std: add try_parse_addr and change an alt w/ ip_addr::ipv6 to avoid warning

src/libstd/net_ip.rs

@@ -5,10 +5,9 @@ Types/fns concerning Internet Protocol (IP), versions 4 & 6
 import vec;
 import uint;
 
-export ip_addr;
+export ip_addr, parse_addr_err;
 export format_addr;
 export v4;
-//format_addr, parse_addr;
 
 #[doc = "An IP address"]
 enum ip_addr {
@@ -17,6 +16,13 @@ enum ip_addr {
     ipv6(u16,u16,u16,u16,u16,u16,u16,u16)
 }
 
+#[doc="
+Human-friendly feedback on why a parse_addr attempt failed
+"]
+type parse_addr_err = {
+    err_msg: str
+};
+
 #[doc="
 Convert a `ip_addr` to a str
 
@@ -29,7 +35,7 @@ fn format_addr(ip: ip_addr) -> str {
       ipv4(a, b, c, d) {
         #fmt["%u.%u.%u.%u", a as uint, b as uint, c as uint, d as uint]
       }
-      ipv6(a,b,c,d,e,f,g,h) {
+      ipv6(_, _, _, _, _, _, _, _) {
         fail "FIXME impl parsing of ipv6 addr";
       }
     }
@@ -52,14 +58,32 @@ j    Fails if the string is not a valid IPv4 address
     * an `ip_addr` of the `ipv4` variant
     "]
     fn parse_addr(ip: str) -> ip_addr {
+        alt try_parse_addr(ip) {
+          result::ok(addr) { addr }
+          result::err(err_data) {
+            fail err_data.err_msg
+          }
+        }
+    }
+    fn try_parse_addr(ip: str) -> result::result<ip_addr,parse_addr_err> {
         let parts = vec::map(str::split_char(ip, '.'), {|s|
             alt uint::from_str(s) {
               some(n) if n <= 255u { n }
-              _ { fail "Invalid IP Address part." }
+              _ { 256u }
             }
         });
-        if vec::len(parts) != 4u { fail "Too many dots in IP address"; }
-        ipv4(parts[0] as u8, parts[1] as u8, parts[2] as u8, parts[3] as u8)
+        if vec::len(parts) != 4u {
+            result::err({err_msg: #fmt("'%s' doesn't have 4 parts",
+                        ip)})
+        }
+        else if vec::contains(parts, 256u) {
+            result::err({err_msg: #fmt("invalid octal in provided addr '%s'",
+                        ip)})
+        }
+        else {
+            result::ok(ipv4(parts[0] as u8, parts[1] as u8,
+                 parts[2] as u8, parts[3] as u8))
+        }
     }
 }