added token truncate filter

closes #49

analysis/token_filters/truncate_token_filter/truncate_token_filter.go

@@ -0,0 +1,47 @@
+//  Copyright (c) 2014 Couchbase, 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 truncate_token_filter
+
+import (
+	"bytes"
+	"unicode/utf8"
+
+	"github.com/couchbaselabs/bleve/analysis"
+)
+
+type TruncateTokenFilter struct {
+	length int
+}
+
+func NewTruncateTokenFilter(length int) *TruncateTokenFilter {
+	return &TruncateTokenFilter{
+		length: length,
+	}
+}
+
+func (s *TruncateTokenFilter) Filter(input analysis.TokenStream) analysis.TokenStream {
+	rv := make(analysis.TokenStream, 0)
+
+	for _, token := range input {
+		wordLen := utf8.RuneCount(token.Term)
+		if wordLen > s.length {
+			runes := bytes.Runes(token.Term)[0:s.length]
+			newterm := make([]byte, 0, s.length*4)
+			for _, r := range runes {
+				runeBytes := make([]byte, utf8.RuneLen(r))
+				utf8.EncodeRune(runeBytes, r)
+				newterm = append(newterm, runeBytes...)
+			}
+			token.Term = newterm
+		}
+		rv = append(rv, token)
+	}
+
+	return rv
+}

analysis/token_filters/truncate_token_filter/truncate_token_filter_test.go

@@ -0,0 +1,73 @@
+//  Copyright (c) 2014 Couchbase, 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 truncate_token_filter
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/couchbaselabs/bleve/analysis"
+)
+
+func TestTruncateTokenFilter(t *testing.T) {
+
+	tests := []struct {
+		length int
+		input  analysis.TokenStream
+		output analysis.TokenStream
+	}{
+		{
+			length: 5,
+			input: analysis.TokenStream{
+				&analysis.Token{
+					Term: []byte("abcdefgh"),
+				},
+			},
+			output: analysis.TokenStream{
+				&analysis.Token{
+					Term: []byte("abcde"),
+				},
+			},
+		},
+		{
+			length: 3,
+			input: analysis.TokenStream{
+				&analysis.Token{
+					Term: []byte("こんにちは世界"),
+				},
+			},
+			output: analysis.TokenStream{
+				&analysis.Token{
+					Term: []byte("こんに"),
+				},
+			},
+		},
+		{
+			length: 10,
+			input: analysis.TokenStream{
+				&analysis.Token{
+					Term: []byte("แยกคำภาษาไทยก็ทำได้นะจ้ะ"),
+				},
+			},
+			output: analysis.TokenStream{
+				&analysis.Token{
+					Term: []byte("แยกคำภาษาไ"),
+				},
+			},
+		},
+	}
+
+	for _, test := range tests {
+		truncateTokenFilter := NewTruncateTokenFilter(test.length)
+		actual := truncateTokenFilter.Filter(test.input)
+		if !reflect.DeepEqual(actual, test.output) {
+			t.Errorf("expected %s, got %s", test.output[0].Term, actual[0].Term)
+		}
+	}
+}

config.go

@@ -30,6 +30,7 @@ import (
 	"github.com/couchbaselabs/bleve/analysis/token_filters/lower_case_filter"
 	"github.com/couchbaselabs/bleve/analysis/token_filters/stemmer_filter"
 	"github.com/couchbaselabs/bleve/analysis/token_filters/stop_words_filter"
+	"github.com/couchbaselabs/bleve/analysis/token_filters/truncate_token_filter"
 	"github.com/couchbaselabs/bleve/analysis/token_filters/unicode_normalize"
 
 	"github.com/couchbaselabs/bleve/search"
@@ -181,6 +182,7 @@ func init() {
 	Config.Analysis.TokenFilters["long"] = length_filter.NewLengthFilter(-1, 255)
 	Config.Analysis.TokenFilters["to_lower"] = lower_case_filter.NewLowerCaseFilter()
 	Config.Analysis.TokenFilters["apostrophe"] = apostrophe_filter.NewApostropheFilter()
+	Config.Analysis.TokenFilters["truncate_token"] = truncate_token_filter.NewTruncateTokenFilter(25)
 
 	// register stemmer filters
 	Config.Analysis.TokenFilters["stemmer_da"] = stemmer_filter.MustNewStemmerFilter("danish")