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Published: Sep 11, 2020 License: Apache-2.0 Imports: 14 Imported by: 4



Package config provides functionality for working with configuration files and command line arguments to a Granitic application.

Grantic uses JSON files to store component definitions (declarations of, and relationships between, components to run in the IoC container) and configuration (variables used by IoC components that may vary between environments and settings for Grantic's built-in facilities). A definition of the use and syntax of these files are outside of the scope of a GoDoc page, but are described in detail at and

This package defines functionality for loading a JSON file (from a filesystem or via HTTP) and merging multiple files into a single view. This is a key concept in Granitic.

Given a folder of configuration files called conf:


starting a Grantic application with:


The following will take place. Firstly the files would be expanded into a flat list of paths/URIs

The the files will be merged together from left, using the the first file as a base. In this example, and conf/sub/a.json will be merged together, then result of that merge will be merged with conf/sub/b.json and so on.

For named fields (in a JSON object/map), the process of merging is fairly obvious. When merging files A and B, a field that is defined in both files will have the value of the field used in file B in the merged output. For example,


	"database": {
		"host": "localhost",
		"port": 3306,
		"flags": ["a", "b", "c"]



	"database": {
		"host": "remotehost",
		"flags": ["d"]

woud merge to:

	"database": {
		"host": "remotehost",
		"port": 3306,
		"flags": ["d"]

The merging of configuration files occurs exactly above, but when component definition files are merged, arrays are joined, not overwritten. For example:

{ "methods": ["GET"] }

merged with;

{ "methods": ["POST"] }

would result in:

{ "methods": ["GET", "POST"] }

Another core concept used by the types in this package is a config path. This is the absolute path to field in the eventual merged configuration file with a dot-delimited notation. E.g "".



View Source
const (
	Unset       = -2
	JSONUnknown = -1
	JSONString  = 1
	JSONArray   = 2
	JSONMap     = 3
	JSONBool    = 4

Used by code that needs to know what type of JSON data structure resides at a particular path before operating on it.

View Source
const JSONPathSeparator string = "."

JSONPathSeparator is the character used to delimit paths to config values.


This section is empty.


func ExpandToFilesAndURLs

func ExpandToFilesAndURLs(paths []string) ([]string, error)

ExpandToFilesAndURLs takes a slice that may be a mixture of URLs, file paths and directory paths and returns a list of URLs and file paths, recursively expanding any non-empty directories into a list of files. Returns an error if there is a problem traversing directories of if any of the supplied file paths does not exist.

func FileListFromPath

func FileListFromPath(path string) ([]string, error)

FileListFromPath takes a string that could represent a path to a directory or a path to a file and returns a list of file paths. If the path is to directory, any files in that directory are included in the result. Any sub-directories are recursively entered.

func FindJSONFilesInDir

func FindJSONFilesInDir(dirPath string) ([]string, error)

FindJSONFilesInDir finds all files with a .json extension in the supplied directory path, recursively checking sub-directories. Note that each directory's contents are examined and added to the list of files lexicographically, so any files in a sub-directory 'b' would appear in the resulting list of files before 'c.json'

func JSONType

func JSONType(value interface{}) int

JSONType determines the apparent JSONType of the supplied Go interface.

func WriteJSONConfig added in v2.2.0

func WriteJSONConfig(a *Accessor, f string) error

WriteJSONConfig writes the contents of a config.Accessor to a file


type Accessor

type Accessor struct {
	// The merged JSON configuration in object form.
	JSONData map[string]interface{}

	// Logger used by Granitic framework components. Automatically injected.
	FrameworkLogger logging.Logger

A Accessor provides access to a merged view of configuration files during the initialisation and configuration of the Granitic IoC container.

func (*Accessor) Array

func (ac *Accessor) Array(path string) ([]interface{}, error)

Array returns the value of an array of JSON obects at the supplied path. Caution should be used when calling this method as behaviour is undefined for JSON arrays of JSON types other than object.

func (*Accessor) BoolVal

func (ac *Accessor) BoolVal(path string) (bool, error)

BoolVal returns the bool value of the JSON bool at the supplied path. An error will be returned if the value is not a JSON bool. Note this method only suports the JSON definition of bools (true, false) not the Go definition (true, false, 1, 0 etc).

func (*Accessor) Float64Val

func (ac *Accessor) Float64Val(path string) (float64, error)

Float64Val returns the float64 value of the JSON number at the supplied path. An error will be returned if the value is not a JSON number.

func (*Accessor) Flush

func (ac *Accessor) Flush()

Flush removes internal references to the (potentially very large) merged JSON data so the associated memory can be recovered during the next garbage collection.

func (*Accessor) IntVal

func (ac *Accessor) IntVal(path string) (int, error)

IntVal returns the int value of the JSON number at the supplied path. JSON numbers are internally represented by Go as a float64, so no error will be returned, but data might be lost if the JSON number does not actually represent an int. An error will be returned if the value is not a JSON number or cannot be converted to an int.

func (*Accessor) ObjectVal

func (ac *Accessor) ObjectVal(path string) (map[string]interface{}, error)

ObjectVal returns a map representing a JSON object or nil if the path does not exist of points to a null JSON value. An error is returned if the value cannot be interpreted as a JSON object.

func (*Accessor) PathExists

func (ac *Accessor) PathExists(path string) bool

PathExists check to see whether the supplied dot-delimited path exists in the configuration and points to a non-null JSON value.

func (*Accessor) Populate

func (ac *Accessor) Populate(path string, target interface{}) error

Populate sets the fields on the supplied target object using the JSON data at the supplied path. This is achieved using Go's json.Marshal to convert the data back into text JSON and then json.Unmarshal to unmarshal back into the target.

func (*Accessor) SetField

func (ac *Accessor) SetField(fieldName string, path string, target interface{}) error

SetField takes a target Go interface and uses the data a the supplied path to populated the named field on the target. The target must be a pointer to a struct. The field must be a string, bool, int, float63, string[interface{}] map or a slice of one of those types. An eror will be returned if the target field, is missing, not settable or incompatible with the JSON value at the supplied path.

func (*Accessor) StringVal

func (ac *Accessor) StringVal(path string) (string, error)

StringVal returns the string value of the JSON string at the supplied path. Does not convert other types to a string, so will return an error if the value is not a JSON string.

func (*Accessor) Value

func (ac *Accessor) Value(path string) interface{}

Value returns the JSON value at the supplied path or nil if the path does not exist of points to a null JSON value.

type ContentParser

type ContentParser interface {
	ParseInto(data []byte, target interface{}) error
	Extensions() []string
	ContentTypes() []string

A ContentParser can take a []byte of some structured file type (e.g. YAML, JSON() and convert into a map[string]interface{} representation

type EmptyFileError

type EmptyFileError struct {
	Message string

EmptyFileError is a marker error to indicate that a config file was logically empty

func (EmptyFileError) Error

func (efe EmptyFileError) Error() string

Error returns the message associated with this error

type InitialSettings

type InitialSettings struct {

	// The level at which messages from Granitic components used before configuration files can be loaded (the initiator,
	// logger, IoC container, JSON merger etc.) will be logged. As soon as configuration has been loaded, this value will
	// be discarded in favour of LogLevels defined in that configuration.
	FrameworkLogLevel logging.LogLevel

	// Files, directories and URLs from which JSON configuration should be loaded and merged.
	Configuration []string

	// The time at which the application was started (to allow accurate timing of the IoC container start process).
	StartTime time.Time

	// An (optional) unique identifier for this instance of a Granitic application.
	InstanceID string

	// A base 64 serialised version of Granitic's built-in configuration files
	BuiltInConfig *string

	// Additional parsers to support config files in a format other than JSON
	ConfigParsers []ContentParser

	// Exit immediately after container has successfully started
	DryRun bool

	// Buffer messages and only log them when application logging has been configured
	DeferBootstrapLogging bool

	// A path to write the merged view of configuration to (then exit)
	MergedConfigPath string

	// Create a UUID and use it as the instance ID
	GenerateInstanceUUID bool

InitialSettings contains settings that are needed by Granitic before configuration files can be loaded and parsed. See package granitic for more information on how this is used when starting a Granitic application with command line arguments or supplying an instance of this struct programmatically.

func InitialSettingsFromEnvironment

func InitialSettingsFromEnvironment() *InitialSettings

InitialSettingsFromEnvironment builds an InitialSettings and populates it with defaults or the values of command line arguments if available.

type JSONContentParser

type JSONContentParser struct {

JSONContentParser supports the loading and parsing of JSON configuration and component definition files

func (*JSONContentParser) ContentTypes

func (jcp *JSONContentParser) ContentTypes() []string

ContentTypes returns the MIME media types/HTTP content-types that will be considered to represent JSON

func (*JSONContentParser) Extensions

func (jcp *JSONContentParser) Extensions() []string

Extensions returns the list of filename extensions (lowercase, without leading dot) that will be considered to be JSON files.

func (*JSONContentParser) ParseInto

func (jcp *JSONContentParser) ParseInto(data []byte, target interface{}) error

ParseInto takes a byte array that is assumed to be serialised JSON and attempts to parse that into the supplied target object

type JSONMerger

type JSONMerger struct {
	// Logger used by Granitic framework components. Automatically injected.
	Logger logging.Logger

	// True if arrays should be joined when merging; false if the entire conetnts of the array should be overwritten.
	MergeArrays bool

	DefaultParser ContentParser
	// contains filtered or unexported fields

A JSONMerger can merge a sequence of JSON configuration files (from a filesystem or HTTP URL) into a single view of configuration that will be used to configure Grantic's facilities and the user's IoC components. See the top of this page for a brief explanation of how merging works.

func NewJSONMergerWithDirectLogging

func NewJSONMergerWithDirectLogging(l logging.Logger, cp ContentParser) *JSONMerger

NewJSONMergerWithDirectLogging creates a JSONMerger that uses the supplied logger

func NewJSONMergerWithManagedLogging

func NewJSONMergerWithManagedLogging(flm *logging.ComponentLoggerManager, cp ContentParser) *JSONMerger

NewJSONMergerWithManagedLogging creates a JSONMerger with a Logger managed by Granitic

func (*JSONMerger) LoadAndMergeConfig

func (jm *JSONMerger) LoadAndMergeConfig(files []string) (map[string]interface{}, error)

LoadAndMergeConfig takes a list of file paths or URIs to JSON files and merges them into a single in-memory object representation. See the top of this page for a brief explanation of how merging works. Returns an error if a remote URI returned a 4xx or 5xx response code, a file or folder could not be accessed or if two files could not be merged dued to JSON parsing errors.

func (*JSONMerger) LoadAndMergeConfigWithBase

func (jm *JSONMerger) LoadAndMergeConfigWithBase(config map[string]interface{}, files []string) (map[string]interface{}, error)

LoadAndMergeConfigWithBase takes a representation of a JSON file that has already been parsed and merges the contents of the supplied list of JSON files into that in-memory representation and returns the file merged version.

func (*JSONMerger) RegisterContentParser

func (jm *JSONMerger) RegisterContentParser(cp ContentParser)

RegisterContentParser adds the supplied ContentParser to the set of parsers that might be eligible to parse a file/stream

type MissingPathError

type MissingPathError struct {
	// contains filtered or unexported fields

MissingPathError indicates that the a problem was caused by there being no value at the supplied config path

func (MissingPathError) Error

func (mp MissingPathError) Error() string

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