Fix error handling for array parsing (#18)

Addresses an error introduced when rearranging error handling
in array parsers. The validation of `count` being non-negative
was dropped at some point along the way; this change brings that
check back and switches the `Array(parsing:count:parser:)`
initializer to throw `ThrownParsingError` instead of having a
generic error type parameter.

Author: natecook1000

Sources/BinaryParsing/Parser Types/ParsingError.swift

@@ -121,7 +121,7 @@ extension ParsingError.Status: CustomStringConvertible {
 /// In a build for embedded Swift, `ThrownParsingError` instead aliases the
 /// specific `ParsingError` type. Because embedded Swift supports only
 /// fully-typed throws, and not the existential `any Error`, this allows you to
-/// still take use error-throwing APIs in an embedded context.
+/// still use error-throwing APIs in an embedded context.
 public typealias ThrownParsingError = any Error
 #else
 // Documentation is built using the non-embedded build.

Sources/BinaryParsing/Parsers/Array.swift

@@ -80,7 +80,9 @@ extension Array {
     count: some FixedWidthInteger,
     parser: (inout ParserSpan) throws -> Element
   ) throws {
-    let count = try Int(throwingOnOverflow: count)
+    guard let count = Int(exactly: count), count >= 0 else {
+      throw ParsingError(statusOnly: .invalidValue)
+    }
     self = []
     self.reserveCapacity(count)
     // This doesn't throw (e.g. on empty) because `parser` can produce valid
@@ -118,11 +120,14 @@ extension Array {
   /// - Throws: An error if one is thrown from `parser`.
   @inlinable
   @lifetime(&input)
-  public init<E>(
+  public init(
     parsing input: inout ParserSpan,
     count: Int,
-    parser: (inout ParserSpan) throws(E) -> Element
-  ) throws(E) {
+    parser: (inout ParserSpan) throws(ThrownParsingError) -> Element
+  ) throws(ThrownParsingError) {
+    guard count >= 0 else {
+      throw ParsingError(statusOnly: .invalidValue)
+    }
     self = []
     self.reserveCapacity(count)
     // This doesn't throw (e.g. on empty) because `parser` can produce valid

Tests/BinaryParsingTests/ArrayParsingTests.swift

@@ -21,23 +21,23 @@ struct ArrayParsingTests {
 
   @Test
   func parseRemainingBytes() throws {
-    try testBuffer.withParserSpan { span in
-      let parsedArray = try Array(parsingRemainingBytes: &span)
+    testBuffer.withParserSpan { span in
+      let parsedArray = Array(parsingRemainingBytes: &span)
       #expect(parsedArray == testBuffer)
       #expect(span.count == 0)
     }
 
     // Test parsing after consuming part of the buffer
     try testBuffer.withParserSpan { span in
       try span.seek(toRelativeOffset: 3)
-      let parsedArray = try Array(parsingRemainingBytes: &span)
+      let parsedArray = Array(parsingRemainingBytes: &span)
       #expect(parsedArray[...] == testBuffer.dropFirst(3))
       #expect(span.count == 0)
     }
 
     // Test with an empty span
-    try emptyBuffer.withParserSpan { span in
-      let parsedArray = try [UInt8](parsingRemainingBytes: &span)
+    emptyBuffer.withParserSpan { span in
+      let parsedArray = [UInt8](parsingRemainingBytes: &span)
       #expect(parsedArray.isEmpty)
     }
   }
@@ -68,6 +68,14 @@ struct ArrayParsingTests {
       }
       #expect(span.count == testBuffer.count)
     }
+
+    // Negative 'byteCount'
+    testBuffer.withParserSpan { span in
+      #expect(throws: ParsingError.self) {
+        _ = try [UInt8](parsing: &span, byteCount: -1)
+      }
+      #expect(span.count == testBuffer.count)
+    }
   }
 
   @Test
@@ -118,13 +126,21 @@ struct ArrayParsingTests {
       #expect(span.count == 0)
     }
 
-    // Non-'Int' count that would overflow
-    _ = testBuffer.withParserSpan { span in
+    // Error checking
+    testBuffer.withParserSpan { span in
+      // Overflow when 'Int'
       #expect(throws: ParsingError.self) {
         _ = try [UInt8](parsing: &span, count: UInt.max) { input in
           try UInt8(parsing: &input)
         }
       }
+
+      // Negative count
+      #expect(throws: ParsingError.self) {
+        _ = try [UInt8](parsing: &span, count: -1) { input in
+          try UInt8(parsing: &input)
+        }
+      }
     }
   }