metadata.go

// Package metadata is a way of defining message headers
package metadata

import (
	"net/textproto"
	"sort"
)

var (
	// HeaderTopic is the header name that contains topic name
	HeaderTopic = "Micro-Topic"
	// HeaderContentType specifies content type of message
	HeaderContentType = "Content-Type"
	// HeaderEndpoint specifies endpoint in service
	HeaderEndpoint = "Micro-Endpoint"
	// HeaderService specifies service
	HeaderService = "Micro-Service"
	// HeaderTimeout specifies timeout of operation
	HeaderTimeout = "Micro-Timeout"
	// HeaderAuthorization specifies Authorization header
	HeaderAuthorization = "Authorization"
)

// Metadata is our way of representing request headers internally.
// They're used at the RPC level and translate back and forth
// from Transport headers.
type Metadata map[string]string

type rawMetadata struct {
	md Metadata
}

// defaultMetadataSize used when need to init new Metadata
var defaultMetadataSize = 2

// Iterator used to iterate over metadata with order
type Iterator struct {
	md   Metadata
	keys []string
	cur  int
	cnt  int
}

// Next advance iterator to next element
func (iter *Iterator) Next(k, v *string) bool {
	if iter.cur+1 > iter.cnt {
		return false
	}

	*k = iter.keys[iter.cur]
	*v = iter.md[*k]
	iter.cur++
	return true
}

// Iterator returns the itarator for metadata in sorted order
func (md Metadata) Iterator() *Iterator {
	iter := &Iterator{md: md, cnt: len(md)}
	iter.keys = make([]string, 0, iter.cnt)
	for k := range md {
		iter.keys = append(iter.keys, k)
	}
	sort.Strings(iter.keys)
	return iter
}

// Get returns value from metadata by key
func (md Metadata) Get(key string) (string, bool) {
	// fast path
	val, ok := md[key]
	if !ok {
		// slow path
		val, ok = md[textproto.CanonicalMIMEHeaderKey(key)]
	}
	return val, ok
}

// Set is used to store value in metadata
func (md Metadata) Set(key, val string) {
	md[textproto.CanonicalMIMEHeaderKey(key)] = val
}

// Del is used to remove value from metadata
func (md Metadata) Del(key string) {
	// fast path
	delete(md, key)
	// slow path
	delete(md, textproto.CanonicalMIMEHeaderKey(key))
}

// Copy makes a copy of the metadata
func Copy(md Metadata) Metadata {
	nmd := New(len(md))
	for key, val := range md {
		nmd.Set(key, val)
	}
	return nmd
}

// New return new sized metadata
func New(size int) Metadata {
	if size == 0 {
		size = defaultMetadataSize
	}
	return make(Metadata, size)
}

// Merge merges metadata to existing metadata, overwriting if specified
func Merge(omd Metadata, mmd Metadata, overwrite bool) Metadata {
	var ok bool
	nmd := Copy(omd)
	for key, val := range mmd {
		_, ok = nmd[key]
		switch {
		case ok && !overwrite:
			continue
		case val != "":
			nmd.Set(key, val)
		case ok && val == "":
			nmd.Del(key)
		}
	}
	return nmd
}

// Pairs from which metadata created
func Pairs(kv ...string) (Metadata, bool) {
	if len(kv)%2 == 1 {
		return nil, false
	}
	md := New(len(kv) / 2)
	var k string
	for i, v := range kv {
		if i%2 == 0 {
			k = v
			continue
		}
		md.Set(k, v)
	}
	return md, true
}