Consider using brotli compression instead of gzip

[philipphofmann]

Description

The Cocoa SDK currently uses gzip to compress its HTTP requests to Sentry.

sentry-cocoa/Sources/Sentry/SentryNSDataUtils.m

Lines 10 to 54 in 1223af7

	NSData *_Nullable sentry_gzippedWithCompressionLevel(
	NSData *data, NSInteger compressionLevel, NSError *_Nullable *_Nullable error)
	{
	uInt length = (uInt)[data length];
	if (length == 0) {
	return [NSData data];
	}
	/// Init empty z_stream
	z_stream stream;
	stream.zalloc = Z_NULL;
	stream.zfree = Z_NULL;
	stream.opaque = Z_NULL;
	stream.next_in = (Bytef *)(void *)data.bytes;
	stream.total_out = 0;
	stream.avail_out = 0;
	stream.avail_in = length;
	int err;
	err = deflateInit2(
	&stream, compressionLevel, Z_DEFLATED, (16 + MAX_WBITS), 9, Z_DEFAULT_STRATEGY);
	if (err != Z_OK) {
	if (error) {
	*error = NSErrorFromSentryError(kSentryErrorCompressionError, @"deflateInit2 error");
	}
	return nil;
	}
	NSMutableData *compressedData = [NSMutableData dataWithLength:(NSUInteger)(length * 1.02 + 50)];
	Bytef *compressedBytes = [compressedData mutableBytes];
	NSUInteger compressedLength = [compressedData length];
	/// compress
	while (err == Z_OK) {
	stream.next_out = compressedBytes + stream.total_out;
	stream.avail_out = (uInt)(compressedLength - stream.total_out);
	err = deflate(&stream, Z_FINISH);
	}
	[compressedData setLength:stream.total_out];
	deflateEnd(&stream);
	return compressedData;
	}

It uses the zlib for the compression.

sentry-cocoa/Sources/Sentry/SentryNSDataUtils.m

Lines 1 to 3 in 1223af7

	#if __has_include(<zlib.h>)
	# import <zlib.h>
	#endif

When bumping our min SDK version to iOS 13, we can consider switching to the Apple Compression framework and use brotli, which is slightly faster and better at compression JSON. Furthermore, we can remove the dependency libz.tbd.

sentry-cocoa/Sentry.xcodeproj/project.pbxproj

Line 2039 in 1223af7

63AF656C1ED87B8C00EBCFF7 /* libz.tbd in Frameworks */,

[brustolin]

Actually, the dependency libz.tbd is not really necessary.
But if Brotli is native of iOS 13, I agree with the change, we just need to check whether our server support it.

[BYK]

Relay supports gzip, brotli, and zstd. Python SDK has added support for Brotli recently.