewReader([]byte("abcd")),
+			size: 4,
+		},
+		// Failure md5 mismatch.
+		{
+			src:    bytes.NewReader([]byte("abcd")),
+			size:   4,
+			md5hex: "d41d8cd98f00b204e9800998ecf8427f",
+			err: BadDigest{
+				"d41d8cd98f00b204e9800998ecf8427f",
+				"e2fc714c4727ee9395f324cd2e7f331f",
+			},
+		},
+		// Failure sha256 mismatch.
+		{
+			src:       bytes.NewReader([]byte("abcd")),
+			size:      4,
+			sha256hex: "88d4266fd4e6338d13b845fcf289579d209c897823b9217da3e161936f031580",
+			err: SHA256Mismatch{
+				"88d4266fd4e6338d13b845fcf289579d209c897823b9217da3e161936f031580",
+				"88d4266fd4e6338d13b845fcf289579d209c897823b9217da3e161936f031589",
+			},
+		},
+	}
+	for i, testCase := range testCases {
+		r, err := NewReader(testCase.src, testCase.size, testCase.md5hex, testCase.sha256hex)
+		if err != nil {
+			t.Fatalf("Test %d: Initializing reader failed %s", i+1, err)
+		}
+		_, err = io.Copy(ioutil.Discard, r)
+		if err != nil {
+			if err.Error() != testCase.err.Error() {
+				t.Errorf("Test %d: Expected error %s, got error %s", i+1, testCase.err, err)
+			}
+		}
+	}
+}
+
+// Tests NewReader() constructor with invalid arguments.
+func TestHashReaderInvalidArguments(t *testing.T) {
+	testCases := []struct {
+		src               io.Reader
+		size              int64
+		md5hex, sha256hex string
+		success           bool
+	}{
+		// Invalid md5sum NewReader() will fail.
+		{
+			src:     bytes.NewReader([]byte("abcd")),
+			size:    4,
+			md5hex:  "invalid-md5",
+			success: false,
+		},
+		// Invalid sha256 NewReader() will fail.
+		{
+			src:       bytes.NewReader([]byte("abcd")),
+			size:      4,
+			sha256hex: "invalid-sha256",
+			success:   false,
+		},
+		// Nested hash reader NewReader() will fail.
+		{
+			src:     &Reader{src: bytes.NewReader([]byte("abcd"))},
+			size:    4,
+			success: false,
+		},
+		// Expected inputs, NewReader() will succeed.
+		{
+			src:     bytes.NewReader([]byte("abcd")),
+			size:    4,
+			success: true,
+		},
+	}
+
+	for i, testCase := range testCases {
+		_, err := NewReader(testCase.src, testCase.size, testCase.md5hex, testCase.sha256hex)
+		if err != nil && testCase.success {
+			t.Errorf("Test %d: Expected success, but got error %s instead", i+1, err)
+		}
+		if err == nil && !testCase.success {
+			t.Errorf("Test %d: Expected error, but got success", i+1)
+		}
+	}
+}