don't leak FD in AutoProxyDetect command return parsing

Just closing the fd would be enough, but while we are at it we can also
use the Popen interface to have an easier time with this.

apt-pkg/contrib/proxy.cc

@@ -16,9 +16,9 @@
 #include <unistd.h>
 
 #include "proxy.h"
+									/*}}}*/
 
-
-// AutoDetectProxy - auto detect proxy          			/*{{{*/
+// AutoDetectProxy - auto detect proxy					/*{{{*/
 // ---------------------------------------------------------------------
 /* */
 bool AutoDetectProxy(URI &URL)
@@ -41,45 +41,30 @@ bool AutoDetectProxy(URI &URL)
    if (Debug)
       std::clog << "Using auto proxy detect command: " << AutoDetectProxyCmd << std::endl;
 
-   int Pipes[2] = {-1,-1};
-   if (pipe(Pipes) != 0)
-      return _error->Errno("pipe", "Failed to create Pipe");
-
-   pid_t Process = ExecFork();
-   if (Process == 0)
-   {
-      close(Pipes[0]);
-      dup2(Pipes[1],STDOUT_FILENO);
-      SetCloseExec(STDOUT_FILENO,false);
-
-      std::string foo = URL;
-      const char *Args[4];
-      Args[0] = AutoDetectProxyCmd.c_str();
-      Args[1] = foo.c_str();
-      Args[2] = 0;
-      execv(Args[0],(char **)Args);
-      std::cerr << "Failed to exec method " << Args[0] << std::endl;
-      _exit(100);
-   }
+   std::string const urlstring = URL;
+   std::vector<const char *> Args;
+   Args.push_back(AutoDetectProxyCmd.c_str());
+   Args.push_back(urlstring.c_str());
+   Args.push_back(nullptr);
+   FileFd PipeFd;
+   pid_t Child;
+   if(Popen(&Args[0], PipeFd, Child, FileFd::ReadOnly) == false)
+      return _error->Error("ProxyAutoDetect command '%s' failed!", AutoDetectProxyCmd.c_str());
    char buf[512];
-   int InFd = Pipes[0];
-   close(Pipes[1]);
-   int res = read(InFd, buf, sizeof(buf)-1);
-   ExecWait(Process, "ProxyAutoDetect", true);
+   if (PipeFd.ReadLine(buf, sizeof(buf)) == nullptr)
+      return _error->Error("Failed to read in AutoDetectProxy");
+   PipeFd.Close();
+   ExecWait(Child, "ProxyAutoDetect", true);
+   auto const cleanedbuf = _strstrip(buf);
 
-   if (res < 0)
-      return _error->Errno("read", "Failed to read");
-   if (res == 0)
+   if (cleanedbuf[0] == '\0')
       return _error->Warning("ProxyAutoDetect returned no data");
 
-   // add trailing \0
-   buf[res] = 0;
-
    if (Debug)
-      std::clog << "auto detect command returned: '" << buf << "'" << std::endl;
+      std::clog << "auto detect command returned: '" << cleanedbuf << "'" << std::endl;
 
-   if (strstr(buf, URL.Access.c_str()) == buf)
-      _config->Set("Acquire::"+URL.Access+"::proxy::"+URL.Host, _strstrip(buf));
+   if (strstr(cleanedbuf, URL.Access.c_str()) == cleanedbuf)
+      _config->Set("Acquire::"+URL.Access+"::proxy::"+URL.Host, cleanedbuf);
 
    return true;
 }