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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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