问题描述
我一生无法从打开街道地图反序列化protobuf文件.
For the life of me I cannot deserialize the protobuf file from Open Street Maps.
我正在尝试反序列化以下摘录: http://download.geofabrik.de/osm/north-america/us-northeast.osm.pbf 获取节点，我正在使用 http://code.google.com/p/protobuf-net/作为库.我试图反序列化一堆不同的对象，但是它们都为空.
I am trying to deserialize the following extract: http://download.geofabrik.de/osm/north-america/us-northeast.osm.pbf to get Nodes and I am using http://code.google.com/p/protobuf-net/ as the library. I have tried to deserialize a bunch of different objects but they all come up null.
可以在以下位置找到原始文件: http://trac. openstreetmap.org/browser/applications/utils/export/osm2pgsql/protobuf
The proto files can be found here: http://trac.openstreetmap.org/browser/applications/utils/export/osm2pgsql/protobuf
有什么建议吗?
推荐答案
正确；问题在于这不是 just protobuf-它是一种混合文件格式( 定义为内部将 protobuf包含在各种格式中，并且还合并了压缩功能(尽管看起来是可选的).
Right; the problem is that this isn't just protobuf - it is a hybrid file format (defined here that includes protobuf among various formats internally. It also incorporates compression (although that looks to be optional).
我已经从规范中分离出了我能做的一切，并且我这里有一个C#阅读器，它使用protobuf-net处理块-它很高兴地读取该文件到最后-我可以告诉你4515个块(BlockHeader).当涉及到Blob时，我对规范如何标记OSMHeader和OSMData感到有些困惑-我愿意在这里提出建议！我还使用 ZLIB.NET 来处理正在使用.在无法解决这个问题的情况下，我决定处理ZLIB数据并根据所声明的大小对其进行验证，以检查它是否至少是理智的.
I've pulled apart what I can from the spec, and I've got a C# reader here that uses protobuf-net to handle the chunks - it happily reads through that file to the end - I can tell you there are 4515 blocks (BlockHeader). When it gets to the Blob I'm a bit confused as to how the spec demarks OSMHeader and OSMData - I'm open to suggestions here! I've also used ZLIB.NET to handle the zlib compression that is being used. In the absence of getting my head around this, I've settled for processing the ZLIB data and validating it against the claimed size, to check it is at least sane.
如果您能弄清楚(或问作者)它们是如何分隔OSMHeader和OSMData的，我会很乐意地添加其他内容.希望您不要介意我已经在这里停下来了-但是已经几个小时了； p
If you can figure out (or ask the author) how they are separating OSMHeader and OSMData I'll happily crank something else in. I hope you don't mind that I've stopped here - but it has been a few hours ;p
using System;
using System.IO;
using OpenStreetMap; // where my .proto-generated entities are living
using ProtoBuf; // protobuf-net
using zlib; // ZLIB.NET
class OpenStreetMapParser
{
static void Main()
{
using (var file = File.OpenRead("us-northeast.osm.pbf"))
{
// from http://wiki.openstreetmap.org/wiki/ProtocolBufBinary:
//A file contains a header followed by a sequence of fileblocks. The design is intended to allow future random-access to the contents of the file and skipping past not-understood or unwanted data.
//The format is a repeating sequence of:
//int4: length of the BlockHeader message in network byte order
//serialized BlockHeader message
//serialized Blob message (size is given in the header)
int length, blockCount = 0;
while (Serializer.TryReadLengthPrefix(file, PrefixStyle.Fixed32, out length))
{
// I'm just being lazy and re-using something "close enough" here
// note that v2 has a big-endian option, but Fixed32 assumes little-endian - we
// actually need the other way around (network byte order):
uint len = (uint)length;
len = ((len & 0xFF) << 24) | ((len & 0xFF00) << 8) | ((len & 0xFF0000) >> 8) | ((len & 0xFF000000) >> 24);
length = (int)len;
BlockHeader header;
// again, v2 has capped-streams built in, but I'm deliberately
// limiting myself to v1 features
using (var tmp = new LimitedStream(file, length))
{
header = Serializer.Deserialize<BlockHeader>(tmp);
}
Blob blob;
using (var tmp = new LimitedStream(file, header.datasize))
{
blob = Serializer.Deserialize<Blob>(tmp);
}
if(blob.zlib_data == null) throw new NotSupportedException("I'm only handling zlib here!");
using(var ms = new MemoryStream(blob.zlib_data))
using(var zlib = new ZLibStream(ms))
{ // at this point I'm very unclear how the OSMHeader and OSMData are packed - it isn't clear
// read this to the end, to check we can parse the zlib
int payloadLen = 0;
while (zlib.ReadByte() >= 0) payloadLen++;
if (payloadLen != blob.raw_size) throw new FormatException("Screwed that up...");
}
blockCount++;
Console.WriteLine("Read block " + blockCount.ToString());
}
Console.WriteLine("all done");
Console.ReadLine();
}
}
}
abstract class InputStream : Stream
{
protected abstract int ReadNextBlock(byte[] buffer, int offset, int count);
public sealed override int Read(byte[] buffer, int offset, int count)
{
int bytesRead, totalRead = 0;
while (count > 0 && (bytesRead = ReadNextBlock(buffer, offset, count)) > 0)
{
count -= bytesRead;
offset += bytesRead;
totalRead += bytesRead;
pos += bytesRead;
}
return totalRead;
}
long pos;
public override void Write(byte[] buffer, int offset, int count)
{
throw new NotImplementedException();
}
public override void SetLength(long value)
{
throw new NotImplementedException();
}
public override long Position
{
get
{
return pos;
}
set
{
if (pos != value) throw new NotImplementedException();
}
}
public override long Length
{
get { throw new NotImplementedException(); }
}
public override void Flush()
{
throw new NotImplementedException();
}
public override bool CanWrite
{
get { return false; }
}
public override bool CanRead
{
get { return true; }
}
public override bool CanSeek
{
get { return false; }
}
public override long Seek(long offset, SeekOrigin origin)
{
throw new NotImplementedException();
}
}
class ZLibStream : InputStream
{ // uses ZLIB.NET: http://www.componentace.com/download/download.php?editionid=25
private ZInputStream reader; // seriously, why isn't this a stream?
public ZLibStream(Stream stream)
{
reader = new ZInputStream(stream);
}
public override void Close()
{
reader.Close();
base.Close();
}
protected override int ReadNextBlock(byte[] buffer, int offset, int count)
{
// OMG! reader.Read is the base-stream, reader.read is decompressed! yeuch
return reader.read(buffer, offset, count);
}
}
// deliberately doesn't dispose the base-stream
class LimitedStream : InputStream
{
private Stream stream;
private long remaining;
public LimitedStream(Stream stream, long length)
{
if (length < 0) throw new ArgumentOutOfRangeException("length");
if (stream == null) throw new ArgumentNullException("stream");
if (!stream.CanRead) throw new ArgumentException("stream");
this.stream = stream;
this.remaining = length;
}
protected override int ReadNextBlock(byte[] buffer, int offset, int count)
{
if(count > remaining) count = (int)remaining;
int bytesRead = stream.Read(buffer, offset, count);
if (bytesRead > 0) remaining -= bytesRead;
return bytesRead;
}
}
这篇关于Protobuf-net反序列化开放街道地图的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！