jschoubben
2478b5f127
The mesh runs on the seat's bus alone (novox/hq ADR 0131, design 28 task 5.5). The host's old dialling and enrolment paths are deleted with the switch that chose between them; a membership or a token naming another bus is refused before anything is sent, rather than dialled on a transport that no longer exists.
76 lines
3.0 KiB
Go
76 lines
3.0 KiB
Go
package link
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import (
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"context"
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"fmt"
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"time"
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)
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// What a host hears, as the host's own words for it.
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//
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// The outbound half is behind `Bus` (bus.go); this is the other half — dialling, and the
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// declarations that arrive. The run loop reads its own words for a declaration rather than the
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// client library's delivery type, so nothing past this file knows what carried it.
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//
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// **The host still imports nothing of the mesh's own** (novox/hq ADR 0005). This is its own
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// interface over its own libraries, and it agrees with the controller only because a conformance
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// fixture holds both to one envelope.
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// Link is this node's live connection to its mesh: what it hears, and what it says.
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//
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// One interface rather than two, because dialling once is what keeps both halves of a node on the
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// same connection.
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type Link interface {
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// Bus is what this node says: what it applied, and that it is here.
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Bus
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// Declarations is what the mesh tells this node to be.
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Declarations() <-chan Declaration
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// Lost says the link ended, and why.
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//
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// **Read rather than discovered.** A node that finds out by noticing silence is a node that
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// believed it was in the mesh for as long as the silence lasted, which is the one state ADR
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// 0004 says must never look like being connected.
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Lost() <-chan error
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// Close lets go of whatever was dialled.
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Close()
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}
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// Declaration is one thing the mesh told this node to be.
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//
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// **Handled, once — after the report is published.** A node that dies between applying and
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// reporting leaves the declaration with the mesh and applies it again on return, which is safe
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// because applying is reconciliation: it converges rather than repeating.
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//
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// There is one way of being done rather than two. A declaration set aside because a newer arrived
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// with it is settled exactly as an applied one is, and the difference between them is a fact the
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// *report* carries — a second method here would be a distinction the bus does not make.
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type Declaration interface {
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// Body is the signed declaration as it arrived, bytes unchanged: a node verifies what it
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// received rather than what it re-encoded.
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Body() []byte
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// Handled settles it. Called after the report for it has been published, either way.
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Handled() error
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}
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// Open opens this node's link to its mesh.
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//
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// Named Open rather than Dial because Dial is this package's raw TLS dial, which the enrolment path
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// uses to see a certificate before it trusts anything.
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//
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// **The mesh has one bus** (novox/hq ADR 0131): the one the broker seat delivers. A membership
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// still records which transport it was minted for, so a host can say what it is dialling, and a
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// membership recorded for anything else is a membership this host cannot use.
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func Open(ctx context.Context, m Membership, timeout time.Duration) (Link, error) {
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if m.Transport != OnNATS {
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return nil, fmt.Errorf("this membership is for %q, and the mesh's bus is %s", m.Transport, OnNATS)
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}
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return dialNats(ctx, m, timeout)
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}
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// OnNATS is the bus a membership names: the mesh's own, and the only one.
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const OnNATS = "nats"
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