Use native netlink code instead of /sbin/ip to manipulate routes

Shelling out to /sbin/ip is slow, and more importantly it does
not preserve the error messages returned by the kernel when
adding or deleting a route fails.  Instead, use netlink directly.

This change does not yet pass the errors back to CommandListener;
that is done in the next change in the series.

Change-Id: I5ad3c8583580857be6386a620ff5c4f3872d685b
diff --git a/server/NetdConstants.cpp b/server/NetdConstants.cpp
index ea31410..4823c91 100644
--- a/server/NetdConstants.cpp
+++ b/server/NetdConstants.cpp
@@ -15,6 +15,9 @@
  */
 
 #include <fcntl.h>
+#include <netdb.h>
+#include <netinet/in.h>
+#include <stdlib.h>
 #include <string.h>
 #include <sys/wait.h>
 #include <ctype.h>
@@ -170,3 +173,78 @@
 
     return true;
 }
+
+int parsePrefix(const char *prefix, uint8_t *family, void *address, int size, uint8_t *prefixlen) {
+    if (!prefix || !family || !address || !prefixlen) {
+        return -EFAULT;
+    }
+
+    // Find the '/' separating address from prefix length.
+    const char *slash = strchr(prefix, '/');
+    const char *prefixlenString = slash + 1;
+    if (!slash || !*prefixlenString)
+        return -EINVAL;
+
+    // Convert the prefix length to a uint8_t.
+    char *endptr;
+    unsigned templen;
+    templen = strtoul(prefixlenString, &endptr, 10);
+    if (*endptr || templen > 255) {
+        return -EINVAL;
+    }
+    *prefixlen = templen;
+
+    // Copy the address part of the prefix to a local buffer. We have to copy
+    // because inet_pton and getaddrinfo operate on null-terminated address
+    // strings, but prefix is const and has '/' after the address.
+    std::string addressString(prefix, slash - prefix);
+
+    // Parse the address.
+    addrinfo *res;
+    addrinfo hints = {
+        .ai_flags = AI_NUMERICHOST,
+    };
+    int ret = getaddrinfo(addressString.c_str(), NULL, &hints, &res);
+    if (ret || !res) {
+        return -EINVAL;  // getaddrinfo return values are not errno values.
+    }
+
+    // Convert the address string to raw address bytes.
+    void *rawAddress;
+    int rawLength;
+    switch (res[0].ai_family) {
+        case AF_INET: {
+            if (*prefixlen > 32) {
+                return -EINVAL;
+            }
+            sockaddr_in *sin = (sockaddr_in *) res[0].ai_addr;
+            rawAddress = &sin->sin_addr;
+            rawLength = 4;
+            break;
+        }
+        case AF_INET6: {
+            if (*prefixlen > 128) {
+                return -EINVAL;
+            }
+            sockaddr_in6 *sin6 = (sockaddr_in6 *) res[0].ai_addr;
+            rawAddress = &sin6->sin6_addr;
+            rawLength = 16;
+            break;
+        }
+        default: {
+            freeaddrinfo(res);
+            return -EAFNOSUPPORT;
+        }
+    }
+
+    if (rawLength > size) {
+        freeaddrinfo(res);
+        return -ENOSPC;
+    }
+
+    *family = res[0].ai_family;
+    memcpy(address, rawAddress, rawLength);
+    freeaddrinfo(res);
+
+    return rawLength;
+}