Resolve the current user home even when $HOME is not set

* Fixes oracle#2784
* Use getpwuid_r(getuid()) for simplicity and reliability.

CHANGELOG.md

@@ -39,6 +39,7 @@ Compatibility:
 * Support `offset` keyword argument for `String#unpack` and `String#unpack1` (@andrykonchin).
 * Fix `Process.detach` and cast `pid` argument to `Integer` (#2782, @andrykonchin).
 * `rb_to_id()` should create a static `ID`, used by RMagick (@eregon).
+* Resolve the current user home even when `$HOME` is not set (#2784, @eregon)
 
 Performance:
 

mx.truffleruby/native

@@ -1,6 +1,6 @@
 GRAALVM_SKIP_ARCHIVE=true
 DYNAMIC_IMPORTS=/tools,/compiler,/substratevm
-COMPONENTS=TruffleRuby,suite:tools,GraalVM compiler,SubstrateVM
+COMPONENTS=TruffleRuby,suite:tools,GraalVM compiler,SubstrateVM,Native Image
 NATIVE_IMAGES=suite:sulong,lib:rubyvm
 # To also create the standalone
 DISABLE_INSTALLABLES=false

spec/ruby/core/dir/home_spec.rb

@@ -19,6 +19,18 @@
     it "returns a non-frozen string" do
       Dir.home.should_not.frozen?
     end
+
+    it "returns a string with the filesystem encoding" do
+      Dir.home.encoding.should == Encoding.find("filesystem")
+    end
+
+    platform_is_not :windows do
+      it "works even if HOME is unset" do
+        ENV.delete('HOME')
+        Dir.home.should.start_with?('/')
+        Dir.home.encoding.should == Encoding.find("filesystem")
+      end
+    end
   end
 
   describe "when called with the current user name" do
@@ -37,6 +49,10 @@
     it "returns a non-frozen string" do
       Dir.home(ENV['USER']).should_not.frozen?
     end
+
+    it "returns a string with the filesystem encoding" do
+      Dir.home(ENV['USER']).encoding.should == Encoding.find("filesystem")
+    end
   end
 
   it "raises an ArgumentError if the named user doesn't exist" do

src/main/c/truffleposix/truffleposix.c

@@ -177,6 +177,52 @@ int truffleposix_getrusage(double times[4]) {
    return 0;
 }
 
+// Keep in sync with truffleposix_get_user_home() below
+char* truffleposix_get_current_user_home(void) {
+  uid_t uid = getuid();
+
+  struct passwd entry;
+  struct passwd *result = NULL;
+  int ret;
+
+  size_t buffer_size = sysconf(_SC_GETPW_R_SIZE_MAX);
+  if (buffer_size <= 0) {
+    buffer_size = 16384;
+  }
+
+  char *buffer = malloc(buffer_size);
+  if (buffer == NULL) {
+    return NULL;
+  }
+
+retry:
+  ret = getpwuid_r(uid, &entry, buffer, buffer_size, &result);
+  if (result != NULL) {
+    char *home = strdup(entry.pw_dir);
+    free(buffer);
+    return home;
+  } else if (ret == ERANGE) {
+    buffer_size *= 2;
+    free(buffer);
+    buffer = malloc(buffer_size);
+    if (buffer == NULL) {
+      return NULL;
+    }
+    goto retry;
+  } else if (ret == EINTR) {
+    goto retry;
+  } else if (ret == EIO || ret == EMFILE || ret == ENFILE) {
+    free(buffer);
+    errno = ret;
+    return NULL;
+  } else { // result == NULL, which means not found
+    // ret should be 0 in that case according to the man page, but it doesn't seem to always hold
+    free(buffer);
+    return strdup("");
+  }
+}
+
+// Keep in sync with truffleposix_get_current_user_home() above
 char* truffleposix_get_user_home(const char *name) {
   struct passwd entry;
   struct passwd *result = NULL;

src/main/ruby/truffleruby/core/dir.rb

@@ -209,21 +209,36 @@ def exist?(path)
     alias_method :exists?, :exist?
 
     def home(user = nil)
-      if user
+      user = StringValue(user) unless Primitive.nil?(user)
+
+      if user and !user.empty?
         ptr = Truffle::POSIX.truffleposix_get_user_home(user)
         if !ptr.null?
-          home = ptr.read_string
+          home = ptr.read_string.force_encoding(Encoding.filesystem)
           Truffle::POSIX.truffleposix_free ptr
           raise ArgumentError, "user #{user} does not exist" if home.empty?
           home
         else
           Errno.handle
         end
       else
-        home = ENV['HOME']
-        raise ArgumentError, "couldn't find HOME environment variable when expanding '~'" if Primitive.nil? home
+        home = ENV['HOME'].dup
+        if home
+          home = home.dup.force_encoding(Encoding.filesystem)
+        else
+          ptr = Truffle::POSIX.truffleposix_get_current_user_home
+          if !ptr.null?
+            home = ptr.read_string.force_encoding(Encoding.filesystem)
+            Truffle::POSIX.truffleposix_free ptr
+            raise ArgumentError, "couldn't find home for uid `#{Process.uid}'" if home.empty?
+            home
+          else
+            Errno.handle
+          end
+        end
+
         raise ArgumentError, 'non-absolute home' unless home.start_with?('/')
-        home.dup
+        home
       end
     end
 

src/main/ruby/truffleruby/core/posix.rb

@@ -301,6 +301,7 @@ def self.unsetenv(name)
 
   # Other routines
   attach_function :crypt, [:string, :string], :string, LIBCRYPT
+  attach_function :truffleposix_get_current_user_home, [], :pointer, LIBTRUFFLEPOSIX
   attach_function :truffleposix_get_user_home, [:string], :pointer, LIBTRUFFLEPOSIX
   attach_function :truffleposix_free, [:pointer], :void, LIBTRUFFLEPOSIX