fix: StreamableHttpBody with sliced Data (#859)

Author: jbelkins

Diff for: Sources/SmithyStreams/StreamableHttpBody.swift

@@ -16,6 +16,11 @@ import enum Smithy.StreamError
 /// It acts as a bridge between AWS SDK and CRT.
 public class StreamableHttpBody: IStreamable {
 
+    /// The index of the data being transferred.
+    ///
+    /// When the body is `.data`, `position` is the index of the next byte to be transferred
+    /// (note that the startIndex of `Data` need not be zero if the Data is a "slice" of some other Data.)
+    /// When the body is `.stream`, `position` is the number of bytes from the start of the stream.
     var position: Data.Index
     let body: ByteStream
     let logger: SwiftLogger
@@ -82,10 +87,8 @@ public class StreamableHttpBody: IStreamable {
     public func read(buffer: UnsafeMutableBufferPointer<UInt8>) throws -> Int? {
         switch body {
         case .data(let data):
-            guard let data = data else {
-                return nil
-            }
-            let toRead = min(buffer.count, data.count - position)
+            guard let data = data else { return nil }
+            let toRead = min(buffer.count, data.endIndex - position)
             data.copyBytes(to: buffer, from: position..<position.advanced(by: toRead))
             position = position.advanced(by: toRead)
             logger.debug("read \(toRead) bytes from data")
@@ -94,9 +97,7 @@ public class StreamableHttpBody: IStreamable {
             }
             return toRead
         case .stream(let stream):
-            guard let data = try stream.read(upToCount: buffer.count) else {
-                return nil
-            }
+            guard let data = try stream.read(upToCount: buffer.count) else { return nil }
             data.copyBytes(to: buffer, from: data.startIndex..<data.endIndex)
             position = position.advanced(by: data.count)
             logger.debug("read \(data.count) bytes from stream")

Diff for: Tests/ClientRuntimeTests/NetworkingTests/Streaming/StreamableHttpBodyTests.swift

@@ -12,60 +12,73 @@ import AwsCommonRuntimeKit
 
 final class StreamableHttpBodyTests: XCTestCase {
 
-    let testData = Data([0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A])
+    let testData = Data([
+        0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A,
+        0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A
+    ])
 
-    func testRead() throws {
-        let sut = StreamableHttpBody(body: .data(testData))
+    func test_streamWholeData() throws {
+        try read(data: Data(testData[..<11]))
+        try seek(data: Data(testData[11...]))
+    }
+
+    func test_streamSlicedData() throws {
+        try read(data: testData[..<11])
+        try seek(data: testData[11...])
+    }
+
+    private func read(data: Data, file: StaticString = #file, line: UInt = #line) throws {
+        let sut = StreamableHttpBody(body: .data(data))
 
         // read first 4 bytes
         let buffer = UnsafeMutableBufferPointer<UInt8>.allocate(capacity: 4)
         let bytesRead1 = try sut.read(buffer: buffer)
         let bytes1 = Data(bytes: buffer.baseAddress!, count: bytesRead1!)
-        XCTAssertEqual(bytesRead1, 4)
-        XCTAssertEqual(bytes1, Data([0x00, 0x01, 0x02, 0x03]))
+        XCTAssertEqual(bytesRead1, 4, file: file, line: line)
+        XCTAssertEqual(bytes1, Data([0x00, 0x01, 0x02, 0x03]), file: file, line: line)
 
         // read next 4 bytes from current position
         let bytesRead2 = try sut.read(buffer: buffer)
         let bytes2 = Data(bytes: buffer.baseAddress!, count: bytesRead2!)
-        XCTAssertEqual(bytesRead2, 4)
-        XCTAssertEqual(bytes2, Data([0x04, 0x05, 0x06, 0x07]))
+        XCTAssertEqual(bytesRead2, 4, file: file, line: line)
+        XCTAssertEqual(bytes2, Data([0x04, 0x05, 0x06, 0x07]), file: file, line: line)
 
         // read next 4 bytes from current position
         // this should only read 3 bytes since we are at the end of the stream
         let bytesRead3 = try sut.read(buffer: buffer)
         let bytes3 = Data(bytes: buffer.baseAddress!, count: bytesRead3!)
-        XCTAssertEqual(bytesRead3, 3)
-        XCTAssertEqual(bytes3, Data([0x08, 0x09, 0x0A]))
+        XCTAssertEqual(bytesRead3, 3, file: file, line: line)
+        XCTAssertEqual(bytes3, Data([0x08, 0x09, 0x0A]), file: file, line: line)
 
         // read next 4 bytes from current position
         // this should return nil since we are at the end of the stream
         let bytesRead4 = try sut.read(buffer: buffer)
-        XCTAssertNil(bytesRead4)
+        XCTAssertNil(bytesRead4, file: file, line: line)
     }
 
-    func testSeek() throws {
-        let sut = StreamableHttpBody(body: .data(testData))
+    private func seek(data: Data, file: StaticString = #file, line: UInt = #line) throws {
+        let sut = StreamableHttpBody(body: .data(data))
 
         // read first 4 bytes
         let buffer = UnsafeMutableBufferPointer<UInt8>.allocate(capacity: 4)
         let bytesRead1 = try sut.read(buffer: buffer)
         let bytes1 = Data(bytes: buffer.baseAddress!, count: bytesRead1!)
-        XCTAssertEqual(bytesRead1!, 4)
-        XCTAssertEqual(bytes1, Data([0x00, 0x01, 0x02, 0x03]))
+        XCTAssertEqual(bytesRead1!, 4, file: file, line: line)
+        XCTAssertEqual(bytes1, Data([0x00, 0x01, 0x02, 0x03]), file: file, line: line)
 
         // seek to offset 2 and read 4 bytes
         try sut.seek(offset: 2, streamSeekType: .begin)
         let bytesRead2 = try sut.read(buffer: buffer)
         let bytes2 = Data(bytes: buffer.baseAddress!, count: bytesRead2!)
-        XCTAssertEqual(bytesRead2!, 4)
-        XCTAssertEqual(bytes2, Data([0x02, 0x03, 0x04, 0x05]))
+        XCTAssertEqual(bytesRead2!, 4, file: file, line: line)
+        XCTAssertEqual(bytes2, Data([0x02, 0x03, 0x04, 0x05]), file: file, line: line)
 
         // seek to offset 8 and read 3 bytes
         // this should only read 3 bytes since we are at the end of the stream
         try sut.seek(offset: 8, streamSeekType: .begin)
         let bytesRead3 = try sut.read(buffer: buffer)
         let bytes3 = Data(bytes: buffer.baseAddress!, count: bytesRead3!)
-        XCTAssertEqual(bytesRead3!, 3)
-        XCTAssertEqual(bytes3, Data([0x08, 0x09, 0x0A]))
+        XCTAssertEqual(bytesRead3!, 3, file: file, line: line)
+        XCTAssertEqual(bytes3, Data([0x08, 0x09, 0x0A]), file: file, line: line)
     }
 }