testing/iotest: add TestReader to test readers
There are many reader behaviors that are subtle and
worth testing, and it's nice to have one complete tester
instead of many incomplete ones.
For #41190, which will use this as part of a larger
file system implementation tester.
Change-Id: Ib4cc7fae94b0d9b45dfacadc52baa77ad3761322
Reviewed-on: https://go-review.googlesource.com/c/go/+/243909
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
diff --git a/src/testing/iotest/reader.go b/src/testing/iotest/reader.go
index bc2f72a..33b782d 100644
--- a/src/testing/iotest/reader.go
+++ b/src/testing/iotest/reader.go
@@ -6,8 +6,11 @@
package iotest
import (
+ "bytes"
"errors"
+ "fmt"
"io"
+ "io/ioutil"
)
// OneByteReader returns a Reader that implements
@@ -90,13 +93,177 @@
// ErrReader returns an io.Reader that returns 0, err from all Read calls.
func ErrReader(err error) io.Reader {
- return &alwaysErrReader{err: err}
+ return &errReader{err: err}
}
-type alwaysErrReader struct {
+type errReader struct {
err error
}
-func (aer *alwaysErrReader) Read(p []byte) (int, error) {
- return 0, aer.err
+func (r *errReader) Read(p []byte) (int, error) {
+ return 0, r.err
+}
+
+type smallByteReader struct {
+ r io.Reader
+ off int
+ n int
+}
+
+func (r *smallByteReader) Read(p []byte) (int, error) {
+ if len(p) == 0 {
+ return 0, nil
+ }
+ r.n = r.n%3 + 1
+ n := r.n
+ if n > len(p) {
+ n = len(p)
+ }
+ n, err := r.r.Read(p[0:n])
+ if err != nil && err != io.EOF {
+ err = fmt.Errorf("Read(%d bytes at offset %d): %v", n, r.off, err)
+ }
+ r.off += n
+ return n, err
+}
+
+// TestReader tests that reading from r returns the expected file content.
+// It does reads of different sizes, until EOF.
+// If r implements io.ReaderAt or io.Seeker, TestReader also checks
+// that those operations behave as they should.
+//
+// If TestReader finds any misbehaviors, it returns an error reporting them.
+// The error text may span multiple lines.
+func TestReader(r io.Reader, content []byte) error {
+ if len(content) > 0 {
+ n, err := r.Read(nil)
+ if n != 0 || err != nil {
+ return fmt.Errorf("Read(0) = %d, %v, want 0, nil", n, err)
+ }
+ }
+
+ data, err := ioutil.ReadAll(&smallByteReader{r: r})
+ if err != nil {
+ return err
+ }
+ if !bytes.Equal(data, content) {
+ return fmt.Errorf("ReadAll(small amounts) = %q\n\twant %q", data, content)
+ }
+ n, err := r.Read(make([]byte, 10))
+ if n != 0 || err != io.EOF {
+ return fmt.Errorf("Read(10) at EOF = %v, %v, want 0, EOF", n, err)
+ }
+
+ if r, ok := r.(io.ReadSeeker); ok {
+ // Seek(0, 1) should report the current file position (EOF).
+ if off, err := r.Seek(0, 1); off != int64(len(content)) || err != nil {
+ return fmt.Errorf("Seek(0, 1) from EOF = %d, %v, want %d, nil", off, err, len(content))
+ }
+
+ // Seek backward partway through file, in two steps.
+ // If middle == 0, len(content) == 0, can't use the -1 and +1 seeks.
+ middle := len(content) - len(content)/3
+ if middle > 0 {
+ if off, err := r.Seek(-1, 1); off != int64(len(content)-1) || err != nil {
+ return fmt.Errorf("Seek(-1, 1) from EOF = %d, %v, want %d, nil", -off, err, len(content)-1)
+ }
+ if off, err := r.Seek(int64(-len(content)/3), 1); off != int64(middle-1) || err != nil {
+ return fmt.Errorf("Seek(%d, 1) from %d = %d, %v, want %d, nil", -len(content)/3, len(content)-1, off, err, middle-1)
+ }
+ if off, err := r.Seek(+1, 1); off != int64(middle) || err != nil {
+ return fmt.Errorf("Seek(+1, 1) from %d = %d, %v, want %d, nil", middle-1, off, err, middle)
+ }
+ }
+
+ // Seek(0, 1) should report the current file position (middle).
+ if off, err := r.Seek(0, 1); off != int64(middle) || err != nil {
+ return fmt.Errorf("Seek(0, 1) from %d = %d, %v, want %d, nil", middle, off, err, middle)
+ }
+
+ // Reading forward should return the last part of the file.
+ data, err := ioutil.ReadAll(&smallByteReader{r: r})
+ if err != nil {
+ return fmt.Errorf("ReadAll from offset %d: %v", middle, err)
+ }
+ if !bytes.Equal(data, content[middle:]) {
+ return fmt.Errorf("ReadAll from offset %d = %q\n\twant %q", middle, data, content[middle:])
+ }
+
+ // Seek relative to end of file, but start elsewhere.
+ if off, err := r.Seek(int64(middle/2), 0); off != int64(middle/2) || err != nil {
+ return fmt.Errorf("Seek(%d, 0) from EOF = %d, %v, want %d, nil", middle/2, off, err, middle/2)
+ }
+ if off, err := r.Seek(int64(-len(content)/3), 2); off != int64(middle) || err != nil {
+ return fmt.Errorf("Seek(%d, 2) from %d = %d, %v, want %d, nil", -len(content)/3, middle/2, off, err, middle)
+ }
+
+ // Reading forward should return the last part of the file (again).
+ data, err = ioutil.ReadAll(&smallByteReader{r: r})
+ if err != nil {
+ return fmt.Errorf("ReadAll from offset %d: %v", middle, err)
+ }
+ if !bytes.Equal(data, content[middle:]) {
+ return fmt.Errorf("ReadAll from offset %d = %q\n\twant %q", middle, data, content[middle:])
+ }
+
+ // Absolute seek & read forward.
+ if off, err := r.Seek(int64(middle/2), 0); off != int64(middle/2) || err != nil {
+ return fmt.Errorf("Seek(%d, 0) from EOF = %d, %v, want %d, nil", middle/2, off, err, middle/2)
+ }
+ data, err = ioutil.ReadAll(r)
+ if err != nil {
+ return fmt.Errorf("ReadAll from offset %d: %v", middle/2, err)
+ }
+ if !bytes.Equal(data, content[middle/2:]) {
+ return fmt.Errorf("ReadAll from offset %d = %q\n\twant %q", middle/2, data, content[middle/2:])
+ }
+ }
+
+ if r, ok := r.(io.ReaderAt); ok {
+ data := make([]byte, len(content), len(content)+1)
+ for i := range data {
+ data[i] = 0xfe
+ }
+ n, err := r.ReadAt(data, 0)
+ if n != len(data) || err != nil && err != io.EOF {
+ return fmt.Errorf("ReadAt(%d, 0) = %v, %v, want %d, nil or EOF", len(data), n, err, len(data))
+ }
+ if !bytes.Equal(data, content) {
+ return fmt.Errorf("ReadAt(%d, 0) = %q\n\twant %q", len(data), data, content)
+ }
+
+ n, err = r.ReadAt(data[:1], int64(len(data)))
+ if n != 0 || err != io.EOF {
+ return fmt.Errorf("ReadAt(1, %d) = %v, %v, want 0, EOF", len(data), n, err)
+ }
+
+ for i := range data {
+ data[i] = 0xfe
+ }
+ n, err = r.ReadAt(data[:cap(data)], 0)
+ if n != len(data) || err != io.EOF {
+ return fmt.Errorf("ReadAt(%d, 0) = %v, %v, want %d, EOF", cap(data), n, err, len(data))
+ }
+ if !bytes.Equal(data, content) {
+ return fmt.Errorf("ReadAt(%d, 0) = %q\n\twant %q", len(data), data, content)
+ }
+
+ for i := range data {
+ data[i] = 0xfe
+ }
+ for i := range data {
+ n, err = r.ReadAt(data[i:i+1], int64(i))
+ if n != 1 || err != nil && (i != len(data)-1 || err != io.EOF) {
+ want := "nil"
+ if i == len(data)-1 {
+ want = "nil or EOF"
+ }
+ return fmt.Errorf("ReadAt(1, %d) = %v, %v, want 1, %s", i, n, err, want)
+ }
+ if data[i] != content[i] {
+ return fmt.Errorf("ReadAt(1, %d) = %q want %q", i, data[i:i+1], content[i:i+1])
+ }
+ }
+ }
+ return nil
}
diff --git a/src/testing/iotest/reader_test.go b/src/testing/iotest/reader_test.go
index 6004e84..f149e74 100644
--- a/src/testing/iotest/reader_test.go
+++ b/src/testing/iotest/reader_test.go
@@ -8,6 +8,7 @@
"bytes"
"errors"
"io"
+ "strings"
"testing"
)
@@ -249,3 +250,12 @@
})
}
}
+
+func TestStringsReader(t *testing.T) {
+ const msg = "Now is the time for all good gophers."
+
+ r := strings.NewReader(msg)
+ if err := TestReader(r, []byte(msg)); err != nil {
+ t.Fatal(err)
+ }
+}
