Implement User/Group from_name?/from_id? like Ruby

src/crystal/system/unix.cr

@@ -0,0 +1,19 @@
+# :nodoc:
+module Crystal::System
+  def self.retry_with_buffer(function_name, max_buffer)
+    initial_buf = uninitialized UInt8[1024]
+    buf = initial_buf
+
+    while (ret = yield buf.to_slice) != 0
+      case ret
+      when LibC::ENOENT, LibC::ESRCH, LibC::EBADF, LibC::EPERM
+        return nil
+      when LibC::ERANGE
+        raise RuntimeError.from_errno(function_name) if buf.size >= max_buffer
+        buf = Bytes.new(buf.size * 2)
+      else
+        raise RuntimeError.from_errno(function_name)
+      end
+    end
+  end
+end

src/crystal/system/unix/group.cr

@@ -1,4 +1,5 @@
 require "c/grp"
+require "../unix"
 
 module Crystal::System::Group
   private GETGR_R_SIZE_MAX = 1024 * 16
@@ -12,17 +13,10 @@ module Crystal::System::Group
 
     grp = uninitialized LibC::Group
     grp_pointer = pointerof(grp)
-    initial_buf = uninitialized UInt8[1024]
-    buf = initial_buf.to_slice
-
-    ret = LibC.getgrnam_r(groupname, grp_pointer, buf, buf.size, pointerof(grp_pointer))
-    while ret == LibC::ERANGE && buf.size < GETGR_R_SIZE_MAX
-      buf = Bytes.new(buf.size * 2)
-      ret = LibC.getgrnam_r(groupname, grp_pointer, buf, buf.size, pointerof(grp_pointer))
+    System.retry_with_buffer("getgrnam_r", GETGR_R_SIZE_MAX) do |buf|
+      LibC.getgrnam_r(groupname, grp_pointer, buf, buf.size, pointerof(grp_pointer))
     end
 
-    raise RuntimeError.from_errno("getgrnam_r") if ret != 0
-
     from_struct(grp) if grp_pointer
   end
 
@@ -32,17 +26,9 @@ module Crystal::System::Group
 
     grp = uninitialized LibC::Group
     grp_pointer = pointerof(grp)
-    initial_buf = uninitialized UInt8[1024]
-    buf = initial_buf.to_slice
-
-    ret = LibC.getgrgid_r(groupid, grp_pointer, buf, buf.size, pointerof(grp_pointer))
-    while ret == LibC::ERANGE && buf.size < GETGR_R_SIZE_MAX
-      buf = Bytes.new(buf.size * 2)
-      ret = LibC.getgrgid_r(groupid, grp_pointer, buf, buf.size, pointerof(grp_pointer))
+    System.retry_with_buffer("getgrgid_r", GETGR_R_SIZE_MAX) do |buf|
+      LibC.getgrgid_r(groupid, grp_pointer, buf, buf.size, pointerof(grp_pointer))
     end
-
-    raise RuntimeError.from_errno("getgrgid_r") if ret != 0
-
     from_struct(grp) if grp_pointer
   end
 end

src/crystal/system/unix/user.cr

@@ -1,4 +1,5 @@
 require "c/pwd"
+require "../unix"
 
 module Crystal::System::User
   private GETPW_R_SIZE_MAX = 1024 * 16
@@ -13,17 +14,10 @@ module Crystal::System::User
 
     pwd = uninitialized LibC::Passwd
     pwd_pointer = pointerof(pwd)
-    initial_buf = uninitialized UInt8[1024]
-    buf = initial_buf.to_slice
-
-    ret = LibC.getpwnam_r(username, pwd_pointer, buf, buf.size, pointerof(pwd_pointer))
-    while ret == LibC::ERANGE && buf.size < GETPW_R_SIZE_MAX
-      buf = Bytes.new(buf.size * 2)
-      ret = LibC.getpwnam_r(username, pwd_pointer, buf, buf.size, pointerof(pwd_pointer))
+    System.retry_with_buffer("getpwnam_r", GETPW_R_SIZE_MAX) do |buf|
+      LibC.getpwnam_r(username, pwd_pointer, buf, buf.size, pointerof(pwd_pointer))
     end
 
-    raise RuntimeError.from_errno("getpwnam_r") if ret != 0
-
     from_struct(pwd) if pwd_pointer
   end
 
@@ -33,17 +27,10 @@ module Crystal::System::User
 
     pwd = uninitialized LibC::Passwd
     pwd_pointer = pointerof(pwd)
-    initial_buf = uninitialized UInt8[1024]
-    buf = initial_buf.to_slice
-
-    ret = LibC.getpwuid_r(id, pwd_pointer, buf, buf.size, pointerof(pwd_pointer))
-    while ret == LibC::ERANGE && buf.size < GETPW_R_SIZE_MAX
-      buf = Bytes.new(buf.size * 2)
-      ret = LibC.getpwuid_r(id, pwd_pointer, buf, buf.size, pointerof(pwd_pointer))
+    System.retry_with_buffer("getpwuid_r", GETPW_R_SIZE_MAX) do |buf|
+      LibC.getpwuid_r(id, pwd_pointer, buf, buf.size, pointerof(pwd_pointer))
     end
 
-    raise RuntimeError.from_errno("getpwuid_r") if ret != 0
-
     from_struct(pwd) if pwd_pointer
   end
 end