fix(IP): The IP() function breaks for 128/8 and higher

documentation/advanced-features/debugging-with-dlv.md

@@ -1,4 +1,4 @@
-# Debugger
+# Debugging Tips
 
 - [Debugger](#debugger)
   - [Debug a particular function](#debug-a-particular-function)
@@ -80,3 +80,31 @@ VSCode equivalent configuration is:
 
     ]
 ```
+
+## Debug `helpers.js`
+
+Develop a function:
+
+```
+node -e "
+function IP(dot) {
+    var d = dot.split('.');
+    return ((((((+d[0]) * 256) + (+d[1])) * 256) + (+d[2])) * 256) + (+d[3]);
+}
+console.log(IP('135.181.247.240'));
+"
+```
+
+Debug a function within helpers.js:
+
+```
+$ node -e "
+const fs = require('fs');
+const vm = require('vm');
+const code = fs.readFileSync('/Users/tlimoncelli/gitthings/dnscontrol/pkg/js/helpers.js', 'utf8');
+const sandbox = {};
+vm.createContext(sandbox);
+vm.runInContext(code, sandbox);
+console.log(vm.runInContext(\" IP('135.181.247.240') \", sandbox));
+"
+```

pkg/js/parse_tests/004-ips.js

@@ -7,4 +7,7 @@ D("foo.com", REG, DnsProvider(CF, 0),
     A("@", BASE),
     A("p1", BASE + 1),
     A("p255", BASE + 255),
+
+    // An IP address with the highest bit set, to catch uint/int bugs.
+    A("yyy", IP("190.2.3.4"))
 );

pkg/js/parse_tests/004-ips.json

@@ -47,6 +47,18 @@
           "ttl": 300,
           "type": "A",
           "typenum": 1
+        },
+        {
+          "comparablev3": "190.2.3.4",
+          "filepos": "[line:12:5]",
+          "name": "yyy",
+          "name_unicode": "yyy",
+          "rdata": {
+            "Addr": "190.2.3.4"
+          },
+          "ttl": 300,
+          "type": "A",
+          "typenum": 1
         }
       ],
       "registrar": "Third-Party",

pkg/js/parse_tests/004-ips/foo.com.zone

@@ -2,3 +2,4 @@ $TTL 300
 @                IN A     1.2.3.4
 p1               IN A     1.2.3.5
 p255             IN A     1.2.4.3
+yyy              IN A     190.2.3.4

pkg/mustbe/ip.go

@@ -9,16 +9,14 @@ import (
 func IPv4(a any) (netip.Addr, error) {
 	switch v := a.(type) {
 	case float64:
-		i := int32(v)
-		a := (i >> 24) % 256
-		b := (i >> 16) % 256
-		c := (i >> 8) % 256
-		d := i % 256
+		// IP addresses expressed as a number (e.g. via the IP() helper in
+		// dnsconfig.js) range from 0 to 4294967295 (2^32-1)
+		i := uint32(v)
 		x := netip.AddrFrom4([4]byte{
-			byte(a),
-			byte(b),
-			byte(c),
-			byte(d),
+			byte(i >> 24), // NB(tlim): byte() silently truncates the upper bits.
+			byte(i >> 16),
+			byte(i >> 8),
+			byte(i),
 		})
 		return x, nil
 	case string:

pkg/mustbe/ip_test.go

@@ -45,6 +45,11 @@ func TestIPv4_Parse(t *testing.T) {
 		{"a", "1.2.3.4", netip.MustParseAddr("1.2.3.4")},
 		{"b", float64((2 << 24) + (3 << 16) + (4 << 8) + 5), netip.MustParseAddr("2.3.4.5")},
 		{"c", netip.MustParseAddr("3.4.5.6"), netip.MustParseAddr("3.4.5.6")},
+		// Regression test for https://github.com/DNSControl/dnscontrol/issues/4825:
+		// addresses with a first octet >= 128 produce a number greater than
+		// math.MaxInt32, which used to overflow when converted via int32.
+		{"d", float64((135 << 24) + (181 << 16) + (247 << 8) + 240), netip.MustParseAddr("135.181.247.240")},
+		{"e", float64((255 << 24) + (255 << 16) + (255 << 8) + 255), netip.MustParseAddr("255.255.255.255")},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {