SWIFT-959 Support userInfo in ExtendedJSONDecoder (#37)

Author: patrickfreed

Sources/BSON/ExtendedJSONDecoder.swift

@@ -13,6 +13,9 @@ public class ExtendedJSONDecoder {
         return formatter
     }()
 
+    /// Contextual user-provided information for use during decoding.
+    public var userInfo: [CodingUserInfoKey: Any] = [:]
+
     /// Initialize an `ExtendedJSONDecoder`.
     public init() {}
 
@@ -28,11 +31,18 @@ public class ExtendedJSONDecoder {
         // Data --> JSON --> BSON --> T
         // Takes in JSON as `Data` encoded with `.utf8` and runs it through a `JSONDecoder` to get an
         // instance of the `JSON` enum.
+
+        // In earlier versions of Swift, JSONDecoder doesn't support decoding "fragments" at the top level, so we wrap
+        // the data in an array to guarantee it always decodes properly.
         let wrappedData = "[".utf8 + data + "]".utf8
         let json = try JSONDecoder().decode([JSON].self, from: wrappedData)[0]
+
         // Then a `BSON` enum instance is created via the `JSON`.
         let bson = try BSON(fromExtJSON: json, keyPath: [])
+
         // The `BSON` is then passed through a `BSONDecoder` where it is outputted as a `T`
-        return try BSONDecoder().decode(T.self, fromBSON: bson)
+        let bsonDecoder = BSONDecoder()
+        bsonDecoder.userInfo = self.userInfo
+        return try bsonDecoder.decode(T.self, fromBSON: bson)
     }
 }

Tests/BSONTests/ExtendedJSONConversionTests.swift

@@ -41,6 +41,48 @@ open class ExtendedJSONConversionTestCase: BSONTestCase {
         expect(decoded).to(equal(test))
     }
 
+    func testExtendedJSONDecodingWithUserInfo() throws {
+        struct Foo: Decodable, Equatable {
+            let val: BSON
+            let bar: Bar
+
+            init(from decoder: Decoder) throws {
+                guard let info = decoder.userInfo[.barInfo] as? BSON else {
+                    throw TestError(message: "userInfo not present")
+                }
+                self.val = info
+
+                // test userinfo is propogated to sub containers
+                let container = try decoder.singleValueContainer()
+                self.bar = try container.decode(Bar.self)
+            }
+        }
+
+        struct Bar: Decodable, Equatable {
+            let val: BSON
+
+            init(from decoder: Decoder) throws {
+                guard let info = decoder.userInfo[.barInfo] as? BSON else {
+                    throw TestError(message: "userInfo not present")
+                }
+                self.val = info
+            }
+        }
+
+        let obj = "{}".data(using: .utf8)!
+        let decoder = ExtendedJSONDecoder()
+
+        decoder.userInfo[.barInfo] = BSON.bool(true)
+        let boolDecoded = try decoder.decode(Foo.self, from: obj)
+        expect(boolDecoded.val).to(equal(true))
+        expect(boolDecoded.bar.val).to(equal(true))
+
+        decoder.userInfo[.barInfo] = BSON.string("hello world")
+        let stringDecoded = try decoder.decode(Foo.self, from: obj)
+        expect(stringDecoded.val).to(equal("hello world"))
+        expect(stringDecoded.bar.val).to(equal("hello world"))
+    }
+
     func testExtendedJSONEncodingWithUserInfo() throws {
         struct Foo: Codable, Equatable {
             func encode(to encoder: Encoder) throws {