[ios] #3979 compress telemetry events (#5490)

* [ios] #3979 wip gzip telemetry events

* [ios] expose compression from core instead of adding a new dependency

* [ios] #3979 Exposed decompress from mbgl and added a test case

* [ios] #3979 cleanup

* [ios] #3979 cleaned up test case

* [ios] #3979 cleanup

* [ios] #3979 gzip -> deflate

2 files changed, 38 insertions, 0 deletions

diff --git a/platform/darwin/src/NSData+MGLAdditions.h b/platform/darwin/src/NSData+MGLAdditions.h
new file mode 100644
index 0000000000..0c68c81f45
--- /dev/null
+++ b/platform/darwin/src/NSData+MGLAdditions.h
@@ -0,0 +1,15 @@
+#import <Foundation/Foundation.h>
+
+#import "MGLTypes.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface NSData (MGLAdditions)
+
+- (NSData *)mgl_compressedData;
+
+- (NSData *)mgl_decompressedData;
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/platform/darwin/src/NSData+MGLAdditions.mm b/platform/darwin/src/NSData+MGLAdditions.mm
new file mode 100644
index 0000000000..ef171c5e1e
--- /dev/null
+++ b/platform/darwin/src/NSData+MGLAdditions.mm
@@ -0,0 +1,23 @@
+#import "NSData+MGLAdditions.h"
+
+#include <mbgl/util/compression.hpp>
+
+@implementation NSData (MGLAdditions)
+
+- (NSData *)mgl_compressedData
+{
+    std::string string(static_cast<const char*>(self.bytes), self.length);
+    std::string compressed_string = mbgl::util::compress(string);
+    
+    return [NSData dataWithBytes:&compressed_string[0] length:compressed_string.length()];
+}
+
+- (NSData *)mgl_decompressedData
+{
+    std::string string(static_cast<const char*>(self.bytes), self.length);
+    std::string decompressed_string = mbgl::util::decompress(string);
+    
+    return [NSData dataWithBytes:&decompressed_string[0] length:decompressed_string.length()];
+}
+
+@end