Refactor HTTP code and add proxy support. (#578)

This refactors the HTTP interaction in the library + Segment
integration. Internally, it moves away from `NSURLConnection` to
`NSURLSession`. `SEGAnalyticsRequest` is replaced by `NSURLSessionTask`,
and a thin wrapper class `SEGHTTPClient` is introduced to simplify the
interaction between the library and the Segment API.

This also adds tests for the networking code by stubbing  the Segment
API using https://github.com/luisobo/Nocilla so the behaviour of
`SEGHTTPClient` can be verified under different responses from the
server.

Publicly, it also adds a `SEGRequestFactory` abstraction that given a
URL returns a `NSMutableURLRequest `. The default implementation simply
calls `[NSMutableURLRequest requestWithURL:url]`.  It is configurable,
and this lets users customize the `NSMutableURLRequest` made by the
library. e.g. users could change it to point the SDK to a custom proxy
instance.

Analytics/Classes/Internal/SEGHTTPClient.h

@@ -0,0 +1,23 @@
+#import <Foundation/Foundation.h>
+#import "SEGAnalytics.h"
+
+
+@interface SEGHTTPClient : NSObject
+
+@property (nonatomic, strong) SEGRequestFactory requestFactory;
+
++ (SEGRequestFactory)defaultRequestFactory;
+
+- (instancetype)initWithRequestFactory:(SEGRequestFactory)requestFactory;
+
+/**
+ * Upload dictionary formatted as per https://segment.com/docs/sources/server/http/#batch.
+ * This method will convert the dictionary to json, gzip it and upload the data.
+ * It will respond with retry = YES if the batch should be reuploaded at a later time.
+ * It will ask to retry for json errors and 3xx/5xx codes, and not retry for 2xx/4xx response codes.
+ */
+- (NSURLSessionUploadTask *)upload:(NSDictionary *)batch forWriteKey:(NSString *)writeKey completionHandler:(void (^)(BOOL retry))completionHandler;
+
+- (NSURLSessionDataTask *)settingsForWriteKey:(NSString *)writeKey completionHandler:(void (^)(BOOL success, NSDictionary *settings))completionHandler;
+
+@end

Analytics/Classes/Internal/SEGHTTPClient.m

@@ -0,0 +1,141 @@
+#import "SEGHTTPClient.h"
+#import "NSData+GZIP.h"
+#import "SEGAnalyticsUtils.h"
+
+
+@implementation SEGHTTPClient
+
++ (NSMutableURLRequest * (^)(NSURL *))defaultRequestFactory
+{
+    return ^(NSURL *url) {
+        return [NSMutableURLRequest requestWithURL:url];
+    };
+}
+
+- (instancetype)initWithRequestFactory:(SEGRequestFactory)requestFactory
+{
+    if (self = [self init]) {
+        if (requestFactory == nil) {
+            self.requestFactory = [SEGHTTPClient defaultRequestFactory];
+        } else {
+            self.requestFactory = requestFactory;
+        }
+    }
+    return self;
+}
+
+- (NSString *)authorizationHeader:(NSString *)writeKey
+{
+    NSString *rawHeader = [writeKey stringByAppendingString:@":"];
+    NSData *userPasswordData = [rawHeader dataUsingEncoding:NSUTF8StringEncoding];
+    return [userPasswordData base64EncodedStringWithOptions:0];
+}
+
+- (NSURLSessionUploadTask *)upload:(NSDictionary *)batch forWriteKey:(NSString *)writeKey completionHandler:(void (^)(BOOL retry))completionHandler
+{
+    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
+    config.HTTPAdditionalHeaders = @{
+        @"Accept-Encoding" : @"gzip",
+        @"Content-Encoding" : @"gzip",
+        @"Content-Type" : @"application/json",
+        @"Authorization" : [@"Basic " stringByAppendingString:[self authorizationHeader:writeKey]],
+    };
+    NSURLSession *session = [NSURLSession sessionWithConfiguration:config];
+
+    NSURL *url = [NSURL URLWithString:@"https://api.segment.io/v1/batch"];
+    NSMutableURLRequest *request = self.requestFactory(url);
+    [request setHTTPMethod:@"POST"];
+
+    NSError *error = nil;
+    NSException *exception = nil;
+    NSData *payload = nil;
+    @try {
+        payload = [NSJSONSerialization dataWithJSONObject:batch options:0 error:&error];
+    }
+    @catch (NSException *exc) {
+        exception = exc;
+    }
+    if (error || exception) {
+        SEGLog(@"%@ Error serializing JSON for batch upload %@", self, error);
+        completionHandler(NO); // Don't retry this batch.
+        return nil;
+    }
+    NSData *gzippedPayload = [payload seg_gzippedData];
+
+    NSURLSessionUploadTask *task = [session uploadTaskWithRequest:request fromData:gzippedPayload completionHandler:^(NSData *_Nullable data, NSURLResponse *_Nullable response, NSError *_Nullable error) {
+        if (error) {
+            SEGLog(@"Error uploading request %@.", error);
+            completionHandler(YES);
+            return;
+        }
+
+        NSInteger code = ((NSHTTPURLResponse *)response).statusCode;
+        if (code < 300) {
+            // 2xx response codes.
+            completionHandler(NO);
+            return;
+        }
+        if (code < 400) {
+            // 3xx response codes.
+            SEGLog(@"Server responded with unexpected HTTP code %d.", code);
+            completionHandler(YES);
+            return;
+        }
+        if (code < 500) {
+            // 4xx response codes.
+            SEGLog(@"Server rejected payload with HTTP code %d.", code);
+            completionHandler(NO);
+            return;
+        }
+
+        // 5xx response codes.
+        SEGLog(@"Server error with HTTP code %d.", code);
+        completionHandler(YES);
+    }];
+    [task resume];
+    return task;
+}
+
+- (NSURLSessionDataTask *)settingsForWriteKey:(NSString *)writeKey completionHandler:(void (^)(BOOL success, NSDictionary *settings))completionHandler
+{
+    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
+    config.HTTPAdditionalHeaders = @{
+        @"Accept-Encoding" : @"gzip"
+    };
+    NSURLSession *session = [NSURLSession sessionWithConfiguration:config];
+
+    NSString *rawURL = [NSString stringWithFormat:@"https://cdn.segment.com/v1/projects/%@/settings", writeKey];
+    NSURL *url = [NSURL URLWithString:rawURL];
+    NSMutableURLRequest *request = self.requestFactory(url);
+    [request setHTTPMethod:@"GET"];
+
+    NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:^(NSData *_Nullable data, NSURLResponse *_Nullable response, NSError *_Nullable error) {
+        if (error != nil) {
+            SEGLog(@"Error fetching settings %@.", error);
+            completionHandler(NO, nil);
+            return;
+        }
+
+        NSInteger code = ((NSHTTPURLResponse *)response).statusCode;
+        if (code > 300) {
+            SEGLog(@"Server responded with unexpected HTTP code %d.", code);
+            completionHandler(NO, nil);
+            return;
+        }
+
+        NSError *jsonError = nil;
+        id responseJson = [NSJSONSerialization JSONObjectWithData:data options:0 error:&jsonError];
+        if (jsonError != nil) {
+            SEGLog(@"Error deserializing response body %@.", jsonError);
+            completionHandler(NO, nil);
+            return;
+        }
+
+        // 2xx response codes.
+        completionHandler(YES, responseJson);
+    }];
+    [task resume];
+    return task;
+}
+
+@end

Analytics/Classes/Internal/SEGSegmentIntegration.h

@@ -8,9 +8,6 @@ extern NSString *const SEGSegmentRequestDidFailNotification;
 
 @interface SEGSegmentIntegration : NSObject <SEGIntegration>
 
-@property (nonatomic, copy) NSString *userId;
-@property (nonatomic, strong) NSURL *apiURL;
-
 - (id)initWithAnalytics:(SEGAnalytics *)analytics;
 
 @end