[CLATJ#4] libclat: move selectIpv4Address() and isIpv4AddressFree() from netd to apex
isIpv4AddressFree() is moved from ClatdController without behavior
change.
selectIpv4Address() and its test are moved from ClatdController as well.
They have been refactored slightly for testing because function pointer
of isIpv4AddressFreeFunc is not a global variable anymore. We can't set
global function pointer to change selectIpv4Address() behavior for
testing. Instead isIpv4AddressFree is sent as an argument of function
pointer. For public caller, selectIpv4Address() has no behavior change.
For test caller, they can call an internal selectIpv4AddressInternal
(.., fn) to change isIpv4AddrFreeFn function pointer for testing.
Bug: 212345928
Test: build and boot
atest libclat_test
Change-Id: Iab5e6fd5ebbccf10e7b3be2251b45949cf3f3464
diff --git a/service/native/libs/libclat/clatutils.cpp b/service/native/libs/libclat/clatutils.cpp
index 69076c5..9ceed75 100644
--- a/service/native/libs/libclat/clatutils.cpp
+++ b/service/native/libs/libclat/clatutils.cpp
@@ -27,6 +27,68 @@
namespace net {
namespace clat {
+bool isIpv4AddressFree(in_addr_t addr) {
+ int s = socket(AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0);
+ if (s == -1) {
+ return 0;
+ }
+
+ // Attempt to connect to the address. If the connection succeeds and getsockname returns the
+ // same then the address is already assigned to the system and we can't use it.
+ struct sockaddr_in sin = {
+ .sin_family = AF_INET,
+ .sin_port = htons(53),
+ .sin_addr = {addr},
+ };
+ socklen_t len = sizeof(sin);
+ bool inuse = connect(s, (struct sockaddr*)&sin, sizeof(sin)) == 0 &&
+ getsockname(s, (struct sockaddr*)&sin, &len) == 0 && (size_t)len >= sizeof(sin) &&
+ sin.sin_addr.s_addr == addr;
+
+ close(s);
+ return !inuse;
+}
+
+// Picks a free IPv4 address, starting from ip and trying all addresses in the prefix in order.
+// ip - the IP address from the configuration file
+// prefixlen - the length of the prefix from which addresses may be selected.
+// returns: the IPv4 address, or INADDR_NONE if no addresses were available
+in_addr_t selectIpv4Address(const in_addr ip, int16_t prefixlen) {
+ return selectIpv4AddressInternal(ip, prefixlen, isIpv4AddressFree);
+}
+
+// Only allow testing to use this function directly. Otherwise call selectIpv4Address(ip, pfxlen)
+// which has applied valid isIpv4AddressFree function pointer.
+in_addr_t selectIpv4AddressInternal(const in_addr ip, int16_t prefixlen,
+ isIpv4AddrFreeFn isIpv4AddressFreeFunc) {
+ // Impossible! Only test allows to apply fn.
+ if (isIpv4AddressFreeFunc == nullptr) {
+ return INADDR_NONE;
+ }
+
+ // Don't accept prefixes that are too large because we scan addresses one by one.
+ if (prefixlen < 16 || prefixlen > 32) {
+ return INADDR_NONE;
+ }
+
+ // All these are in host byte order.
+ in_addr_t mask = 0xffffffff >> (32 - prefixlen) << (32 - prefixlen);
+ in_addr_t ipv4 = ntohl(ip.s_addr);
+ in_addr_t first_ipv4 = ipv4;
+ in_addr_t prefix = ipv4 & mask;
+
+ // Pick the first IPv4 address in the pool, wrapping around if necessary.
+ // So, for example, 192.0.0.4 -> 192.0.0.5 -> 192.0.0.6 -> 192.0.0.7 -> 192.0.0.0.
+ do {
+ if (isIpv4AddressFreeFunc(htonl(ipv4))) {
+ return htonl(ipv4);
+ }
+ ipv4 = prefix | ((ipv4 + 1) & ~mask);
+ } while (ipv4 != first_ipv4);
+
+ return INADDR_NONE;
+}
+
// Alters the bits in the IPv6 address to make them checksum neutral with v4 and nat64Prefix.
void makeChecksumNeutral(in6_addr* v6, const in_addr v4, const in6_addr& nat64Prefix) {
// Fill last 8 bytes of IPv6 address with random bits.