jschoubben
ca59b685b0
Builds: design 47 G §57, §345 Claude-Session: https://claude.ai/code/session_01JG73KEq4zoDfM9WtYpcQgZ
72 lines
2.6 KiB
Go
72 lines
2.6 KiB
Go
// Package stateobjects keeps values of any size on the bus (novox/hq ADR 0666 §16, ADR 0595 §9): a value over the bus's
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// limit for one value, or a verb reply or an event over the limit for one message, is put in an object store and only its
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// reference travels. It is a small package of its own, imported only by the modules that use it: the module library (the
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// root package) and the process package do not import it, so their importers are not rebuilt when it changes. It names no
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// seat and no module, and imports no contracts module.
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package stateobjects
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import (
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"bytes"
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"encoding/hex"
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"encoding/json"
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"fmt"
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)
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// FormVersion is the version of the reference form; a reader refuses a reference of another.
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const FormVersion = 1
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// refField is the one field of a body that is a reference.
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const refField = "mesh-object"
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// Ref names an object in an object store: a body that is exactly `{"mesh-object": Ref}` is a reference, and anything
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// else is a value.
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type Ref struct {
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// Store is the object store's name as its reader asks for it: a bundle's local name, or the name a process opens.
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Store string `json:"store"`
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// Object is the object's name in that store.
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Object string `json:"object"`
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// Size is the object's size in bytes.
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Size int64 `json:"size"`
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// Digest is the hex SHA-256 of the object's bytes; a reader checks it after the read.
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Digest string `json:"sha256"`
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// Form is FormVersion.
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Form int `json:"form"`
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}
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func (r Ref) valid() bool {
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if r.Store == "" || r.Object == "" || r.Size < 0 || r.Form != FormVersion || len(r.Digest) != 64 {
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return false
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}
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_, err := hex.DecodeString(r.Digest)
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return err == nil
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}
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// Wrap is the body that holds r.
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func Wrap(r Ref) []byte {
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raw, _ := json.Marshal(map[string]Ref{refField: r})
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return raw
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}
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// ReadRef reads a body as a reference: ok is false for a value, including one that only looks like a reference (another
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// field beside it, a field it does not know, a digest that is no digest, another form).
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func ReadRef(body []byte) (Ref, bool) {
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var outer map[string]json.RawMessage
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if err := json.Unmarshal(body, &outer); err != nil || len(outer) != 1 {
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return Ref{}, false
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}
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raw, ok := outer[refField]
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if !ok {
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return Ref{}, false
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}
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dec := json.NewDecoder(bytes.NewReader(raw))
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dec.DisallowUnknownFields()
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var r Ref
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if err := dec.Decode(&r); err != nil || !r.valid() {
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return Ref{}, false
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}
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return r, true
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}
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// errLooksLikeRef refuses a value that would be read back as a reference.
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var errLooksLikeRef = fmt.Errorf("the value is exactly a reference to an object (a body of the one field %q): it would be read as one", refField)
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