[NaCl SDK] nacl_io: Fix inet_ntop to be consistent with glibc.

native_client_sdk/src/libraries/nacl_io/syscalls/inet_ntop.cc

Index: native_client_sdk/src/libraries/nacl_io/syscalls/inet_ntop.cc
diff --git a/native_client_sdk/src/libraries/nacl_io/syscalls/inet_ntop.cc b/native_client_sdk/src/libraries/nacl_io/syscalls/inet_ntop.cc
index ceabae5815f016286ab7049d9f58802f20072b98..e9bde2b13332c205b33646cecf69a4c0def1b378 100644
--- a/native_client_sdk/src/libraries/nacl_io/syscalls/inet_ntop.cc
+++ b/native_client_sdk/src/libraries/nacl_io/syscalls/inet_ntop.cc
@@ -14,7 +14,6 @@
 
 #include "sdk_util/macros.h"
 
-
 EXTERN_C_BEGIN
 
 const char* inet_ntop(int af, const void* src, char* dst, socklen_t size) {
@@ -35,16 +34,58 @@ const char* inet_ntop(int af, const void* src, char* dst, socklen_t size) {
       errno = ENOSPC;
       return NULL;
     }
-    const uint8_t* tuples = static_cast<const uint8_t*>(src);
-    std::stringstream output;
+
+    // Convert to an array of 8 host order shorts
+    const uint16_t* tuples = static_cast<const uint16_t*>(src);
+    uint16_t host_tuples[8];
+    int zero_run_start = -1;
+    int zero_run_end = -1;
     for (int i = 0; i < 8; i++) {
-      uint16_t tuple = (tuples[2*i] << 8) + tuples[2*i+1];
-      output << std::hex << tuple;
-      if (i < 7) {
-        output << ":";
+      host_tuples[i] = ntohs(tuples[i]);
+      if (host_tuples[i] == 0) {
+         if (zero_run_start == -1)
+           zero_run_start = i;
+      } else if (zero_run_start != -1 && zero_run_end == -1) {
+         zero_run_end = i;
+      }
+    }
+
+    if (zero_run_start != -1) {
+      if (zero_run_end == -1)
+        zero_run_end = 8;
+      if (zero_run_end - zero_run_start < 2) {
+        zero_run_start = -1;
+        zero_run_end = -1;
       }
     }
-    memcpy(dst, output.str().c_str(), output.str().size() + 1);
+
+    // Mimick glibc's behaviour here and allow ipv4 address to be specified
+    // as either ::A.B.C.D or ::ffff:A.B.C.D.
+    if (zero_run_start == 0 &&
+        (zero_run_end == 6 ||
+         (zero_run_end == 5 && host_tuples[zero_run_end] == 0xffff))) {
+
+      if (zero_run_end == 5) {
+        strcpy(dst, "::ffff:");
+      } else {
+        strcpy(dst, "::");
+      }
+      inet_ntop(AF_INET, host_tuples+6, dst+strlen(dst), INET_ADDRSTRLEN);
+    } else {
+      std::stringstream output;
+      for (int i = 0; i < 8; i++) {
+        if (i == zero_run_start) {
+          output << "::";
+          continue;
+        }
+        if (i > zero_run_start && i < zero_run_end)
+          continue;
+        output << std::hex << host_tuples[i];
+        if (i < 7 && i + 1 != zero_run_start)
+          output << ":";
+      }
+      memcpy(dst, output.str().c_str(), output.str().size() + 1);
+    }
     return dst;
   }
 
@@ -55,4 +96,3 @@ const char* inet_ntop(int af, const void* src, char* dst, socklen_t size) {
 EXTERN_C_END
 
 #endif  // defined(PROVIDES_SOCKET_API) && !defined(__GLIBC__)
-