Add FLIPPER_PORTS env var to iOS SDK

Summary:
Part 2 of changing flipper to use customizable ports: iOS SDK.
Still to go: JS app.

env var should be of the format:

`FLIPPER_PORTS=1111,2222` for insecure port: 1111 and secure port: 2222.

Reviewed By: danielbuechele

Differential Revision: D13800988

fbshipit-source-id: 3560ba850389964f4b784551b803c45c6524e6f0

iOS/FlipperKit/SKEnvironmentVariables.m

@@ -0,0 +1,30 @@
+#ifdef FB_SONARKIT_ENABLED
+
+#import "SKEnvironmentVariables.h"
+
+static int const DEFAULT_INSECURE_PORT = 8089;
+static int const DEFAULT_SECURE_PORT = 8088;
+
+@implementation SKEnvironmentVariables
+
++ (int)getInsecurePort {
+    NSString *envVar = [self getFlipperPortsVariable];
+    return [self extractIntFromPropValue:envVar atIndex:0 withDefault:DEFAULT_INSECURE_PORT];
+}
++ (int)getSecurePort {
+    NSString *envVar = [self getFlipperPortsVariable];
+   return [self extractIntFromPropValue:envVar atIndex:1 withDefault:DEFAULT_SECURE_PORT];
+}
++ (int)extractIntFromPropValue:(NSString *)propValue atIndex:(int)index withDefault:(int)fallback {
+    NSArray<NSString *> *components = [propValue componentsSeparatedByString:@","];
+    NSString *component = [components objectAtIndex:index];
+    int envInt = [component intValue];
+    return envInt > 0 ? envInt : fallback;
+}
++ (NSString *)getFlipperPortsVariable {
+    NSString *value = NSProcessInfo.processInfo.environment[@"FLIPPER_PORTS"];
+    return value;
+}
+@end
+
+#endif