Add a package for doing YAML-to-JSON streaming, one document at a time

pkg/util/yaml/decoder.go

+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+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 yaml
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/json"
+	"io"
+	"unicode"
+
+	"github.com/ghodss/yaml"
+	"github.com/golang/glog"
+)
+
+// YAMLToJSONDecoder decodes YAML documents from an io.Reader by
+// separating individual documents. It first converts the YAML
+// body to JSON, then unmarshals the JSON.
+type YAMLToJSONDecoder struct {
+	scanner *bufio.Scanner
+}
+
+// NewYAMLToJSONDecoder decodes YAML documents from the provided
+// stream in chunks by converting each document (as defined by
+// the YAML spec) into its own chunk, converting it to JSON via
+// yaml.YAMLToJSON, and then passing it to json.Decoder.
+func NewYAMLToJSONDecoder(r io.Reader) *YAMLToJSONDecoder {
+	scanner := bufio.NewScanner(r)
+	scanner.Split(splitYAMLDocument)
+	return &YAMLToJSONDecoder{
+		scanner: scanner,
+	}
+}
+
+// Decode reads a YAML document as JSON from the stream or returns
+// an error. The decoding rules match json.Unmarshal, not
+// yaml.Unmarshal.
+func (d *YAMLToJSONDecoder) Decode(into interface{}) error {
+	if d.scanner.Scan() {
+		data, err := yaml.YAMLToJSON(d.scanner.Bytes())
+		if err != nil {
+			return err
+		}
+		return json.Unmarshal(data, into)
+	}
+	err := d.scanner.Err()
+	if err == nil {
+		err = io.EOF
+	}
+	return err
+}
+
+const yamlSeparator = "\n---"
+
+// splitYAMLDocument is a bufio.SplitFunc for splitting YAML streams into individual documents.
+func splitYAMLDocument(data []byte, atEOF bool) (advance int, token []byte, err error) {
+	if atEOF && len(data) == 0 {
+		return 0, nil, nil
+	}
+	sep := len([]byte(yamlSeparator))
+	if i := bytes.Index(data, []byte(yamlSeparator)); i >= 0 {
+		// We have a potential document terminator
+		i += sep
+		after := data[i:]
+		if len(after) == 0 {
+			// we can't read any more characters
+			if atEOF {
+				return len(data), data[:len(data)-sep], nil
+			}
+			return 0, nil, nil
+		}
+		if j := bytes.IndexByte(after, '\n'); j >= 0 {
+			return i + j + 1, data[0 : i-sep], nil
+		}
+		return 0, nil, nil
+	}
+	// If we're at EOF, we have a final, non-terminated line. Return it.
+	if atEOF {
+		return len(data), data, nil
+	}
+	// Request more data.
+	return 0, nil, nil
+}
+
+// decoder is a convenience interface for Decode.
+type decoder interface {
+	Decode(into interface{}) error
+}
+
+// YAMLOrJSONDecoder attempts to decode a stream of JSON documents or
+// YAML documents by sniffing for a leading { character.
+type YAMLOrJSONDecoder struct {
+	r          io.Reader
+	bufferSize int
+
+	decoder decoder
+}
+
+// NewYAMLOrJSONDecoder returns a decoder that will process YAML documents
+// or JSON documents from the given reader as a stream. bufferSize determines
+// how far into the stream the decoder will look to figure out whether this
+// is a JSON stream (has whitespace followed by an open brace).
+func NewYAMLOrJSONDecoder(r io.Reader, bufferSize int) *YAMLOrJSONDecoder {
+	return &YAMLOrJSONDecoder{
+		r:          r,
+		bufferSize: bufferSize,
+	}
+}
+
+// Decode unmarshals the next object from the underlying stream into the
+// provide object, or returns an error.
+func (d *YAMLOrJSONDecoder) Decode(into interface{}) error {
+	if d.decoder == nil {
+		buffer, isJSON := guessJSONStream(d.r, d.bufferSize)
+		if isJSON {
+			glog.V(4).Infof("decoding stream as JSON")
+			d.decoder = json.NewDecoder(buffer)
+		} else {
+			glog.V(4).Infof("decoding stream as YAML")
+			d.decoder = NewYAMLToJSONDecoder(buffer)
+		}
+	}
+	return d.decoder.Decode(into)
+}
+
+// guessJSONStream scans the provided reader up to size, looking
+// for an open brace indicating this is JSON. It will return the
+// bufio.Reader it creates for the consumer.
+func guessJSONStream(r io.Reader, size int) (io.Reader, bool) {
+	buffer := bufio.NewReaderSize(r, size)
+	b, _ := buffer.Peek(size)
+	return buffer, hasPrefix(b, []byte("{"))
+}
+
+// Return true if the first non-whitespace bytes in buf is
+// prefix
+func hasPrefix(buf []byte, prefix []byte) bool {
+	buf = bytes.TrimLeftFunc(buf, unicode.IsSpace)
+	return bytes.HasPrefix(buf, prefix)
+}

pkg/util/yaml/decoder_test.go

+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+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 yaml
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"testing"
+)
+
+func TestSplitYAMLDocument(t *testing.T) {
+	testCases := []struct {
+		input  string
+		atEOF  bool
+		expect string
+		adv    int
+	}{
+		{"foo", true, "foo", 3},
+		{"fo", false, "", 0},
+
+		{"---", true, "---", 3},
+		{"---\n", true, "---\n", 4},
+		{"---\n", false, "", 0},
+
+		{"\n---\n", false, "", 5},
+		{"\n---\n", true, "", 5},
+
+		{"abc\n---\ndef", true, "abc", 8},
+		{"def", true, "def", 3},
+		{"", true, "", 0},
+	}
+	for i, testCase := range testCases {
+		adv, token, err := splitYAMLDocument([]byte(testCase.input), testCase.atEOF)
+		if err != nil {
+			t.Errorf("%d: unexpected error: %v", i, err)
+			continue
+		}
+		if adv != testCase.adv {
+			t.Errorf("%d: advance did not match: %d %d", i, testCase.adv, adv)
+		}
+		if testCase.expect != string(token) {
+			t.Errorf("%d: token did not match: %q %q", i, testCase.expect, string(token))
+		}
+	}
+}
+
+func TestScanYAML(t *testing.T) {
+	s := bufio.NewScanner(bytes.NewReader([]byte(`---
+stuff: 1
+
+---       
+  `)))
+	s.Split(splitYAMLDocument)
+	if !s.Scan() {
+		t.Fatalf("should have been able to scan")
+	}
+	t.Logf("scan: %s", s.Text())
+	if !s.Scan() {
+		t.Fatalf("should have been able to scan")
+	}
+	t.Logf("scan: %s", s.Text())
+	if s.Scan() {
+		t.Fatalf("scan should have been done")
+	}
+	if s.Err() != nil {
+		t.Fatalf("err should have been nil: %v", s.Err())
+	}
+}
+
+func TestDecodeYAML(t *testing.T) {
+	s := NewYAMLToJSONDecoder(bytes.NewReader([]byte(`---
+stuff: 1
+
+---       
+  `)))
+	obj := generic{}
+	if err := s.Decode(&obj); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if fmt.Sprintf("%#v", obj) != `yaml.generic{"stuff":1}` {
+		t.Errorf("unexpected object: %#v", obj)
+	}
+	obj = generic{}
+	if err := s.Decode(&obj); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(obj) != 0 {
+		t.Fatalf("unexpected object: %#v", obj)
+	}
+	obj = generic{}
+	if err := s.Decode(&obj); err != io.EOF {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
+type generic map[string]interface{}
+
+func TestYAMLOrJSONDecoder(t *testing.T) {
+	testCases := []struct {
+		input  string
+		buffer int
+		isJSON bool
+		err    bool
+		out    []generic
+	}{
+		{` {"1":2}{"3":4}`, 2, true, false, []generic{
+			{"1": 2},
+			{"3": 4},
+		}},
+		{" \n{}", 3, true, false, []generic{
+			{},
+		}},
+		{" \na: b", 2, false, false, []generic{
+			{"a": "b"},
+		}},
+		{` \n{"a": "b"}`, 2, false, true, []generic{
+			{"a": "b"},
+		}},
+		{`   {"a":"b"}`, 100, true, false, []generic{
+			{"a": "b"},
+		}},
+		{"", 1, false, false, []generic{}},
+		{"foo: bar\n---\nbaz: biz", 100, false, false, []generic{
+			{"foo": "bar"},
+			{"baz": "biz"},
+		}},
+		{"foo: bar\n---\n", 100, false, false, []generic{
+			{"foo": "bar"},
+		}},
+		{"foo: bar\n---", 100, false, false, []generic{
+			{"foo": "bar"},
+		}},
+		{"foo: bar\n--", 100, false, true, []generic{
+			{"foo": "bar"},
+		}},
+		{"foo: bar\n-", 100, false, true, []generic{
+			{"foo": "bar"},
+		}},
+		{"foo: bar\n", 100, false, false, []generic{
+			{"foo": "bar"},
+		}},
+	}
+	for i, testCase := range testCases {
+		decoder := NewYAMLOrJSONDecoder(bytes.NewReader([]byte(testCase.input)), testCase.buffer)
+		objs := []generic{}
+
+		var err error
+		for {
+			out := make(generic)
+			err = decoder.Decode(&out)
+			if err != nil {
+				break
+			}
+			objs = append(objs, out)
+		}
+		if err != io.EOF {
+			switch {
+			case testCase.err && err == nil:
+				t.Errorf("%d: unexpected non-error", i)
+				continue
+			case !testCase.err && err != nil:
+				t.Errorf("%d: unexpected error: %v", i, err)
+				continue
+			case err != nil:
+				continue
+			}
+		}
+		switch decoder.decoder.(type) {
+		case *YAMLToJSONDecoder:
+			if testCase.isJSON {
+				t.Errorf("%d: expected JSON decoder, got YAML", i)
+			}
+		case *json.Decoder:
+			if !testCase.isJSON {
+				t.Errorf("%d: expected YAML decoder, got JSON", i)
+			}
+		}
+		if fmt.Sprintf("%#v", testCase.out) != fmt.Sprintf("%#v", objs) {
+			t.Errorf("%d: objects were not equal: \n%#v\n%#v", i, testCase.out, objs)
+		}
+	}
+}