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file.go
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file.go
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// Package contains Node File struct and MultiReaderAt implementation
package file
import (
"io"
"os"
)
// File is the Node file structure. Contains the json/bson marshalling controls.
type File struct {
Name string `bson:"name" json:"name"`
Size int64 `bson:"size" json:"size"`
Checksum map[string]string `bson:"checksum" json:"checksum"`
Format string `bson:"format" json:"format"`
Path string `bson:"path" json:"-"`
Virtual bool `bson:"virtual" json:"virtual"`
VirtualParts []string `bson:"virtual_parts" json:"virtual_parts"`
}
// SectionReader interface required for MultiReaderAt
type SectionReader interface {
io.Reader
io.ReaderAt
}
// ReaderAt interface that is compatiable with os.File types.
type ReaderAt interface {
SectionReader
Stat() (os.FileInfo, error)
Close() error
}
// multifd contains file boundary information
type multifd struct {
start int64
end int64
size int64
}
// multiReaderAt is private struct for the multi-file ReaderAt
// that provides the ablity to use indexes with vitrual files.
type multiReaderAt struct {
readers []ReaderAt
boundaries []multifd
size int64
}
// MultiReaderAt returns a ReaderAt that's the logical concatenation of
// the provided input readers. BUG / KNOW-ISSUE: all file handles are opened
// initially. May not be suitiable for large numbers of files.
func MultiReaderAt(readers ...ReaderAt) ReaderAt {
mr := &multiReaderAt{readers: readers}
b := []multifd{}
start := int64(0)
for _, r := range mr.readers {
fi, _ := r.Stat()
b = append(b, multifd{start: start, end: start + fi.Size(), size: fi.Size()})
start = start + fi.Size()
}
mr.boundaries = b
mr.size = b[len(b)-1].end
return mr
}
// Read same as io.MultiReader
func (mr *multiReaderAt) Read(p []byte) (n int, err error) {
for len(mr.readers) > 0 {
n, err = mr.readers[0].Read(p)
if n > 0 || err != io.EOF {
if err == io.EOF {
// Don't return EOF yet. There may be more bytes
// in the remaining readers.
err = nil
}
return
}
mr.readers = mr.readers[1:]
}
return 0, io.EOF
}
// ReadAt is the magic sauce. Heavily commented to include all logic.
func (mr *multiReaderAt) ReadAt(p []byte, off int64) (n int, err error) {
startF, endF := 0, 0
startPos, endPos, length := int64(0), int64(0), int64(len(p))
if off > mr.size {
return 0, io.EOF
}
// find start
for i, fd := range mr.boundaries {
if off >= fd.start && off <= fd.end {
startF = i
startPos = off - fd.start
break
}
}
// find end
if off+length > mr.size {
endF = len(mr.readers) - 1
endPos = mr.size - mr.boundaries[endF].start
} else {
for i, fd := range mr.boundaries {
if off+length >= fd.start && off+length <= fd.end {
endF = i
endPos = off + length - fd.start
break
}
}
}
if startF == endF {
// read startpos till endpos
// println("--> readat: startpos till endpos")
// fmt.Printf("file: %d, offset: %d, length: %d\n", startF, startPos, endPos-startPos)
return mr.readers[startF].ReadAt(p[0:length], startPos)
} else {
buffPos := 0
for i := startF; i <= endF; i++ {
if i == startF {
// read startpos till end of file
// println("--> readat: startpos till end of file")
// fmt.Printf("file: %d, offset: %d, length: %d, buffPos: %d\n", i, startPos, mr.boundaries[i].size-startPos, buffPos)
if rn, err := mr.readers[i].ReadAt(p[buffPos:buffPos+int(mr.boundaries[i].size-startPos)], startPos); err != nil && err != io.EOF {
return 0, err
} else {
buffPos = buffPos + int(mr.boundaries[i].size-startPos)
n = n + rn
}
} else if i == endF {
// read start of file till endpos
// println("--> readat: start of file till endpos")
// fmt.Printf("file: %d, offset: %d, length: %d, buffPos: %d\n", i, 0, endPos, buffPos)
if rn, err := mr.readers[i].ReadAt(p[buffPos:buffPos+int(endPos)], 0); err != nil && err != io.EOF {
println("--> error here: ", err.Error())
return 0, err
} else {
buffPos = buffPos + int(endPos)
n = n + rn
}
} else {
// read entire file
// println("--> readat: entire file")
// fmt.Printf("file: %d, offset: %d, length: %d, buffPos: %d\n", i, 0, mr.boundaries[i].size, buffPos)
if rn, err := mr.readers[i].ReadAt(p[buffPos:buffPos+int(mr.boundaries[i].size)], 0); err != nil && err != io.EOF {
return 0, err
} else {
buffPos = buffPos + int(mr.boundaries[i].size)
n = n + rn
}
}
}
}
if n < int(length) {
return n, io.EOF
}
return
}
// Required for the ReaderAt interface but non-implemented
func (mr *multiReaderAt) Stat() (fi os.FileInfo, err error) {
return
}
// Required for the ReaderAt interface but non-implemented
func (mr *multiReaderAt) Close() (err error) {
return
}