Handle wrong group memberships better with info messages.

src/util.cc

@@ -18,6 +18,8 @@
 #include"util.h"
 #include<dirent.h>
 #include<functional>
+#include<grp.h>
+#include<pwd.h>
 #include<signal.h>
 #include<stdarg.h>
 #include<stddef.h>
@@ -721,3 +723,32 @@ string strdatetime(struct tm *datetime)
     strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M", datetime);
     return string(buf);
 }
+
+AccessCheck checkIfExistsAndSameGroup(string device)
+{
+    struct stat sb;
+
+    int ok = stat(device.c_str(), &sb);
+
+    // The file did not exist.
+    if (ok) return AccessCheck::NotThere;
+
+    gid_t groups[256];
+    int ngroups = 256;
+
+    struct passwd *p = getpwuid(getuid());
+
+    int rc = getgrouplist(p->pw_name, p->pw_gid, groups, &ngroups);
+    if (rc < 0) {
+        error("(wmbusmeters) cannot handle users with more than 256 groups\n");
+    }
+    struct group *g = getgrgid(sb.st_gid);
+
+    for (int i=0; i<ngroups; ++i) {
+        if (groups[i] == g->gr_gid) {
+            return AccessCheck::OK;
+        }
+    }
+
+    return AccessCheck::NotSameGroup;
+}

src/util.h

@@ -103,5 +103,9 @@ void eatWhitespace(std::vector<char> &v, std::vector<char>::iterator &i, bool *e
 std::string eatToSkipWhitespace(std::vector<char> &v, std::vector<char>::iterator &i, int c, size_t max, bool *eof, bool *err);
 // Remove leading and trailing white space
 void trimWhitespace(std::string *s);
+// Returns true if device exists and this programs user, belongs
+// to the same group that the device belongs to.
+enum class AccessCheck { NotThere, NotSameGroup, OK };
+AccessCheck checkIfExistsAndSameGroup(std::string device);
 
 #endif

src/wmbus.cc

@@ -16,7 +16,6 @@
 */
 
 #include"wmbus.h"
-#include<grp.h>
 #include<stdarg.h>
 #include<string.h>
 #include<sys/stat.h>
@@ -273,24 +272,6 @@ bool detectIM871A(string device, SerialCommunicationManager *handler);
 bool detectAMB8465(string device, SerialCommunicationManager *handler);
 bool detectRTLSDR(string device, SerialCommunicationManager *handler);
 
-bool existsButWrongGroup(string device)
-{
-    struct stat sb;
-
-    int ok = stat(device.c_str(), &sb);
-
-    // The file did not exist.
-    if (ok) return false;
-
-    struct group *g = getgrgid(sb.st_gid);
-    if (g && getegid() != g->gr_gid)
-    {
-        // Our group is not the same as the device.
-        return true;
-    }
-    return false;
-}
-
 pair<MBusDeviceType,string> detectMBusDevice(string device, SerialCommunicationManager *handler)
 {
     // If auto, then assume that uev has been configured with
@@ -307,22 +288,37 @@ pair<MBusDeviceType,string> detectMBusDevice(string device, SerialCommunicationM
         if (detectIM871A("/dev/im871a", handler))
         {
             return { DEVICE_IM871A, "/dev/im871a" };
-        } else if (existsButWrongGroup("/dev/im871a")) {
-            error("You are not in the same group as the device /dev/im871a\n");
+        }
+        else
+        {
+            AccessCheck ac = checkIfExistsAndSameGroup("/dev/im871a");
+            if (ac == AccessCheck::NotSameGroup) {
+                error("You are not in the same group as the device /dev/im871a\n");
+            }
         }
 
         if (detectAMB8465("/dev/amb8465", handler))
         {
             return { DEVICE_AMB8465, "/dev/amb8465" };
-        } else if (existsButWrongGroup("/dev/amb8465")) {
-            error("You are not in the same group as the device /dev/amb8465\n");
+        }
+        else
+        {
+            AccessCheck ac = checkIfExistsAndSameGroup("/dev/amb8465");
+            if (ac == AccessCheck::NotSameGroup) {
+                error("You are not in the same group as the device /dev/amb8465\n");
+            }
         }
 
         if (detectRTLSDR("/dev/rtlsdr", handler))
         {
             return { DEVICE_RTLWMBUS, "rtlwmbus" };
-        } else if (existsButWrongGroup("/dev/rtlsdr")) {
-            error("You are not in the same group as the device /dev/rtlsdr\n");
+        }
+        else
+        {
+            AccessCheck ac = checkIfExistsAndSameGroup("/dev/amb8465");
+            if (ac == AccessCheck::NotSameGroup) {
+                error("You are not in the same group as the device /dev/rtlsdr\n");
+            }
         }
 
         return { DEVICE_UNKNOWN, "" };
@@ -355,9 +351,6 @@ pair<MBusDeviceType,string> detectMBusDevice(string device, SerialCommunicationM
     {
         return { DEVICE_IM871A, device };
     }
-    if (existsButWrongGroup(device)) {
-        error("You are not in the same group as the device %s\n", device.c_str());
-    }
 
     return { DEVICE_UNKNOWN, "" };
 }

src/wmbus_rtlwmbus.cc

@@ -196,16 +196,6 @@ FrameStatus WMBusRTLWMBUS::checkRTLWMBUSFrame(vector<uchar> &data,
 bool detectRTLSDR(string device, SerialCommunicationManager *manager)
 {
     // No more advanced test than that the /dev/rtlsdr link exists.
-    struct stat sb;
-    int rc = stat(device.c_str(), &sb);
-    if (rc) return false;
-
-    struct group *g = getgrgid(sb.st_gid);
-    if (g && getegid() != g->gr_gid)
-    {
-        // Our group is not the same as the device.
-        return false;
-    }
-
-    return true;
+    AccessCheck ac = checkIfExistsAndSameGroup(device);
+    return ac == AccessCheck::OK;
 }