* luci/libs: uvl: Major rewrite of internal element handling, reworked error model...
[project/luci.git] / libs / uvl / luasrc / uvl.lua
index aaeb875f524e572e1e6837d460ef862942891c26..560be3070aa1e6f81e311192c390ab9b1f640556 100644 (file)
@@ -24,15 +24,18 @@ module( "luci.uvl", package.seeall )
 require("luci.fs")
 require("luci.util")
 require("luci.model.uci")
-require("luci.uvl.loghelper")
+require("luci.uvl.errors")
 require("luci.uvl.datatypes")
 require("luci.uvl.validation")
 require("luci.uvl.dependencies")
 
 
-TYPE_SECTION  = 0x01
-TYPE_VARIABLE = 0x02
-TYPE_ENUM     = 0x03
+TYPE_SCHEME   = 0x00
+TYPE_CONFIG   = 0x01
+TYPE_SECTION  = 0x02
+TYPE_VARIABLE = 0x03
+TYPE_OPTION   = 0x04
+TYPE_ENUM     = 0x05
 
 --- Boolean; default true;
 -- treat sections found in config but not in scheme as error
@@ -52,14 +55,7 @@ STRICT_LIST_TYPE           = true
 
 
 local default_schemedir = "/lib/uci/schema"
-
-local function _assert( condition, fmt, ... )
-       if not condition then
-               return assert( nil, string.format( fmt, ... ) )
-       else
-               return condition
-       end
-end
+local ERR = luci.uvl.errors
 
 
 --- Object constructor
@@ -74,8 +70,8 @@ function UVL.__init__( self, schemedir )
        self.packages   = { }
        self.beenthere  = { }
        self.uci                = luci.model.uci
+       self.err                = luci.uvl.errors
        self.dep                = luci.uvl.dependencies
-       self.log        = luci.uvl.loghelper
        self.datatypes  = luci.uvl.datatypes
 end
 
@@ -86,53 +82,14 @@ end
 -- @return                     String containing the reason for errors (if any)
 function UVL.get_scheme( self, scheme )
        if not self.packages[scheme] then
-               local ok, err = pcall( self.read_scheme, self, scheme )
+               local ok, err = self:read_scheme( scheme )
                if not ok then
-                       return nil, self.log.scheme_error( scheme, err )
+                       return nil, err
                end
        end
        return self.packages[scheme], nil
 end
 
---- Return a table containing the dependencies of specified section or option.
--- @param config       Name of the configuration or parsed scheme object
--- @param section      Type of the section
--- @param option       Name of the option (optional)
--- @return                     Table containing the dependencies or nil on error
--- @return                     String containing the reason for errors (if any)
-function UVL.get_dependencies( self, config, section, option )
-       config = ( type(config) == "string" and self:get_scheme(config) or config )
-
-       local deps = { }
-       local dt
-
-       if not config.sections[section] then return deps end
-
-       if option and config.variables[section][option] then
-               dt = config.variables[section][option].depends
-       else
-               dt = config.sections[section].depends
-       end
-
-       if dt then
-               for _, d in ipairs(dt) do
-                       local sdeps = { }
-                       for k, v in pairs(d) do
-                               local r = self.dep._parse_reference( k )
-                               if r then
-                                       sdeps[r] = v
-                               else
-                                       return nil,
-                                               'Ambiguous dependency reference "%s" for object "%s" given'
-                                                       %{ k, self.log.id( config.name, section, option ) }
-                               end
-                       end
-                       table.insert( deps, sdeps )
-               end
-       end
-       return deps
-end
-
 --- Validate given configuration, section or option.
 -- @param config       Name of the configuration to validate
 -- @param section      Name of the section to validate (optional)
@@ -156,71 +113,59 @@ end
 function UVL.validate_config( self, config )
 
        if not self.packages[config] then
-               local ok, err = pcall( self.read_scheme, self, config )
+               local ok, err = self:read_scheme(config)
                if not ok then
-                       return false, self.log.scheme_error( config, err )
+                       return false, err
                end
        end
 
-       self.uci.load_config( config )
-       self.beenthere = { }
-
-       local co = self.uci.get_all( config )
+       local co = luci.uvl.config( self, config )
        local sc = { }
 
-       if not co then
-               return false, 'Unable to load configuration "%s"' % config
+       self.beenthere = { }
+
+       if not co:config() then
+               return false, ERR.UCILOAD(co)
        end
 
        local function _uci_foreach( type, func )
-               local ok, err
-               for k, v in pairs(co) do
-                       if co[k]['.type'] == type then
+               for k, v in pairs(co:config()) do
+                       if v['.type'] == type then
                                sc[type] = sc[type] + 1
-                               ok, err = func( k, v )
-                               if not ok then
-                                       err = self.log.config_error( config, err )
-                                       break
-                               end
+                               local ok, err = func( k, v )
+                               if not ok then co:error(err) end
                        end
                end
-               return ok, err
        end
 
        for k, v in pairs( self.packages[config].sections ) do
                sc[k] = 0
-               local ok, err = _uci_foreach( k,
+               _uci_foreach( k,
                        function(s)
-                               local sect = luci.uvl.section( self, co, k, config, s )
-                               return self:_validate_section( sect )
+                               return self:_validate_section( co:section(s) )
                        end
                )
-               if not ok then return false, err end
        end
 
        if STRICT_UNKNOWN_SECTIONS then
-               for k, v in pairs(co) do
-                       if not self.beenthere[config..'.'..k] then
-                               return false, self.log.config_error( config,
-                                       'Section "%s" not found in scheme'
-                                               % self.log.id( config, co[k]['.type'] ) )
+               for k, v in pairs(co:config()) do
+                       local so = co:section(k)
+                       if not self.beenthere[so:cid()] then
+                               co:error(ERR.SECT_UNKNOWN(so))
                        end
                end
        end
 
        for _, k in ipairs(luci.util.keys(sc)) do
-               local s = self.packages[config].sections[k]
-
-               if s.required and sc[k] == 0 then
-                       return false, self.log.config_error( config,
-                               'Required section "%s" not found in config' % k )
-               elseif s.unique and sc[k] > 1 then
-                       return false, self.log.config_error( config,
-                               'Unique section "%s" occurs multiple times in config' % k )
+               local so = co:section(k)
+               if so:scheme('required') and sc[k] == 0 then
+                       co:error(ERR.SECT_REQUIRED(so))
+               elseif so:scheme('unique') and sc[k] > 1 then
+                       co:error(ERR.SECT_UNIQUE(so))
                end
        end
 
-       return true, nil
+       return co:ok(), co:errors()
 end
 
 --- Validate given config section.
@@ -231,28 +176,25 @@ end
 function UVL.validate_section( self, config, section )
 
        if not self.packages[config] then
-               local ok, err = pcall( self.read_scheme, self, config )
+               local ok, err = self:read_scheme( config )
                if not ok then
-                       return false, self.log.scheme_error( config, err )
+                       return false, err
                end
        end
 
-       self.uci.load_config( config )
-       self.beenthere = { }
+       local co = luci.uvl.config( self, config )
+       local so = co:section( section )
 
-       local co = self.uci.get_all( config )
+       self.beenthere = { }
 
-       if not co then
-               return false, 'Unable to load configuration "%s"' % config
+       if not co:config() then
+               return false, ERR.UCILOAD(co)
        end
 
-       if co[section] then
-               return self:_validate_section( luci.uvl.section(
-                       self, co, co[section]['.type'], config, section
-               ) )
+       if so:config() then
+               return self:_validate_section( so )
        else
-               return false, 'Section "%s" not found in config. Nothing to do.'
-                       % self.log.id( config, section )
+               return false, ERR.SECT_NOTFOUND(so)
        end
 end
 
@@ -265,131 +207,124 @@ end
 function UVL.validate_option( self, config, section, option )
 
        if not self.packages[config] then
-               local ok, err = pcall( self.read_scheme, self, config )
+               local ok, err = self:read_scheme( config )
                if not ok then
-                       return false, self.log.scheme_error( config, err )
+                       return false, err
                end
        end
 
-       self.uci.load_config( config )
-       self.beenthere = { }
-
-       local co = self.uci.get_all( config )
+       local co = luci.uvl.config( self, config )
+       local so = co:section( section )
+       local oo = so:option( option )
 
        if not co then
-               return false, 'Unable to load configuration "%s"' % config
+               return false, oerr:child(ERR.UCILOAD(config))
        end
 
-       if co[section] and co[section][option] then
-               return self:_validate_option( luci.uvl.option(
-                       self, co, co[section]['.type'], config, section, option
-               ) )
+       if so:config() and oo:config() then
+               return self:_validate_option( oo )
        else
-               return false, 'Option "%s" not found in config. Nothing to do.'
-                       % self.log.id( config, section, option )
+               return false, ERR.OPT_NOTFOUND(oo)
        end
 end
 
 
 function UVL._validate_section( self, section )
 
-       if section:values() then
-               if section:section().named == true and
-                  section:values()['.anonymous'] == true
+       if section:config() then
+               if section:scheme('named') == true and
+                  section:config('.anonymous') == true
                then
-                       return false, self.log.section_error( section,
-                               'The section of type "%s" is stored anonymously in config but must be named'
-                                       % section:sid() )
+                       return false, ERR.SECT_NAMED(section)
                end
 
                for _, v in ipairs(section:variables()) do
                        local ok, err = self:_validate_option( v )
-
                        if not ok then
-                               return ok, self.log.section_error( section, err )
+                               section:error(err)
                        end
                end
 
                local ok, err = luci.uvl.dependencies.check( self, section )
-
                if not ok then
-                       return false, err
+                       section:error(err)
                end
        else
-               return false, 'Option "%s" not found in config' % section:sid()
+               return false, ERR.SECT_NOTFOUND(section)
        end
 
-       if STRICT_UNKNOWN_OPTIONS and not section:section().dynamic then
-               for k, v in pairs(section:values()) do
-                       if k:sub(1,1) ~= "." and not self.beenthere[
-                               section:cid() .. '.' .. k
-                       ] then
-                               return false, 'Option "%s" not found in scheme'
-                                       % self.log.id( section:sid(), k )
+       if STRICT_UNKNOWN_OPTIONS and not section:scheme('dynamic') then
+               for k, v in pairs(section:config()) do
+                       local oo = section:option(k)
+                       if k:sub(1,1) ~= "." and not self.beenthere[oo:cid()] then
+                               section:error(ERR.OPT_NOTFOUND(oo))
                        end
                end
        end
 
-       return true, nil
+       return section:ok(), section:errors()
 end
 
 function UVL._validate_option( self, option, nodeps )
 
-       local item = option:option()
-       local val  = option:value()
-
-       if not item and not ( option:section() and option:section().dynamic ) then
-               return false, 'Option "%s" not found in scheme' % option:cid()
-
-       elseif item then
-               if item.required and not val then
-                       return false, 'Mandatory variable "%s" does not have a value'
-                               % option:cid()
-               end
-
-               if ( item.type == "reference" or item.type == "enum" ) and val then
-                       if not item.values or not item.values[val] then
-                               return false,
-                                       'Value "%s" of given option "%s" is not defined in %s { %s }'
-                                               %{ val or '<nil>', option:cid(), item.type,
-                                                  table.concat( luci.util.keys(item.values or {}), ", " ) }
-                       end
-               elseif item.type == "list" and val then
-                       if type(val) ~= "table" and STRICT_LIST_TYPE then
-                               return false,
-                                       'Option "%s" is defined as list but stored as plain value'
-                                               % option:cid()
-                       end
-               end
-
-               if item.datatype and val then
-                       if self.datatypes[item.datatype] then
-                               val = ( type(val) == "table" and val or { val } )
-                               for i, v in ipairs(val) do
-                                       if not self.datatypes[item.datatype]( v ) then
-                                               return false,
-                                                       'Value%s "%s" of given option "%s" does not validate as datatype "%s"'
-                                                               %{ ( #val>1 and ' #' .. i or '' ), v,
-                                                                  option:cid(), item.datatype }
+       if not option:scheme() and not option:parent():scheme('dynamic') then
+               return false, option:error(ERR.OPT_UNKNOWN(option))
+
+       elseif option:scheme() then
+               if option:scheme('required') and not option:value() then
+                       return false, option:error(ERR.OPT_REQUIRED(option))
+
+               elseif option:value() then
+                       local val = option:value()
+
+                       if option:scheme('type') == "reference" or
+                          option:scheme('type') == "enum"
+                       then
+                               if not option:scheme('values') or
+                                  not option:scheme('values')[val]
+                               then
+                                       return false, option:error( ERR.OPT_BADVALUE(
+                                               option, { val, table.concat(
+                                                       luci.util.keys(option:scheme('values') or {}), ", "
+                                               ) }
+                                       ) )
+                               end
+                       elseif option:scheme('type') == "list" then
+                               if type(val) ~= "table" and STRICT_LIST_TYPE then
+                                       return false, option:error(ERR.OPT_NOTLIST(option))
+                               end
+                       elseif option:scheme('datatype') then
+                               local dt = option:scheme('datatype')
+
+                               if self.datatypes[dt] then
+                                       val = ( type(val) == "table" and val or { val } )
+                                       for i, v in ipairs(val) do
+                                               if not self.datatypes[dt]( v ) then
+                                                       return false, option:error(
+                                                               ERR.OPT_INVVALUE(option, {v, dt})
+                                                       )
+                                               end
                                        end
+                               else
+                                       return false, option:error(ERR.OPT_DATATYPE(option, dt))
                                end
-                       else
-                               return false, 'Unknown datatype "%s" encountered'
-                                       % item.datatype
                        end
                end
 
                if not nodeps then
-                       return luci.uvl.dependencies.check( self, option )
+                       local ok, err = luci.uvl.dependencies.check( self, option )
+                       if not ok then
+                               option:error(err)
+                       end
                end
 
                local ok, err = luci.uvl.validation.check( self, option )
                if not ok and STRICT_EXTERNAL_VALIDATORS then
-                       return false, self.log.validator_error( option, err )
+                       return false, option:error(err)
                end
        end
 
-       return true, nil
+       return option:ok(), option:errors()
 end
 
 --- Find all parts of given scheme and construct validation tree.
@@ -397,67 +332,69 @@ end
 -- by yourself.
 -- @param scheme       Name of the scheme to parse
 function UVL.read_scheme( self, scheme )
+
+       local so = luci.uvl.scheme( self, scheme )
+
        local schemes = { }
        local files = luci.fs.glob(self.schemedir .. '/*/' .. scheme)
 
        if files then
                for i, file in ipairs( files ) do
-                       _assert( luci.fs.access(file), "Can't access file '%s'", file )
+                       if not luci.fs.access(file) then
+                               return so:error(ERR.SME_READ(so,file))
+                       end
 
-                       self.uci.set_confdir( luci.fs.dirname(file) )
-                       self.uci.load( luci.fs.basename(file) )
+                       local uci = luci.model.uci.cursor()
+                             uci:set_confdir( luci.fs.dirname(file) )
 
-                       table.insert( schemes, self.uci.get_all( luci.fs.basename(file) ) )
+                       local sd = uci:get_all( luci.fs.basename(file) )
+
+                       if not sd then
+                               return false, ERR.UCILOAD(so)
+                       end
+
+                       table.insert( schemes, sd )
                end
 
-               return self:_read_scheme_parts( scheme, schemes )
+               return self:_read_scheme_parts( so, schemes )
        else
-               error( 'Can not find scheme "%s" in "%s"' %{ scheme, self.schemedir } )
+               return false, so:error(ERR.SME_FIND(so, self.schemedir))
        end
 end
 
 -- Process all given parts and construct validation tree
 function UVL._read_scheme_parts( self, scheme, schemes )
 
-       -- helper function to construct identifiers for given elements
-       local function _id( c, t )
-               if c == TYPE_SECTION then
-                       return string.format(
-                               'section "%s.%s"',
-                                       scheme, t.name or '?' )
-               elseif c == TYPE_VARIABLE then
-                       return string.format(
-                               'variable "%s.%s.%s"',
-                                       scheme, t.section or '?.?', t.name or '?' )
-               elseif c == TYPE_ENUM then
-                       return string.format(
-                               'enum "%s.%s.%s"',
-                                       scheme, t.variable or '?.?.?', t.value or '?' )
-               end
-       end
-
        -- helper function to check for required fields
        local function _req( c, t, r )
                for i, v in ipairs(r) do
-                       _assert( t[v], 'Missing required field "%s" in %s', v, _id(c, t) )
+                       if not t[v] then
+                               return false, ERR.SME_REQFLD({c,t}, v)
+                       end
                end
+               return true
        end
 
        -- helper function to validate references
        local function _ref( c, t )
-               local k
+               local k, n
                if c == TYPE_SECTION then
                        k = "package"
+                       n = 1
                elseif c == TYPE_VARIABLE then
                        k = "section"
+                       n = 2
                elseif c == TYPE_ENUM then
                        k = "variable"
+                       n = 3
                end
 
                local r = luci.util.split( t[k], "." )
-               r[1] = ( #r[1] > 0 and r[1] or scheme )
+               r[1] = ( #r[1] > 0 and r[1] or scheme:sid() )
 
-               _assert( #r == c, 'Malformed %s reference in %s', k, _id(c, t) )
+               if #r ~= n then
+                       return false, ERR.SME_BADREF(scheme, k)
+               end
 
                return r
        end
@@ -467,14 +404,19 @@ function UVL._read_scheme_parts( self, scheme, schemes )
                return ( v == "true" or v == "yes" or v == "on" or v == "1" )
        end
 
+
+       local ok, err
+
        -- Step 1: get all sections
        for i, conf in ipairs( schemes ) do
                for k, v in pairs( conf ) do
                        if v['.type'] == 'section' then
 
-                               _req( TYPE_SECTION, v, { "name", "package" } )
+                               ok, err = _req( TYPE_SECTION, v, { "name", "package" } )
+                               if err then return false, scheme:error(err) end
 
-                               local r = _ref( TYPE_SECTION, v )
+                               local r, err = _ref( TYPE_SECTION, v )
+                               if err then return false, scheme:error(err) end
 
                                self.packages[r[1]] =
                                        self.packages[r[1]] or {
@@ -487,17 +429,18 @@ function UVL._read_scheme_parts( self, scheme, schemes )
                                          p.sections[v.name]  = p.sections[v.name]  or { }
                                          p.variables[v.name] = p.variables[v.name] or { }
 
-                               local s = p.sections[v.name]
+                               local s  = p.sections[v.name]
+                               local so = scheme:section(v.name)
 
                                for k, v2 in pairs(v) do
                                        if k ~= "name" and k ~= "package" and k:sub(1,1) ~= "." then
                                                if k == "depends" then
-                                                       s["depends"] = _assert(
-                                                               self:_read_dependency( v2, s["depends"] ),
-                                                               'Section "%s" in scheme "%s" has malformed ' ..
-                                                               'dependency specification in "%s"',
-                                                               v.name or '<nil>', scheme or '<nil>', k
-                                                       )
+                                                       s.depends = self:_read_dependency( v2, s.depends )
+                                                       if not s.depends then
+                                                               return false, scheme:error(
+                                                                       ERR.SME_BADDEP(so, luci.util.serialize_data(s.depends))
+                                                               )
+                                                       end
                                                elseif k == "dynamic" or k == "unique" or
                                                       k == "required" or k == "named"
                                                then
@@ -521,45 +464,55 @@ function UVL._read_scheme_parts( self, scheme, schemes )
                for k, v in pairs( conf ) do
                        if v['.type'] == "variable" then
 
-                               _req( TYPE_VARIABLE, v, { "name", "section" } )
+                               ok, err = _req( TYPE_VARIABLE, v, { "name", "section" } )
+                               if err then return false, scheme:error(err) end
 
-                               local r = _ref( TYPE_VARIABLE, v )
+                               local r, err = _ref( TYPE_VARIABLE, v )
+                               if err then return false, scheme:error(err) end
 
-                               local p = _assert( self.packages[r[1]],
-                                       'Variable "%s" in scheme "%s" references unknown package "%s"',
-                                       v.name, scheme, r[1] )
+                               local p = self.packages[r[1]]
+                               if not p then
+                                       return false, scheme:error(
+                                               ERR.SME_VBADPACK({scheme:sid(), '', v.name}, r[1])
+                                       )
+                               end
 
-                               local s = _assert( p.variables[r[2]],
-                                       'Variable "%s" in scheme "%s" references unknown section "%s"',
-                                       v.name, scheme, r[2] )
+                               local s = p.variables[r[2]]
+                               if not s then
+                                       return false, scheme:error(
+                                               ERR.SME_VBADSECT({scheme:sid(), '', v.name}, r[2])
+                                       )
+                               end
 
                                s[v.name] = s[v.name] or { }
 
-                               local t = s[v.name]
+                               local t  = s[v.name]
+                               local so = scheme:section(r[2])
+                               local to = so:option(v.name)
 
                                for k, v2 in pairs(v) do
                                        if k ~= "name" and k ~= "section" and k:sub(1,1) ~= "." then
                                                if k == "depends" then
-                                                       t["depends"] = _assert(
-                                                               self:_read_dependency( v2, t["depends"] ),
-                                                               'Invalid reference "%s" in "%s.%s.%s"',
-                                                               v2, v.name, scheme, k
-                                                       )
+                                                       t.depends = self:_read_dependency( v2, t.depends )
+                                                       if not t.depends then
+                                                               return false, scheme:error(so:error(
+                                                                       ERR.SME_BADDEP(to, luci.util.serialize_data(v2))
+                                                               ))
+                                                       end
                                                elseif k == "validator" then
-                                                       t["validators"] = _assert(
-                                                               self:_read_validator( v2, t["validators"] ),
-                                                               'Variable "%s" in scheme "%s" has malformed ' ..
-                                                               'validator specification in "%s"',
-                                                               v.name, scheme, k
-                                                       )
+                                                       t.validators = self:_read_validator( v2, t.validators )
+                                                       if not t.validators then
+                                                               return false, scheme:error(so:error(
+                                                                       ERR.SME_BADVAL(to, luci.util.serialize_data(v2))
+                                                               ))
+                                                       end
                                                elseif k == "valueof" then
                                                        local values, err = self:_read_reference( v2 )
-
-                                                       _assert( values,
-                                                               'Variable "%s" in scheme "%s" has invalid ' ..
-                                                               'reference specification:\n%s',
-                                                                       v.name, scheme, err )
-
+                                                       if err then
+                                                               return false, scheme:error(so:error(
+                                                                       ERR.REFERENCE(to, luci.util.serialize_data(v2)):child(err)
+                                                               ))
+                                                       end
                                                        t.type   = "reference"
                                                        t.values = values
                                                elseif k == "required" then
@@ -582,26 +535,41 @@ function UVL._read_scheme_parts( self, scheme, schemes )
                for k, v in pairs( conf ) do
                        if v['.type'] == "enum" then
 
-                               _req( TYPE_ENUM, v, { "value", "variable" } )
+                               ok, err = _req( TYPE_ENUM, v, { "value", "variable" } )
+                               if err then return false, scheme:error(err) end
+
+                               local r, err = _ref( TYPE_ENUM, v )
+                               if err then return false, scheme:error(err) end
+
+                               local p = self.packages[r[1]]
+                               if not p then
+                                       return false, scheme:error(
+                                               ERR.SME_EBADPACK({scheme:sid(), '', '', v.value}, r[1])
+                                       )
+                               end
+
+                               local s = p.variables[r[2]]
+                               if not s then
+                                       return false, scheme:error(
+                                               ERR.SME_EBADSECT({scheme:sid(), '', '', v.value}, r[2])
+                                       )
+                               end
 
-                               local r = _ref( TYPE_ENUM, v )
-                               local p = _assert( self.packages[r[1]],
-                                       'Enum "%s" in scheme "%s" references unknown package "%s"',
-                                       v.value, scheme, r[1] )
+                               local t = s[r[3]]
+                               if not t then
+                                       return false, scheme:error(
+                                               ERR.SME_EBADOPT({scheme:sid(), '', '', v.value}, r[3])
+                                       )
+                               end
 
-                               local s = _assert( p.variables[r[2]],
-                                       'Enum "%s" in scheme "%s" references unknown section "%s"',
-                                       v.value, scheme, r[2] )
 
-                               local t = _assert( s[r[3]],
-                                       'Enum "%s" in scheme "%s", section "%s" references ' ..
-                                       'unknown variable "%s"',
-                                       v.value, scheme, r[2], r[3] )
+                               local so = scheme:section(r[2])
+                               local oo = so:option(r[3])
+                               local eo = oo:enum(v.value)
 
-                               _assert( t.type == "enum",
-                                       'Enum "%s" in scheme "%s", section "%s" references ' ..
-                                       'variable "%s" with non enum type "%s"',
-                                       v.value, scheme, r[2], r[3], t.type )
+                               if t.type ~= "enum" then
+                                       return false, scheme:error(ERR.SME_EBADTYPE(eo))
+                               end
 
                                if not t.values then
                                        t.values = { [v.value] = v.title or v.value }
@@ -614,22 +582,22 @@ function UVL._read_scheme_parts( self, scheme, schemes )
                                end
 
                                if v.default then
-                                       _assert( not t.default,
-                                               'Enum "%s" in scheme "%s", section "%s" redeclares ' ..
-                                               'the default value of variable "%s"',
-                                               v.value, scheme, r[2], v.variable )
-
+                                       if t.default then
+                                               return false, scheme:error(ERR.SME_EBADDEF(eo))
+                                       end
                                        t.default = v.value
                                end
 
                                if v.depends then
-                                       t.enum_depends[v.value] = _assert(
-                                               self:_read_dependency(
-                                                       v.depends, t.enum_depends[v.value]
-                                               ),
-                                               'Invalid reference "%s" in "%s.%s.%s.%s"',
-                                               v.depends, scheme, r[2], r[3], v.value
+                                       t.enum_depends[v.value] = self:_read_dependency(
+                                               v.depends, t.enum_depends[v.value]
                                        )
+
+                                       if not t.enum_depends[v.value] then
+                                               return false, scheme:error(so:error(oo:error(
+                                                       ERR.SME_BADDEP(eo, luci.util.serialize_data(v.depends))
+                                               )))
+                                       end
                                end
                        end
                end
@@ -708,20 +676,14 @@ function UVL._read_reference( self, values )
                local ref = luci.util.split(value, ".")
 
                if #ref == 2 or #ref == 3 then
-                       self.uci.load_config(ref[1])
-                       local co = self.uci.get_all(ref[1])
+                       local co = luci.uvl.config( self, ref[1] )
+                       if not co:config() then return false, ERR.UCILOAD(ref[1]) end
 
-                       if not co then
-                               return nil, 'Can not load config "%s" for reference "%s"'
-                                       %{ ref[1], value }
-                       end
-
-                       for k, v in pairs(co) do
+                       for k, v in pairs(co:config()) do
                                if v['.type'] == ref[2] then
                                        if #ref == 2 then
                                                if v['.anonymous'] == true then
-                                                       return nil, 'Illegal reference "%s" to an anonymous section'
-                                                               % value
+                                                       return false, ERR.SME_INVREF('', value)
                                                end
                                                val[k] = k      -- XXX: title/description would be nice
                                        elseif v[ref[3]] then
@@ -730,7 +692,7 @@ function UVL._read_reference( self, values )
                                end
                        end
                else
-                       return nil, 'Malformed reference "%s"' % value
+                       return false, ERR.SME_BADREF('', value)
                end
        end
 
@@ -742,7 +704,10 @@ function UVL._resolve_function( self, value )
        local path = luci.util.split(value, ".")
 
        for i=1, #path-1 do
-               local stat, mod = pcall(require, table.concat(path, ".", 1, i))
+               local stat, mod = luci.util.copcall(
+                       require, table.concat(path, ".", 1, i)
+               )
+
                if stat and mod then
                        for j=i+1, #path-1 do
                                if not type(mod) == "table" then
@@ -762,73 +727,282 @@ function UVL._resolve_function( self, value )
 end
 
 
---- Object representation of a scheme/config section.
--- @class      module
+--- Object representation of an uvl item - base class.
+uvlitem = luci.util.class()
+
+function uvlitem.cid(self)
+       return table.concat( self.cref, '.' )
+end
+
+function uvlitem.sid(self)
+       return table.concat( self.sref, '.' )
+end
+
+function uvlitem.scheme(self, opt)
+       local s
+
+       if #self.sref == 4 or #self.sref == 3 then
+               s = self.s
+                       .packages[self.sref[1]]
+                       .variables[self.sref[2]][self.sref[3]]
+       elseif #self.sref == 2 then
+               s = self.s
+                       .packages[self.sref[1]]
+                       .sections[self.sref[2]]
+       else
+               s = self.s
+                       .packages[self.sref[1]]
+       end
+
+       if s and opt then
+               return s[opt]
+       elseif s then
+               return s
+       end
+end
+
+function uvlitem.config(self, opt)
+       local c
+
+       if #self.cref == 4 or #self.cref == 3 then
+               c = self.c[self.cref[2]][self.cref[3]]
+       elseif #self.cref == 2 then
+               c = self.c[self.cref[2]]
+       else
+               c = self.c
+       end
+
+       if c and opt then
+               return c[opt]
+       elseif c then
+               return c
+       end
+end
+
+function uvlitem.title(self)
+       return self:scheme() and self:scheme('title') or
+               self.cref[3] or self.cref[2] or self.cref[1]
+end
+
+function uvlitem.type(self)
+       if self.t == luci.uvl.TYPE_CONFIG then
+               return 'config'
+       elseif self.t == luci.uvl.TYPE_SECTION then
+               return 'section'
+       elseif self.t == luci.uvl.TYPE_OPTION then
+               return 'option'
+       elseif self.t == luci.uvl.TYPE_ENUM then
+               return 'enum'
+       end
+end
+
+function uvlitem.error(self, ...)
+       if not self.e then
+               local errconst = { ERR.CONFIG, ERR.SECTION, ERR.OPTION, ERR.OPTION }
+               self.e = errconst[#self.cref]( self )
+       end
+
+       return self.e:child( ... )
+end
+
+function uvlitem.errors(self)
+       return self.e
+end
+
+function uvlitem.ok(self)
+       return not self:errors()
+end
+
+function uvlitem.parent(self)
+       if self.p then
+               return self.p
+       elseif #self.cref == 3 or #self.cref == 4 then
+               return luci.uvl.section( self.s, self.c, self.cref[1], self.cref[2] )
+       elseif #self.cref == 2 then
+               return luci.uvl.config( self.s, self.c, self.cref[1] )
+       else
+               return nil
+       end
+end
+
+
+--- Object representation of a scheme.
+-- @class      scheme
 -- @cstyle     instance
--- @name       luci.uvl.section
+-- @name       luci.uvl.scheme
 
---- Section instance constructor.
+--- Scheme instance constructor.
 -- @class                      function
--- @name                       section
+-- @name                       scheme
 -- @param scheme       Scheme instance
 -- @param co           Configuration data
--- @param st           Section type
 -- @param c                    Configuration name
--- @param s                    Section name
--- @return                     Section instance
-section = luci.util.class()
+-- @return                     Config instance
+scheme = luci.util.class(uvlitem)
+
+function scheme.__init__(self, scheme, co, c)
+       if not c then
+               c, co = co, nil
+       end
 
-function section.__init__(self, scheme, co, st, c, s)
-       self.csection = co[s]
-       self.ssection = scheme.packages[c].sections[st]
-       self.cref     = { c, s }
-       self.sref     = { c, st }
-       self.scheme   = scheme
-       self.config   = co
-       self.type     = luci.uvl.TYPE_SECTION
+       if not co then
+               local uci = luci.model.uci.cursor()
+               co = uci:get_all(c)
+       end
+
+       self.cref = { c }
+       self.sref = { c }
+       self.c    = co
+       self.s    = scheme
+       self.t    = luci.uvl.TYPE_SCHEME
 end
 
---- Get the config path of this section.
--- @return     String containing the identifier
-function section.cid(self)
-       return ( self.cref[1] or '?' ) .. '.' .. ( self.cref[2] or '?' )
+--- Add an error to scheme.
+-- @return     Scheme error context
+function scheme.error(self, ...)
+       if not self.e then self.e = ERR.SCHEME( self ) end
+       return self.e:child( ... )
 end
 
---- Get the scheme path of this section.
--- @return     String containing the identifier
-function section.sid(self)
-       return ( self.sref[1] or '?' ) .. '.' .. ( self.sref[2] or '?' )
+--- Get an associated config object.
+-- @return     Config instance
+function scheme.config(self)
+       local co = luci.uvl.config( self.s, self.cref[1] )
+             co.p = self
+
+       return co
 end
 
---- Get all configuration values within this section.
--- @return     Table containing the values
-function section.values(self)
-       return self.csection
+--- Get all section objects associated with this scheme.
+-- @return     Table containing all associated luci.uvl.section instances
+function scheme.sections(self)
+       local v = { }
+       if self.s.packages[self.sref[1]].sections then
+               for o, _ in pairs( self.s.packages[self.sref[1]].sections ) do
+                       table.insert( v, luci.uvl.option(
+                               self.s, self.c, self.cref[1], self.cref[2], o
+                       ) )
+               end
+       end
+       return v
 end
 
---- Get the associated section information in scheme.
--- @return     Table containing the scheme properties
-function section.section(self)
-       return self.ssection
+--- Get an associated section object.
+-- @param s    Section to select
+-- @return     Section instance
+function scheme.section(self, s)
+       local so = luci.uvl.section( self.s, self.c, self.cref[1], s )
+             so.p = self
+
+       return so
+end
+
+
+--- Object representation of a config.
+-- @class      config
+-- @cstyle     instance
+-- @name       luci.uvl.config
+
+--- Config instance constructor.
+-- @class                      function
+-- @name                       config
+-- @param scheme       Scheme instance
+-- @param co           Configuration data
+-- @param c                    Configuration name
+-- @return                     Config instance
+config = luci.util.class(uvlitem)
+
+function config.__init__(self, scheme, co, c)
+       if not c then
+               c, co = co, nil
+       end
+
+       if not co then
+               local uci = luci.model.uci.cursor()
+               co = uci:get_all(c)
+       end
+
+       self.cref = { c }
+       self.sref = { c }
+       self.c    = co
+       self.s    = scheme
+       self.t    = luci.uvl.TYPE_CONFIG
+end
+
+--- Get all section objects associated with this config.
+-- @return     Table containing all associated luci.uvl.section instances
+function config.sections(self)
+       local v = { }
+       if self.s.packages[self.sref[1]].sections then
+               for o, _ in pairs( self.s.packages[self.sref[1]].sections ) do
+                       table.insert( v, luci.uvl.option(
+                               self.s, self.c, self.cref[1], self.cref[2], o
+                       ) )
+               end
+       end
+       return v
+end
+
+--- Get an associated section object.
+-- @param s    Section to select
+-- @return     Section instance
+function config.section(self, s)
+       local so = luci.uvl.section( self.s, self.c, self.cref[1], s )
+             so.p = self
+
+       return so
+end
+
+
+--- Object representation of a scheme/config section.
+-- @class      module
+-- @cstyle     instance
+-- @name       luci.uvl.section
+
+--- Section instance constructor.
+-- @class                      function
+-- @name                       section
+-- @param scheme       Scheme instance
+-- @param co           Configuration data
+-- @param c                    Configuration name
+-- @param s                    Section name
+-- @return                     Section instance
+section = luci.util.class(uvlitem)
+
+function section.__init__(self, scheme, co, c, s)
+       self.cref = { c, s }
+       self.sref = { c, co[s] and co[s]['.type'] or s }
+       self.c    = co
+       self.s    = scheme
+       self.t    = luci.uvl.TYPE_SECTION
 end
 
 --- Get all option objects associated with this section.
 -- @return     Table containing all associated luci.uvl.option instances
 function section.variables(self)
        local v = { }
-       if self.scheme.packages[self.sref[1]].variables[self.sref[2]] then
+       if self.s.packages[self.sref[1]].variables[self.sref[2]] then
                for o, _ in pairs(
-                       self.scheme.packages[self.sref[1]].variables[self.sref[2]]
+                       self.s.packages[self.sref[1]].variables[self.sref[2]]
                ) do
                        table.insert( v, luci.uvl.option(
-                               self.scheme, self.config, self.sref[2],
-                               self.cref[1], self.cref[2], o
+                               self.s, self.c, self.cref[1], self.cref[2], o
                        ) )
                end
        end
        return v
 end
 
+--- Get an associated option object.
+-- @param o    Option to select
+-- @return     Option instance
+function section.option(self, o)
+       local oo = luci.uvl.option( self.s, self.c, self.cref[1], self.cref[2], o )
+             oo.p = self
+
+       return oo
+end
+
 
 --- Object representation of a scheme/config option.
 -- @class      module
@@ -840,53 +1014,65 @@ end
 -- @name                       option
 -- @param scheme       Scheme instance
 -- @param co           Configuration data
--- @param st           Section type
 -- @param c                    Configuration name
 -- @param s                    Section name
 -- @param o                    Option name
 -- @return                     Option instance
-option = luci.util.class()
-
-function option.__init__(self, scheme, co, st, c, s, o)
-       self.coption = co[s] and co[s][o] or nil
-       self.soption = scheme.packages[c].variables[st][o]
-       self.cref    = { c, s, o }
-       self.sref    = { c, st, o }
-       self.scheme  = scheme
-       self.config  = co
-       self.type    = luci.uvl.TYPE_OPTION
-end
-
---- Get the config path of this option.
--- @return     String containing the identifier
-function option.cid(self)
-       return ( self.cref[1] or '?' ) .. '.' ..
-                  ( self.cref[2] or '?' ) .. '.' ..
-                  ( self.cref[3] or '?' )
-end
-
---- Get the scheme path of this option.
--- @return     String containing the identifier
-function option.sid(self)
-       return ( self.sref[1] or '?' ) .. '.' ..
-                  ( self.sref[2] or '?' ) .. '.' ..
-                  ( self.sref[3] or '?' )
+option = luci.util.class(uvlitem)
+
+function option.__init__(self, scheme, co, c, s, o)
+       self.cref = { c, s, o }
+       self.sref = { c, co[s] and co[s]['.type'] or s, o }
+       self.c    = co
+       self.s    = scheme
+       self.t    = luci.uvl.TYPE_OPTION
 end
 
 --- Get the value of this option.
 -- @return     The associated configuration value
 function option.value(self)
-       return self.coption
-end
-
---- Get the associated option information in scheme.
--- @return     Table containing the scheme properties
-function option.option(self)
-       return self.soption
+       return self:config()
 end
 
 --- Get the associated section information in scheme.
 -- @return     Table containing the scheme properties
 function option.section(self)
-       return self.scheme.packages[self.sref[1]].sections[self.sref[2]]
+       return self.s.packages[self.sref[1]].sections[self.sref[2]]
+end
+
+--- Construct an enum object instance from given or default value.
+-- @param v    Value to select
+-- @return     Enum instance for selected value
+function option.enum(self, val)
+       return enum(
+               self.s, self.c,
+               self.cref[1], self.cref[2], self.cref[3],
+               val or self:value()
+       )
+end
+
+
+--- Object representation of a enum value.
+-- @class      module
+-- @cstyle     instance
+-- @name       luci.uvl.enum
+
+--- Section instance constructor.
+-- @class                      function
+-- @name                       enum
+-- @param scheme       Scheme instance
+-- @param co           Configuration data
+-- @param c                    Configuration name
+-- @param s                    Section name
+-- @param o                    Enum name
+-- @param v                    Enum value
+-- @return                     Enum value instance
+enum = luci.util.class(option)
+
+function enum.__init__(self, scheme, co, c, s, o, v)
+       self.cref = { c, s, o, v }
+       self.sref = { c, co[s] and co[s]['.type'] or s, o, v }
+       self.c    = co
+       self.s    = scheme
+       self.t    = luci.uvl.TYPE_ENUM
 end