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62 lines
2.7 KiB
62 lines
2.7 KiB
6 years ago
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type: google.api.Service
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config_version: 3
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name: cel.googleapis.com
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title: Common Expression Language
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apis:
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- name: google.api.expr.v1alpha1.ConformanceService
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- name: google.api.expr.v1alpha1.CelService
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documentation:
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summary: Defines common types for the Common Expression Language.
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overview: |-
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# Common Expression Language
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The Common Expression Language (CEL) implements common semantics for
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expression evaluation, enabling different applications to more easily
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interoperate.
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Key Applications
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* Security policy: organization have complex infrastructure and need
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common tooling to reason about the system as a whole * Protocols:
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expressions are a useful data type and require interoperability across
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programming languages and platforms.
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Guiding philosophy:
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1. Keep it small & fast. * CEL evaluates in linear time, is mutation
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free, and not Turing-complete. This limitation is a feature of the language
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design, which allows the implementation to evaluate orders of magnitude
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faster than equivalently sandboxed JavaScript. 2. Make it extensible. *
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CEL is designed to be embedded in applications, and allows for extensibility
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via its context which allows for functions and data to be provided by the
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software that embeds it. 3. Developer-friendly * The language is
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approachable to developers. The initial spec was based on the experience of
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developing Firebase Rules and usability testing many prior iterations. *
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The library itself and accompanying toolings should be easy to adopt by
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teams that seek to integrate CEL into their platforms.
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The required components of a system that supports CEL are:
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* The textual representation of an expression as written by a developer.
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It is of similar syntax of expressions in C/C++/Java/JavaScript * A binary
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representation of an expression. It is an abstract syntax tree (AST). * A
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compiler library that converts the textual representation to the binary
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representation. This can be done ahead of time (in the control plane) or
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just before evaluation (in the data plane). * A context containing one or
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more typed variables, often protobuf messages. Most use-case will use
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attribute_context.proto * An evaluator library that takes the binary
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format in the context and produces a result, usually a Boolean.
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Example of boolean conditions and object construction:
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``` c // Condition account.balance >= transaction.withdrawal ||
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(account.overdraftProtection && account.overdraftLimit >=
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transaction.withdrawal - account.balance)
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// Object construction common.GeoPoint{ latitude: 10.0, longitude: -5.5 }
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```
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