Add docker fetch fuzzer

Signed-off-by: AdamKorcz <adam@adalogics.com>

contrib/fuzz/docker_fuzzer.go

@@ -0,0 +1,78 @@
+// +build gofuzz
+
+/*
+   Copyright The containerd Authors.
+   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.
+*/
+
+/*
+   This fuzzer is run continuously by OSS-fuzz.
+   It is stored in contrib/fuzz for organization,
+   but in order to execute it, it must be moved to
+   remotes/docker first.
+*/
+
+package docker
+
+import (
+	"context"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+)
+
+func FuzzFetcher(data []byte) int {
+	dataLen := len(data)
+	if dataLen == 0 {
+		return -1
+	}
+
+	s := httptest.NewServer(http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+		rw.Header().Set("content-range", fmt.Sprintf("bytes %d-%d/%d", 0, dataLen-1, dataLen))
+		rw.Header().Set("content-length", fmt.Sprintf("%d", dataLen))
+		rw.Write(data)
+	}))
+	defer s.Close()
+
+	u, err := url.Parse(s.URL)
+	if err != nil {
+		return 0
+	}
+
+	f := dockerFetcher{&dockerBase{
+		repository: "nonempty",
+	}}
+	host := RegistryHost{
+		Client: s.Client(),
+		Host:   u.Host,
+		Scheme: u.Scheme,
+		Path:   u.Path,
+	}
+
+	ctx := context.Background()
+	req := f.request(host, http.MethodGet)
+	rc, err := f.open(ctx, req, "", 0)
+	if err != nil {
+		return 0
+	}
+	b, err := ioutil.ReadAll(rc)
+	if err != nil {
+		return 0
+	}
+
+	expected := data
+	if len(b) != len(expected) {
+		panic("len of request is not equal to len of expected but should be")
+	}
+	return 1
+}