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reader.go
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/
reader.go
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// Copyright 2021 Joshua J Baker. All rights reserved.
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.
package osmfile
import (
"bytes"
"compress/zlib"
"encoding/binary"
"errors"
"io"
"io/ioutil"
"github.com/tidwall/osmfile/internal/pbf"
)
type rawBlockReader struct {
r io.Reader
err error
pos int64
}
func newRawBlockReader(r io.Reader) *rawBlockReader {
return &rawBlockReader{r: r}
}
type rawBlock struct {
Type string
Data []byte
}
func (r *rawBlockReader) ReadBlock() (n int, block rawBlock, err error) {
if r.err != nil {
return 0, rawBlock{}, r.err
}
bpos := r.pos
var buf [4]byte
if _, err := io.ReadFull(r.r, buf[:]); err != nil {
r.err = err
return 0, rawBlock{}, r.err
}
r.pos += 4
hdrLen := binary.BigEndian.Uint32(buf[:])
hdr := make([]byte, hdrLen)
if _, err := io.ReadFull(r.r, hdr); err != nil {
r.err = err
return 0, rawBlock{}, r.err
}
r.pos += int64(hdrLen)
/*
message BlobHeader {
required string type = 1;
optional bytes indexdata = 2;
required int32 datasize = 3;
}
*/
var btype string
var bsize int
err = pbf.ForEachField(hdr, func(f pbf.Field) error {
switch f.Num() {
case 1:
btype = string(f.Data())
case 3:
bsize = int(f.Uint64())
}
return nil
})
if err != nil {
r.err = err
return 0, rawBlock{}, err
}
bdata := make([]byte, bsize)
if _, err := io.ReadFull(r.r, bdata); err != nil {
r.err = err
return 0, rawBlock{}, r.err
}
r.pos += int64(bsize)
return int(r.pos - bpos), rawBlock{Type: btype, Data: bdata}, nil
}
// BlockReader is a reader for reading OSMData blocks from an OSM Planet
// protobuf file.
type BlockReader struct {
rr *rawBlockReader
}
// NewBlockReader returns a reader for reading OSMData blocks from an OSM Planet
// protobuf file.
func NewBlockReader(r io.Reader) *BlockReader {
return &BlockReader{rr: newRawBlockReader(r)}
}
// ReadBlock reads the next OSMData block.
// Returns the number of bytes read and the block.
func (r *BlockReader) ReadBlock() (n int, block Block, err error) {
for {
nn, rblock, err := r.rr.ReadBlock()
if err != nil {
return 0, Block{}, err
}
n += nn
if rblock.Type != "OSMData" {
continue
}
data, err := inflate(rblock.Data)
if err != nil {
return 0, Block{}, err
}
block, err := procBlock(Everything, data)
if err != nil {
return 0, Block{}, err
}
return n, block, nil
}
}
// SkipBlock skips over the next block. Like ReadBlock but faster.
func (r *BlockReader) SkipBlock() (n int, err error) {
for {
nn, rblock, err := r.rr.ReadBlock()
if err != nil {
return 0, err
}
n += nn
if rblock.Type != "OSMData" {
continue
}
return n, nil
}
}
func inflate(bdata []byte) (data []byte, err error) {
/*
message Blob {
optional bytes raw = 1; // No compression
optional int32 raw_size = 2; // When compressed, the uncompressed size
// Possible compressed versions of the data.
optional bytes zlib_data = 3;
// PROPOSED feature for LZMA compressed data. SUPPORT IS NOT REQUIRED.
optional bytes lzma_data = 4;
// Formerly used for bzip2 compressed data. Depreciated in 2010.
optional bytes OBSOLETE_bzip2_data = 5 [deprecated=true]; // Don't ...
// ... reuse this tag number.
}
*/
var rawSize int
err = pbf.ForEachField(bdata, func(f pbf.Field) error {
switch f.Num() {
case 1:
data = bdata
case 2:
rawSize = int(f.Uint64())
case 3:
data, err = zlibInflateGo(f.Data(), rawSize)
if err != nil {
return err
}
}
return nil
})
return data, err
}
func zlibInflateGo(data []byte, expectedInflatedSize int) ([]byte, error) {
rd, err := zlib.NewReader(bytes.NewBuffer(data))
if err != nil {
return nil, err
}
defer rd.Close()
out, err := ioutil.ReadAll(rd)
if err != nil {
return nil, err
}
if len(out) != expectedInflatedSize {
return nil, errors.New("size mismatch")
}
return out, nil
}