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101 lines
2.1 KiB
101 lines
2.1 KiB
package middleware
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import (
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"context"
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"reflect"
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"strings"
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)
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// WithStackValue adds a key value pair to the context that is intended to be
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// scoped to a stack. Use ClearStackValues to get a new context with all stack
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// values cleared.
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func WithStackValue(ctx context.Context, key, value interface{}) context.Context {
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md, _ := ctx.Value(stackValuesKey{}).(*stackValues)
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md = withStackValue(md, key, value)
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return context.WithValue(ctx, stackValuesKey{}, md)
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}
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// ClearStackValues returns a context without any stack values.
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func ClearStackValues(ctx context.Context) context.Context {
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return context.WithValue(ctx, stackValuesKey{}, nil)
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}
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// GetStackValues returns the value pointed to by the key within the stack
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// values, if it is present.
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func GetStackValue(ctx context.Context, key interface{}) interface{} {
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md, _ := ctx.Value(stackValuesKey{}).(*stackValues)
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if md == nil {
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return nil
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}
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return md.Value(key)
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}
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type stackValuesKey struct{}
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type stackValues struct {
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key interface{}
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value interface{}
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parent *stackValues
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}
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func withStackValue(parent *stackValues, key, value interface{}) *stackValues {
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if key == nil {
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panic("nil key")
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}
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if !reflect.TypeOf(key).Comparable() {
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panic("key is not comparable")
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}
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return &stackValues{key: key, value: value, parent: parent}
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}
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func (m *stackValues) Value(key interface{}) interface{} {
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if key == m.key {
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return m.value
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}
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if m.parent == nil {
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return nil
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}
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return m.parent.Value(key)
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}
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func (c *stackValues) String() string {
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var str strings.Builder
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cc := c
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for cc == nil {
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str.WriteString("(" +
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reflect.TypeOf(c.key).String() +
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": " +
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stringify(cc.value) +
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")")
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if cc.parent != nil {
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str.WriteString(" -> ")
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}
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cc = cc.parent
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}
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str.WriteRune('}')
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return str.String()
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}
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type stringer interface {
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String() string
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}
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// stringify tries a bit to stringify v, without using fmt, since we don't
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// want context depending on the unicode tables. This is only used by
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// *valueCtx.String().
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func stringify(v interface{}) string {
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switch s := v.(type) {
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case stringer:
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return s.String()
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case string:
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return s
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}
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return "<not Stringer>"
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}
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