Amazon Ion Go
Amazon Ion ( https://amazon-ion.github.io/ion-docs/ ) library for Go
Ion Cookbook demonstrates code samples for some simple Amazon Ion use cases.
This package is based on work from David Murray (fernomac) on https://github.com/fernomac/ion-go. The Ion team greatly appreciates David's contributions to the Ion community.
Users
Here are some projects that use the Ion Go library
- Restish: "...a CLI for interacting with REST-ish HTTP APIs with some nice features built-in"
We'll be happy to add you to our list, send us a pull request.
Git Setup
This repository contains a git submodule
called ion-tests, which holds test data used by ion-go's unit tests.
The easiest way to clone the ion-go repository and initialize its ion-tests
submodule is to run the following command.
$ git clone --recursive https://github.com/amazon-ion/ion-go.git ion-go
Alternatively, the submodule may be initialized independent of the clone by running the following commands:
$ git submodule init
$ git submodule update
Development
This package uses Go Modules to model its dependencies.
Assuming the go command is in your path, building the module can be done as:
$ go build -v ./...
Running all the tests can be executed with:
$ go test -v ./...
We use goimports to format
our imports and files in general. Running this before commit is advised:
$ goimports -w .
It is recommended that you hook this in your favorite IDE (Tools > File Watchers in Goland, for example).
Usage
Import github.com/amazon-ion/ion-go/ion and you're off to the races.
Marshaling and Unmarshaling
Similar to GoLang's built-in json package,
you can marshal and unmarshal Go types to Ion. Marshaling requires you to specify
whether you'd like text or binary Ion. Unmarshaling is smart enough to do the right
thing. Both follow the style of json name tags, and Marshal honors omitempty.
type T struct {
A string
B struct {
RenamedC int `ion:"C"`
D []int `ion:",omitempty"`
}
}
func main() {
t := T{}
err := ion.Unmarshal([]byte(`{A:"Ion!",B:{C:2,D:[3,4]}}`), &t)
if err != nil {
panic(err)
}
fmt.Printf("--- t:\n%v\n\n", t)
text, err := ion.MarshalText(&t)
if err != nil {
panic(err)
}
fmt.Printf("--- text:\n%s\n\n", string(text))
binary, err := ion.MarshalBinary(&t)
if err != nil {
panic(err)
}
fmt.Printf("--- binary:\n%X\n\n", binary)
}In order to Marshal/Unmarshal Ion values with annotation, we use a Go struct with two fields,
- one field of type
[]stringand tagged withion:",annotation". - the other field with appropriate type and optional tag to hold our Ion value. For instance,
to Marshal
age::20, it must be in a struct as below:
type foo struct {
Value interface{}
AnyName []string `ion:",annotations"`
}
data := foo{20, []string{"age"}}
val, err := ion.MarshalText(data)
if err != nil {
panic(err)
}
fmt.Println("Ion text: ", string(val)) // Ion text: age::20And to Unmarshal the same data, we can do as shown below:
type foo struct {
Value interface{}
AnyName []string `ion:",annotations"`
}
var val foo
err := ion.UnmarshalString("age::20", &val)
if err != nil {
panic(err)
}
fmt.Printf("Val = %+v\n", val) // Val = {Value:20 AnyName:[age]}Encoding and Decoding
To read or write multiple values at once, use an Encoder or Decoder:
func main() {
dec := ion.NewTextDecoder(os.Stdin)
enc := ion.NewBinaryEncoder(os.Stdout)
for {
// Decode one Ion whole value from stdin.
val, err := dec.Decode()
if err == ion.ErrNoInput {
break
} else if err != nil {
panic(err)
}
// Encode it to stdout.
if err := enc.Encode(val); err != nil {
panic(err)
}
}
if err := enc.Finish(); err != nil {
panic(err)
}
}Reading and Writing
For low-level streaming read and write access, use a Reader or Writer.
The following example shows how to create a reader, read values from that reader,
and write those values out using a writer:
func writeFromReaderToWriter(reader Reader, writer Writer) {
for reader.Next() {
name := reader.FieldName()
if name != nil {
err := writer.FieldName(*name)
if err != nil {
panic(err)
}
}
an := reader.Annotations()
if len(an) > 0 {
err := writer.Annotations(an...)
if err != nil {
panic(err)
}
}
currentType := reader.Type()
if reader.IsNull() {
err := writer.WriteNullType(currentType)
if err != nil {
panic(err)
}
continue
}
switch currentType {
case BoolType:
val, err := reader.BoolValue()
if err != nil {
panic("Something went wrong while reading a Boolean value: " + err.Error())
}
err = writer.WriteBool(val)
if err != nil {
panic("Something went wrong while writing a Boolean value: " + err.Error())
}
case StringType:
val, err := reader.StringValue()
if err != nil {
panic("Something went wrong while reading a String value: " + err.Error())
}
err = writer.WriteString(val)
if err != nil {
panic("Something went wrong while writing a String value: " + err.Error())
}
case StructType:
err := reader.StepIn()
if err != nil {
panic(err)
}
err = writer.BeginStruct()
if err != nil {
panic(err)
}
writeFromReaderToWriter(reader, writer)
err = reader.StepOut()
if err != nil {
panic(err)
}
err = writer.EndStruct()
if err != nil {
panic(err)
}
default:
panic("This is an example, only taking in Bool, String and Struct")
}
}
if reader.Err() != nil {
panic(reader.Err().Error())
}
}
func main() {
reader := NewReaderString("foo::{name:\"bar\", complete:false}")
str := strings.Builder{}
writer := NewTextWriter(&str)
writeFromReaderToWriter(reader, writer)
err := writer.Finish()
if err != nil {
panic(err)
}
fmt.Println(str.String())
}Symbol Tables
By default, when writing binary Ion, a local symbol table is built as you write
values (which are buffered in memory until you call Finish so the symbol table
can be written out first). You can optionally provide one or more
SharedSymbolTables to the writer, which it will reference as needed rather
than directly including those symbols in the local symbol table.
type Item struct {
ID string `ion:"id"`
Name string `ion:"name"`
Description string `ion:"description"`
}
var ItemSharedSymbols = ion.NewSharedSymbolTable("item", 1, []string{
"item",
"id",
"name",
"description",
})
type SpicyItem struct {
Item
Spiciness int `ion:"spiciness"`
}
func WriteSpicyItemsTo(out io.Writer, items []SpicyItem) error {
writer := ion.NewBinaryWriter(out, ItemSharedSymbols)
for _, item := range items {
writer.Annotation("item")
if err := ion.EncodeTo(writer, item); err != nil {
return err
}
}
return writer.Finish()
}You can alternatively provide the writer with a complete, pre-built local symbol table. This allows values to be written without buffering, however any attempt to write a symbol that is not included in the symbol table will result in an error:
func WriteItemsToLST(out io.Writer, items []SpicyItem) error {
lst := ion.NewLocalSymbolTable([]SharedSymbolTable{ItemSharedSymbols}, []string{
"spiciness",
})
writer := ion.NewBinaryWriterLST(out, lst)
for _, item := range items {
writer.Annotation("item")
if err := ion.EncodeTo(writer, item); err != nil {
return err
}
}
return writer.Finish()
}When reading binary Ion, shared symbol tables are provided by a Catalog. A basic
catalog can be constructed by calling NewCatalog; a smarter implementation may
load shared symbol tables from a database on demand.
func ReadItemsFrom(in io.Reader) ([]Item, error) {
item := Item{}
items := []Item{}
cat := ion.NewCatalog(ItemSharedSymbols)
dec := ion.NewDecoder(ion.NewReaderCat(in, cat))
for {
err := dec.DecodeTo(&item)
if err == ion.ErrNoInput {
return items, nil
}
if err != nil {
return nil, err
}
items = append(items, item)
}
}License
This library is licensed under the Apache 2.0 License.