Fix crash on decoding partial YAML (#1)

Sources/UniYAML/Decoder.swift

@@ -297,6 +297,9 @@ public struct UniYAML {
 			return nil
 		}
 		_ = parseIndent(stream, index: &index)
+		guard index < stream.endIndex else {
+			return nil
+		}
 		var search = Range(uncheckedBounds: (index, stream.endIndex))
 		var location = search
 		var fragments = ""
@@ -402,12 +405,18 @@ public struct UniYAML {
 			guard i >= block else {
 				throw UniYAMLError.error(detail: "unexpected indentation")
 			}
-			index = stream.index(index, offsetBy: i)
+			index = stream.index(index, offsetBy: i, limitedBy: stream.endIndex) ?? stream.endIndex
+			guard index < stream.endIndex else {
+				break
+			}
 			var location = Range(uncheckedBounds: (index, stream.endIndex))
 			if let border = stream.rangeOfCharacter(from: CharacterSet(charactersIn: "\r\n\u{85}"), range: location) {
 				location = Range(uncheckedBounds: (index, border.lowerBound))
 				glue = (folded) ? " ":stream[border.lowerBound]
 			}
+			guard location.upperBound < stream.endIndex else {
+				break
+			}
 			index = stream.index(after: location.upperBound)
 			line += 1
 			if !value.isEmpty {
@@ -427,8 +436,14 @@ public struct UniYAML {
 		}
 		let s = ss.replacingOccurrences(of: "\r", with: "").replacingOccurrences(of: "\n", with: "").replacingOccurrences(of: "\u{85}", with: "")
 		if s.hasPrefix("'"), s.hasSuffix("'") {
+			guard s.count >= 2 else {
+				return nil
+			}
 			return String(s[s.index(after: s.startIndex)..<s.index(before: s.endIndex)])
 		} else if s.hasPrefix("\""), s.hasSuffix("\"") {
+			guard s.count >= 2 else {
+				return nil
+			}
 			return String(s[s.index(after: s.startIndex)..<s.index(before: s.endIndex)]
 					.replacingOccurrences(of: "\\\\", with: "_backslash_holder_") // XXX: bad ugly hack
 					.replacingOccurrences(of: "\\0", with: "\0")

Tests/UniYAMLTests/UniYAMLTests.swift

@@ -32,6 +32,10 @@ class UniYAMLTests: XCTestCase {
 		("testYAMLUnexpectedColon", testYAMLUnexpectedColon),
 		("testYAMLUnexpectedBrace", testYAMLUnexpectedBrace),
 		("testYAMLUnexpectedEnd", testYAMLUnexpectedEnd),
+		("testPartialYAML", testPartialYAML),
+		("testPartialYAML2", testPartialYAML2),
+		("testPartialYAML3", testPartialYAML3),
+		("testPartialYAML4", testPartialYAML4),
 	]
 
 	let types = "---\n\nsimple string: a text\nquoted string: 'john ''beatle''\n lennon'\nsplit string: >\n  two\n  words\nrows: |\n  first\n  second\n  last\nint: -12345\nuint: 67890\ndouble: 3.14159265\npositive: yes\nnegative: off\n"
@@ -456,4 +460,52 @@ classic:
 		XCTAssert(obj == nil && err.hasPrefix("unexpected stream end"))
 	}
 
+	func testPartialYAML() throws {
+		let yaml = "a: "
+		let obj = try UniYAML.decode(yaml)
+		XCTAssert(
+			obj.type == .dictionary &&
+			obj.keys!.count == 1 &&
+			obj["a"]?.type == .pending
+		)
+	}
+
+	func testPartialYAML2() {
+		let yaml = "a: 3\n "
+		var obj: YAML?
+		var err: String = ""
+		do {
+			obj = try UniYAML.decode(yaml)
+		} catch UniYAMLError.error(let detail) {
+			err = detail
+		} catch {
+			print(error)
+		}
+		XCTAssert(obj == nil && err.hasPrefix("missing value at line 2"))
+	}
+
+	func testPartialYAML3() {
+		let yaml = "a: 3\n  b"
+		var obj: YAML?
+		var err: String = ""
+		do {
+			obj = try UniYAML.decode(yaml)
+		} catch UniYAMLError.error(let detail) {
+			err = detail
+		} catch {
+			print(error)
+		}
+		XCTAssert(obj == nil && err.hasPrefix("missing value at line 2"))
+	}
+
+	func testPartialYAML4() throws {
+		let yaml = "a: '"
+		let obj = try UniYAML.decode(yaml)
+		XCTAssert(
+			obj.type == .dictionary &&
+			obj.keys!.count == 1 &&
+			obj["a"]?.type == .pending
+		)
+	}
+
 }