Add lib/zlibcut/example_test.go
diff --git a/lib/zlibcut/example_test.go b/lib/zlibcut/example_test.go
new file mode 100644
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+++ b/lib/zlibcut/example_test.go
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+// Copyright 2019 The Wuffs 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
+//
+// https://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 zlibcut_test
+
+import (
+ "bytes"
+ "compress/zlib"
+ "fmt"
+ "io/ioutil"
+ "strings"
+
+ "github.com/google/wuffs/lib/zlibcut"
+)
+
+func ExampleCut() {
+ const sonnet18 = "" +
+ "Shall I compare thee to a summer’s day?\n" +
+ "Thou art more lovely and more temperate.\n" +
+ "Rough winds do shake the darling buds of May,\n" +
+ "And summer’s lease hath all too short a date.\n" +
+ "Sometime too hot the eye of heaven shines,\n" +
+ "And often is his gold complexion dimmed;\n" +
+ "And every fair from fair sometime declines,\n" +
+ "By chance, or nature’s changing course, untrimmed;\n" +
+ "But thy eternal summer shall not fade,\n" +
+ "Nor lose possession of that fair thou ow’st,\n" +
+ "Nor shall death brag thou wand'rest in his shade,\n" +
+ "When in eternal lines to Time thou grow'st.\n" +
+ "So long as men can breathe, or eyes can see,\n" +
+ "So long lives this, and this gives life to thee.\n"
+
+ if n := len(sonnet18); n != 632 {
+ fmt.Printf("len(sonnet18): got %d, want 632", n)
+ return
+ }
+
+ // Compress the input text, sonnet18.
+ buffer := &bytes.Buffer{}
+ w := zlib.NewWriter(buffer)
+ w.Write([]byte(sonnet18))
+ w.Close()
+ compressed := buffer.Bytes()
+
+ // The exact length of the zlib-compressed form of sonnet18 depends on the
+ // compression algorithm used, which can change from version to version of
+ // the Go standard library. Nonetheless, for a 632 byte input, we expect
+ // the compressed form to be between 300 and 500 bytes.
+ if n := len(compressed); (n < 300) || (500 < n) {
+ fmt.Printf("len(compressed): got %d, want something in [300, 500]", n)
+ return
+ }
+
+ // Cut the 300-or-more bytes to be 200.
+ encodedLen, decodedLen, err := zlibcut.Cut(nil, compressed, 200)
+ if err != nil {
+ fmt.Printf("Cut: %v", err)
+ return
+ }
+
+ // The encodedLen should be equal to or just under the requested 200.
+ cut := compressed[:encodedLen]
+ if n := len(cut); (n < 190) || (200 < n) {
+ fmt.Printf("len(cut): got %d, want something in [190, 200]", n)
+ return
+ }
+
+ // At this point, a real program would write that cut slice somewhere. The
+ // rest of this example verifies that the cut data has the properties we
+ // expect, given the semantics of zlibcut.Cut.
+
+ // Uncompress the cut data. It should be a valid zlib-compressed stream, so
+ // no errors should be encountered.
+ r, err := zlib.NewReader(bytes.NewReader(cut))
+ if err != nil {
+ fmt.Printf("NewReader: %v", err)
+ return
+ }
+ uncompressed, err := ioutil.ReadAll(r)
+ if err != nil {
+ fmt.Printf("ReadAll: %v", err)
+ return
+ }
+ err = r.Close()
+ if err != nil {
+ fmt.Printf("Close: %v", err)
+ return
+ }
+
+ // The uncompressed form of the cut data should be a prefix (of length
+ // decodedLen) of the original input, sonnet18. Again, the exact length
+ // depends on the zlib compression algorithm, but uncompressing 200 or so
+ // bytes should give between 250 and 400 bytes.
+ if n := len(uncompressed); n != decodedLen {
+ fmt.Printf("len(uncompressed): got %d, want %d", n, decodedLen)
+ return
+ } else if (n < 250) || (400 < n) {
+ fmt.Printf("len(uncompressed): got %d, want something in [250, 400]", n)
+ return
+ } else if !strings.HasPrefix(sonnet18, string(uncompressed)) {
+ fmt.Printf("uncompressed was not a prefix of the original input")
+ return
+ }
+
+ // The first two lines of the sonnet take 83 bytes.
+ fmt.Println(string(uncompressed[:83]))
+ // Output:
+ // Shall I compare thee to a summer’s day?
+ // Thou art more lovely and more temperate.
+}
