Nicolas Lenepveu
39 lines
1.2 KiB
Go
39 lines
1.2 KiB
Go
// Package optional provides JSON field types that distinguish "absent" from
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// "explicitly null" in PATCH-style request payloads — a distinction a plain
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// `*int` cannot make, because both decode to a nil pointer.
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package optional
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import "encoding/json"
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// Int is a tri-state integer field for partial-update request bodies:
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//
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// - key absent → Present == false (leave the target unchanged)
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// - key present null → Present == true, Value == nil (clear to "unset")
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// - key present N → Present == true, Value == &N (set to N)
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//
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// Declare it as a plain (non-pointer) struct field WITHOUT `omitempty`:
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//
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// MaxInflightTasks optional.Int `json:"maxInflightTasks"`
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//
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// encoding/json only invokes UnmarshalJSON when the key is present in the
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// payload, so Present reliably reports whether the client sent the field.
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type Int struct {
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Present bool
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Value *int
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}
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// UnmarshalJSON records that the key was present and decodes null vs. number.
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func (o *Int) UnmarshalJSON(data []byte) error {
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o.Present = true
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if string(data) == "null" {
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o.Value = nil
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return nil
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}
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var v int
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if err := json.Unmarshal(data, &v); err != nil {
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return err
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}
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o.Value = &v
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return nil
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}
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