(#4666) Remove duplicate export folders before writing /etc/exports

Prior to this commit, if you set up multiple folders to export with NFS
on linux with the exact same hostpath, the template used to write
/etc/exports would end up placing the same path with the same IP in
/etc/exports and cause an error preventing the folders from being
properly mounted. This commit fixes that by first looking at which
folders are being exported and if there are any duplicates. If so,
remove the duplicates and only export 1 hostpath folder. If these
duplicate folders have differing nfs linux options, an exception must be
thrown because we cannot assume which options the user intended to
export with.

lib/vagrant/errors.rb

@@ -468,6 +468,10 @@ module Vagrant
       error_key(:nfs_bad_exports)
     end
 
+    class NFSDupePerms < VagrantError
+      error_key(:nfs_dupe_permissions)
+    end
+
     class NFSExportsFailed < VagrantError
       error_key(:nfs_exports_failed)
     end

plugins/hosts/linux/cap/nfs.rb

@@ -29,6 +29,7 @@ module VagrantPlugins
           nfs_start_command = env.host.capability(:nfs_start_command)
 
           nfs_opts_setup(folders)
+          folders = folder_dupe_check(folders)
           output = Vagrant::Util::TemplateRenderer.render('nfs/exports_linux',
                                            uuid: id,
                                            ips: ips,
@@ -84,6 +85,37 @@ module VagrantPlugins
 
         protected
 
+        # Takes a hash of folders and removes any duplicate exports that
+        # share the same hostpath to avoid duplicate entries in /etc/exports
+        # ref: GH-4666
+        def self.folder_dupe_check(folders)
+          return_folders = {}
+          # Group by hostpath to see if there are multiple exports coming
+          # from the same folder
+          export_groups = folders.values.group_by { |h| h[:hostpath] }
+
+          # We need to check that each group key only has 1 value,
+          # and if not, check each nfs option. If all nfs options are the same
+          # we're good, otherwise throw an exception
+          export_groups.each do |path,group|
+            if group.size > 1
+              # if the linux nfs options aren't all the same throw an exception
+              group1_opts = group.first[:linux__nfs_options]
+
+              if !group.all? {|g| g[:linux__nfs_options] == group1_opts}
+                raise Vagrant::Errors::NFSDupePerms, hostpath: group.first[:hostpath]
+              else
+                # if they're the same just pick the first one
+                return_folders[path] = group.first
+              end
+            else
+              # just return folder, there are no duplicates
+              return_folders[path] = group.first
+            end
+          end
+          return_folders
+        end
+
         def self.nfs_cleanup(remove_ids)
           return if !File.exist?(NFS_EXPORTS_PATH)
 

templates/locales/en.yml

@@ -912,6 +912,9 @@ en:
         command: %{command}
         stdout: %{stdout}
         stderr: %{stderr}
+      nfs_dupe_permissions: |-
+        You have attempted to export the same nfs host path at %{hostpath} with
+        different nfs permissions. Please pick one permission and reload your guest.
       nfs_cant_read_exports: |-
         Vagrant can't read your current NFS exports! The exports file should be
         readable by any user. This is usually caused by invalid permissions

test/unit/plugins/hosts/linux/cap/nfs_test.rb

@@ -79,6 +79,42 @@ EOH
       expect(exports_content).to include("/tmp")
       expect(exports_content).not_to include("/var")
     end
+
+    it "throws an exception with at least 2 different nfs options" do
+      folders = {"/vagrant"=>
+                 {:hostpath=>"/home/vagrant",
+                  :linux__nfs_options=>["rw","all_squash"]},
+                 "/var/www/project"=>
+                 {:hostpath=>"/home/vagrant",
+                  :linux__nfs_options=>["rw","sync"]}}
+
+      expect { cap.nfs_export(env, ui, SecureRandom.uuid, ["127.0.0.1"], folders) }.
+        to raise_error Vagrant::Errors::NFSDupePerms
+    end
+
+    it "writes only 1 hostpath for multiple exports" do
+      folders = {"/vagrant"=>
+                 {:hostpath=>"/home/vagrant",
+                  :linux__nfs_options=>["rw","all_squash"]},
+                 "/var/www/otherproject"=>
+                 {:hostpath=>"/newhome/otherproject",
+                  :linux__nfs_options=>["rw","all_squash"]},
+                 "/var/www/project"=>
+                 {:hostpath=>"/home/vagrant",
+                  :linux__nfs_options=>["rw","all_squash"]}}
+      valid_id = SecureRandom.uuid
+      content =<<-EOH
+\n# VAGRANT-BEGIN: #{Process.uid} #{valid_id}
+"/home/vagrant" 127.0.0.1(rw,all_squash,anonuid=,anongid=,fsid=)
+"/newhome/otherproject" 127.0.0.1(rw,all_squash,anonuid=,anongid=,fsid=)
+# VAGRANT-END: #{Process.uid} #{valid_id}
+EOH
+
+      cap.nfs_export(env, ui, valid_id, ["127.0.0.1"], folders)
+      exports_content = File.read(exports_path)
+      expect(exports_content).to eq(content)
+    end
+
   end
 
   describe ".nfs_prune" do