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"
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"strings"
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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
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func (md Metadata) Get(key string) (string, bool) {
// attempt to get as is
val, ok := md[key]
if ok {
return val, ok
}
// attempt to get lower case
val, ok = md[strings.Title(key)]
return val, ok
}
func (md Metadata) Delete(key string) {
// delete key as-is
delete(md, key)
// delete also Title key
delete(md, strings.Title(key))
}
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// Copy makes a copy of the metadata
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func Copy(md Metadata) Metadata {
cmd := make(Metadata)
for k, v := range md {
cmd[k] = v
}
return cmd
}
// Delete key from metadata
func Delete(ctx context.Context, k string) context.Context {
return Set(ctx, k, "")
}
// Set add key with val to metadata
func Set(ctx context.Context, k, v string) context.Context {
md, ok := FromContext(ctx)
if !ok {
md = make(Metadata)
}
if v == "" {
delete(md, k)
} else {
md[k] = v
}
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
}
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// attempt to get as is
val, ok := md[key]
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if ok {
return val, ok
}
// attempt to get lower case
val, ok = md[strings.Title(key)]
return val, ok
}
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// FromContext returns metadata from the given context
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func FromContext(ctx context.Context) (Metadata, bool) {
md, ok := ctx.Value(MetadataKey{}).(Metadata)
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if !ok {
return nil, ok
}
// capitalise all values
newMD := make(map[string]string, len(md))
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for k, v := range md {
newMD[strings.Title(k)] = v
}
return newMD, ok
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}
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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{}, md)
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}
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// MergeContext merges metadata to existing metadata, overwriting if specified
func MergeContext(ctx context.Context, patchMd Metadata, overwrite bool) context.Context {
if ctx == nil {
ctx = context.Background()
}
md, _ := ctx.Value(MetadataKey{}).(Metadata)
cmd := make(Metadata)
for k, v := range md {
cmd[k] = v
}
for k, v := range patchMd {
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if _, ok := cmd[k]; ok && !overwrite {
// skip
} else if v != "" {
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cmd[k] = v
} else {
delete(cmd, k)
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}
}
return context.WithValue(ctx, MetadataKey{}, cmd)
}