[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

8 files changed, 138 insertions, 16 deletions

diff --git a/include/mbgl/util/compression.hpp b/include/mbgl/util/compression.hpp
new file mode 100644
index 0000000000..5e232187c3
--- /dev/null
+++ b/include/mbgl/util/compression.hpp
@@ -0,0 +1,12 @@
+#pragma once
+
+#include <string>
+
+namespace mbgl {
+namespace util {
+        
+std::string compress(const std::string& raw);
+std::string decompress(const std::string& raw);
+    
+} // namespace util
+} // namespace mbgl
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
diff --git a/platform/ios/ios.xcodeproj/project.pbxproj b/platform/ios/ios.xcodeproj/project.pbxproj
index f817583f26..bdc0fbd900 100644
--- a/platform/ios/ios.xcodeproj/project.pbxproj
+++ b/platform/ios/ios.xcodeproj/project.pbxproj
@@ -7,7 +7,12 @@
 	objects = {
 
 /* Begin PBXBuildFile section */
+		35305D481D22AA680007D005 /* NSData+MGLAdditions.mm in Sources */ = {isa = PBXBuildFile; fileRef = 35305D471D22AA450007D005 /* NSData+MGLAdditions.mm */; };
+		35305D491D22AA680007D005 /* NSData+MGLAdditions.mm in Sources */ = {isa = PBXBuildFile; fileRef = 35305D471D22AA450007D005 /* NSData+MGLAdditions.mm */; };
+		35305D4A1D22AA6A0007D005 /* NSData+MGLAdditions.h in Headers */ = {isa = PBXBuildFile; fileRef = 35305D461D22AA450007D005 /* NSData+MGLAdditions.h */; settings = {ATTRIBUTES = (Private, ); }; };
+		353794D01D22B3BD002C281C /* NSData+MGLAdditions.h in Headers */ = {isa = PBXBuildFile; fileRef = 35305D461D22AA450007D005 /* NSData+MGLAdditions.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		353D23961D0B0DFE002BE09D /* MGLAnnotationViewTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 353D23951D0B0DFE002BE09D /* MGLAnnotationViewTests.m */; };
+		35E208A71D24210F00EC9A46 /* MGLNSDataAdditionsTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 35E208A61D24210F00EC9A46 /* MGLNSDataAdditionsTests.m */; };
 		4018B1C71CDC287F00F666AF /* MGLAnnotationView.mm in Sources */ = {isa = PBXBuildFile; fileRef = 4018B1C41CDC277F00F666AF /* MGLAnnotationView.mm */; };
 		4018B1C81CDC287F00F666AF /* MGLAnnotationView.mm in Sources */ = {isa = PBXBuildFile; fileRef = 4018B1C41CDC277F00F666AF /* MGLAnnotationView.mm */; };
 		4018B1C91CDC288A00F666AF /* MGLAnnotationView_Private.h in Headers */ = {isa = PBXBuildFile; fileRef = 4018B1C31CDC277F00F666AF /* MGLAnnotationView_Private.h */; };
@@ -326,7 +331,10 @@
 /* End PBXCopyFilesBuildPhase section */
 
 /* Begin PBXFileReference section */
+		35305D461D22AA450007D005 /* NSData+MGLAdditions.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = "NSData+MGLAdditions.h"; sourceTree = "<group>"; };
+		35305D471D22AA450007D005 /* NSData+MGLAdditions.mm */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.objcpp; path = "NSData+MGLAdditions.mm"; sourceTree = "<group>"; };
 		353D23951D0B0DFE002BE09D /* MGLAnnotationViewTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MGLAnnotationViewTests.m; sourceTree = "<group>"; };
+		35E208A61D24210F00EC9A46 /* MGLNSDataAdditionsTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MGLNSDataAdditionsTests.m; sourceTree = "<group>"; };
 		4018B1C31CDC277F00F666AF /* MGLAnnotationView_Private.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MGLAnnotationView_Private.h; sourceTree = "<group>"; };
 		4018B1C41CDC277F00F666AF /* MGLAnnotationView.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = MGLAnnotationView.mm; sourceTree = "<group>"; };
 		4018B1C51CDC277F00F666AF /* MGLAnnotationView.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MGLAnnotationView.h; sourceTree = "<group>"; };
@@ -647,17 +655,18 @@
 		DA2E88521CC036F400F24E7B /* SDK Tests */ = {
 			isa = PBXGroup;
 			children = (
+				DA2E88551CC036F400F24E7B /* Info.plist */,
+				353D23951D0B0DFE002BE09D /* MGLAnnotationViewTests.m */,
 				DA35A2C31CCA9F8300E826B2 /* MGLClockDirectionFormatterTests.m */,
 				DA35A2C41CCA9F8300E826B2 /* MGLCompassDirectionFormatterTests.m */,
 				DA35A2A91CCA058D00E826B2 /* MGLCoordinateFormatterTests.m */,
 				DA0CD58F1CF56F6A00A5F5A5 /* MGLFeatureTests.mm */,
 				DA2E885C1CC0382C00F24E7B /* MGLGeometryTests.mm */,
+				35E208A61D24210F00EC9A46 /* MGLNSDataAdditionsTests.m */,
 				DA2E885D1CC0382C00F24E7B /* MGLOfflinePackTests.m */,
 				DA2E885E1CC0382C00F24E7B /* MGLOfflineRegionTests.m */,
 				DA2E885F1CC0382C00F24E7B /* MGLOfflineStorageTests.m */,
-				353D23951D0B0DFE002BE09D /* MGLAnnotationViewTests.m */,
 				DA2E88601CC0382C00F24E7B /* MGLStyleTests.mm */,
-				DA2E88551CC036F400F24E7B /* Info.plist */,
 			);
 			name = "SDK Tests";
 			path = test;
@@ -895,6 +904,8 @@
 			children = (
 				DA8848121CBAFA6200AB86E3 /* NSBundle+MGLAdditions.h */,
 				DA8848131CBAFA6200AB86E3 /* NSBundle+MGLAdditions.m */,
+				35305D461D22AA450007D005 /* NSData+MGLAdditions.h */,
+				35305D471D22AA450007D005 /* NSData+MGLAdditions.mm */,
 				DA8848141CBAFA6200AB86E3 /* NSException+MGLAdditions.h */,
 				DA8848151CBAFA6200AB86E3 /* NSProcessInfo+MGLAdditions.h */,
 				DA8848161CBAFA6200AB86E3 /* NSProcessInfo+MGLAdditions.m */,
@@ -1000,6 +1011,7 @@
 				DA88481B1CBAFA6200AB86E3 /* MGLGeometry_Private.h in Headers */,
 				DA88485C1CBAFB9800AB86E3 /* MGLUserLocationAnnotationView.h in Headers */,
 				DA8848871CBB033F00AB86E3 /* Fabric.h in Headers */,
+				35305D4A1D22AA6A0007D005 /* NSData+MGLAdditions.h in Headers */,
 				DA8848841CBB033F00AB86E3 /* FABAttributes.h in Headers */,
 				DA8847FD1CBAFA5100AB86E3 /* MGLTilePyramidOfflineRegion.h in Headers */,
 				DA88482F1CBAFA6200AB86E3 /* NSProcessInfo+MGLAdditions.h in Headers */,
@@ -1045,6 +1057,7 @@
 				DABFB86E1CBE9A0F00D62B32 /* MGLCalloutView.h in Headers */,
 				DABFB8601CBE99E500D62B32 /* MGLMapCamera.h in Headers */,
 				DA737EE21D056A4E005BDA16 /* MGLMapViewDelegate.h in Headers */,
+				353794D01D22B3BD002C281C /* NSData+MGLAdditions.h in Headers */,
 				DABFB86A1CBE99E500D62B32 /* MGLStyle.h in Headers */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
@@ -1355,6 +1368,7 @@
 				DA2E88621CC0382C00F24E7B /* MGLOfflinePackTests.m in Sources */,
 				DA35A2AA1CCA058D00E826B2 /* MGLCoordinateFormatterTests.m in Sources */,
 				353D23961D0B0DFE002BE09D /* MGLAnnotationViewTests.m in Sources */,
+				35E208A71D24210F00EC9A46 /* MGLNSDataAdditionsTests.m in Sources */,
 				DA0CD5901CF56F6A00A5F5A5 /* MGLFeatureTests.mm in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
@@ -1382,6 +1396,7 @@
 				DA35A2CB1CCAAAD200E826B2 /* NSValue+MGLAdditions.m in Sources */,
 				DA8848321CBAFA6200AB86E3 /* NSString+MGLAdditions.m in Sources */,
 				DA35A2A11CC9E95F00E826B2 /* MGLCoordinateFormatter.m in Sources */,
+				35305D481D22AA680007D005 /* NSData+MGLAdditions.mm in Sources */,
 				DA8848291CBAFA6200AB86E3 /* MGLStyle.mm in Sources */,
 				DA88481C1CBAFA6200AB86E3 /* MGLGeometry.mm in Sources */,
 				DA88481F1CBAFA6200AB86E3 /* MGLMultiPoint.mm in Sources */,
@@ -1423,6 +1438,7 @@
 				DA35A2CC1CCAAAD200E826B2 /* NSValue+MGLAdditions.m in Sources */,
 				DAA4E4281CBB730400178DFB /* MGLTypes.m in Sources */,
 				DA35A2A21CC9E95F00E826B2 /* MGLCoordinateFormatter.m in Sources */,
+				35305D491D22AA680007D005 /* NSData+MGLAdditions.mm in Sources */,
 				DAA4E42D1CBB730400178DFB /* MGLAnnotationImage.m in Sources */,
 				DAA4E4301CBB730400178DFB /* MGLLocationManager.m in Sources */,
 				DAA4E4321CBB730400178DFB /* MGLMapView.mm in Sources */,
diff --git a/platform/ios/src/MGLAPIClient.m b/platform/ios/src/MGLAPIClient.m
index 31fd39c83d..fb13113c81 100644
--- a/platform/ios/src/MGLAPIClient.m
+++ b/platform/ios/src/MGLAPIClient.m
@@ -1,5 +1,6 @@
 #import "MGLAPIClient.h"
 #import "NSBundle+MGLAdditions.h"
+#import "NSData+MGLAdditions.h"
 #import "MGLAccountManager.h"
 
 static NSString * const MGLAPIClientUserAgentBase = @"MapboxEventsiOS";
@@ -9,6 +10,7 @@ static NSString * const MGLAPIClientEventsPath = @"events/v2";
 static NSString * const MGLAPIClientHeaderFieldUserAgentKey = @"User-Agent";
 static NSString * const MGLAPIClientHeaderFieldContentTypeKey = @"Content-Type";
 static NSString * const MGLAPIClientHeaderFieldContentTypeValue = @"application/json";
+static NSString * const MGLAPIClientHeaderFieldContentEncodingKey = @"Content-Encoding";
 static NSString * const MGLAPIClientHTTPMethodPost = @"POST";
 
 @interface MGLAPIClient ()
@@ -82,8 +84,22 @@ static NSString * const MGLAPIClientHTTPMethodPost = @"POST";
     [request setValue:self.userAgent forHTTPHeaderField:MGLAPIClientHeaderFieldUserAgentKey];
     [request setValue:MGLAPIClientHeaderFieldContentTypeValue forHTTPHeaderField:MGLAPIClientHeaderFieldContentTypeKey];
     [request setHTTPMethod:MGLAPIClientHTTPMethodPost];
+    
     NSData *jsonData = [self serializedDataForEvents:events];
-    [request setHTTPBody:jsonData];
+    
+    // Compressing less than 3 events can have a negative impact on the size.
+    if (events.count > 2) {
+        NSData *compressedData = [jsonData mgl_compressedData];
+        [request setValue:@"deflate" forHTTPHeaderField:MGLAPIClientHeaderFieldContentEncodingKey];
+        [request setHTTPBody:compressedData];
+    }
+    
+    // Set JSON data if events.count were less than 3 or something went wrong with compressing HTTP body data.
+    if (!request.HTTPBody) {
+        [request setValue:nil forHTTPHeaderField:MGLAPIClientHeaderFieldContentEncodingKey];
+        [request setHTTPBody:jsonData];
+    }
+    
     return [request copy];
 }
 
diff --git a/platform/ios/test/MGLNSDataAdditionsTests.m b/platform/ios/test/MGLNSDataAdditionsTests.m
new file mode 100644
index 0000000000..38f19a9703
--- /dev/null
+++ b/platform/ios/test/MGLNSDataAdditionsTests.m
@@ -0,0 +1,52 @@
+#import <XCTest/XCTest.h>
+
+#import "../../darwin/src/NSData+MGLAdditions.h"
+
+@interface MGLNSDataAdditionsTests : XCTestCase
+@end
+
+@implementation MGLNSDataAdditionsTests
+
+- (void)setUp {
+    [super setUp];
+}
+
+- (void)testCompressDecompress
+{
+    NSArray *originalArray = [self mockDataWithCount:180];
+    
+    NSData *originalData = [NSJSONSerialization dataWithJSONObject:originalArray options:0 error:nil];
+    
+    NSData *compressedData = [originalData mgl_compressedData];
+    NSData *decompressedData = [compressedData mgl_decompressedData];
+    
+    NSArray *decompressedArray = [NSJSONSerialization JSONObjectWithData:decompressedData options:0 error:nil];
+    
+    XCTAssertTrue([originalArray isEqualToArray:decompressedArray], @"originalArray and decompressedArray should be equal");
+}
+
+- (NSArray *)mockDataWithCount:(NSUInteger)count
+{
+    NSMutableArray *array = [NSMutableArray array];
+    
+    for (NSUInteger i=0;i<count;i++)
+    {
+        [array addObject:@{@"lat": @([self safeValueBetween:-90 and:90]),
+                           @"lng": @([self safeValueBetween:-180 and:180]),
+                           @"timestamp": @((floor([NSDate date].timeIntervalSince1970) * 100) / 100)}];
+    }
+    
+    return array;
+}
+
+- (double)safeValueBetween:(double)lowerBound and:(double)upperBound
+{
+    return floor([self randomBetween:lowerBound and:upperBound] * 100 ) / 100;
+}
+
+- (double)randomBetween:(double)lowerBound and:(double)upperBound
+{
+    return lowerBound * drand48() + upperBound * drand48();
+}
+
+@end
diff --git a/src/mbgl/util/compression.cpp b/src/mbgl/util/compression.cpp
index e189991b55..18cb189d02 100644
--- a/src/mbgl/util/compression.cpp
+++ b/src/mbgl/util/compression.cpp
@@ -1,4 +1,4 @@
-#include "compression.hpp"
+#include <mbgl/util/compression.hpp>
 
 #include <zlib.h>
 
diff --git a/src/mbgl/util/compression.hpp b/src/mbgl/util/compression.hpp
deleted file mode 100644
index 8f89a3ac03..0000000000
--- a/src/mbgl/util/compression.hpp
+++ /dev/null
@@ -1,12 +0,0 @@
-#pragma once
-
-#include <string>
-
-namespace mbgl {
-namespace util {
-
-std::string compress(const std::string &raw);
-std::string decompress(const std::string &raw);
-
-} // namespace util
-} // namespace mbgl