computer-science law

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Proxy

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Description

A proxy is a stand-in that preserves the subject’s interface but interposes itself between client and subject. From the client’s perspective the proxy is indistinguishable from the subject — same calls, same return shapes — but the proxy gets to do something on the way through: check permissions, cache results, lazy-instantiate the real subject, log accesses, throttle, encrypt, marshal to a remote process. The defining contrast is with adapter: an adapter changes the interface shape, a proxy preserves it. The defining contrast with decorator is orientation: a decorator adds behavior to operations; a proxy controls access to operations.

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Triggers

User-initiated: User describes wanting to add caching, access control, logging, or remoting without changing the surface the rest of the code calls. Vocabulary cues: “transparent,” “intercept,” “on the way through,” “without the caller noticing,” “stand-in.” Agent-initiated: Agent notices that some cross-cutting concern (auth, logging, caching, rate-limiting, remoting) is being repeatedly tangled into call sites and would be better absorbed at a single interception point. Candidate inference: “introduce a proxy in front of the subject; pull the cross-cutting concern out of the call-site noise.” Situation-shape signals: Repeated boilerplate around access to a single resource. A subject that’s expensive to construct but cheap to wrap. A boundary between two trust domains where access deserves checking. A subject that needs to be reachable from another process / machine.

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Exclusions

• No cross-cutting concern to absorb — if every call site has its own bespoke pre/post logic, there’s nothing for the proxy to factor out; adding a proxy is then overhead without reuse.
• The control is semantic, not structural — if “controlling access” means changing what the operation means (different return values, different effects), it’s not a proxy anymore; it’s an alternate implementation pretending to be a proxy, which leaks badly.
• Performance budget can’t afford the indirection — tight loops and hot paths sometimes can’t tolerate even a virtual-method-call layer; the proxy must be inlined or omitted.

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Structure

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Relationships

• active-gate-vs-passive-audit — the protection-proxy variant is exactly active-gate; the proxy blocks before passing through, vs. audit that records and surfaces later.
• surface — the proxy is the surface the client sees; the subject is what’s behind the surface, possibly with structural detail the client never needs to see.
• adapter — proxy and adapter are siblings at the interface boundary; proxy preserves the shape, adapter changes it.
• decorator — proxy and decorator share the wrap-the-subject shell but differ in intent: control vs. extend.
• cost-cascade — caching proxies are the canonical cheap-default → expensive-fallback case; the proxy serves from cache and only falls through to the subject on miss.

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Examples