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// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package protodelim marshals and unmarshals varint size-delimited messages.
package protodelim
import (
"bufio"
"encoding/binary"
"fmt"
"io"
"google.golang.org/protobuf/encoding/protowire"
"google.golang.org/protobuf/internal/errors"
"google.golang.org/protobuf/proto"
)
// MarshalOptions is a configurable varint size-delimited marshaler.
type MarshalOptions struct{ proto.MarshalOptions }
// MarshalTo writes a varint size-delimited wire-format message to w.
// If w returns an error, MarshalTo returns it unchanged.
func (o MarshalOptions) MarshalTo(w io.Writer, m proto.Message) (int, error) {
msgBytes, err := o.MarshalOptions.Marshal(m)
if err != nil {
return 0, err
}
sizeBytes := protowire.AppendVarint(nil, uint64(len(msgBytes)))
sizeWritten, err := w.Write(sizeBytes)
if err != nil {
return sizeWritten, err
}
msgWritten, err := w.Write(msgBytes)
if err != nil {
return sizeWritten + msgWritten, err
}
return sizeWritten + msgWritten, nil
}
// MarshalTo writes a varint size-delimited wire-format message to w
// with the default options.
//
// See the documentation for [MarshalOptions.MarshalTo].
func MarshalTo(w io.Writer, m proto.Message) (int, error) {
return MarshalOptions{}.MarshalTo(w, m)
}
// UnmarshalOptions is a configurable varint size-delimited unmarshaler.
type UnmarshalOptions struct {
proto.UnmarshalOptions
// MaxSize is the maximum size in wire-format bytes of a single message.
// Unmarshaling a message larger than MaxSize will return an error.
// A zero MaxSize will default to 4 MiB.
// Setting MaxSize to -1 disables the limit.
MaxSize int64
}
const defaultMaxSize = 4 << 20 // 4 MiB, corresponds to the default gRPC max request/response size
// SizeTooLargeError is an error that is returned when the unmarshaler encounters a message size
// that is larger than its configured [UnmarshalOptions.MaxSize].
type SizeTooLargeError struct {
// Size is the varint size of the message encountered
// that was larger than the provided MaxSize.
Size uint64
// MaxSize is the MaxSize limit configured in UnmarshalOptions, which Size exceeded.
MaxSize uint64
}
func (e *SizeTooLargeError) Error() string {
return fmt.Sprintf("message size %d exceeded unmarshaler's maximum configured size %d", e.Size, e.MaxSize)
}
// Reader is the interface expected by [UnmarshalFrom].
// It is implemented by *[bufio.Reader].
type Reader interface {
io.Reader
io.ByteReader
}
// UnmarshalFrom parses and consumes a varint size-delimited wire-format message
// from r.
// The provided message must be mutable (e.g., a non-nil pointer to a message).
//
// The error is [io.EOF] error only if no bytes are read.
// If an EOF happens after reading some but not all the bytes,
// UnmarshalFrom returns a non-io.EOF error.
// In particular if r returns a non-io.EOF error, UnmarshalFrom returns it unchanged,
// and if only a size is read with no subsequent message, [io.ErrUnexpectedEOF] is returned.
func (o UnmarshalOptions) UnmarshalFrom(r Reader, m proto.Message) error {
var sizeArr [binary.MaxVarintLen64]byte
sizeBuf := sizeArr[:0]
for i := range sizeArr {
b, err := r.ReadByte()
if err != nil {
// Immediate EOF is unexpected.
if err == io.EOF && i != 0 {
break
}
return err
}
sizeBuf = append(sizeBuf, b)
if b < 0x80 {
break
}
}
size, n := protowire.ConsumeVarint(sizeBuf)
if n < 0 {
return protowire.ParseError(n)
}
maxSize := o.MaxSize
if maxSize == 0 {
maxSize = defaultMaxSize
}
if maxSize != -1 && size > uint64(maxSize) {
return errors.Wrap(&SizeTooLargeError{Size: size, MaxSize: uint64(maxSize)}, "")
}
var b []byte
var err error
if br, ok := r.(*bufio.Reader); ok {
// Use the []byte from the bufio.Reader instead of having to allocate one.
// This reduces CPU usage and allocated bytes.
b, err = br.Peek(int(size))
if err == nil {
defer br.Discard(int(size))
} else {
b = nil
}
}
if b == nil {
b = make([]byte, size)
_, err = io.ReadFull(r, b)
}
if err == io.EOF {
return io.ErrUnexpectedEOF
}
if err != nil {
return err
}
if err := o.Unmarshal(b, m); err != nil {
return err
}
return nil
}
// UnmarshalFrom parses and consumes a varint size-delimited wire-format message
// from r with the default options.
// The provided message must be mutable (e.g., a non-nil pointer to a message).
//
// See the documentation for [UnmarshalOptions.UnmarshalFrom].
func UnmarshalFrom(r Reader, m proto.Message) error {
return UnmarshalOptions{}.UnmarshalFrom(r, m)
}
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