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package middleware
// MetadataReader provides an interface for reading metadata from the
// underlying metadata container.
type MetadataReader interface {
Get(key interface{}) interface{}
}
// Metadata provides storing and reading metadata values. Keys may be any
// comparable value type. Get and set will panic if key is not a comparable
// value type.
//
// Metadata uses lazy initialization, and Set method must be called as an
// addressable value, or pointer. Not doing so may cause key/value pair to not
// be set.
type Metadata struct {
values map[interface{}]interface{}
}
// Get attempts to retrieve the value the key points to. Returns nil if the
// key was not found.
//
// Panics if key type is not comparable.
func (m Metadata) Get(key interface{}) interface{} {
return m.values[key]
}
// Clone creates a shallow copy of Metadata entries, returning a new Metadata
// value with the original entries copied into it.
func (m Metadata) Clone() Metadata {
vs := make(map[interface{}]interface{}, len(m.values))
for k, v := range m.values {
vs[k] = v
}
return Metadata{
values: vs,
}
}
// Set stores the value pointed to by the key. If a value already exists at
// that key it will be replaced with the new value.
//
// Set method must be called as an addressable value, or pointer. If Set is not
// called as an addressable value or pointer, the key value pair being set may
// be lost.
//
// Panics if the key type is not comparable.
func (m *Metadata) Set(key, value interface{}) {
if m.values == nil {
m.values = map[interface{}]interface{}{}
}
m.values[key] = value
}
// Has returns whether the key exists in the metadata.
//
// Panics if the key type is not comparable.
func (m Metadata) Has(key interface{}) bool {
if m.values == nil {
return false
}
_, ok := m.values[key]
return ok
}
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