cedar_policy_core/entities/json/
context.rs

1/*
2 * Copyright Cedar Contributors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      https://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17use super::{
18    err::{JsonDeserializationError, JsonDeserializationErrorContext},
19    SchemaType, ValueParser,
20};
21use crate::ast::{Context, ContextCreationError};
22use crate::extensions::Extensions;
23use miette::Diagnostic;
24use std::collections::BTreeMap;
25use thiserror::Error;
26
27/// Trait for schemas that can inform the parsing of Context data
28pub trait ContextSchema {
29    /// `SchemaType` (expected to be a `Record`) for the context.
30    fn context_type(&self) -> SchemaType;
31}
32
33/// Simple type that implements `ContextSchema` by expecting an empty context
34#[derive(Debug, Clone)]
35pub struct NullContextSchema;
36impl ContextSchema for NullContextSchema {
37    fn context_type(&self) -> SchemaType {
38        SchemaType::Record {
39            attrs: BTreeMap::new(),
40            open_attrs: false,
41        }
42    }
43}
44
45/// Struct used to parse context from JSON.
46#[derive(Debug, Clone)]
47pub struct ContextJsonParser<'e, 's, S: ContextSchema = NullContextSchema> {
48    /// If a `schema` is present, this will inform the parsing: for instance, it
49    /// will allow `__entity` and `__extn` escapes to be implicit.
50    /// It will also ensure that the produced `Context` fully conforms to the
51    /// `schema` -- for instance, it will error if attributes have the wrong
52    /// types (e.g., string instead of integer), or if required attributes are
53    /// missing or superfluous attributes are provided.
54    schema: Option<&'s S>,
55
56    /// Extensions which are active for the JSON parsing.
57    extensions: &'e Extensions<'e>,
58}
59
60impl<'e, 's, S: ContextSchema> ContextJsonParser<'e, 's, S> {
61    /// Create a new `ContextJsonParser`.
62    ///
63    /// If a `schema` is present, this will inform the parsing: for instance, it
64    /// will allow `__entity` and `__extn` escapes to be implicit.
65    /// It will also ensure that the produced `Context` fully conforms to the
66    /// `schema` -- for instance, it will error if attributes have the wrong
67    /// types (e.g., string instead of integer), or if required attributes are
68    /// missing or superfluous attributes are provided.
69    pub fn new(schema: Option<&'s S>, extensions: &'e Extensions<'e>) -> Self {
70        Self { schema, extensions }
71    }
72
73    /// Parse context JSON (in `&str` form) into a `Context` object
74    pub fn from_json_str(&self, json: &str) -> Result<Context, ContextJsonDeserializationError> {
75        let val =
76            serde_json::from_str(json).map_err(|e| JsonDeserializationError::Serde(e.into()))?;
77        self.from_json_value(val)
78    }
79
80    /// Parse context JSON (in `serde_json::Value` form) into a `Context` object
81    pub fn from_json_value(
82        &self,
83        json: serde_json::Value,
84    ) -> Result<Context, ContextJsonDeserializationError> {
85        let vparser = ValueParser::new(self.extensions);
86        let expected_ty = self.schema.map(|s| s.context_type());
87        let rexpr = vparser.val_into_restricted_expr(json, expected_ty.as_ref(), || {
88            JsonDeserializationErrorContext::Context
89        })?;
90        Context::from_expr(rexpr.as_borrowed(), self.extensions)
91            .map_err(ContextJsonDeserializationError::ContextCreation)
92    }
93
94    /// Parse context JSON (in `std::io::Read` form) into a `Context` object
95    pub fn from_json_file(
96        &self,
97        json: impl std::io::Read,
98    ) -> Result<Context, ContextJsonDeserializationError> {
99        let val = serde_json::from_reader(json).map_err(JsonDeserializationError::from)?;
100        self.from_json_value(val)
101    }
102}
103
104/// Errors possible when deserializing request context from JSON
105#[derive(Debug, Diagnostic, Error)]
106pub enum ContextJsonDeserializationError {
107    /// Any JSON deserialization error
108    ///
109    /// (Note: as of this writing, `JsonDeserializationError` actually contains
110    /// many variants that aren't possible here)
111    #[error(transparent)]
112    #[diagnostic(transparent)]
113    JsonDeserialization(#[from] JsonDeserializationError),
114    /// Error constructing the `Context` itself
115    #[error(transparent)]
116    #[diagnostic(transparent)]
117    ContextCreation(#[from] ContextCreationError),
118}
cedar_policy_core/entities/json/context.rs

cedar_policy_core/entities/json/
context.rs
