add files

Makefile

@@ -0,0 +1,7 @@
+CFLAGS = -dynamiclib -lpthread
+
+all:
+	$(CC) $(CFLAGS) sketchtrial.c -o libsketchtrial.dylib
+
+clean:
+	rm -rf *.o libsketchtrial.dylib

sketch.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
+export DYLD_FORCE_FLAT_NAMESPACE=1 
+export DYLD_INSERT_LIBRARIES=$DIR/libsketchtrial.dylib
+/Applications/Sketch.app/Contents/MacOS/Sketch

sketchtrial.c

@@ -0,0 +1,99 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <sys/time.h>
+#include <unistd.h>
+#include <execinfo.h>
+#include <dlfcn.h>
+#include <pthread.h>
+
+static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
+static int nstime_calls_left = 3;
+static bool done = false;
+static char buf[32];
+static long days = -5000;
+
+// pointer to the original function
+int (*orig_gettimeofday) (struct timeval *restrict tp, void *restrict tzp) = NULL;
+
+void parse_bt_source(char* src, char* dst, int len) {
+    int pos = 0;
+    int state = 0;
+    for (char *c = src; *c != '\0' && pos < len-1; c++) {
+        if (!state) {
+            if (*c == ' ') {
+                state = 1;
+            }
+            continue;
+        }
+        if (state == 1) {
+            if (*c != ' ') {
+                state = 2;
+            }
+        }
+        if (state == 2) {
+            if (*c != ' ') {
+                dst[pos++] = *c;
+            } else {
+                dst[pos] = '\0';
+                break;
+            }
+        }
+    }
+}
+
+int gettimeofday(struct timeval *restrict tp, void *restrict tzp) {
+    if (!orig_gettimeofday) {
+        orig_gettimeofday = dlsym(RTLD_NEXT, "gettimeofday");
+    }
+
+    int result = orig_gettimeofday(tp, tzp);
+    if (result == 0 && !done) {
+        pthread_mutex_lock(&mutex);
+        if (nstime_calls_left > 0) {
+            void *callstack[128];
+            int frames = backtrace(callstack, 128);
+            char **strs = backtrace_symbols(callstack, frames);
+
+            bool is_sketch = false, is_nstime = false, is_cfnet = false, is_nt = false;
+            int i;
+
+            for (i = 0; i < frames; ++i) {
+                parse_bt_source(strs[i], buf, 32);
+                if (!is_nstime && strstr(strs[i], "NSDate") != NULL) {
+                    is_nstime = true;
+                }
+                if (!is_nt && strstr(strs[i], "NSNotification") != NULL) {
+                    is_nt = true;
+                }
+                if (!is_sketch && !strcmp(buf, "Sketch")) {
+                    is_sketch = true;
+                }
+                if (!is_cfnet && !strcmp(buf, "CFNetwork")) {
+                    is_cfnet = true;
+                }
+            }
+
+            if (is_sketch && is_nstime && !is_cfnet && !is_nt) {
+                tp->tv_sec += days * 86400;
+                tp->tv_usec = tp->tv_sec * 1000000;
+                nstime_calls_left--;
+
+                printf("spoofed time on call stack:\n");
+                for (i = 0; i < frames; i++) {
+                    printf("    %s\n", strs[i]);
+                }
+                printf("\n");
+            }
+
+            free(strs);
+            if (!nstime_calls_left) {
+                done = true;
+            }
+        }
+        pthread_mutex_unlock(&mutex);
+    }
+
+    return result;
+}