67 lines
2.2 KiB
Markdown
67 lines
2.2 KiB
Markdown
# kaya-session-memcache
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Memcached-backed session storage for the Kaya web framework.
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Provides `MemcacheSessionStore`, a `SessionStore` implementation (from
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`kaya-session`) that persists session data in memcached via `aiomcache`, so
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sessions are shared across processes and hosts.
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## Usage
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```python
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import aiomcache
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from kaya.core import KayaApp, HttpContext
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from kaya.session import SessionMixin
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from kaya.session.memcache import MemcacheSessionStore
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client = aiomcache.Client('127.0.0.1', 11211)
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session = SessionMixin(MemcacheSessionStore(client))
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app = KayaApp(mixins=[session])
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@app.GET('/')
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async def home(ctx: HttpContext):
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n = ctx.session.get('visits', 0) + 1
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ctx.session['visits'] = n
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await ctx.send_str(200, f'visits: {n}')
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```
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Sessions are stored under keys with the prefix `kaya:session:` (configurable
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via the `prefix` argument). Server-side expiry uses memcached item expiration
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and slides on each access when the session mixin passes a `max_age`. TTLs
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larger than 30 days are automatically converted to absolute Unix timestamps,
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as required by the memcached protocol.
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## Session indexes
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`MemcacheSessionStore` supports `Session.add_index()`,
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`SessionStore.find_sessions()`, and `delete_by_index()`. Reverse memberships
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are stored as sets and updated with memcached CAS operations. Bucket keys use
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a SHA-256 digest of the index name and value, and stale members are pruned
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during lookups.
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Memcached's item-size limit (normally 1 MB) applies to each index bucket. Use
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the Redis store when one index value can have a very large number of active
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sessions.
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## Serialization
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Session data is serialized with `pickle` by default, so arbitrary Python
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objects can be stored. The serialized value is an envelope containing the
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session dictionary and index metadata; legacy plain-dict values are still
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accepted. A different serializer can be plugged in via the `dumps`/`loads`
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arguments:
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```python
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import json
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store = MemcacheSessionStore(
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client,
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dumps=lambda d: json.dumps(d).encode('utf-8'),
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loads=lambda b: json.loads(b.decode('utf-8')),
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)
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```
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**Warning:** pickle deserialization of untrusted data is unsafe. Only use the
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default serializer with a trusted memcached server.
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