v2 – github.com/pelletier/go-toml/v2 Index | Examples | Files | Directories

package toml

import "github.com/pelletier/go-toml/v2"

Package toml is a library to read and write TOML documents.

Index

Examples

Functions

func Marshal 

func Marshal(v interface{}) ([]byte, error)

Marshal serializes a Go value as a TOML document.

It is a shortcut for Encoder.Encode() with the default options.

Example

Code: 

{
	type MyConfig struct {
		Version int
		Name    string
		Tags    []string
	}

	cfg := MyConfig{
		Version: 2,
		Name:    "go-toml",
		Tags:    []string{"go", "toml"},
	}

	b, err := toml.Marshal(cfg)
	if err != nil {
		panic(err)
	}
	fmt.Println(string(b))

	// Output:
	// Version = 2
	// Name = 'go-toml'
	// Tags = ['go', 'toml']
}

Output:

Version = 2
Name = 'go-toml'
Tags = ['go', 'toml']
Example (Commented)

Example that uses the 'commented' field tag option to generate an example configuration file that has commented out sections (example from go-graphite/graphite-clickhouse).

Code: 

{
	type Common struct {
		Listen               string        `toml:"listen"                     comment:"general listener"`
		PprofListen          string        `toml:"pprof-listen"               comment:"listener to serve /debug/pprof requests. '-pprof' argument overrides it"`
		MaxMetricsPerTarget  int           `toml:"max-metrics-per-target"     comment:"limit numbers of queried metrics per target in /render requests, 0 or negative = unlimited"`
		MemoryReturnInterval time.Duration `toml:"memory-return-interval"     comment:"daemon will return the freed memory to the OS when it>0"`
	}

	type Costs struct {
		Cost       *int           `toml:"cost"        comment:"default cost (for wildcarded equivalence or matched with regex, or if no value cost set)"`
		ValuesCost map[string]int `toml:"values-cost" comment:"cost with some value (for equivalence without wildcards) (additional tuning, usually not needed)"`
	}

	type ClickHouse struct {
		URL string `toml:"url" comment:"default url, see https://clickhouse.tech/docs/en/interfaces/http. Can be overwritten with query-params"`

		RenderMaxQueries        int               `toml:"render-max-queries" comment:"Max queries to render queries"`
		RenderConcurrentQueries int               `toml:"render-concurrent-queries" comment:"Concurrent queries to render queries"`
		TaggedCosts             map[string]*Costs `toml:"tagged-costs,commented"`
		TreeTable               string            `toml:"tree-table,commented"`
		ReverseTreeTable        string            `toml:"reverse-tree-table,commented"`
		DateTreeTable           string            `toml:"date-tree-table,commented"`
		DateTreeTableVersion    int               `toml:"date-tree-table-version,commented"`
		TreeTimeout             time.Duration     `toml:"tree-timeout,commented"`
		TagTable                string            `toml:"tag-table,commented"`
		ExtraPrefix             string            `toml:"extra-prefix"             comment:"add extra prefix (directory in graphite) for all metrics, w/o trailing dot"`
		ConnectTimeout          time.Duration     `toml:"connect-timeout"          comment:"TCP connection timeout"`
		DataTableLegacy         string            `toml:"data-table,commented"`
		RollupConfLegacy        string            `toml:"rollup-conf,commented"`
		MaxDataPoints           int               `toml:"max-data-points"          comment:"max points per metric when internal-aggregation=true"`
		InternalAggregation     bool              `toml:"internal-aggregation"     comment:"ClickHouse-side aggregation, see doc/aggregation.md"`
	}

	type Tags struct {
		Rules      string `toml:"rules"`
		Date       string `toml:"date"`
		ExtraWhere string `toml:"extra-where"`
		InputFile  string `toml:"input-file"`
		OutputFile string `toml:"output-file"`
	}

	type Config struct {
		Common     Common     `toml:"common"`
		ClickHouse ClickHouse `toml:"clickhouse"`
		Tags       Tags       `toml:"tags,commented"`
	}

	cfg := &Config{
		Common: Common{
			Listen:               ":9090",
			PprofListen:          "",
			MaxMetricsPerTarget:  15000, // This is arbitrary value to protect CH from overload
			MemoryReturnInterval: 0,
		},
		ClickHouse: ClickHouse{
			URL:                 "http://localhost:8123?cancel_http_readonly_queries_on_client_close=1",
			ExtraPrefix:         "",
			ConnectTimeout:      time.Second,
			DataTableLegacy:     "",
			RollupConfLegacy:    "auto",
			MaxDataPoints:       1048576,
			InternalAggregation: true,
		},
		Tags: Tags{},
	}

	out, err := toml.Marshal(cfg)
	if err != nil {
		panic(err)
	}
	err = toml.Unmarshal(out, &cfg)
	if err != nil {
		panic(err)
	}

	fmt.Println(string(out))

	// Output:
	// [common]
	// # general listener
	// listen = ':9090'
	// # listener to serve /debug/pprof requests. '-pprof' argument overrides it
	// pprof-listen = ''
	// # limit numbers of queried metrics per target in /render requests, 0 or negative = unlimited
	// max-metrics-per-target = 15000
	// # daemon will return the freed memory to the OS when it>0
	// memory-return-interval = 0
	//
	// [clickhouse]
	// # default url, see https://clickhouse.tech/docs/en/interfaces/http. Can be overwritten with query-params
	// url = 'http://localhost:8123?cancel_http_readonly_queries_on_client_close=1'
	// # Max queries to render queries
	// render-max-queries = 0
	// # Concurrent queries to render queries
	// render-concurrent-queries = 0
	// # tree-table = ''
	// # reverse-tree-table = ''
	// # date-tree-table = ''
	// # date-tree-table-version = 0
	// # tree-timeout = 0
	// # tag-table = ''
	// # add extra prefix (directory in graphite) for all metrics, w/o trailing dot
	// extra-prefix = ''
	// # TCP connection timeout
	// connect-timeout = 1000000000
	// # data-table = ''
	// # rollup-conf = 'auto'
	// # max points per metric when internal-aggregation=true
	// max-data-points = 1048576
	// # ClickHouse-side aggregation, see doc/aggregation.md
	// internal-aggregation = true
	//
	// # [tags]
	// # rules = ''
	// # date = ''
	// # extra-where = ''
	// # input-file = ''
	// # output-file = ''
}

Output:

[common]
# general listener
listen = ':9090'
# listener to serve /debug/pprof requests. '-pprof' argument overrides it
pprof-listen = ''
# limit numbers of queried metrics per target in /render requests, 0 or negative = unlimited
max-metrics-per-target = 15000
# daemon will return the freed memory to the OS when it>0
memory-return-interval = 0

[clickhouse]
# default url, see https://clickhouse.tech/docs/en/interfaces/http. Can be overwritten with query-params
url = 'http://localhost:8123?cancel_http_readonly_queries_on_client_close=1'
# Max queries to render queries
render-max-queries = 0
# Concurrent queries to render queries
render-concurrent-queries = 0
# tree-table = ''
# reverse-tree-table = ''
# date-tree-table = ''
# date-tree-table-version = 0
# tree-timeout = 0
# tag-table = ''
# add extra prefix (directory in graphite) for all metrics, w/o trailing dot
extra-prefix = ''
# TCP connection timeout
connect-timeout = 1000000000
# data-table = ''
# rollup-conf = 'auto'
# max points per metric when internal-aggregation=true
max-data-points = 1048576
# ClickHouse-side aggregation, see doc/aggregation.md
internal-aggregation = true

# [tags]
# rules = ''
# date = ''
# extra-where = ''
# input-file = ''
# output-file = ''

func Unmarshal 

func Unmarshal(data []byte, v interface{}) error

Unmarshal deserializes a TOML document into a Go value.

It is a shortcut for Decoder.Decode() with the default options.

Example

Code: 

{
	type MyConfig struct {
		Version int
		Name    string
		Tags    []string
	}

	doc := `
	version = 2
	name = "go-toml"
	tags = ["go", "toml"]
	`

	var cfg MyConfig
	err := toml.Unmarshal([]byte(doc), &cfg)
	if err != nil {
		panic(err)
	}
	fmt.Println("version:", cfg.Version)
	fmt.Println("name:", cfg.Name)
	fmt.Println("tags:", cfg.Tags)
	// Output:
	// version: 2
	// name: go-toml
	// tags: [go toml]
}

Output:

version: 2
name: go-toml
tags: [go toml]
Example (TextUnmarshal)

Code:play  

package main

import (
	"fmt"
	"log"
	"strconv"

	"github.com/pelletier/go-toml/v2"
)

type customInt int

func (i *customInt) UnmarshalText(b []byte) error {
	x, err := strconv.ParseInt(string(b), 10, 32)
	if err != nil {
		return err
	}
	*i = customInt(x * 100)
	return nil
}

type doc struct {
	Value customInt
}

func main() {
	var x doc

	data := []byte(`value  = "42"`)
	err := toml.Unmarshal(data, &x)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(x)
}

Output:

{4200}

Types

type DecodeError 

type DecodeError struct {
	// contains filtered or unexported fields
}

DecodeError represents an error encountered during the parsing or decoding of a TOML document.

In addition to the error message, it contains the position in the document where it happened, as well as a human-readable representation that shows where the error occurred in the document.

Example

Code: 

{
	doc := `name = 123__456`

	s := map[string]interface{}{}
	err := Unmarshal([]byte(doc), &s)

	fmt.Println(err)

	var derr *DecodeError
	if errors.As(err, &derr) {
		fmt.Println(derr.String())
		row, col := derr.Position()
		fmt.Println("error occurred at row", row, "column", col)
	}
	// Output:
	// toml: number must have at least one digit between underscores
	// 1| name = 123__456
	//  |           ~~ number must have at least one digit between underscores
	// error occurred at row 1 column 11
}

Output:

toml: number must have at least one digit between underscores
1| name = 123__456
 |           ~~ number must have at least one digit between underscores
error occurred at row 1 column 11

func (*DecodeError) Error 

func (e *DecodeError) Error() string

Error returns the error message contained in the DecodeError.

func (*DecodeError) Key 

func (e *DecodeError) Key() Key

Key that was being processed when the error occurred. The key is present only if this DecodeError is part of a StrictMissingError.

func (*DecodeError) Position 

func (e *DecodeError) Position() (row int, column int)

Position returns the (line, column) pair indicating where the error occurred in the document. Positions are 1-indexed.

func (*DecodeError) String 

func (e *DecodeError) String() string

String returns the human-readable contextualized error. This string is multi-line.

type Decoder 

type Decoder struct {
	// contains filtered or unexported fields
}

Decoder reads and decode a TOML document from an input stream.

func NewDecoder 

func NewDecoder(r io.Reader) *Decoder

NewDecoder creates a new Decoder that will read from r.

func (*Decoder) Decode 

func (d *Decoder) Decode(v interface{}) error

Decode the whole content of r into v.

By default, values in the document that don't exist in the target Go value are ignored. See Decoder.DisallowUnknownFields() to change this behavior.

When a TOML local date, time, or date-time is decoded into a time.Time, its value is represented in time.Local timezone. Otherwise the appropriate Local* structure is used. For time values, precision up to the nanosecond is supported by truncating extra digits.

Empty tables decoded in an interface{} create an empty initialized map[string]interface{}.

Types implementing the encoding.TextUnmarshaler interface are decoded from a TOML string.

When decoding a number, go-toml will return an error if the number is out of bounds for the target type (which includes negative numbers when decoding into an unsigned int).

If an error occurs while decoding the content of the document, this function returns a toml.DecodeError, providing context about the issue. When using strict mode and a field is missing, a `toml.StrictMissingError` is returned. In any other case, this function returns a standard Go error.

Type mapping

List of supported TOML types and their associated accepted Go types: 

String           -> string
Integer          -> uint*, int*, depending on size
Float            -> float*, depending on size
Boolean          -> bool
Offset Date-Time -> time.Time
Local Date-time  -> LocalDateTime, time.Time
Local Date       -> LocalDate, time.Time
Local Time       -> LocalTime, time.Time
Array            -> slice and array, depending on elements types
Table            -> map and struct
Inline Table     -> same as Table
Array of Tables  -> same as Array and Table

func (*Decoder) DisallowUnknownFields 

func (d *Decoder) DisallowUnknownFields() *Decoder

DisallowUnknownFields causes the Decoder to return an error when the destination is a struct and the input contains a key that does not match a non-ignored field.

In that case, the Decoder returns a StrictMissingError that can be used to retrieve the individual errors as well as generate a human readable description of the missing fields.

Example

Code: 

{
	type S struct {
		Key1 string
		Key3 string
	}
	doc := `
key1 = "value1"
key2 = "value2"
key3 = "value3"
`
	r := strings.NewReader(doc)
	d := toml.NewDecoder(r)
	d.DisallowUnknownFields()
	s := S{}
	err := d.Decode(&s)

	fmt.Println(err.Error())

	var details *toml.StrictMissingError
	if !errors.As(err, &details) {
		panic(fmt.Sprintf("err should have been a *toml.StrictMissingError, but got %s (%T)", err, err))
	}

	fmt.Println(details.String())
	// Output:
	// strict mode: fields in the document are missing in the target struct
	// 2| key1 = "value1"
	// 3| key2 = "value2"
	//  | ~~~~ missing field
	// 4| key3 = "value3"
}

Output:

strict mode: fields in the document are missing in the target struct
2| key1 = "value1"
3| key2 = "value2"
 | ~~~~ missing field
4| key3 = "value3"

func (*Decoder) EnableUnmarshalerInterface 

func (d *Decoder) EnableUnmarshalerInterface() *Decoder

EnableUnmarshalerInterface allows to enable unmarshaler interface.

With this feature enabled, types implementing the unstable/Unmarshaler interface can be decoded from any structure of the document. It allows types that don't have a straightforward TOML representation to provide their own decoding logic.

Currently, types can only decode from a single value. Tables and array tables are not supported.

*Unstable:* This method does not follow the compatibility guarantees of semver. It can be changed or removed without a new major version being issued.

type Encoder 

type Encoder struct {
	// contains filtered or unexported fields
}

Encoder writes a TOML document to an output stream.

func NewEncoder 

func NewEncoder(w io.Writer) *Encoder

NewEncoder returns a new Encoder that writes to w.

func (*Encoder) Encode 

func (enc *Encoder) Encode(v interface{}) error

Encode writes a TOML representation of v to the stream.

If v cannot be represented to TOML it returns an error.

Encoding rules

A top level slice containing only maps or structs is encoded as [[table array]].

All slices not matching rule 1 are encoded as [array]. As a result, any map or struct they contain is encoded as an {inline table}.

Nil interfaces and nil pointers are not supported.

Keys in key-values always have one part.

Intermediate tables are always printed.

By default, strings are encoded as literal string, unless they contain either a newline character or a single quote. In that case they are emitted as quoted strings.

Unsigned integers larger than math.MaxInt64 cannot be encoded. Doing so results in an error. This rule exists because the TOML specification only requires parsers to support at least the 64 bits integer range. Allowing larger numbers would create non-standard TOML documents, which may not be readable (at best) by other implementations. To encode such numbers, a solution is a custom type that implements encoding.TextMarshaler.

When encoding structs, fields are encoded in order of definition, with their exact name.

Tables and array tables are separated by empty lines. However, consecutive subtables definitions are not. For example: 

[top1]

[top2]
[top2.child1]

[[array]]

[[array]]
[array.child2]

Struct tags

The encoding of each public struct field can be customized by the format string in the "toml" key of the struct field's tag. This follows encoding/json's convention. The format string starts with the name of the field, optionally followed by a comma-separated list of options. The name may be empty in order to provide options without overriding the default name.

The "multiline" option emits strings as quoted multi-line TOML strings. It has no effect on fields that would not be encoded as strings.

The "inline" option turns fields that would be emitted as tables into inline tables instead. It has no effect on other fields.

The "omitempty" option prevents empty values or groups from being emitted.

The "commented" option prefixes the value and all its children with a comment symbol.

In addition to the "toml" tag struct tag, a "comment" tag can be used to emit a TOML comment before the value being annotated. Comments are ignored inside inline tables. For array tables, the comment is only present before the first element of the array.

func (*Encoder) SetArraysMultiline 

func (enc *Encoder) SetArraysMultiline(multiline bool) *Encoder

SetArraysMultiline forces the encoder to emit all arrays with one element per line.

This behavior can be controlled on an individual struct field basis with the multiline tag: 

MyField `multiline:"true"`

func (*Encoder) SetIndentSymbol 

func (enc *Encoder) SetIndentSymbol(s string) *Encoder

SetIndentSymbol defines the string that should be used for indentation. The provided string is repeated for each indentation level. Defaults to two spaces.

func (*Encoder) SetIndentTables 

func (enc *Encoder) SetIndentTables(indent bool) *Encoder

SetIndentTables forces the encoder to intent tables and array tables.

func (*Encoder) SetMarshalJsonNumbers 

func (enc *Encoder) SetMarshalJsonNumbers(indent bool) *Encoder

SetMarshalJsonNumbers forces the encoder to serialize `json.Number` as a float or integer instead of relying on TextMarshaler to emit a string.

*Unstable:* This method does not follow the compatibility guarantees of semver. It can be changed or removed without a new major version being issued.

func (*Encoder) SetTablesInline 

func (enc *Encoder) SetTablesInline(inline bool) *Encoder

SetTablesInline forces the encoder to emit all tables inline.

This behavior can be controlled on an individual struct field basis with the inline tag: 

MyField `toml:",inline"`

type Key 

type Key []string

type LocalDate 

type LocalDate struct {
	Year  int
	Month int
	Day   int
}

LocalDate represents a calendar day in no specific timezone.

func (LocalDate) AsTime 

func (d LocalDate) AsTime(zone *time.Location) time.Time

AsTime converts d into a specific time instance at midnight in zone.

func (LocalDate) MarshalText 

func (d LocalDate) MarshalText() ([]byte, error)

MarshalText returns RFC 3339 representation of d.

func (LocalDate) String 

func (d LocalDate) String() string

String returns RFC 3339 representation of d.

func (*LocalDate) UnmarshalText 

func (d *LocalDate) UnmarshalText(b []byte) error

UnmarshalText parses b using RFC 3339 to fill d.

type LocalDateTime 

type LocalDateTime struct {
	LocalDate
	LocalTime
}

LocalDateTime represents a time of a specific day in no specific timezone.

func (LocalDateTime) AsTime 

func (d LocalDateTime) AsTime(zone *time.Location) time.Time

AsTime converts d into a specific time instance in zone.

func (LocalDateTime) MarshalText 

func (d LocalDateTime) MarshalText() ([]byte, error)

MarshalText returns RFC 3339 representation of d.

func (LocalDateTime) String 

func (d LocalDateTime) String() string

String returns RFC 3339 representation of d.

func (*LocalDateTime) UnmarshalText 

func (d *LocalDateTime) UnmarshalText(data []byte) error

UnmarshalText parses b using RFC 3339 to fill d.

type LocalTime 

type LocalTime struct {
	Hour       int // Hour of the day: [0; 24[
	Minute     int // Minute of the hour: [0; 60[
	Second     int // Second of the minute: [0; 60[
	Nanosecond int // Nanoseconds within the second:  [0, 1000000000[
	Precision  int // Number of digits to display for Nanosecond.
}

LocalTime represents a time of day of no specific day in no specific timezone.

func (LocalTime) MarshalText 

func (d LocalTime) MarshalText() ([]byte, error)

MarshalText returns RFC 3339 representation of d.

func (LocalTime) String 

func (d LocalTime) String() string

String returns RFC 3339 representation of d. If d.Nanosecond and d.Precision are zero, the time won't have a nanosecond component. If d.Nanosecond > 0 but d.Precision = 0, then the minimum number of digits for nanoseconds is provided.

func (*LocalTime) UnmarshalText 

func (d *LocalTime) UnmarshalText(b []byte) error

UnmarshalText parses b using RFC 3339 to fill d.

type StrictMissingError 

type StrictMissingError struct {
	// One error per field that could not be found.
	Errors []DecodeError
}

StrictMissingError occurs in a TOML document that does not have a corresponding field in the target value. It contains all the missing fields in Errors.

Emitted by Decoder when DisallowUnknownFields() was called.

func (*StrictMissingError) Error 

func (s *StrictMissingError) Error() string

Error returns the canonical string for this error.

func (*StrictMissingError) String 

func (s *StrictMissingError) String() string

String returns a human readable description of all errors.

Source Files

decode.go doc.go errors.go localtime.go marshaler.go strict.go types.go unmarshaler.go

Directories

PathSynopsis
benchmark
cmd
cmd/gotoml-test-decoder
cmd/gotoml-test-encoder
cmd/jsontomlPackage jsontoml is a program that converts JSON to TOML.
cmd/tomljsonPackage tomljson is a program that converts TOML to JSON.
cmd/tomllPackage tomll is a linter program for TOML.
cmd/tomltestgentomltestgen retrieves a given version of the language-agnostic TOML test suite in https://github.com/BurntSushi/toml-test and generates go-toml unit tests.
internal
ossfuzz
unstablePackage unstable provides APIs that do not meet the backward compatibility guarantees yet.
Version
v2.2.4 (latest)
Published
Apr 7, 2025
Platform
windows/amd64
Imports
18 packages
Last checked
3 hours ago –

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