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Use UnsafeMutablePointer for handling z_stream #12

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merged 2 commits into from
Feb 26, 2025
Merged

Use UnsafeMutablePointer for handling z_stream #12

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a43fecc
Use UnsafeMutablePointer for handling z_stream
Cyberbeni Feb 26, 2025
2c44659
Add comment explaining the UnsafeMutablePointer usage
Cyberbeni Feb 26, 2025
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88 changes: 51 additions & 37 deletions Sources/CompressNIO/zlib/Zlib.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -138,7 +138,11 @@ public struct ZlibConfiguration: Sendable {

/// Compressor using Zlib
public final class ZlibCompressor {
var stream: z_stream
// zlib expects the z_stream pointer to stay the same over the whole process, so we need to
// ensure that it doesn't accidentally get copied or moved. There is no 'safe' way to signal
// that a variable can't be moved in Swift (like ~Copyable), so we wrap it in an
// UnsafeMutablePointer, so any move or copy has to be explicit.
var stream: UnsafeMutablePointer<z_stream>
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Can we add a comment detailing why we need to use an UnsafeMutablePointer

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Ok, added comment to both places.

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Thanks. This is great. It might be worthwhile pointing this out in the swift-nio-extras repository. They have some request/response compression channel handlers use Zlib in a similar manner.

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I was already on the fence but then Apple decided that they want to play both sides (donating to Trump's inauguration, returning to advertising on X versus https://www.swift.org/diversity/ ), so I decided to not do any free QA for them unless absolutely necessary.

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Fair enough


/// Initialize Zlib deflate stream for compression
/// - Parameters:
Expand All @@ -157,13 +161,14 @@ public final class ZlibCompressor {
configuration.windowSize = -configuration.windowSize
}

self.stream = z_stream()
self.stream.zalloc = nil
self.stream.zfree = nil
self.stream.opaque = nil
self.stream = UnsafeMutablePointer<z_stream>.allocate(capacity: 1)
self.stream.initialize(to: z_stream())
self.stream.pointee.zalloc = nil
self.stream.pointee.zfree = nil
self.stream.pointee.opaque = nil

let rt = CCompressZlib_deflateInit2(
&self.stream,
self.stream,
configuration.compressionLevel,
Z_DEFLATED,
configuration.windowSize,
Expand All @@ -181,8 +186,10 @@ public final class ZlibCompressor {
}

deinit {
var stream = self.stream
deflateEnd(&stream)
let rt = deflateEnd(self.stream)
assert(rt == Z_OK, "deflateEnd returned error: \(rt)")
self.stream.deinitialize(count: 1)
self.stream.deallocate()
}

/// Deflate Zlib stream
Expand Down Expand Up @@ -211,14 +218,14 @@ public final class ZlibCompressor {
flag = Z_FINISH
}

self.stream.avail_in = UInt32(fromBuffer.count)
self.stream.next_in = CCompressZlib_voidPtr_to_BytefPtr(fromBuffer.baseAddress!)
self.stream.avail_out = UInt32(toBuffer.count)
self.stream.next_out = CCompressZlib_voidPtr_to_BytefPtr(toBuffer.baseAddress!)
self.stream.pointee.avail_in = UInt32(fromBuffer.count)
self.stream.pointee.next_in = CCompressZlib_voidPtr_to_BytefPtr(fromBuffer.baseAddress!)
self.stream.pointee.avail_out = UInt32(toBuffer.count)
self.stream.pointee.next_out = CCompressZlib_voidPtr_to_BytefPtr(toBuffer.baseAddress!)

let rt = CCompressZlib.deflate(&self.stream, flag)
bytesRead = self.stream.next_in - CCompressZlib_voidPtr_to_BytefPtr(fromBuffer.baseAddress!)
bytesWritten = self.stream.next_out - CCompressZlib_voidPtr_to_BytefPtr(toBuffer.baseAddress!)
let rt = CCompressZlib.deflate(self.stream, flag)
bytesRead = self.stream.pointee.next_in - CCompressZlib_voidPtr_to_BytefPtr(fromBuffer.baseAddress!)
bytesWritten = self.stream.pointee.next_out - CCompressZlib_voidPtr_to_BytefPtr(toBuffer.baseAddress!)
switch rt {
case Z_OK:
if flush == .finish {
Expand Down Expand Up @@ -249,14 +256,14 @@ public final class ZlibCompressor {
// some compression algorithms and so it should be used only when necessary. This completes the current deflate block and
// follows it with an empty stored block that is three bits plus filler bits to the next byte, followed by four bytes
// (00 00 ff ff)."
let bufferSize = Int(CCompressZlib.deflateBound(&self.stream, UInt(from.readableBytes)))
let bufferSize = Int(CCompressZlib.deflateBound(self.stream, UInt(from.readableBytes)))
return bufferSize + 6
}

/// Reset deflate stream
/// - Throws: ``CompressNIOError`` if reset fails
public func reset() throws {
let rt = deflateReset(&self.stream)
let rt = deflateReset(self.stream)
switch rt {
case Z_OK:
break
Expand All @@ -268,7 +275,11 @@ public final class ZlibCompressor {

/// Decompressor using Zlib
public final class ZlibDecompressor {
var stream: z_stream
// zlib expects the z_stream pointer to stay the same over the whole process, so we need to
// ensure that it doesn't accidentally get copied or moved. There is no 'safe' way to signal
// that a variable can't be moved in Swift (like ~Copyable), so we wrap it in an
// UnsafeMutablePointer, so any move or copy has to be explicit.
var stream: UnsafeMutablePointer<z_stream>

/// Initialize Zlib inflate stream for decompression
/// - Parameters:
Expand All @@ -287,15 +298,16 @@ public final class ZlibDecompressor {
windowSize = -windowSize
}

self.stream = z_stream()
self.stream = UnsafeMutablePointer<z_stream>.allocate(capacity: 1)
self.stream.initialize(to: z_stream())
// zlib docs say: The application must initialize zalloc, zfree and opaque before calling the init function.
self.stream.zalloc = nil
self.stream.zfree = nil
self.stream.opaque = nil
self.stream.avail_in = 0
self.stream.next_in = nil
self.stream.pointee.zalloc = nil
self.stream.pointee.zfree = nil
self.stream.pointee.opaque = nil
self.stream.pointee.avail_in = 0
self.stream.pointee.next_in = nil

let rt = CCompressZlib_inflateInit2(&self.stream, windowSize)
let rt = CCompressZlib_inflateInit2(self.stream, windowSize)
switch rt {
case Z_MEM_ERROR:
throw CompressNIOError.noMoreMemory
Expand All @@ -307,8 +319,10 @@ public final class ZlibDecompressor {
}

deinit {
var stream = self.stream
inflateEnd(&stream)
let rt = inflateEnd(self.stream)
assert(rt == Z_OK, "inflateEnd returned error: \(rt)")
self.stream.deinitialize(count: 1)
self.stream.deallocate()
}

/// Inflate Zlib stream
Expand All @@ -327,22 +341,22 @@ public final class ZlibDecompressor {
}

try from.withUnsafeProcess(to: &to) { fromBuffer, toBuffer in
self.stream.avail_in = UInt32(fromBuffer.count)
self.stream.next_in = CCompressZlib_voidPtr_to_BytefPtr(fromBuffer.baseAddress!)
self.stream.avail_out = UInt32(toBuffer.count)
self.stream.next_out = CCompressZlib_voidPtr_to_BytefPtr(toBuffer.baseAddress!)
self.stream.pointee.avail_in = UInt32(fromBuffer.count)
self.stream.pointee.next_in = CCompressZlib_voidPtr_to_BytefPtr(fromBuffer.baseAddress!)
self.stream.pointee.avail_out = UInt32(toBuffer.count)
self.stream.pointee.next_out = CCompressZlib_voidPtr_to_BytefPtr(toBuffer.baseAddress!)

let rt = CCompressZlib.inflate(&self.stream, Z_NO_FLUSH)
let rt = CCompressZlib.inflate(self.stream, Z_NO_FLUSH)

bytesRead = self.stream.next_in - CCompressZlib_voidPtr_to_BytefPtr(fromBuffer.baseAddress!)
bytesWritten = self.stream.next_out - CCompressZlib_voidPtr_to_BytefPtr(toBuffer.baseAddress!)
bytesRead = self.stream.pointee.next_in - CCompressZlib_voidPtr_to_BytefPtr(fromBuffer.baseAddress!)
bytesWritten = self.stream.pointee.next_out - CCompressZlib_voidPtr_to_BytefPtr(toBuffer.baseAddress!)
switch rt {
case Z_OK:
if self.stream.avail_out == 0 {
if self.stream.pointee.avail_out == 0 {
throw CompressNIOError.bufferOverflow
}
case Z_BUF_ERROR:
if self.stream.avail_in == 0 {
if self.stream.pointee.avail_in == 0 {
throw CompressNIOError.inputBufferOverflow
} else {
throw CompressNIOError.bufferOverflow
Expand All @@ -363,7 +377,7 @@ public final class ZlibDecompressor {
/// - Throws: ``CompressNIOError`` if reset fails
public func reset() throws {
// inflateReset is a more optimal than calling finish and then start
let rt = inflateReset(&self.stream)
let rt = inflateReset(self.stream)
switch rt {
case Z_OK:
break
Expand Down