mesh-delivery/modules/mesh-delivery-builder/internal/build/choose.go

package build

import (
	"fmt"
	"sort"
	"strings"

	"git.novox.be/novox/mesh-sdk/go/delivery"
)

// ChooseNodes picks up to want build nodes for a language (ADR 0478 clause 3): the nodes whose toolchains key reports the
// version the nodes agree on, the ones with room under their build capacity first (places), then the fewest lanes the
// builder has running or chosen there, a tie broken by the node's name. A place is reserved on each node chosen, in the
// same step as the choice, so builds choosing at once do not choose the same full node while another has room; the
// caller takes the place (Places.Acquire) or gives it up (Places.Cancel). A node at its capacity is still chosen when
// the others are too (fewer than want have room): its lane waits for a place. A node qualifies only when qualifies is true
// of it (online and its build module healthy; nil means every node does). It answers the toolchain all the reporting nodes
// agree on, qualifying or not, as the indexer computes it. When nothing is reported, or the nodes report different
// versions (so the indexer agreed none), it fails naming the language and why; when no reporting node qualifies it fails
// naming the nodes. A node whose build module refuses on its toolchain refuses the step, and the build fails naming it.
func ChooseNodes(language string, entries []delivery.NodeToolchain, places *Places, qualifies func(node string) bool, want int) ([]string, delivery.Toolchain2, error) {
	tc, none := delivery.AgreedToolchain(entries)
	if none != "" {
		return nil, delivery.Toolchain2{}, fmt.Errorf("no %s build node qualifies: %s", language, none)
	}
	nodes, err := choose(language, entries, places, qualifies, want)
	return nodes, tc, err
}

// ChooseAnyNodes is ChooseNodes for artifacts that need no toolchain, such as an archive (ADR 0478 clause 1): the
// build module's nodes agree on nothing, so any node of the build module that qualifies is chosen, by capacity and load only.
func ChooseAnyNodes(language string, entries []delivery.NodeToolchain, places *Places, qualifies func(node string) bool, want int) ([]string, error) {
	return choose(language, entries, places, qualifies, want)
}

func choose(language string, entries []delivery.NodeToolchain, places *Places, qualifies func(node string) bool, want int) ([]string, error) {
	nodes := make([]string, 0, len(entries))
	var reporting []string
	seen := map[string]bool{}
	for _, e := range entries {
		if seen[e.Node] {
			continue
		}
		seen[e.Node] = true
		reporting = append(reporting, e.Node)
		if qualifies == nil || qualifies(e.Node) {
			nodes = append(nodes, e.Node)
		}
	}
	if len(nodes) == 0 {
		sort.Strings(reporting)
		return nil, fmt.Errorf("no %s build node qualifies: %s report the toolchain, and none is online with a healthy build module", language, strings.Join(reporting, ", "))
	}
	if places == nil {
		places = &Places{}
	}
	return places.choose(nodes, want), nil
}

// DigestsDifferPrefix opens the error of a build whose nodes built an artifact to different digests (ADR 0478 clause 4):
// such a key is not built again as a new revision, since the same source on the same toolchains gave two answers and
// building again settles nothing; it waits for another fingerprint.
const DigestsDifferPrefix = "digests differ:"

// Agree is the one digest every node built an artifact to (ADR 0478 clause 4), or an error naming each node and its
// digest when they differ. One node's digest agrees with itself.
func Agree(artifact string, byNode map[string]string) (string, error) {
	nodes := make([]string, 0, len(byNode))
	for n := range byNode {
		nodes = append(nodes, n)
	}
	sort.Strings(nodes)
	var first string
	for i, n := range nodes {
		if i == 0 {
			first = byNode[n]
			continue
		}
		if byNode[n] != first {
			msg := fmt.Sprintf("%s the nodes built %s to different digests:", DigestsDifferPrefix, artifact)
			for _, n := range nodes {
				msg += fmt.Sprintf(" %s %s;", n, byNode[n])
			}
			return "", fmt.Errorf("%s", msg[:len(msg)-1])
		}
	}
	return first, nil
}