引入
作为一个维护时间更长久的地图服务器(从2010年至今),Python编写的TileStache有着跟Nodejs编写的Tiletrata不同的设计理念:
- 全面专业.包含较多常用或不常用的专业地理信息功能.
- 配置文件.与Tilestrata的代码即配置不同,TileStache完全基于一个独立的配置文件来调配整个系统.
功能
相比Tilestrata的只编写框架,功能完全靠插件加载,Tilestache内置了相当多的功能.了解其具体的功能对于理解架构是必不可少的.
功能的分类其实与Tilestrata相似:主要分为数据提供者,缓存,和图片处理.
数据提供者:
- Mapnik
- Proxy
- Vector
- mbtiles
- Sandwitch
附加提供者:
- PostGeoJSON
- Mapnik Grid
- UtfGrid
- TileDataOSM
- SolrGeoJSON
- MirrorOSM
- Grid
- GDAL
缓存:
- disk
- memchache
- s3
- redis
附加缓存:
- Monkeycache
- GoogleCloud
对各种后期功能的添加是不可预料的,因此TileStache在设计时也把握了类似Tilestrata的插件式挂载的理念,便于编写更多的插件,减轻主框架维护的压力.
结构
如果将所有具体功能模块剔除,那么就剩下TileStache的核心框架文件:
- __init__.py
- Core.py
- Config.py
以及挂载不同功能的模块:
- Caches.py
- PixelEffects.py
- Pixels.py
- Providers.py
__init__.py
整个框架的入口,也是TileStache实现处理网络请求的模块.默认实现了兼容WSGI协议.
启动TileStache的非常简单:
from werkzeug.serving import run_simple
import TileStache
app = TileStache.WSGITileServer(config=options.file, autoreload=True)
run_simple(options.ip, options.port, app)
那就来看一下这个WSGITileServer是如何实现的:
class WSGITileServer:
def __init__(self, config, autoreload=False):
if is_string_type(config):
self.autoreload = autoreload
self.config_path = config
# 解析配置文件
try:
self.config = parseConfig(config)
except:
print("Error loading Tilestache config:")
raise
else:
# 配置文件为对象时检查其格式
assert hasattr(
config, 'cache'), 'Configuration object must have a cache.'
assert hasattr(
config, 'layers'), 'Configuration object must have layers.'
assert hasattr(
config, 'dirpath'), 'Configuration object must have a dirpath.'
self.autoreload = False
self.config_path = None
self.config = config
def __call__(self, environ, start_response):
# 每次请求时刷新配置
if self.autoreload:
try:
self.config = parseConfig(self.config_path)
except Exception as e:
raise Core.KnownUnknown(
"Error loading Tilestache config file:\n%s" % str(e))
# 尝试从请求中解析路径信息
try:
layer, coord, ext = splitPathInfo(environ['PATH_INFO'])
except Core.KnownUnknown as e:
return self._response(start_response, 400, str(e))
if layer and layer not in self.config.layers:
return self._response(start_response, 404)
path_info = environ.get('PATH_INFO', None)
query_string = environ.get('QUERY_STRING', None)
script_name = environ.get('SCRIPT_NAME', None)
# 获取请求的内容
status_code, headers, content = requestHandler2(
self.config, path_info, query_string, script_name)
# 响应请求
return self._response(start_response, status_code, bytes(content), headers)
def _response(self, start_response, code, content='', headers=None):
headers = headers or Headers([])
if content:
headers.setdefault('Content-Length', str(len(content)))
start_response('%d %s' %
(code, httplib.responses[code]), headers.items())
return [content]
其实它就做了两件事:
- 初始化
- 读取配置:parseConfig(config)
- 处理请求:
- 拆解请求参数:splitPathInfo(environ['PATH_INFO'])
- 返回相应的内容:requestHandler2(self.config, path_info, query_string, script_name)
初始化
配置的读取是比较复杂的功能,有专门的模块,在此直接调用:
from . import Config
def parseConfig(configHandle):
if isinstance(configHandle, dict):
config_dict = configHandle
dirpath = '.'
else:
# 兼容本地配置文件或者在线配置文件
scheme, host, path, p, q, f = urlparse(configHandle)
if scheme == '':
scheme = 'file'
path = realpath(path)
if scheme == 'file':
with open(path) as file:
config_dict = json_load(file)
else:
config_dict = json_load(urlopen(configHandle))
dirpath = '%s://%s%s' % (scheme, host, dirname(path).rstrip('/') + '/')
return Config.buildConfiguration(config_dict, dirpath)
处理请求
拆解请求参数很简单:
_pathinfo_pat = re.compile(
r'^/?(?P<l>\w.+)/(?P<z>\d+)/(?P<x>-?\d+)/(?P<y>-?\d+)\.(?P<e>\w+)$')
_preview_pat = re.compile(r'^/?(?P<l>\w.+)/(preview\.html)?$')
def splitPathInfo(pathinfo):
if pathinfo == '/':
return None, None, None
if _pathinfo_pat.match(pathinfo or ''):
path = _pathinfo_pat.match(pathinfo)
# 格式为:图层名/y/x/z/扩展名
layer, row, column, zoom, extension = [path.group(p) for p in 'lyxze']
# 解析成经纬度
coord = Coordinate(int(row), int(column), int(zoom))
elif _preview_pat.match(pathinfo or ''):
# 返回图层的预览页面
path = _preview_pat.match(pathinfo)
layer, extension = path.group('l'), 'html'
coord = None
else:
raise Core.KnownUnknown(
'Bad path: "{}". I was expecting something more like "/example/0/0/0.png"'.format(pathinfo))
return layer, coord, extension
返回响应内容则是比较复杂的部分:
from . import Core
def requestHandler2(config_hint, path_info, query_string=None, script_name=''):
headers = Headers([])
try:
# 确保path_info起码有一个 "/"
path_info = '/' + (path_info or '').lstrip('/')
# 获取指定的图层
layer = requestLayer(config_hint, path_info)
query = parse_qs(query_string or '')
try:
callback = query['callback'][0]
except KeyError:
callback = None
coord, extension = splitPathInfo(path_info)[1:]
# 针对特定请求返回预览页面
if extension == 'html' and coord is None:
status_code, headers, content = getPreview(layer)
# 重定向处理
elif extension.lower() in layer.redirects:
other_extension = layer.redirects[extension.lower()]
redirect_uri = script_name
redirect_uri += mergePathInfo(layer.name(), coord, other_extension)
if query_string:
redirect_uri += '?' + query_string
headers['Location'] = redirect_uri
headers['Content-Type'] = 'text/plain'
return 302, headers, 'You are being redirected to %s\n' % redirect_uri
else:
# 获取瓦片
status_code, headers, content = layer.getTileResponse(
coord, extension)
if layer.allowed_origin:
headers.setdefault('Access-Control-Allow-Origin',
layer.allowed_origin)
if callback and 'json' in headers['Content-Type']:
headers['Content-Type'] = 'application/javascript; charset=utf-8'
content = '%s(%s)' % (callback, content)
if layer.max_cache_age is not None:
expires = datetime.utcnow() + timedelta(seconds=layer.max_cache_age)
headers.setdefault('Expires', expires.strftime(
'%a, %d %b %Y %H:%M:%S GMT'))
headers.setdefault(
'Cache-Control', 'public, max-age=%d' % layer.max_cache_age)
except Core.KnownUnknown as e:
out = StringIO()
print('Known unknown!', file=out)
print(e, file=out)
print('', file=out)
print('\n'.join(Core._rummy()), file=out)
headers['Content-Type'] = 'text/plain'
status_code, content = 500, out.getvalue().encode('ascii')
return status_code, headers, content
def requestLayer(config, path_info):
if is_string_type(config):
key = hasattr(config, '__hash__') and (config, getcwd())
# 从缓存中获取配置,避免重复解析
if key in _previous_configs:
config = _previous_configs[key]
# 不存在就缓存配置
else:
config = parseConfig(config)
if key:
_previous_configs[key] = config
else:
assert hasattr(
config, 'cache'), 'Configuration object must have a cache.'
assert hasattr(
config, 'layers'), 'Configuration object must have layers.'
assert hasattr(
config, 'dirpath'), 'Configuration object must have a dirpath.'
path_info = '/' + (path_info or '').lstrip('/')
if path_info == '/':
return Core.Layer(config, None, None)
# 又重新获取了一遍图层名,不知道为什么
layername = splitPathInfo(path_info)[0]
if layername not in config.layers:
raise Core.KnownUnknown('"{}" is not a layer I know about. Here are some that I do know about: {}.'.format(
layername, ', '.join(sorted(config.layers.keys()))))
return config.layers[layername]
# 获取图层预览
def getPreview(layer):
return 200, Headers([('Content-Type', 'text/html')]), Core._preview(layer)
其中有我认为比较难以理解的地方:重复调用函数.
比如解析路径的函数,在拆解请求参数获取图层名,扩展名和坐标时调用了一次,在返回内容时,又为了获取坐标和扩展名调用了一次,在获取图层对象时,为了获取图层名又调用一次.其实可以通过变量在函数之间传递这些参数的.
整个TileStache的入口基本上就是这些功能.下面进入两大核心.
Config.py
从__init__.py加载配置的buildConfiguration方法入手:
def buildConfiguration(config_dict, dirpath='.'):
scheme, h, path, p, q, f = urlparse(dirpath)
# 配置文件路径加入环境变量
if scheme in ('', 'file'):
sys.path.insert(0, path)
# 初始化缓存,缓存只能有一个,但可以是复合缓存
cache_dict = config_dict.get('cache', {})
cache = _parseConfigCache(cache_dict, dirpath)
# 新建一个配置文件对象
config = Configuration(cache, dirpath)
# 初始化所有图层
for (name, layer_dict) in config_dict.get('layers', {}).items():
config.layers[name] = _parseConfigLayer(layer_dict, config, dirpath)
# 初始化日志等级
if 'logging' in config_dict:
level = config_dict['logging'].upper()
if hasattr(logging, level):
logging.basicConfig(level=getattr(logging, level))
return config
其实也是干了两个事:
- 初始化缓存
- 初始化图层
配置文件中,缓存和图层的配置以如下方式存在
{
"cache":
{
"name": "Test",
"path": "/tmp/stache",
"umask": "0000"
},
"layers":
{
"osm":
{
"provider": {"name": "proxy", "provider": "OPENSTREETMAP"},
"png options": {"palette": "http://tilestache.org/example-palette-openstreetmap-mapnik.act"}
},
"example":
{
"provider": {"name": "mapnik", "mapfile": "examples/style.xml"},
"projection": "spherical mercator"
}
}
}
初始化缓存
def _parseConfigCache(cache_dict, dirpath):
if 'name' in cache_dict:
# 获取缓存的名称
_class = Caches.getCacheByName(cache_dict['name'])
kwargs = {}
# 获取对应配置值
def add_kwargs(*keys):
for key in keys:
if key in cache_dict:
kwargs[key] = cache_dict[key]
# 文件缓存
if _class is Caches.Disk:
kwargs['path'] = enforcedLocalPath(cache_dict['path'], dirpath, 'Disk cache path')
if 'umask' in cache_dict:
kwargs['umask'] = int(cache_dict['umask'], 8)
add_kwargs('dirs', 'gzip')
# 复合缓存
elif _class is Caches.Multi:
kwargs['tiers'] = [_parseConfigCache(tier_dict, dirpath)
for tier_dict in cache_dict['tiers']]
......
elif 'class' in cache_dict:
# 应对扩展的非内置缓存
_class = Core.loadClassPath(cache_dict['class'])
kwargs = cache_dict.get('kwargs', {})
kwargs = dict( [(str(k), v) for (k, v) in kwargs.items()] )
# 初始化这个缓存
cache = _class(**kwargs)
return cache
初始化图层
def _parseConfigLayer(layer_dict, config, dirpath):
#获取坐标系
projection = layer_dict.get('projection', 'spherical mercator')
projection = Geography.getProjectionByName(projection)
# 添加一系列缓存相关参数
layer_kwargs = {}
if 'cache lifespan' in layer_dict:
layer_kwargs['cache_lifespan'] = int(layer_dict['cache lifespan'])
if 'stale lock timeout' in layer_dict:
layer_kwargs['stale_lock_timeout'] = int(layer_dict['stale lock timeout'])
.........
if 'preview' in layer_dict:
preview_dict = layer_dict['preview']
for (key, func) in zip(('lat', 'lon', 'zoom', 'ext'), (float, float, int, str)):
if key in preview_dict:
layer_kwargs['preview_' + key] = func(preview_dict[key])
# 获取图层的四至
if 'bounds' in layer_dict:
if type(layer_dict['bounds']) is dict:
layer_kwargs['bounds'] = _parseLayerBounds(layer_dict['bounds'], projection)
elif type(layer_dict['bounds']) is list:
bounds = [_parseLayerBounds(b, projection) for b in layer_dict['bounds']]
layer_kwargs['bounds'] = BoundsList(bounds)
else:
raise Core.KnownUnknown('Layer bounds must be a dictionary, not: ' + dumps(layer_dict['bounds']))
# 元瓦片
# 关于元瓦片,可以参照https://www.geowebcache.org/docs/current/concepts/metatiles.html
meta_dict = layer_dict.get('metatile', {})
metatile_kwargs = {}
for k in ('buffer', 'rows', 'columns'):
if k in meta_dict:
metatile_kwargs[k] = int(meta_dict[k])
metatile = Core.Metatile(**metatile_kwargs)
# 处理jpg/png格式参数
jpeg_kwargs = {}
png_kwargs = {}
if 'jpeg options' in layer_dict:
jpeg_kwargs = dict([(str(k), v) for (k, v) in layer_dict['jpeg options'].items()])
if 'png options' in layer_dict:
png_kwargs = dict([(str(k), v) for (k, v) in layer_dict['png options'].items()])
# 图片处理
pixel_effect = None
if 'pixel effect' in layer_dict:
pixel_effect_dict = layer_dict['pixel effect']
pixel_effect_name = pixel_effect_dict.get('name')
if pixel_effect_name in PixelEffects.all:
pixel_effect_kwargs = {}
for k, v in pixel_effect_dict.items():
if k != 'name':
pixel_effect_kwargs[str(k)] = float(v)
PixelEffectClass = PixelEffects.all[pixel_effect_name]
pixel_effect = PixelEffectClass(**pixel_effect_kwargs)
# 绑定提供者
provider_dict = layer_dict['provider']
# 加载内置和额外的提供者
if 'name' in provider_dict:
_class = Providers.getProviderByName(provider_dict['name'])
provider_kwargs = _class.prepareKeywordArgs(provider_dict)
elif 'class' in provider_dict:
_class = Core.loadClassPath(provider_dict['class'])
provider_kwargs = provider_dict.get('kwargs', {})
provider_kwargs = dict( [(str(k), v) for (k, v) in provider_kwargs.items()] )
else:
raise Exception('Missing required provider name or class: %s' % json_dumps(provider_dict))
# 实例化图层
layer = Core.Layer(config, projection, metatile, **layer_kwargs)
layer.provider = _class(layer, **provider_kwargs)
layer.setSaveOptionsJPEG(**jpeg_kwargs)
layer.setSaveOptionsPNG(**png_kwargs)
layer.pixel_effect = pixel_effect
return layer
可以看出TileStache是通过读取配置的方式加载不同的插件的.这是很传统的方式,也有很大的麻烦,那就是如果扩展一种,就要在if判断里多写一种情况.
回顾一下Tilestrata是怎么做的:
strata.layer('basemap')
.route('tile@2x.png')
.use(disk.cache({dir: '/var/lib/tiles/basemap'}))
.use(mapnik({
pathname: '/path/to/map.xml',
tileSize: 512,
scale: 2
}))
是的,代码即配置,简洁多了,实现起来也完全没有加载配置项这一步了.
Core.py
Core.py其实可以说是Layer.py,因为基本上是为图层服务的.
我们回到一开始处理请求的__init__.py,那里获取请求调用的是如下方法:
status_code, headers, content = layer.getTileResponse(coord, extension)
获取瓦片可以说是图层存在的目的了,因此也是整个Layer类的最重头戏:
def getTileResponse(self, coord, extension, ignore_cached=False):
# 记录响应的时间点
start_time = time()
# 获取文件类型从而确定mime类型
mimetype, format = self.getTypeByExtension(extension)
# 定义默认的响应状态
status_code = 200
headers = Headers([('Content-Type', mimetype)])
body = None
cache = self.config.cache
if not ignore_cached:
#尝试从缓存中获取瓦片
try:
body = cache.read(self, coord, format)
except TheTileLeftANote as e:
headers = e.headers
status_code = e.status_code
body = e.content
if e.emit_content_type:
headers.setdefault('Content-Type', mimetype)
tile_from = 'cache'
else:
# 从最近的文件获取
# 这个其实如果有redis或者memcache缓存的话就有些多此一举了
body = _getRecentTile(self, coord, format)
tile_from = 'recent tiles'
# 缓存里没有就深究
if body is None:
try:
lockCoord = None
if self.write_cache:
# 对该位置的缓存上锁,保证后期写入缓存时不冲突
lockCoord = self.metatile.firstCoord(coord)
cache.lock(self, lockCoord, format)
if not ignore_cached:
# 上锁后再次确认能否获取到缓存
# 因为有可能第一次获取时其他进程正在写入,导致获取失败
body = cache.read(self, coord, format)
tile_from = 'cache after all'
if body is None:
# No one else wrote the tile, do it here.
buff = BytesIO()
# 从缓存里找不到,就直接渲染
try:
tile = self.render(coord, format)
save = True
except NoTileLeftBehind as e:
# 出现NoTileLeftBehind时,返回正常瓦片,但不进入缓存
# 这种情况面向空白瓦片,这样的瓦片不需要缓存,可以减小缓存体积
tile = e.tile
save = False
status_code = 404
if not self.write_cache:
save = False
if format.lower() == 'jpeg':
save_kwargs = self.jpeg_options
elif format.lower() == 'png':
save_kwargs = self.png_options
else:
save_kwargs = {}
# 将生成的瓦片存入buff中
tile.save(buff, format, **save_kwargs)
body = buff.getvalue()
# 将瓦片存入缓存
if save:
cache.save(body, self, coord, format)
tile_from = 'layer.render()'
except TheTileLeftANote as e:
# 处理带附言的瓦片
headers = e.headers
status_code = e.status_code
body = e.content
if e.emit_content_type:
headers.setdefault('Content-Type', mimetype)
finally:
if lockCoord:
# 解锁对应缓存
cache.unlock(self, lockCoord, format)
# 将瓦片存入自带的内存缓存
_addRecentTile(self, coord, format, body)
return status_code, headers, body
在其中我们可以看到它实现了一个简单的实效缓存:
_recent_tiles = dict(hash={}, list=[])
# 存入缓存
def _addRecentTile(layer, coord, format, body, age=300):
key = (layer, coord, format)
# 应过期时间
due = time() + age
# 存入缓存字典
_recent_tiles['hash'][key] = body, due
_recent_tiles['list'].append((key, due))
#寻找第一个超时的key
cutoff = 0
for i, (key, due_by) in enumerate(_recent_tiles['list']):
# 找到第一个未超时就停止
if time() < due_by:
cutoff = i
break
# 删掉超时的key
try:
del _recent_tiles['hash'][key]
except KeyError:
pass
# 将全部超时瓦片缓存删除
del _recent_tiles['list'][:cutoff]
# 取缓存
def _getRecentTile(layer, coord, format):
key = (layer, coord, format)
body, use_by = _recent_tiles['hash'].get(key, (None, 0))
if body is None:
return None
# 是否够新
if time() < use_by:
return body
# 过旧就删除
try:
del _recent_tiles['hash'][key]
except KeyError:
pass
return None
说实话我觉得这样是没必要的,每次存入都要遍历一遍缓存列表删除过期,每次取都要检查当前时间并对比是否过期,都是对资源的消耗,同时,因为是按时间过期来删除,如果短时间内产生大量缓存,会对内存产生影响.
获取瓦片有一个重要的部分就是瓦片的渲染:
def render(self, coord, format):
# 所取区域是否超过范围,超过就返回空白图
if self.bounds and self.bounds.excludes(coord):
raise NoTileLeftBehind(Image.new('RGBA', (self.dim, self.dim), (0, 0, 0, 0)))
srs = self.projection.srs
# 当前所取瓦片的四至
xmin, ymin, xmax, ymax = self.envelope(coord)
width, height = self.dim, self.dim
provider = self.provider
metatile = self.metatile
pass_through = provider.pass_through if hasattr(provider, 'pass_through') else False
# 元瓦片模式
if self.doMetatile():
# 调整瓦片四至,变为该瓦片周围8个瓦片所包含范围的四至
xmin, ymin, xmax, ymax = self.metaEnvelope(coord)
width, height = self.metaSize(coord)
subtiles = self.metaSubtiles(coord)
# 在某些情况下,同时渲染特定瓦片和其周围的瓦片与只渲染特定瓦片的效果不一样
if self.doMetatile() or hasattr(provider, 'renderArea'):
# 周围瓦片区域渲染
tile = provider.renderArea(width, height, srs, xmin, ymin, xmax, ymax, coord.zoom)
elif hasattr(provider, 'renderTile'):
# 只对特定瓦片渲染
width, height = self.dim, self.dim
tile = provider.renderTile(width, height, srs, coord)
if self.bitmap_palette:
# 调色
if format.lower() == 'png':
t_index = self.png_options.get('transparency', None)
tile = apply_palette(tile, self.bitmap_palette, t_index)
if self.pixel_effect:
# 图像处理
if format.lower() in ('png', 'jpeg', 'tiff', 'bmp', 'gif'):
tile = self.pixel_effect.apply(tile)
if self.doMetatile():
tile, surtile = None, tile
# 将元瓦片切割成瓦片
for (other, x, y) in subtiles:
buff = BytesIO()
bbox = (x, y, x + self.dim, y + self.dim)
subtile = surtile.crop(bbox)
if self.palette256:
subtile = apply_palette256(subtile)
subtile.save(buff, format)
body = buff.getvalue()
# 所有9个瓦片存入缓存
if self.write_cache:
self.config.cache.save(body, self, other, format)
if other == coord:
#只将重心瓦片返回
tile = subtile
_addRecentTile(self, other, format, body)
return tile
Metatile 元瓦片
瓦片渲染时,反复提到了一个metatile(元瓦片)模式,这是一种加速响应的策略.
元瓦片的思路来源于这样一个假设:
对任何瓦片的获取都潜在的要获取它周围的8张瓦片,因为地图一定是连续的.
这与一般的通用缓存不同,它是针对地图这种特殊业务而进行优化的.
一般流程是:
- 服务器收到瓦片请求
- 服务器真实的去渲染了该瓦片及其周围8张瓦片范围的地图
- 将这张图按井字切为9个小瓦片
- 缓存这9张瓦片
- 只返回正中心的那张瓦片
- 等到该瓦片任意一个方向的瓦片因为地图加载顺序而被随后请求时,直接从缓存取得.
从时间耗费来说:
渲染1张瓦片的时间<渲染1张元瓦片的时间+切割成9份的时间<渲染9张瓦片的时间
只要用户拖动地图,缓存就会命中,就有加速的效果.
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