micro/metadata/metadata.go

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// Package metadata is a way of defining message headers
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package metadata
import (
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"context"
"net/textproto"
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)
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type metadataKey struct{}
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// Metadata is our way of representing request headers internally.
// They're used at the RPC level and translate back and forth
// from Transport headers.
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type Metadata map[string]string
var (
// DefaultMetadataSize used when need to init new Metadata
DefaultMetadataSize = 6
)
// Get returns value from metadata by key
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func (md Metadata) Get(key string) (string, bool) {
// fast path
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val, ok := md[key]
if !ok {
// slow path
val, ok = md[textproto.CanonicalMIMEHeaderKey(key)]
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}
return val, ok
}
// Set is used to store value in metadata
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func (md Metadata) Set(key, val string) {
md[textproto.CanonicalMIMEHeaderKey(key)] = val
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}
// Del is used to remove value from metadata
func (md Metadata) Del(key string) {
// fast path
if _, ok := md[key]; ok {
delete(md, key)
} else {
// slow path
delete(md, textproto.CanonicalMIMEHeaderKey(key))
}
}
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// Copy makes a copy of the metadata
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func Copy(md Metadata) Metadata {
nmd := New(len(md))
for key, val := range md {
nmd.Set(key, val)
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}
return nmd
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}
func Del(ctx context.Context, key string) context.Context {
md, ok := FromContext(ctx)
if !ok {
md = New(0)
}
md.Del(key)
return context.WithValue(ctx, metadataKey{}, md)
}
// Set add key with val to metadata
func Set(ctx context.Context, key, val string) context.Context {
md, ok := FromContext(ctx)
if !ok {
md = New(0)
}
md.Set(key, val)
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return context.WithValue(ctx, metadataKey{}, md)
}
// Get returns a single value from metadata in the context
func Get(ctx context.Context, key string) (string, bool) {
md, ok := FromContext(ctx)
if !ok {
return "", ok
}
return md.Get(key)
}
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// FromContext returns metadata from the given context
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func FromContext(ctx context.Context) (Metadata, bool) {
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md, ok := ctx.Value(metadataKey{}).(Metadata)
if !ok {
return nil, ok
}
nmd := Copy(md)
return nmd, ok
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}
// New return new sized metadata
func New(size int) Metadata {
if size == 0 {
size = DefaultMetadataSize
}
return make(Metadata, size)
}
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// NewContext creates a new context with the given metadata
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func NewContext(ctx context.Context, md Metadata) context.Context {
return context.WithValue(ctx, metadataKey{}, Copy(md))
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}
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// MergeContext merges metadata to existing metadata, overwriting if specified
func MergeContext(ctx context.Context, pmd Metadata, overwrite bool) context.Context {
if ctx == nil {
ctx = context.Background()
}
md, ok := FromContext(ctx)
if !ok {
return context.WithValue(ctx, metadataKey{}, Copy(pmd))
}
nmd := Copy(md)
for key, val := range pmd {
if _, ok := nmd[key]; ok && !overwrite {
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// skip
} else if val != "" {
nmd.Set(key, val)
} else {
nmd.Del(key)
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}
}
return context.WithValue(ctx, metadataKey{}, nmd)
}