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bytes.Buffer: restore panic on out-of-memory
Make the panic detectable, and use that in ioutil.ReadFile to give an error if the file is too big. R=golang-dev, minux.ma, bradfitz CC=golang-dev https://golang.org/cl/5563045
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@ -33,7 +33,7 @@ const (
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opRead // Any other read operation.
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)
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// ErrTooLarge is returned if there is too much data to fit in a buffer.
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// ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer.
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var ErrTooLarge = errors.New("bytes.Buffer: too large")
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// Bytes returns a slice of the contents of the unread portion of the buffer;
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@ -73,8 +73,7 @@ func (b *Buffer) Reset() { b.Truncate(0) }
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// grow grows the buffer to guarantee space for n more bytes.
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// It returns the index where bytes should be written.
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// If the buffer can't grow, it returns -1, which will
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// become ErrTooLarge in the caller.
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// If the buffer can't grow it will panic with ErrTooLarge.
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func (b *Buffer) grow(n int) int {
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m := b.Len()
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// If buffer is empty, reset to recover space.
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@ -88,9 +87,6 @@ func (b *Buffer) grow(n int) int {
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} else {
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// not enough space anywhere
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buf = makeSlice(2*cap(b.buf) + n)
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if buf == nil {
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return -1
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}
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copy(buf, b.buf[b.off:])
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}
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b.buf = buf
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@ -102,6 +98,8 @@ func (b *Buffer) grow(n int) int {
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// Write appends the contents of p to the buffer. The return
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// value n is the length of p; err is always nil.
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// If the buffer becomes too large, Write will panic with
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// ErrTooLarge.
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func (b *Buffer) Write(p []byte) (n int, err error) {
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b.lastRead = opInvalid
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m := b.grow(len(p))
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@ -146,9 +144,6 @@ func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) {
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// not enough space using beginning of buffer;
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// double buffer capacity
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newBuf = makeSlice(2*cap(b.buf) + MinRead)
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if newBuf == nil {
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return n, ErrTooLarge
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}
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}
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copy(newBuf, b.buf[b.off:])
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b.buf = newBuf[:len(b.buf)-b.off]
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@ -167,14 +162,14 @@ func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) {
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return n, nil // err is EOF, so return nil explicitly
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}
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// makeSlice allocates a slice of size n, returning nil if the slice cannot be allocated.
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// makeSlice allocates a slice of size n. If the allocation fails, it panics
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// with ErrTooLarge.
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func makeSlice(n int) []byte {
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if n < 0 {
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return nil
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}
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// Catch out of memory panics.
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// If the make fails, give a known error.
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defer func() {
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recover()
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if recover() != nil {
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panic(ErrTooLarge)
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}
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}()
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return make([]byte, n)
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}
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@ -392,13 +392,18 @@ func TestHuge(t *testing.T) {
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if testing.Short() {
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return
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}
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// We expect a panic.
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defer func() {
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if err, ok := recover().(error); ok && err == ErrTooLarge {
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return
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} else {
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t.Error(`expected "too large" error; got`, err)
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}
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}()
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b := new(Buffer)
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big := make([]byte, 500e6)
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for i := 0; i < 1000; i++ {
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if _, err := b.Write(big); err != nil {
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// Got error as expected. Stop
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return
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}
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b.Write(big)
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}
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t.Error("error expected")
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t.Error("panic expected")
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}
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@ -14,9 +14,22 @@ import (
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// readAll reads from r until an error or EOF and returns the data it read
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// from the internal buffer allocated with a specified capacity.
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func readAll(r io.Reader, capacity int64) ([]byte, error) {
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func readAll(r io.Reader, capacity int64) (b []byte, err error) {
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buf := bytes.NewBuffer(make([]byte, 0, capacity))
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_, err := buf.ReadFrom(r)
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// If the buffer overflows, we will get bytes.ErrTooLarge.
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// Return that as an error. Any other panic remains.
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defer func() {
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e := recover()
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if e == nil {
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return
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}
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if panicErr, ok := e.(error); ok && panicErr == bytes.ErrTooLarge {
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err = panicErr
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} else {
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panic(e)
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}
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}()
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_, err = buf.ReadFrom(r)
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return buf.Bytes(), err
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}
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