[cancelled, not using Crystal anymore] Add abstract unix socket handling

spec/std/socket_spec.cr

@@ -169,15 +169,67 @@ describe Socket::IPAddress do
 end
 
 describe Socket::UNIXAddress do
+  {% if flag?(:linux) %}
+    it "can be abstract on Linux" do
+      path = "/abstract.sock"
+      addr = Socket::UNIXAddress.new('@' + path)
+      addr.abstract?.should be_true
+      addr.path.should eq(path)
+    end
+  {% else %}
+    it "raises for abstract UNIX address on non-Linux" do
+      expect_raises(ArgumentError, "Unsupported") do
+        Socket::UNIXAddress.new("@/abstract.sock")
+      end
+    end
+  {% end %}
+
+  it "is not abstract for a non-abstract address" do
+    path = "/tmp/unix.sock"
+    addr = Socket::UNIXAddress.new(path)
+    addr.abstract?.should be_false
+    addr.path.should eq(path)
+  end
+
+  it "creates a non-abstract UNIX address starting with @" do
+    path = "./@non-abstract.sock"
+    addr = Socket::UNIXAddress.new(path)
+    addr.abstract?.should be_false
+    addr.path.should eq(path)
+  end
+
   it "transforms into a C struct and back" do
-    addr1 = Socket::UNIXAddress.new("/tmp/service.sock")
-    addr2 = Socket::UNIXAddress.from(addr1.to_unsafe, addr1.size)
+    path = "/tmp/service.sock"
 
+    addr1 = Socket::UNIXAddress.new(path)
+    addr1.abstract?.should be_false
+    addr1.path.should eq(path)
+
+    addr2 = Socket::UNIXAddress.from(addr1.to_unsafe, addr1.size)
     addr2.family.should eq(addr1.family)
     addr2.path.should eq(addr1.path)
-    addr2.to_s.should eq("/tmp/service.sock")
+    addr2.abstract?.should eq(addr1.abstract?)
+    addr2.to_s.should eq(path)
   end
 
+  {% if flag?(:linux) %}
+    it "transforms an abstract address into a C struct and back" do
+      path = "/abstract-service.sock"
+
+      addr1 = Socket::UNIXAddress.new('@' + path)
+      addr1.path.should eq(path)
+      addr1.abstract?.should be_true
+
+      sockaddr_un = addr1.to_unsafe.as(LibC::SockaddrUn*).value
+      sockaddr_un.sun_path[0].should eq(0_u8)
+      String.new(sockaddr_un.sun_path.to_unsafe + 1).should eq(path)
+
+      addr2 = Socket::UNIXAddress.new(pointerof(sockaddr_un), nil)
+      addr2.path.should eq(addr1.path)
+      addr2.abstract?.should eq(addr1.abstract?)
+    end
+  {% end %}
+
   it "raises when path is too long" do
     path = "/tmp/crystal-test-too-long-unix-socket-#{("a" * 2048)}.sock"
     expect_raises(ArgumentError, "Path size exceeds the maximum size") { Socket::UNIXAddress.new(path) }
@@ -186,6 +238,12 @@ describe Socket::UNIXAddress do
   it "to_s" do
     Socket::UNIXAddress.new("some_path").to_s.should eq("some_path")
   end
+
+  {% if flag?(:linux) %}
+    it "to_s for abstract UNIX address" do
+      Socket::UNIXAddress.new("@some_path").to_s.should eq("@some_path")
+    end
+  {% end %}
 end
 
 describe UNIXServer do
@@ -195,6 +253,26 @@ describe UNIXServer do
     File.exists?(path).should be_false
   end
 
+  {% if flag?(:linux) %}
+    it "is not abstract when path is not an abstract address" do
+      path = "/tmp/crystal-test-unix-sock"
+
+      UNIXServer.open(path) do |server|
+        server.abstract?.should be_false
+      end
+    end
+  {% end %}
+
+  {% if flag?(:linux) %}
+    it "is abstract when path is an abstract address" do
+      path = "/tmp/crystal-test-unix-abstract-sock"
+
+      UNIXServer.open('@' + path) do |server|
+        server.abstract?.should be_true
+      end
+    end
+  {% end %}
+
   it "creates the socket file" do
     path = "/tmp/crystal-test-unix-sock"
 
@@ -205,6 +283,34 @@ describe UNIXServer do
     File.exists?(path).should be_false
   end
 
+  it "creates the socket file with path starting with @" do
+    path = "@crystal-test-unix-sock-starting-with-at-symbol"
+    forced_non_abstract_path = "./#{path}"
+
+    File.exists?(path).should be_false
+
+    UNIXServer.open(forced_non_abstract_path) do
+      File.exists?(path).should be_true
+    end
+
+    File.exists?(path).should be_false
+  end
+
+  {% if flag?(:linux) %}
+    it "does not create any file for abstract server" do
+      path = "/tmp/crystal-test-unix-abstract-sock"
+      abstract_path = '@' + path
+
+      File.exists?(path).should be_false
+      File.exists?(abstract_path).should be_false
+
+      UNIXServer.open(abstract_path) do
+        File.exists?(path).should be_false
+        File.exists?(abstract_path).should be_false
+      end
+    end
+  {% end %}
+
   it "deletes socket file on close" do
     path = "/tmp/crystal-test-unix-sock"
 
@@ -217,6 +323,23 @@ describe UNIXServer do
     end
   end
 
+  {% if flag?(:linux) %}
+    it "does not delete any file on close for abstract server" do
+      path = "/tmp/crystal-test-close-unix-abstract-sock"
+
+      File.touch(path)
+      File.exists?(path).should be_true
+
+      begin
+        server = UNIXServer.new('@' + path)
+        server.close
+        File.exists?(path).should be_true
+      ensure
+        File.delete(path) if File.exists?(path)
+      end
+    end
+  {% end %}
+
   it "raises when socket file already exists" do
     path = "/tmp/crystal-test-unix-sock"
     server = UNIXServer.new(path)
@@ -231,7 +354,7 @@ describe UNIXServer do
   it "won't delete existing file on bind failure" do
     path = "/tmp/crystal-test-unix.sock"
 
-    File.write(path, "")
+    File.touch(path)
     File.exists?(path).should be_true
 
     begin
@@ -247,15 +370,34 @@ describe UNIXServer do
 
   describe "accept" do
     it "returns the client UNIXSocket" do
-      UNIXServer.open("/tmp/crystal-test-unix-sock") do |server|
-        UNIXSocket.open("/tmp/crystal-test-unix-sock") do |_|
+      path = "/tmp/crystal-test-unix-sock"
+
+      UNIXServer.open(path) do |server|
+        UNIXSocket.open(path) do |_|
           client = server.accept
           client.should be_a(UNIXSocket)
+          client.abstract?.should be_false
           client.close
         end
       end
     end
 
+    {% if flag?(:linux) %}
+      it "returns an abstract client UNIXSocket for abstract server" do
+        path = "/tmp/crystal-test-abstract-unix-sock"
+        abstract_path = '@' + path
+
+        UNIXServer.open(abstract_path) do |server|
+          UNIXSocket.open(abstract_path) do |_|
+            client = server.accept
+            client.should be_a(UNIXSocket)
+            client.abstract?.should be_true
+            client.close
+          end
+        end
+      end
+    {% end %}
+
     it "raises when server is closed" do
       server = UNIXServer.new("/tmp/crystal-test-unix-sock")
       exception = nil
@@ -280,8 +422,10 @@ describe UNIXServer do
 
   describe "accept?" do
     it "returns the client UNIXSocket" do
-      UNIXServer.open("/tmp/crystal-test-unix-sock") do |server|
-        UNIXSocket.open("/tmp/crystal-test-unix-sock") do |_|
+      path = "/tmp/crystal-test-unix-sock"
+
+      UNIXServer.open(path) do |server|
+        UNIXSocket.open(path) do |_|
           client = server.accept?.not_nil!
           client.should be_a(UNIXSocket)
           client.close
@@ -339,6 +483,36 @@ describe UNIXSocket do
     end
   end
 
+  {% if flag?(:linux) %}
+    it "sends and receives messages over an abstract STREAM socket" do
+      path = "/abstract-service.sock"
+      abstract_path = '@' + path
+
+      UNIXServer.open(abstract_path) do |server|
+        server.local_address.abstract?.should be_true
+        server.local_address.path.should eq(path)
+
+        UNIXSocket.open(abstract_path) do |client|
+          client.local_address.abstract?.should be_true
+          client.local_address.path.should eq(path)
+
+          server.accept do |sock|
+            sock.local_address.path.should eq("")
+            sock.local_address.abstract?.should be_true
+
+            sock.remote_address.path.should eq("")
+            sock.remote_address.abstract?.should be_true
+
+            client << "ping"
+            sock.gets(4).should eq("ping")
+            sock << "pong"
+            client.gets(4).should eq("pong")
+          end
+        end
+      end
+    end
+  {% end %}
+
   it "sync flag after accept" do
     path = "/tmp/crystal-test-unix-sock"
 

src/socket/address.cr

@@ -179,20 +179,46 @@ class Socket
   # Holds the local path of an UNIX address, usually coming from an opened
   # connection (e.g. `Socket#local_address`, `Socket#receive`).
   #
+  # You may also declare an abstract UNIX address, that is a virtual file
+  # that will never be created on the filesystem. An abstract UNIX address
+  # path is prefixed by a `@` character.
+  #
+  # NOTE:
+  # - Abstract UNIX addresses are supported only on some Linux systems.
+  # - If you want to use a non-abstract UNIX address starting with a `@`,
+  # prefix it with `./`, like `./@foo`.
+  #
   # Example:
   # ```
   # Socket::UNIXAddress.new("/tmp/my.sock")
+  #
+  # # Abstract UNIX socket on Linux only
+  # Socket::UNIXAddress.new("@/my.sock")
   # ```
   struct UNIXAddress < Address
     getter path : String
+    getter? abstract : Bool
 
     # :nodoc:
     MAX_PATH_SIZE = LibC::SockaddrUn.new.sun_path.size - 1
 
-    def initialize(@path : String)
-      if @path.bytesize + 1 > MAX_PATH_SIZE
+    def initialize(path : String)
+      if path.bytesize + 1 > MAX_PATH_SIZE
         raise ArgumentError.new("Path size exceeds the maximum size of #{MAX_PATH_SIZE} bytes")
       end
+
+      if path.starts_with?('@')
+        {% if flag?(:linux) %}
+          @abstract = true
+          @path = path[1..-1]
+        {% else %}
+          raise ArgumentError.new("Unsupported: cannot use abstract UNIX socket on non-Linux")
+        {% end %}
+      else
+        @abstract = false
+        @path = path
+      end
+
       @family = Family::UNIX
       @size = sizeof(LibC::SockaddrUn)
     end
@@ -204,7 +230,20 @@ class Socket
 
     protected def initialize(sockaddr : LibC::SockaddrUn*, size)
       @family = Family::UNIX
-      @path = String.new(sockaddr.value.sun_path.to_unsafe)
+
+      path = sockaddr.value.sun_path
+      if path[0]? == 0_u8
+        {% if flag?(:linux) %}
+          @abstract = true
+          @path = String.new(path.to_unsafe + 1)
+        {% else %}
+          raise ArgumentError.new("Unsupported: cannot use abstract UNIX socket on non-Linux")
+        {% end %}
+      else
+        @abstract = false
+        @path = String.new(path.to_unsafe)
+      end
+
       @size = size || sizeof(LibC::SockaddrUn)
     end
 
@@ -213,13 +252,24 @@ class Socket
     end
 
     def to_s(io)
+      if abstract?
+        io << '@'
+      end
       io << path
     end
 
     def to_unsafe : LibC::Sockaddr*
       sockaddr = Pointer(LibC::SockaddrUn).malloc
       sockaddr.value.sun_family = family
-      sockaddr.value.sun_path.to_unsafe.copy_from(@path.to_unsafe, @path.bytesize + 1)
+
+      destination = sockaddr.value.sun_path.to_slice
+      if @abstract
+        destination[0] = 0_u8
+        destination += 1
+      end
+      destination.copy_from(@path.to_unsafe, @path.bytesize)
+      destination[@path.bytesize] = 0_u8
+
       sockaddr.as(LibC::Sockaddr*)
     end
   end