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[5.0] Fix off-by-one when initializing Data with discontiguous, underestimated Sequences #1996

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Merged
merged 1 commit into from
Mar 13, 2019
Merged

[5.0] Fix off-by-one when initializing Data with discontiguous, underestimated Sequences #1996

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10 changes: 4 additions & 6 deletions Foundation/Data.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -2086,9 +2086,8 @@ public struct Data : ReferenceConvertible, Equatable, Hashable, RandomAccessColl
// ... and append the rest byte-wise, buffering through an InlineData.
var buffer = InlineData()
while let element = iter.next() {
if buffer.count < buffer.capacity {
buffer.append(byte: element)
} else {
buffer.append(byte: element)
if buffer.count == buffer.capacity {
buffer.withUnsafeBytes { _representation.append(contentsOf: $0) }
buffer.count = 0
}
Expand Down Expand Up @@ -2380,9 +2379,8 @@ public struct Data : ReferenceConvertible, Equatable, Hashable, RandomAccessColl
// ... and append the rest byte-wise, buffering through an InlineData.
var buffer = InlineData()
while let element = iter.next() {
if buffer.count < buffer.capacity {
buffer.append(byte: element)
} else {
buffer.append(byte: element)
if buffer.count == buffer.capacity {
buffer.withUnsafeBytes { _representation.append(contentsOf: $0) }
buffer.count = 0
}
Expand Down
51 changes: 51 additions & 0 deletions TestFoundation/TestNSData.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -521,6 +521,8 @@ class TestNSData: LoopbackServerTest {
("test_copyBytes2", test_copyBytes2),
("test_sliceOfSliceViaRangeExpression", test_sliceOfSliceViaRangeExpression),
("test_appendingSlices", test_appendingSlices),
("test_appendingNonContiguousSequence_exactCount", test_appendingNonContiguousSequence_exactCount),
("test_appendingNonContiguousSequence_underestimatedCount", test_appendingNonContiguousSequence_underestimatedCount),
("test_sequenceInitializers", test_sequenceInitializers),
("test_reversedDataInit", test_reversedDataInit),
("test_replaceSubrangeReferencingMutable", test_replaceSubrangeReferencingMutable),
Expand Down Expand Up @@ -4391,6 +4393,55 @@ extension TestNSData {
d2.append(slice)
XCTAssertEqual(Data(bytes: [1]), slice)
}

// This test uses `repeatElement` to produce a sequence -- the produced sequence reports its actual count as its `.underestimatedCount`.
func test_appendingNonContiguousSequence_exactCount() {
var d = Data()

// d should go from .empty representation to .inline.
// Appending a small enough sequence to fit in .inline should actually be copied.
d.append(contentsOf: 0x00...0x01)
XCTAssertEqual(Data([0x00, 0x01]), d)

// Appending another small sequence should similarly still work.
d.append(contentsOf: 0x02...0x02)
XCTAssertEqual(Data([0x00, 0x01, 0x02]), d)

// If we append a sequence of elements larger than a single InlineData, the internal append here should buffer.
// We want to make sure that buffering in this way does not accidentally drop trailing elements on the floor.
d.append(contentsOf: 0x03...0x2F)
XCTAssertEqual(Data([0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F,
0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F,
0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
0x28, 0x29, 0x2A, 0x2B, 0x2C, 0x2D, 0x2E, 0x2F]), d)
}

// This test is like test_appendingNonContiguousSequence_exactCount but uses a sequence which reports 0 for its `.underestimatedCount`.
// This attempts to hit the worst-case scenario of `Data.append<S>(_:)` -- a discontiguous sequence of unknown length.
func test_appendingNonContiguousSequence_underestimatedCount() {
var d = Data()

// d should go from .empty representation to .inline.
// Appending a small enough sequence to fit in .inline should actually be copied.
d.append(contentsOf: (0x00...0x01).makeIterator()) // `.makeIterator()` produces a sequence whose `.underestimatedCount` is 0.
XCTAssertEqual(Data([0x00, 0x01]), d)

// Appending another small sequence should similarly still work.
d.append(contentsOf: (0x02...0x02).makeIterator()) // `.makeIterator()` produces a sequence whose `.underestimatedCount` is 0.
XCTAssertEqual(Data([0x00, 0x01, 0x02]), d)

// If we append a sequence of elements larger than a single InlineData, the internal append here should buffer.
// We want to make sure that buffering in this way does not accidentally drop trailing elements on the floor.
d.append(contentsOf: (0x03...0x2F).makeIterator()) // `.makeIterator()` produces a sequence whose `.underestimatedCount` is 0.
XCTAssertEqual(Data([0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F,
0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F,
0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
0x28, 0x29, 0x2A, 0x2B, 0x2C, 0x2D, 0x2E, 0x2F]), d)
}

func test_sequenceInitializers() {
let seq = repeatElement(UInt8(0x02), count: 3) // ensure we fall into the sequence case
Expand Down