XCDFakeCarrier.m

//
// Copyright (c) 2012-2013 Cédric Luthi / @0xced. All rights reserved.
//

#if TARGET_IPHONE_SIMULATOR

static const char *fakeCarrier;
static const char *fakeTime;
static int fakeCellSignalStrength = -1;

#import <objc/runtime.h>

// Set itemIsEnabled[3] to 1 to show cell signal strength

/*
 dataNetworkType:
 0 - GPRS
 1 - E (EDGE)
 2 - 3G
 3 - 4G
 4 - LTE
 5 - Wi-Fi
 6 - Personal Hotspot
 7 - 1x
 8 - Blank
 */

typedef struct {
	char itemIsEnabled[23];
	char timeString[64]; // time string in the middle of the status bar
	int gsmSignalStrengthRaw;
	int gsmSignalStrengthBars; // 0-5, cell signal strength
	char serviceString[100];
	BOOL serviceCrossfadeString[100];
	BOOL serviceImages[2][100];
	BOOL operatorDirectory[1024];
	unsigned int serviceContentType;
	int wifiSignalStrengthRaw;
	int wifiSignalStrengthBars; // 0-3, wifi signal strength
	unsigned int dataNetworkType; // network badge next to the carrier string
	// ...
} StatusBarData;

typedef struct {
	char itemIsEnabled[24];
	char timeString[64];
	int gsmSignalStrengthRaw;
	int gsmSignalStrengthBars;
	char serviceString[100];
	BOOL serviceCrossfadeString[100];
	BOOL serviceImages[2][100];
	BOOL operatorDirectory[1024];
	unsigned int serviceContentType;
	int wifiSignalStrengthRaw;
	int wifiSignalStrengthBars;
	unsigned int dataNetworkType;
	// ...
} StatusBarData_6;

typedef struct {
	char itemIsEnabled[25];
	char timeString[64];
	int gsmSignalStrengthRaw;
	int gsmSignalStrengthBars;
	char serviceString[100];
	BOOL serviceCrossfadeString[100];
	BOOL serviceImages[2][100];
	BOOL operatorDirectory[1024];
	unsigned int serviceContentType;
	int wifiSignalStrengthRaw;
	int wifiSignalStrengthBars;
	unsigned int dataNetworkType;
	// ...
} StatusBarData_7;


@interface XCDFakeCarrier : NSObject
@end

@implementation XCDFakeCarrier

+ (void) load
{
	fakeCarrier = getenv("FAKE_CARRIER");
	fakeTime = getenv("FAKE_TIME");
	
	const char *cellSignalEnv = getenv("FAKE_CELL_SIGNAL_STRENGTH");
	
	if (cellSignalEnv) {
		fakeCellSignalStrength = atoi(cellSignalEnv);
	}
	
	if (!fakeCarrier && !fakeTime && !cellSignalEnv)
	{
		NSLog(@"Skipping swizzling, no environment variables set (FAKE_CARRIER, FAKE_TIME, FAKE_CELL_SIGNAL_STRENGTH)");
		return;
	}
	
	BOOL __block success = NO;
	Class UIStatusBarComposedData = objc_getClass("UIStatusBarComposedData");
	SEL selector = NSSelectorFromString(@"rawData");
	Method method = class_getInstanceMethod(UIStatusBarComposedData, selector);
	NSDictionary *statusBarDataInfo = @{ @"^{?=[23c][64c]ii[100c]": @"fake_rawData",
										  @"^{?=[24c][64c]ii[100c]": @"fake_rawData_6",
										  @"^{?=[25c][64c]ii[100c]": @"fake_rawData_7",
										 // use B instead of c for 64-bit
										 @"^{?=[23B][64c]ii[100c]": @"fake_rawData",
										  @"^{?=[24B][64c]ii[100c]": @"fake_rawData_6",
										  @"^{?=[25B][64c]ii[100c]": @"fake_rawData_7" };
	[statusBarDataInfo enumerateKeysAndObjectsUsingBlock:^(NSString *statusBarDataTypeEncoding, NSString *fakeSelectorString, BOOL *stop) {
		if (method && [@(method_getTypeEncoding(method)) hasPrefix:statusBarDataTypeEncoding])
		{
			SEL fakeSelector = NSSelectorFromString(fakeSelectorString);
			Method fakeMethod = class_getInstanceMethod(self, fakeSelector);
			success = class_addMethod(UIStatusBarComposedData, fakeSelector, method_getImplementation(fakeMethod), method_getTypeEncoding(fakeMethod));
			fakeMethod = class_getInstanceMethod(UIStatusBarComposedData, fakeSelector);
			method_exchangeImplementations(method, fakeMethod);
		}
	}];
	
	if (success)
		NSLog(@"Using \"%s\" fake carrier", fakeCarrier);
	else
		NSLog(@"XCDFakeCarrier failed to initialize");
}

- (StatusBarData *) fake_rawData
{
	StatusBarData *rawData = [self fake_rawData];
	
	if (fakeCarrier) {
		strlcpy(rawData->serviceString, fakeCarrier, sizeof(rawData->serviceString));
	}
	
	if (fakeTime) {
		strlcpy(rawData->timeString, fakeTime, sizeof(rawData->timeString));
	}
	
	if (fakeCellSignalStrength > -1) {
		rawData->itemIsEnabled[3] = 1;
		rawData->gsmSignalStrengthBars = fakeCellSignalStrength;
	}
	
	return rawData;
}

- (StatusBarData_6 *) fake_rawData_6
{
	StatusBarData_6 *rawData = [self fake_rawData_6];
	
	if (fakeCarrier) {
		strlcpy(rawData->serviceString, fakeCarrier, sizeof(rawData->serviceString));
	}
	
	if (fakeTime) {
		strlcpy(rawData->timeString, fakeTime, sizeof(rawData->timeString));
	}
	
	if (fakeCellSignalStrength > -1) {
		rawData->itemIsEnabled[3] = 1;
		rawData->gsmSignalStrengthBars = fakeCellSignalStrength;
	}
	
	return rawData;
}

- (StatusBarData_7 *) fake_rawData_7
{
	StatusBarData_7 *rawData = [self fake_rawData_7];
	
	if (fakeCarrier) {
		strlcpy(rawData->serviceString, fakeCarrier, sizeof(rawData->serviceString));
	}
	
	if (fakeTime) {
		strlcpy(rawData->timeString, fakeTime, sizeof(rawData->timeString));
	}
	
	if (fakeCellSignalStrength > -1) {
		rawData->itemIsEnabled[3] = 1;
		rawData->gsmSignalStrengthBars = fakeCellSignalStrength;
	}
	
	return rawData;
}

@end

#endif

Hey! Could you elaborate on what exactly this is meant for, and how exactly does it work?