github.com/lmb/consul@v1.4.1/command/catalog/list/nodes/catalog_list_nodes.go

package nodes

import (
	"flag"
	"fmt"
	"sort"
	"strings"

	"github.com/hashicorp/consul/api"
	"github.com/hashicorp/consul/command/flags"
	"github.com/mitchellh/cli"
	"github.com/ryanuber/columnize"
)

func New(ui cli.Ui) *cmd {
	c := &cmd{UI: ui}
	c.init()
	return c
}

type cmd struct {
	UI    cli.Ui
	flags *flag.FlagSet
	http  *flags.HTTPFlags
	help  string

	// flags
	detailed bool
	near     string
	nodeMeta map[string]string
	service  string
}

// init sets up command flags and help text
func (c *cmd) init() {
	c.flags = flag.NewFlagSet("", flag.ContinueOnError)
	c.flags.BoolVar(&c.detailed, "detailed", false, "Output detailed information about "+
		"the nodes including their addresses and metadata.")
	c.flags.StringVar(&c.near, "near", "", "Node name to sort the node list in ascending "+
		"order based on estimated round-trip time from that node. "+
		"Passing \"_agent\" will use this agent's node for sorting.")
	c.flags.Var((*flags.FlagMapValue)(&c.nodeMeta), "node-meta", "Metadata to "+
		"filter nodes with the given `key=value` pairs. This flag may be "+
		"specified multiple times to filter on multiple sources of metadata.")
	c.flags.StringVar(&c.service, "service", "", "Service `id or name` to filter nodes. "+
		"Only nodes which are providing the given service will be returned.")

	c.http = &flags.HTTPFlags{}
	flags.Merge(c.flags, c.http.ClientFlags())
	flags.Merge(c.flags, c.http.ServerFlags())
	c.help = flags.Usage(help, c.flags)
}

func (c *cmd) Run(args []string) int {
	if err := c.flags.Parse(args); err != nil {
		return 1
	}

	if l := len(c.flags.Args()); l > 0 {
		c.UI.Error(fmt.Sprintf("Too many arguments (expected 0, got %d)", l))
		return 1
	}

	// Create and test the HTTP client
	client, err := c.http.APIClient()
	if err != nil {
		c.UI.Error(fmt.Sprintf("Error connecting to Consul agent: %s", err))
		return 1
	}

	var nodes []*api.Node
	if c.service != "" {
		services, _, err := client.Catalog().Service(c.service, "", &api.QueryOptions{
			Near:     c.near,
			NodeMeta: c.nodeMeta,
		})
		if err != nil {
			c.UI.Error(fmt.Sprintf("Error listing nodes for service: %s", err))
			return 1
		}

		nodes = make([]*api.Node, len(services))
		for i, s := range services {
			nodes[i] = &api.Node{
				ID:              s.ID,
				Node:            s.Node,
				Address:         s.Address,
				Datacenter:      s.Datacenter,
				TaggedAddresses: s.TaggedAddresses,
				Meta:            s.NodeMeta,
				CreateIndex:     s.CreateIndex,
				ModifyIndex:     s.ModifyIndex,
			}
		}
	} else {
		nodes, _, err = client.Catalog().Nodes(&api.QueryOptions{
			Near:     c.near,
			NodeMeta: c.nodeMeta,
		})
		if err != nil {
			c.UI.Error(fmt.Sprintf("Error listing nodes: %s", err))
			return 1
		}
	}

	// Handle the edge case where there are no nodes that match the query.
	if len(nodes) == 0 {
		c.UI.Error("No nodes match the given query - try expanding your search.")
		return 0
	}

	output, err := printNodes(nodes, c.detailed)
	if err != nil {
		c.UI.Error(fmt.Sprintf("Error printing nodes: %s", err))
		return 1
	}

	c.UI.Info(output)

	return 0
}

// printNodes accepts a list of nodes and prints information in a tabular
// format about the nodes.
func printNodes(nodes []*api.Node, detailed bool) (string, error) {
	var result []string
	if detailed {
		result = detailedNodes(nodes)
	} else {
		result = simpleNodes(nodes)
	}

	return columnize.SimpleFormat(result), nil
}

func detailedNodes(nodes []*api.Node) []string {
	result := make([]string, 0, len(nodes)+1)
	header := "Node|ID|Address|DC|TaggedAddresses|Meta"
	result = append(result, header)

	for _, node := range nodes {
		result = append(result, fmt.Sprintf("%s|%s|%s|%s|%s|%s",
			node.Node, node.ID, node.Address, node.Datacenter,
			mapToKV(node.TaggedAddresses, ", "), mapToKV(node.Meta, ", ")))
	}

	return result
}

func simpleNodes(nodes []*api.Node) []string {
	result := make([]string, 0, len(nodes)+1)
	header := "Node|ID|Address|DC"
	result = append(result, header)

	for _, node := range nodes {
		// Shorten the ID in non-detailed mode to just the first octet.
		id := node.ID
		idx := strings.Index(id, "-")
		if idx > 0 {
			id = id[0:idx]
		}
		result = append(result, fmt.Sprintf("%s|%s|%s|%s",
			node.Node, id, node.Address, node.Datacenter))
	}

	return result
}

// mapToKV converts a map[string]string into a human-friendly key=value list,
// sorted by name.
func mapToKV(m map[string]string, joiner string) string {
	keys := make([]string, 0, len(m))
	for k := range m {
		keys = append(keys, k)
	}
	sort.Strings(keys)

	r := make([]string, len(keys))
	for i, k := range keys {
		r[i] = fmt.Sprintf("%s=%s", k, m[k])
	}
	return strings.Join(r, joiner)
}

func (c *cmd) Synopsis() string {
	return synopsis
}

func (c *cmd) Help() string {
	return c.help
}

const synopsis = "Lists all nodes in the given datacenter"
const help = `
Usage: consul catalog nodes [options]

  Retrieves the list nodes registered in a given datacenter. By default, the
  datacenter of the local agent is queried.

  To retrieve the list of nodes:

      $ consul catalog nodes

  To print detailed information including full node IDs, tagged addresses, and
  metadata information:

      $ consul catalog nodes -detailed

  To list nodes which are running a particular service:

      $ consul catalog nodes -service=web

  To filter by node metadata:

      $ consul catalog nodes -node-meta="foo=bar"

  To sort nodes by estimated round-trip time from node-web:

      $ consul catalog nodes -near=node-web

  For a full list of options and examples, please see the Consul documentation.
`