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Request buffering middleware

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Łukasz Harasimowicz 2018-01-31 15:32:04 +01:00 • committed by Traefiker
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vendor/github.com/mailgun/multibuf/buffer.go generated vendored Normal file
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// package multibuf implements buffer optimized for streaming large chunks of data,
// multiple reads and optional partial buffering to disk.
package multibuf
import (
"bytes"
"fmt"
"io"
"io/ioutil"
"os"
)
// MultiReader provides Read, Close, Seek and Size methods. In addition to that it supports WriterTo interface
// to provide efficient writing schemes, as functions like io.Copy use WriterTo when it's available.
type MultiReader interface {
io.Reader
io.Seeker
io.Closer
io.WriterTo
// Size calculates and returns the total size of the reader and not the length remaining.
Size() (int64, error)
}
// WriterOnce implements write once, read many times writer. Create a WriterOnce and write to it, once Reader() function has been
// called, the internal data is transferred to MultiReader and this instance of WriterOnce should be no longer used.
type WriterOnce interface {
// Write implements io.Writer
Write(p []byte) (int, error)
// Reader transfers all data written to this writer to MultiReader. If there was no data written it retuns an error
Reader() (MultiReader, error)
// WriterOnce owns the data before Reader has been called, so Close will close all the underlying files if Reader has not been called.
Close() error
}
// MaxBytes, ignored if set to value >=, if request exceeds the specified limit, the reader will return error,
// by default buffer is not limited, negative values mean no limit
func MaxBytes(m int64) optionSetter {
return func(o *options) error {
o.maxBytes = m
return nil
}
}
// MemBytes specifies the largest buffer to hold in RAM before writing to disk, default is 1MB
func MemBytes(m int64) optionSetter {
return func(o *options) error {
if m < 0 {
return fmt.Errorf("MemBytes should be >= 0")
}
o.memBytes = m
return nil
}
}
// NewWriterOnce returns io.ReadWrite compatible object that can limit the size of the buffer and persist large buffers to disk.
// WriterOnce implements write once, read many times writer. Create a WriterOnce and write to it, once Reader() function has been
// called, the internal data is transferred to MultiReader and this instance of WriterOnce should be no longer used.
// By default NewWriterOnce returns unbound buffer that will allow to write up to 1MB in RAM and will start buffering to disk
// It supports multiple functional optional arguments:
//
// // Buffer up to 1MB in RAM and limit max buffer size to 20MB
// multibuf.NewWriterOnce(r, multibuf.MemBytes(1024 * 1024), multibuf.MaxBytes(1024 * 1024 * 20))
//
//
func NewWriterOnce(setters ...optionSetter) (WriterOnce, error) {
o := options{
memBytes: DefaultMemBytes,
maxBytes: DefaultMaxBytes,
}
if o.memBytes == 0 {
o.memBytes = DefaultMemBytes
}
for _, s := range setters {
if err := s(&o); err != nil {
return nil, err
}
}
return &writerOnce{o: o}, nil
}
// New returns MultiReader that can limit the size of the buffer and persist large buffers to disk.
// By default New returns unbound buffer that will read up to 1MB in RAM and will start buffering to disk
// It supports multiple functional optional arguments:
//
// // Buffer up to 1MB in RAM and limit max buffer size to 20MB
// multibuf.New(r, multibuf.MemBytes(1024 * 1024), multibuf.MaxBytes(1024 * 1024 * 20))
//
//
func New(input io.Reader, setters ...optionSetter) (MultiReader, error) {
o := options{
memBytes: DefaultMemBytes,
maxBytes: DefaultMaxBytes,
}
for _, s := range setters {
if err := s(&o); err != nil {
return nil, err
}
}
if o.memBytes == 0 {
o.memBytes = DefaultMemBytes
}
if o.maxBytes > 0 && o.maxBytes < o.memBytes {
o.memBytes = o.maxBytes
}
memReader := &io.LimitedReader{
R: input, // Read from this reader
N: o.memBytes, // Maximum amount of data to read
}
readers := make([]io.ReadSeeker, 0, 2)
buffer, err := ioutil.ReadAll(memReader)
if err != nil {
return nil, err
}
readers = append(readers, bytes.NewReader(buffer))
var file *os.File
// This means that we have exceeded all the memory capacity and we will start buffering the body to disk.
totalBytes := int64(len(buffer))
if memReader.N <= 0 {
file, err = ioutil.TempFile("", tempFilePrefix)
if err != nil {
return nil, err
}
os.Remove(file.Name())
readSrc := input
if o.maxBytes > 0 {
readSrc = &maxReader{R: input, Max: o.maxBytes - o.memBytes}
}
writtenBytes, err := io.Copy(file, readSrc)
if err != nil {
return nil, err
}
totalBytes += writtenBytes
file.Seek(0, 0)
readers = append(readers, file)
}
var cleanupFn cleanupFunc
if file != nil {
cleanupFn = func() error {
file.Close()
return nil
}
}
return newBuf(totalBytes, cleanupFn, readers...), nil
}
// MaxSizeReachedError is returned when the maximum allowed buffer size is reached when reading
type MaxSizeReachedError struct {
MaxSize int64
}
func (e *MaxSizeReachedError) Error() string {
return fmt.Sprintf("Maximum size %d was reached", e)
}
const (
DefaultMemBytes = 1048576
DefaultMaxBytes = -1
// Equivalent of bytes.MinRead used in ioutil.ReadAll
DefaultBufferBytes = 512
)
// Constraints:
// - Implements io.Reader
// - Implements Seek(0, 0)
// - Designed for Write once, Read many times.
type multiReaderSeek struct {
length int64
readers []io.ReadSeeker
mr io.Reader
cleanup cleanupFunc
}
type cleanupFunc func() error
func newBuf(length int64, cleanup cleanupFunc, readers ...io.ReadSeeker) *multiReaderSeek {
converted := make([]io.Reader, len(readers))
for i, r := range readers {
// This conversion is safe as ReadSeeker includes Reader
converted[i] = r.(io.Reader)
}
return &multiReaderSeek{
length: length,
readers: readers,
mr: io.MultiReader(converted...),
cleanup: cleanup,
}
}
func (mr *multiReaderSeek) Close() (err error) {
if mr.cleanup != nil {
return mr.cleanup()
}
return nil
}
func (mr *multiReaderSeek) WriteTo(w io.Writer) (int64, error) {
b := make([]byte, DefaultBufferBytes)
var total int64
for {
n, err := mr.mr.Read(b)
// Recommended way is to always handle non 0 reads despite the errors
if n > 0 {
nw, errw := w.Write(b[:n])
total += int64(nw)
// Write must return a non-nil error if it returns nw < n
if nw != n || errw != nil {
return total, errw
}
}
if err != nil {
if err == io.EOF {
return total, nil
}
return total, err
}
}
}
func (mr *multiReaderSeek) Read(p []byte) (n int, err error) {
return mr.mr.Read(p)
}
func (mr *multiReaderSeek) Size() (int64, error) {
return mr.length, nil
}
func (mr *multiReaderSeek) Seek(offset int64, whence int) (int64, error) {
// TODO: implement other whence
// TODO: implement real offsets
if whence != 0 {
return 0, fmt.Errorf("multiReaderSeek: unsupported whence")
}
if offset != 0 {
return 0, fmt.Errorf("multiReaderSeek: unsupported offset")
}
for _, seeker := range mr.readers {
seeker.Seek(0, 0)
}
ior := make([]io.Reader, len(mr.readers))
for i, arg := range mr.readers {
ior[i] = arg.(io.Reader)
}
mr.mr = io.MultiReader(ior...)
return 0, nil
}
type options struct {
// MemBufferBytes sets up the size of the memory buffer for this request.
// If the data size exceeds the limit, the remaining request part will be saved on the file system.
memBytes int64
maxBytes int64
}
type optionSetter func(o *options) error
// MaxReader does not allow to read more than Max bytes and returns error if this limit has been exceeded.
type maxReader struct {
R io.Reader // underlying reader
N int64 // bytes read
Max int64 // max bytes to read
}
func (r *maxReader) Read(p []byte) (int, error) {
readBytes, err := r.R.Read(p)
if err != nil && err != io.EOF {
return readBytes, err
}
r.N += int64(readBytes)
if r.N > r.Max {
return readBytes, &MaxSizeReachedError{MaxSize: r.Max}
}
return readBytes, err
}
const (
writerInit = iota
writerMem
writerFile
writerCalledRead
writerErr
)
type writerOnce struct {
o options
err error
state int
mem *bytes.Buffer
file *os.File
total int64
cleanupFn cleanupFunc
}
// how many bytes we can still write to memory
func (w *writerOnce) writeToMem(p []byte) int {
left := w.o.memBytes - w.total
if left <= 0 {
return 0
}
bufLen := len(p)
if int64(bufLen) < left {
return bufLen
}
return int(left)
}
func (w *writerOnce) Write(p []byte) (int, error) {
out, err := w.write(p)
return out, err
}
func (w *writerOnce) Close() error {
if w.file != nil {
return w.file.Close()
}
return nil
}
func (w *writerOnce) write(p []byte) (int, error) {
if w.o.maxBytes > 0 && int64(len(p))+w.total > w.o.maxBytes {
return 0, fmt.Errorf("total size of %d exceeded allowed %d", int64(len(p))+w.total, w.o.maxBytes)
}
switch w.state {
case writerCalledRead:
return 0, fmt.Errorf("can not write after reader has been called")
case writerInit:
w.mem = &bytes.Buffer{}
w.state = writerMem
fallthrough
case writerMem:
writeToMem := w.writeToMem(p)
if writeToMem > 0 {
wrote, err := w.mem.Write(p[:writeToMem])
w.total += int64(wrote)
if err != nil {
return wrote, err
}
}
left := len(p) - writeToMem
if left <= 0 {
return len(p), nil
}
// we can't write to memory any more, switch to file
if err := w.initFile(); err != nil {
return int(writeToMem), err
}
w.state = writerFile
wrote, err := w.file.Write(p[writeToMem:])
w.total += int64(wrote)
return len(p), err
case writerFile:
wrote, err := w.file.Write(p)
w.total += int64(wrote)
return wrote, err
}
return 0, fmt.Errorf("unsupported state: %d", w.state)
}
func (w *writerOnce) initFile() error {
file, err := ioutil.TempFile("", tempFilePrefix)
if err != nil {
return err
}
w.file = file
w.cleanupFn = func() error {
file.Close()
os.Remove(file.Name())
return nil
}
return nil
}
func (w *writerOnce) Reader() (MultiReader, error) {
switch w.state {
case writerInit:
return nil, fmt.Errorf("no data ready")
case writerCalledRead:
return nil, fmt.Errorf("reader has been called")
case writerMem:
w.state = writerCalledRead
return newBuf(w.total, nil, bytes.NewReader(w.mem.Bytes())), nil
case writerFile:
_, err := w.file.Seek(0, 0)
if err != nil {
return nil, err
}
// we are not responsible for file and buffer any more
w.state = writerCalledRead
br, fr := bytes.NewReader(w.mem.Bytes()), w.file
w.file = nil
w.mem = nil
return newBuf(w.total, w.cleanupFn, br, fr), nil
}
return nil, fmt.Errorf("unsupported state: %d\n", w.state)
}
const tempFilePrefix = "temp-multibuf-"