Improve str_replace and add tests for it (#158)

src/Makefile

@@ -87,7 +87,11 @@ jsapi_buildstamp: spidermonkey/js/src
 spidermonkey/libjs.a: spidermonkey/js/src
 	cd spidermonkey && SMCFLAGS="$(SHFLAGS) $(SMCFLAGS)" $(MAKE) jslib
 
-pacparser.o: pacparser.c pac_utils.h pacparser.h jsapi_buildstamp
+pac_utils_test: pac_utils_test.c pac_utils.h
+	$(CC) $(MAINT_CFLAGS) $(CFLAGS) $(SHFLAGS) pac_utils_test.c -o pac_utils_test -lm -L. -I.
+
+pacparser.o: pacparser.c pac_utils.h pacparser.h pac_utils_test jsapi_buildstamp
+	./pac_utils_test
 	$(CC) $(MAINT_CFLAGS) $(CFLAGS) $(SHFLAGS) -c pacparser.c -o pacparser.o
 	touch pymod/pacparser_o_buildstamp
 

src/pac_utils.h

@@ -26,6 +26,9 @@
 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
 // USA
 
+#include <string.h>
+#include <stdlib.h>
+
 static const char *pacUtils =
 "function dnsDomainIs(host, domain) {\n"
 "    return (host.length >= domain.length &&\n"
@@ -335,31 +338,48 @@ static const char *pacUtils =
 
 
 // You must free the result if result is non-NULL.
-char *str_replace(const char *orig, char *rep, char *with) {
-    char *result;  // the return string
-    char *ins;     // the next insert point
-    char *tmp;     // varies
-    int count;     // number of replacements
-    int len_front; // distance between rep and end of last rep
-    int len_rep  = strlen(rep);
-    int len_with = strlen(with);
+char *str_replace(const char *orig, const char *rep, const char *with) {
+    if (orig == NULL || rep == NULL || with == NULL) {
+        return NULL;
+    }
+
+    size_t len_orig  = strnlen(orig, 1024);
+    size_t len_rep  = strnlen(rep, 1024);
+    size_t len_with = strnlen(with, 1024);
+
+    if (len_orig == 0 || len_rep == 0) {
+        char *result = malloc(len_orig + 1);
+        strcpy(result, orig);
+        return result;
+    }
 
-    // Get the count of replacements
-    ins = orig;
-    for (count = 0; (tmp = strstr(ins, rep)); ++count) {
-        ins = tmp + len_rep;
+    // Count replacements needed
+    int count;           // number of replacements
+    char const *start = orig;
+    // Cursor moves through the string, looking for rep.
+    char const *cursor;
+    for (count = 0;; ++count) {
+        cursor = strstr(start, rep);
+        if (cursor == NULL) {
+            break;
+        }
+        start = cursor + len_rep;
     }
 
-    tmp = result = malloc(strlen(orig) + (len_with - len_rep) * count + 1);
+    char *tmp;
+    char *result;
+    tmp = result = malloc(len_orig + (len_with - len_rep) * count + 1);
 
     // first time through the loop, all the variable are set correctly
     // from here on,
     //    tmp points to the end of the result string
     //    ins points to the next occurrence of rep in orig
     //    orig points to the remainder of orig after "end of rep"
     while (count--) {
-        ins = strstr(orig, rep);
-        len_front = ins - orig;
+        const char *ins = strstr(orig, rep);
+        int len_front = (int)(ins - orig); // How far have we moved
+        // Into the tmp, copy everything until we reach the rep.
+        // and move tmp forward.
         tmp = strncpy(tmp, orig, len_front) + len_front;
         tmp = strcpy(tmp, with) + len_with;
         orig += len_front + len_rep; // move to next "end of rep"

src/pac_utils_test.c

@@ -0,0 +1,40 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include "pac_utils.h"
+
+#define STREQ(s1, s2) (strcmp((s1), (s2)) == 0)
+
+// Unit tests
+int main() {
+    // Test case 1: Single replacement
+    assert(STREQ("Hello, universe!", str_replace("Hello, world!", "world", "universe")));
+
+    // Test case 2: Multiple replacements
+    assert(STREQ("one cat, two cat, red cat, blue cat",
+           str_replace("one fish, two fish, red fish, blue fish", "fish", "cat")));
+    // Expected output: "one cat, two cat, red cat, blue cat"
+
+    // Test case 3: No replacements
+    assert(STREQ("AI is amazing", str_replace("AI is amazing", "robot", "AI")));
+
+    // Test case 4: Empty original string
+    assert(STREQ("", str_replace("", "hello", "world")));
+
+    // Test case 5: Empty replacement string
+    assert(STREQ("Hello, world!", str_replace("Hello, world!", "", "universe")));
+
+    // Test case 6: Empty "with" string
+    assert(STREQ("Hello, !", str_replace("Hello, world!", "world", "")));
+
+    // Test case 7: Complex replacements
+    assert(STREQ("abcdeXYZcba", str_replace("abcdeedcba", "ed", "XYZ")));
+
+    // Test case 8: Null inputs
+    assert(str_replace(NULL, "hello", "world") == NULL);
+    assert(str_replace("Hello hello", NULL, "world") == NULL);
+    assert(str_replace("Hello hello", "hello", NULL) == NULL);
+
+    return 0;
+}