blobvar

Documentation

Overview

Package blobvar provides a runtimevar implementation with variables read from a blob.Bucket. Use OpenVariable to construct a *runtimevar.Variable.

URLs

For runtimevar.OpenVariable, blobvar registers for the scheme "blob". The default URL opener will open a blob.Bucket based on the environment variable "BLOBVAR_BUCKET_URL". To customize the URL opener, or for more details on the URL format, see URLOpener. See https://github.com/eliben/gocdkx/concepts/urls/ for background information.

As

blobvar exposes the following types for As:

• Snapshot: Not supported.
• Error: error, which can be passed to blob.ErrorAs.

Example

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/eliben/gocdkx/blob/memblob"
	"github.com/eliben/gocdkx/runtimevar"
	"github.com/eliben/gocdkx/runtimevar/blobvar"
)

// MyConfig is a sample configuration struct.
type MyConfig struct {
	Server string
	Port   int
}

func main() {
	// Create a *blob.Bucket.
	// Here, we use an in-memory implementation and write a sample
	// configuration value.
	bucket := memblob.OpenBucket(nil)
	defer bucket.Close()
	ctx := context.Background()
	err := bucket.WriteAll(ctx, "cfg-variable-name", []byte(`{"Server": "foo.com", "Port": 80}`), nil)
	if err != nil {
		log.Fatal(err)
	}

	// Create a decoder for decoding JSON strings into MyConfig.
	decoder := runtimevar.NewDecoder(MyConfig{}, runtimevar.JSONDecode)

	// Construct a *runtimevar.Variable that watches the blob.
	v, err := blobvar.OpenVariable(bucket, "cfg-variable-name", decoder, nil)
	if err != nil {
		log.Fatal(err)
	}
	defer v.Close()

	// We can now read the current value of the variable from v.
	snapshot, err := v.Latest(ctx)
	if err != nil {
		log.Fatal(err)
	}
	// runtimevar.Snapshot.Value is decoded to type MyConfig.
	cfg := snapshot.Value.(MyConfig)
	fmt.Printf("%s running on port %d", cfg.Server, cfg.Port)

}

Output:

foo.com running on port 80

Example (OpenVariable)

package main

import (
	"context"
	"log"

	"github.com/eliben/gocdkx/runtimevar"
)

func main() {
	// OpenVariable creates a *runtimevar.Variable from a URL.
	// The default opener opens a blob.Bucket via a URL, based on the environment
	// variable BLOBVAR_BUCKET_URL.
	// This example watches a JSON variable.
	ctx := context.Background()
	v, err := runtimevar.OpenVariable(ctx, "blob://myvar.json?decoder=json")
	if err != nil {
		log.Fatal(err)
	}

	snapshot, err := v.Latest(ctx)
	_, _ = snapshot, err
}

Index

• Constants
• func OpenVariable(bucket *blob.Bucket, key string, decoder *runtimevar.Decoder, opts *Options) (*runtimevar.Variable, error)
• type Options
• type URLOpener
  • func (o *URLOpener) OpenVariableURL(ctx context.Context, u *url.URL) (*runtimevar.Variable, error)

Examples

• Package
• Package (OpenVariable)

Constants

const Scheme = "blob"

Scheme is the URL scheme blobvar registers its URLOpener under on runtimevar.DefaultMux.

Functions

func OpenVariable

func OpenVariable(bucket *blob.Bucket, key string, decoder *runtimevar.Decoder, opts *Options) (*runtimevar.Variable, error)

OpenVariable constructs a *runtimevar.Variable backed by the referenced blob. Reads of the blob return raw bytes; provide a decoder to decode the raw bytes into the appropriate type for runtimevar.Snapshot.Value. See the runtimevar package documentation for examples of decoders.

Types

type Options

type Options struct {
	// WaitDuration controls the rate at which the blob is polled.
	// Defaults to 30 seconds.
	WaitDuration time.Duration
}

Options sets options.

type URLOpener

type URLOpener struct {
	// Bucket is required.
	Bucket *blob.Bucket

	// Decoder specifies the decoder to use if one is not specified in the URL.
	// Defaults to runtimevar.BytesDecoder.
	Decoder *runtimevar.Decoder

	// Options specifies the Options for OpenVariable.
	Options Options
}

URLOpener opens blob-backed URLs like "blob://myblobkey?decoder=string". It supports the following URL parameters:

• decoder: The decoder to use. Defaults to URLOpener.Decoder, or runtimevar.BytesDecoder if URLOpener.Decoder is nil. See runtimevar.DecoderByName for supported values.

func (*URLOpener) OpenVariableURL

func (o *URLOpener) OpenVariableURL(ctx context.Context, u *url.URL) (*runtimevar.Variable, error)

OpenVariableURL opens the variable at the URL's path. See the package doc for more details.