iputil: switch to a scapy-inspired SIOCGIFADDR approach, very linux-specific now

src/allmydata/util/iputil.py

@@ -9,9 +9,55 @@ from twisted.internet import reactor
 from twisted.internet.protocol import DatagramProtocol
 from twisted.internet.utils import getProcessOutput
 
+from fcntl import ioctl
+import struct
+SIOCGIFADDR    = 0x8915 # linux-specific
+
+# inspired by scapy
+def get_if_list():
+    f = open("/proc/net/dev","r")
+    f.readline(); f.readline()
+    names = []
+    for l in f.readlines():
+        names.append(l[:l.index(":")].strip())
+    return names
+
+def get_if_addr(ifname):
+    try:
+        s=socket.socket()
+        ifreq = ioctl(s, SIOCGIFADDR, struct.pack("16s16x", ifname))
+        s.close()
+        naddr = ifreq[20:24]
+        return socket.inet_ntoa(naddr)
+    except IOError:
+        return None
+
 def get_local_addresses():
-    """Return a Deferred that fires with a list of IPv4 addresses (as
-    dotted-quad strings) that are currently configured on this host.
+    """Return a list of IPv4 addresses (as dotted-quad strings) that are
+    currently configured on this host.
+
+    This will only work under linux, because it uses both a linux-specific
+    /proc/net/dev devices (to get the interface names) and a SIOCGIFADDR
+    ioctl (to get their addresses). If the listing-the-interfaces were done
+    with an ioctl too (and if if you're lucky enough to be using the same
+    value for the ioctls), then it might work on other forms of unix too.
+    Windows is right out."""
+
+    ifnames = []
+    for ifname in get_if_list():
+        addr = get_if_addr(ifname)
+        if addr:
+            ifnames.append(addr)
+    return ifnames
+
+def get_local_addresses_sync():
+    """Return a list of IPv4 addresses (as dotted-quad strings) that are
+    currently configured on this host.
+
+    Unfortunately this is not compatible with Twisted: it catches SIGCHLD and
+    this usually results in errors about 'Interrupted system call'.
+
+    This will probably work on both linux and OS-X, but probably not windows.
     """
     # eventually I want to use somebody else's cross-platform library for
     # this. For right now, I'm running ifconfig and grepping for the 'inet '
@@ -34,6 +80,8 @@ def get_local_addresses():
 def get_local_addresses_async():
     """Return a Deferred that fires with a list of IPv4 addresses (as
     dotted-quad strings) that are currently configured on this host.
+
+    This will probably work on both linux and OS-X, but probably not windows.
     """
     # eventually I want to use somebody else's cross-platform library for
     # this. For right now, I'm running ifconfig and grepping for the 'inet '