crypto/cipher: make stream examples runnable in the playground

Updates #9679

Change-Id: I53412cf0142364de5f76e8affc15d607bfa2ad23
Reviewed-on: https://go-review.googlesource.com/c/145838
Run-TryBot: Yury Smolsky <yury@smolsky.by>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>

diff --git a/src/crypto/cipher/example_test.go b/src/crypto/cipher/example_test.go
index 6e050a9c0da90e654cd3bdfb659c140ce264184f..9c32d6a934f86c6ecc37c535eba781c088e5bd38 100644 (file)
--- a/src/crypto/cipher/example_test.go
+++ b/src/crypto/cipher/example_test.go
@@ -5,6 +5,7 @@
 package cipher_test
 
 import (
+       "bytes"
        "crypto/aes"
        "crypto/cipher"
        "crypto/rand"
@@ -298,11 +299,8 @@ func ExampleStreamReader() {
        // package like bcrypt or scrypt.
        key, _ := hex.DecodeString("6368616e676520746869732070617373")
 
-       inFile, err := os.Open("encrypted-file")
-       if err != nil {
-               panic(err)
-       }
-       defer inFile.Close()
+       encrypted, _ := hex.DecodeString("cf0495cc6f75dafc23948538e79904a9")
+       bReader := bytes.NewReader(encrypted)
 
        block, err := aes.NewCipher(key)
        if err != nil {
@@ -314,15 +312,9 @@ func ExampleStreamReader() {
        var iv [aes.BlockSize]byte
        stream := cipher.NewOFB(block, iv[:])
 
-       outFile, err := os.OpenFile("decrypted-file", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
-       if err != nil {
-               panic(err)
-       }
-       defer outFile.Close()
-
-       reader := &cipher.StreamReader{S: stream, R: inFile}
-       // Copy the input file to the output file, decrypting as we go.
-       if _, err := io.Copy(outFile, reader); err != nil {
+       reader := &cipher.StreamReader{S: stream, R: bReader}
+       // Copy the input to the output stream, decrypting as we go.
+       if _, err := io.Copy(os.Stdout, reader); err != nil {
                panic(err)
        }
 
@@ -330,6 +322,8 @@ func ExampleStreamReader() {
        // authentication of the encrypted data. If you were actually to use
        // StreamReader in this manner, an attacker could flip arbitrary bits in
        // the output.
+
+       // Output: some secret text
 }
 
 func ExampleStreamWriter() {
@@ -339,11 +333,7 @@ func ExampleStreamWriter() {
        // package like bcrypt or scrypt.
        key, _ := hex.DecodeString("6368616e676520746869732070617373")
 
-       inFile, err := os.Open("plaintext-file")
-       if err != nil {
-               panic(err)
-       }
-       defer inFile.Close()
+       bReader := bytes.NewReader([]byte("some secret text"))
 
        block, err := aes.NewCipher(key)
        if err != nil {
@@ -355,15 +345,11 @@ func ExampleStreamWriter() {
        var iv [aes.BlockSize]byte
        stream := cipher.NewOFB(block, iv[:])
 
-       outFile, err := os.OpenFile("encrypted-file", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
-       if err != nil {
-               panic(err)
-       }
-       defer outFile.Close()
+       var out bytes.Buffer
 
-       writer := &cipher.StreamWriter{S: stream, W: outFile}
-       // Copy the input file to the output file, encrypting as we go.
-       if _, err := io.Copy(writer, inFile); err != nil {
+       writer := &cipher.StreamWriter{S: stream, W: &out}
+       // Copy the input to the output buffer, encrypting as we go.
+       if _, err := io.Copy(writer, bReader); err != nil {
                panic(err)
        }
 
@@ -371,4 +357,7 @@ func ExampleStreamWriter() {
        // authentication of the encrypted data. If you were actually to use
        // StreamReader in this manner, an attacker could flip arbitrary bits in
        // the decrypted result.
+
+       fmt.Printf("%x\n", out.Bytes())
+       // Output: cf0495cc6f75dafc23948538e79904a9
 }