feat(v2): copy DetermineContentType functionality (#230)

v2/content_type.go

@@ -0,0 +1,112 @@
+// Copyright 2022, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package gax
+
+import (
+	"io"
+	"io/ioutil"
+	"net/http"
+)
+
+const sniffBuffSize = 512
+
+func newContentSniffer(r io.Reader) *contentSniffer {
+	return &contentSniffer{r: r}
+}
+
+// contentSniffer wraps a Reader, and reports the content type determined by sniffing up to 512 bytes from the Reader.
+type contentSniffer struct {
+	r     io.Reader
+	start []byte // buffer for the sniffed bytes.
+	err   error  // set to any error encountered while reading bytes to be sniffed.
+
+	ctype   string // set on first sniff.
+	sniffed bool   // set to true on first sniff.
+}
+
+func (cs *contentSniffer) Read(p []byte) (n int, err error) {
+	// Ensure that the content type is sniffed before any data is consumed from Reader.
+	_, _ = cs.ContentType()
+
+	if len(cs.start) > 0 {
+		n := copy(p, cs.start)
+		cs.start = cs.start[n:]
+		return n, nil
+	}
+
+	// We may have read some bytes into start while sniffing, even if the read ended in an error.
+	// We should first return those bytes, then the error.
+	if cs.err != nil {
+		return 0, cs.err
+	}
+
+	// Now we have handled all bytes that were buffered while sniffing.  Now just delegate to the underlying reader.
+	return cs.r.Read(p)
+}
+
+// ContentType returns the sniffed content type, and whether the content type was successfully sniffed.
+func (cs *contentSniffer) ContentType() (string, bool) {
+	if cs.sniffed {
+		return cs.ctype, cs.ctype != ""
+	}
+	cs.sniffed = true
+	// If ReadAll hits EOF, it returns err==nil.
+	cs.start, cs.err = ioutil.ReadAll(io.LimitReader(cs.r, sniffBuffSize))
+
+	// Don't try to detect the content type based on possibly incomplete data.
+	if cs.err != nil {
+		return "", false
+	}
+
+	cs.ctype = http.DetectContentType(cs.start)
+	return cs.ctype, true
+}
+
+// DetermineContentType determines the content type of the supplied reader.
+// The content of media will be sniffed to determine the content type.
+// After calling DetectContentType the caller must not perform further reads on
+// media, but rather read from the Reader that is returned.
+func DetermineContentType(media io.Reader) (io.Reader, string) {
+	// For backwards compatibility, allow clients to set content
+	// type by providing a ContentTyper for media.
+	// Note: This is an anonymous interface definition copied from googleapi.ContentTyper.
+	if typer, ok := media.(interface {
+		ContentType() string
+	}); ok {
+		return media, typer.ContentType()
+	}
+
+	sniffer := newContentSniffer(media)
+	if ctype, ok := sniffer.ContentType(); ok {
+		return sniffer, ctype
+	}
+	// If content type could not be sniffed, reads from sniffer will eventually fail with an error.
+	return sniffer, ""
+}

v2/content_type_test.go

@@ -0,0 +1,179 @@
+// Copyright 2022, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package gax
+
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+	"reflect"
+	"testing"
+)
+
+// errReader reads out of a buffer until it is empty, then returns the specified error.
+type errReader struct {
+	buf []byte
+	err error
+}
+
+func (er *errReader) Read(p []byte) (int, error) {
+	if len(er.buf) == 0 {
+		if er.err == nil {
+			return 0, io.EOF
+		}
+		return 0, er.err
+	}
+	n := copy(p, er.buf)
+	er.buf = er.buf[n:]
+	return n, nil
+}
+
+func TestContentSniffing(t *testing.T) {
+	type testCase struct {
+		data     []byte // the data to read from the Reader
+		finalErr error  // error to return after data has been read
+
+		wantContentType       string
+		wantContentTypeResult bool
+	}
+
+	for _, tc := range []testCase{
+		{
+			data:                  []byte{0, 0, 0, 0},
+			finalErr:              nil,
+			wantContentType:       "application/octet-stream",
+			wantContentTypeResult: true,
+		},
+		{
+			data:                  []byte(""),
+			finalErr:              nil,
+			wantContentType:       "text/plain; charset=utf-8",
+			wantContentTypeResult: true,
+		},
+		{
+			data:                  []byte(""),
+			finalErr:              io.ErrUnexpectedEOF,
+			wantContentType:       "text/plain; charset=utf-8",
+			wantContentTypeResult: false,
+		},
+		{
+			data:                  []byte("abc"),
+			finalErr:              nil,
+			wantContentType:       "text/plain; charset=utf-8",
+			wantContentTypeResult: true,
+		},
+		{
+			data:                  []byte("abc"),
+			finalErr:              io.ErrUnexpectedEOF,
+			wantContentType:       "text/plain; charset=utf-8",
+			wantContentTypeResult: false,
+		},
+		// The following examples contain more bytes than are buffered for sniffing.
+		{
+			data:                  bytes.Repeat([]byte("a"), 513),
+			finalErr:              nil,
+			wantContentType:       "text/plain; charset=utf-8",
+			wantContentTypeResult: true,
+		},
+		{
+			data:                  bytes.Repeat([]byte("a"), 513),
+			finalErr:              io.ErrUnexpectedEOF,
+			wantContentType:       "text/plain; charset=utf-8",
+			wantContentTypeResult: true, // true because error is after first 512 bytes.
+		},
+	} {
+		er := &errReader{buf: tc.data, err: tc.finalErr}
+
+		sct := newContentSniffer(er)
+
+		// Even if was an error during the first 512 bytes, we should still be able to read those bytes.
+		buf, err := ioutil.ReadAll(sct)
+
+		if !reflect.DeepEqual(buf, tc.data) {
+			t.Fatalf("Failed reading buffer: got: %q; want:%q", buf, tc.data)
+		}
+
+		if err != tc.finalErr {
+			t.Fatalf("Reading buffer error: got: %v; want: %v", err, tc.finalErr)
+		}
+
+		ct, ok := sct.ContentType()
+		if ok != tc.wantContentTypeResult {
+			t.Fatalf("Content type result got: %v; want: %v", ok, tc.wantContentTypeResult)
+		}
+		if ok && ct != tc.wantContentType {
+			t.Fatalf("Content type got: %q; want: %q", ct, tc.wantContentType)
+		}
+	}
+}
+
+type staticContentTyper struct {
+	io.Reader
+}
+
+func (sct staticContentTyper) ContentType() string {
+	return "static content type"
+}
+
+func TestDetermineContentType(t *testing.T) {
+	data := []byte("abc")
+	rdr := func() io.Reader {
+		return bytes.NewBuffer(data)
+	}
+
+	type testCase struct {
+		r               io.Reader
+		wantContentType string
+	}
+
+	for _, tc := range []testCase{
+		{
+			r:               rdr(),
+			wantContentType: "text/plain; charset=utf-8",
+		},
+		{
+			r:               staticContentTyper{rdr()},
+			wantContentType: "static content type",
+		},
+	} {
+		r, ctype := DetermineContentType(tc.r)
+		got, err := ioutil.ReadAll(r)
+		if err != nil {
+			t.Fatalf("Failed reading buffer: %v", err)
+		}
+		if !reflect.DeepEqual(got, data) {
+			t.Fatalf("Failed reading buffer: got: %q; want:%q", got, data)
+		}
+
+		if ctype != tc.wantContentType {
+			t.Fatalf("Content type got: %q; want: %q", ctype, tc.wantContentType)
+		}
+	}
+}