fix: support string or string slices when deserializing IamPolicyStatement (#854)

`Action` and `Resource` allow both `string` and `[string]` as values.
Support deserializing `IamPolicyStatement` with either of these values.

fixes: #853

Author: aesterline

lambda-events/src/custom_serde/mod.rs

@@ -92,6 +92,27 @@ where
     Ok(opt.unwrap_or_default())
 }
 
+/// Deserializes `Vec<String>`, from a JSON `string` or `[string]`.
+#[cfg(any(feature = "apigw", test))]
+pub(crate) fn deserialize_string_or_slice<'de, D>(deserializer: D) -> Result<Vec<String>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    #[derive(serde::Deserialize)]
+    #[serde(untagged)]
+    enum StringOrSlice {
+        String(String),
+        Slice(Vec<String>),
+    }
+
+    let string_or_slice = StringOrSlice::deserialize(deserializer)?;
+
+    match string_or_slice {
+        StringOrSlice::Slice(slice) => Ok(slice),
+        StringOrSlice::String(s) => Ok(vec![s]),
+    }
+}
+
 #[cfg(test)]
 #[allow(deprecated)]
 mod test {

lambda-events/src/event/apigw/mod.rs

@@ -1,6 +1,6 @@
 use crate::custom_serde::{
-    deserialize_headers, deserialize_lambda_map, deserialize_nullish_boolean, http_method, serialize_headers,
-    serialize_multi_value_headers,
+    deserialize_headers, deserialize_lambda_map, deserialize_nullish_boolean, deserialize_string_or_slice, http_method,
+    serialize_headers, serialize_multi_value_headers,
 };
 use crate::encodings::Body;
 use http::{HeaderMap, Method};
@@ -737,11 +737,13 @@ pub struct ApiGatewayCustomAuthorizerPolicy {
 #[serde(rename_all = "camelCase")]
 pub struct IamPolicyStatement {
     #[serde(rename = "Action")]
+    #[serde(deserialize_with = "deserialize_string_or_slice")]
     pub action: Vec<String>,
     #[serde(default)]
     #[serde(rename = "Effect")]
     pub effect: Option<String>,
     #[serde(rename = "Resource")]
+    #[serde(deserialize_with = "deserialize_string_or_slice")]
     pub resource: Vec<String>,
 }
 
@@ -832,6 +834,26 @@ mod test {
         assert_eq!(parsed, reparsed);
     }
 
+    #[test]
+    #[cfg(feature = "apigw")]
+    fn example_apigw_custom_auth_response_with_single_value_action() {
+        let data = include_bytes!("../../fixtures/example-apigw-custom-auth-response-with-single-value-action.json");
+        let parsed: ApiGatewayCustomAuthorizerResponse = serde_json::from_slice(data).unwrap();
+        let output: String = serde_json::to_string(&parsed).unwrap();
+        let reparsed: ApiGatewayCustomAuthorizerResponse = serde_json::from_slice(output.as_bytes()).unwrap();
+        assert_eq!(parsed, reparsed);
+    }
+
+    #[test]
+    #[cfg(feature = "apigw")]
+    fn example_apigw_custom_auth_response_with_single_value_resource() {
+        let data = include_bytes!("../../fixtures/example-apigw-custom-auth-response-with-single-value-resource.json");
+        let parsed: ApiGatewayCustomAuthorizerResponse = serde_json::from_slice(data).unwrap();
+        let output: String = serde_json::to_string(&parsed).unwrap();
+        let reparsed: ApiGatewayCustomAuthorizerResponse = serde_json::from_slice(output.as_bytes()).unwrap();
+        assert_eq!(parsed, reparsed);
+    }
+
     #[test]
     #[cfg(feature = "apigw")]
     fn example_apigw_request() {

lambda-events/src/fixtures/example-apigw-custom-auth-response-with-single-value-action.json

@@ -0,0 +1,19 @@
+{
+    "principalId": "yyyyyyyy",
+    "policyDocument": {
+      "Version": "2012-10-17",
+      "Statement": [
+        {
+          "Action": "execute-api:Invoke",
+          "Effect": "Allow",
+          "Resource": ["arn:aws:execute-api:{regionId}:{accountId}:{appId}/{stage}/{httpVerb}/[{resource}/[child-resources]]"]
+        }
+      ]
+    },
+    "context": {
+      "stringKey": "value",
+      "numberKey": "1",
+      "booleanKey": "true"
+    },
+    "usageIdentifierKey": "{api-key}"
+}

lambda-events/src/fixtures/example-apigw-custom-auth-response-with-single-value-resource.json

@@ -0,0 +1,19 @@
+{
+    "principalId": "yyyyyyyy",
+    "policyDocument": {
+      "Version": "2012-10-17",
+      "Statement": [
+        {
+          "Action": ["execute-api:Invoke"],
+          "Effect": "Allow",
+          "Resource": "arn:aws:execute-api:{regionId}:{accountId}:{appId}/{stage}/{httpVerb}/[{resource}/[child-resources]]"
+        }
+      ]
+    },
+    "context": {
+      "stringKey": "value",
+      "numberKey": "1",
+      "booleanKey": "true"
+    },
+    "usageIdentifierKey": "{api-key}"
+}