SWIFT-920 Support Decoding from BSON in BSONDecoder (#26)

Author: nspektor

Sources/BSON/BSONDecoder.swift

@@ -139,18 +139,7 @@ public class BSONDecoder {
         if let doc = document as? T {
             return doc
         }
-        let _decoder = _BSONDecoder(referencing: .document(document), options: self.options)
-        do {
-            return try type.init(from: _decoder)
-        } catch let error as BSONErrorProtocol {
-            let unknownErrorMessage = "Unknown Error occurred while decoding BSON"
-            throw DecodingError.dataCorrupted(
-                DecodingError.Context(
-                    codingPath: [],
-                    debugDescription: "Unable to decode BSON: \(error.errorDescription ?? unknownErrorMessage)"
-                )
-            )
-        }
+        return try self.decode(type, fromBSON: BSON.document(document))
     }
 
     /**
@@ -165,6 +154,29 @@ public class BSONDecoder {
         try self.decode(type, from: BSONDocument(fromBSON: data))
     }
 
+    /**
+     * Decodes a top-level value of the given type from the given BSON.
+     *
+     * - Parameter type: The type of the value to decode.
+     * - Parameter document: The BSON to decode from.
+     * - Returns: A value of the requested type.
+     * - Throws: `DecodingError` if any value throws an error during decoding.
+     */
+    internal func decode<T: Decodable>(_ type: T.Type, fromBSON bson: BSON) throws -> T {
+        let _decoder = _BSONDecoder(referencing: bson, options: self.options)
+        do {
+            return try _decoder.unbox(bson, as: type)
+        } catch let error as BSONErrorProtocol {
+            let unknownErrorMessage = "Unknown Error occurred while decoding BSON"
+            throw DecodingError.dataCorrupted(
+                DecodingError.Context(
+                    codingPath: _decoder.codingPath,
+                    debugDescription: "Unable to decode BSON: \(error.errorDescription ?? unknownErrorMessage)"
+                )
+            )
+        }
+    }
+
     // TODO: SWIFT-930 Implement this
     // /**
     //  * Decodes a top-level value of the given type from the given JSON/extended JSON string.

Tests/BSONTests/CodecTests.swift

@@ -41,6 +41,17 @@ final class CodecTests: BSONTestCase {
         let s: NestedStruct
     }
 
+    /// Test decoding non-document BSON
+    func testAnyBSON() throws {
+        let decoder = BSONDecoder()
+        expect(try decoder.decode(Int32.self, fromBSON: BSON.int32(1))).to(equal(1))
+        let oid = try BSONObjectID("507f1f77bcf86cd799439011")
+        expect(try decoder.decode(BSONObjectID.self, fromBSON: BSON.objectID(oid)))
+            .to(equal(oid))
+        expect(try decoder.decode(Array.self, fromBSON: [BSON.int32(1), BSON.int32(2)]))
+            .to(equal([1, 2]))
+    }
+
     /// Test encoding/decoding a variety of structs containing simple types that have
     /// built in Codable support (strings, arrays, ints, and structs composed of them.)
     func testStructs() throws {