1 files changed, 103 insertions, 0 deletions
diff --git a/peerinfo.c b/peerinfo.c
new file mode 100644
index 0000000..2e9c8e0
--- /dev/null
+++ b/peerinfo.c
@@ -0,0 +1,103 @@
+/*
+ *    Routine to provide information about the other side of a FD.
+ *
+ * Copyright (C) 2015 Peter Wu <peter@lekensteyn.nl>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ *
+ */
+
+#define _GNU_SOURCE             /* for struct ucred on Linux */
+#include "scope.h"
+
+#include <unistd.h>
+#include <stdio.h>
+#include <sys/types.h>          /* for pid_t */
+
+
+static pid_t
+GetPidFromFd(FD fd)
+{
+#ifdef SO_PEERCRED
+    struct ucred cred;
+    socklen_t cred_len = sizeof(cred);
+
+    if (getsockopt(fd, SOL_SOCKET, SO_PEERCRED, &cred, &cred_len) == 0 &&
+        cred_len == sizeof(cred)) {
+        return cred.pid;
+    }
+#endif
+    return 0;
+}
+
+static const char *
+GetProcnameForPid(pid_t pid)
+{
+    /* comm is no longer than TASK_COMM_LEN (16) */
+    static char comm[17];
+    char comm_path[32];
+    char comm_fd;
+    unsigned comm_len = 0;
+
+    snprintf(comm_path, sizeof(comm_path), "/proc/%d/comm", pid);
+    comm_fd = open(comm_path, O_RDONLY);
+    if (comm_fd != -1) {
+        comm_len = read(comm_fd, comm, sizeof(comm) - 1);
+        if (comm_len < 0)
+            comm_len = 0;
+        close(comm_fd);
+    }
+
+    if (comm_len > 0 && comm[comm_len - 1] == '\n')
+        comm_len--;
+    comm[comm_len] = '\0';
+    return comm;
+}
+
+/*
+   Retrieves additional information about the other side of the fd.
+   For Unix domain sockets, this results in the process ID and name.
+ */
+char *
+ReadPeerInfo(FD fd)
+{
+    /* should hold enough for "PID <number> <command name>" */
+    char peer_info[40];
+    unsigned pos;
+    pid_t pid;
+    const char *comm;
+
+    pid = GetPidFromFd(fd);
+    /* Use the fact that pid_t is the first field of struct ucred. */
+    if (pid) {
+        pos = snprintf(peer_info, sizeof(peer_info), "pid %d", pid);
+
+        comm = GetProcnameForPid(pid);
+        if (comm)
+            pos += snprintf(peer_info + pos, sizeof(peer_info) - pos,
+                            " %s", comm);
+
+        return strdup(peer_info);
+    }
+
+    /* (Could add port number here for AF_INET if it helps.) */
+
+    return NULL;
+}