Add unix domain socket support to API (#16872)

- Expose internal HTTP client's Do() via Raw
- Use URL parser to identify scheme
- Align more with curl output
- Add changelog
- Fix test failure; add tests for socket envvars
- Apply review feedback for tests
- Consolidate address parsing
- Address feedback from code reviews

Co-authored-by: Tim Gross <tgross@hashicorp.com>

.changelog/16872.txt

@@ -0,0 +1,3 @@
+```release-note:improvement
+api: Added support for Unix domain sockets
+```

api/api.go

@@ -205,6 +205,16 @@ type Config struct {
 	// retryOptions holds the configuration necessary to perform retries
 	// on put calls.
 	retryOptions *retryOptions
+
+	// url is populated with the initial parsed address and is not modified in the
+	// case of a unix:// URL, as opposed to Address.
+	url *url.URL
+}
+
+// URL returns a copy of the initial parsed address and is not modified in the
+// case of a `unix://` URL, as opposed to Address.
+func (c *Config) URL() *url.URL {
+	return c.url
 }
 
 // ClientConfig copies the configuration with a new client address, region, and
@@ -214,6 +224,7 @@ func (c *Config) ClientConfig(region, address string, tlsEnabled bool) *Config {
 	if tlsEnabled {
 		scheme = "https"
 	}
+
 	config := &Config{
 		Address:    fmt.Sprintf("%s://%s", scheme, address),
 		Region:     region,
@@ -223,6 +234,7 @@ func (c *Config) ClientConfig(region, address string, tlsEnabled bool) *Config {
 		HttpAuth:   c.HttpAuth,
 		WaitTime:   c.WaitTime,
 		TLSConfig:  c.TLSConfig.Copy(),
+		url:        copyURL(c.url),
 	}
 
 	// Update the tls server name for connecting to a client
@@ -278,9 +290,30 @@ func (t *TLSConfig) Copy() *TLSConfig {
 	return nt
 }
 
+// defaultUDSClient creates a unix domain socket client. Errors return a nil
+// http.Client, which is tested for in ConfigureTLS. This function expects that
+// the Address has already been parsed into the config.url value.
+func defaultUDSClient(config *Config) *http.Client {
+
+	config.Address = "http://127.0.0.1"
+
+	httpClient := &http.Client{
+		Transport: &http.Transport{
+			DialContext: func(_ context.Context, _, _ string) (net.Conn, error) {
+				return net.Dial("unix", config.url.EscapedPath())
+			},
+		},
+	}
+	return defaultClient(httpClient)
+}
+
 func defaultHttpClient() *http.Client {
 	httpClient := cleanhttp.DefaultPooledClient()
-	transport := httpClient.Transport.(*http.Transport)
+	return defaultClient(httpClient)
+}
+
+func defaultClient(c *http.Client) *http.Client {
+	transport := c.Transport.(*http.Transport)
 	transport.TLSHandshakeTimeout = 10 * time.Second
 	transport.TLSClientConfig = &tls.Config{
 		MinVersion: tls.VersionTLS12,
@@ -290,7 +323,7 @@ func defaultHttpClient() *http.Client {
 	// well yet: https://github.com/gorilla/websocket/issues/417
 	transport.ForceAttemptHTTP2 = false
 
-	return httpClient
+	return c
 }
 
 // DefaultConfig returns a default configuration for the client
@@ -467,18 +500,29 @@ type Client struct {
 
 // NewClient returns a new client
 func NewClient(config *Config) (*Client, error) {
+	var err error
 	// bootstrap the config
 	defConfig := DefaultConfig()
 
 	if config.Address == "" {
 		config.Address = defConfig.Address
-	} else if _, err := url.Parse(config.Address); err != nil {
+	}
+
+	// we have to test the address that comes from DefaultConfig, because it
+	// could be the value of NOMAD_ADDR which is applied without testing
+	if config.url, err = url.Parse(config.Address); err != nil {
 		return nil, fmt.Errorf("invalid address '%s': %v", config.Address, err)
 	}
 
 	httpClient := config.HttpClient
 	if httpClient == nil {
-		httpClient = defaultHttpClient()
+		switch {
+		case config.url.Scheme == "unix":
+			httpClient = defaultUDSClient(config) // mutates config
+		default:
+			httpClient = defaultHttpClient()
+		}
+
 		if err := ConfigureTLS(httpClient, config.TLSConfig); err != nil {
 			return nil, err
 		}
@@ -760,24 +804,32 @@ func (r *request) toHTTP() (*http.Request, error) {
 
 // newRequest is used to create a new request
 func (c *Client) newRequest(method, path string) (*request, error) {
-	base, _ := url.Parse(c.config.Address)
+
 	u, err := url.Parse(path)
 	if err != nil {
 		return nil, err
 	}
+
 	r := &request{
 		config: &c.config,
 		method: method,
 		url: &url.URL{
-			Scheme:  base.Scheme,
-			User:    base.User,
-			Host:    base.Host,
+			Scheme:  c.config.url.Scheme,
+			User:    c.config.url.User,
+			Host:    c.config.url.Host,
 			Path:    u.Path,
 			RawPath: u.RawPath,
 		},
 		header: make(http.Header),
 		params: make(map[string][]string),
 	}
+
+	// fixup socket paths
+	if r.url.Scheme == "unix" {
+		r.url.Scheme = "http"
+		r.url.Host = "127.0.0.1"
+	}
+
 	if c.config.Region != "" {
 		r.params.Set("region", c.config.Region)
 	}
@@ -1210,3 +1262,16 @@ func (o *WriteOptions) WithContext(ctx context.Context) *WriteOptions {
 	o2.ctx = ctx
 	return o2
 }
+
+// copyURL makes a deep copy of a net/url.URL
+func copyURL(u1 *url.URL) *url.URL {
+	if u1 == nil {
+		return nil
+	}
+	o := *u1
+	if o.User != nil {
+		ou := *u1.User
+		o.User = &ou
+	}
+	return &o
+}

api/raw.go

@@ -3,7 +3,10 @@
 
 package api
 
-import "io"
+import (
+	"io"
+	"net/http"
+)
 
 // Raw can be used to do raw queries against custom endpoints
 type Raw struct {
@@ -39,3 +42,8 @@ func (raw *Raw) Write(endpoint string, in, out interface{}, q *WriteOptions) (*W
 func (raw *Raw) Delete(endpoint string, out interface{}, q *WriteOptions) (*WriteMeta, error) {
 	return raw.c.delete(endpoint, nil, out, q)
 }
+
+// Do uses the raw client's internal httpClient to process the request
+func (raw *Raw) Do(req *http.Request) (*http.Response, error) {
+	return raw.c.httpClient.Do(req)
+}

command/operator_api.go

@@ -5,17 +5,14 @@ package command
 
 import (
 	"bytes"
-	"crypto/tls"
 	"fmt"
 	"io"
 	"net"
 	"net/http"
 	"net/url"
 	"os"
 	"strings"
-	"time"
 
-	"github.com/hashicorp/go-cleanhttp"
 	"github.com/hashicorp/nomad/api"
 	"github.com/posener/complete"
 )
@@ -138,11 +135,18 @@ func (c *OperatorAPICommand) Run(args []string) int {
 
 	// By default verbose func is a noop
 	verbose := func(string, ...interface{}) {}
+	verboseSocket := func(*api.Config, string, ...interface{}) {}
+
 	if c.verboseFlag {
 		verbose = func(format string, a ...interface{}) {
 			// Use Warn instead of Info because Info goes to stdout
 			c.Ui.Warn(fmt.Sprintf(format, a...))
 		}
+		verboseSocket = func(cfg *api.Config, format string, a ...interface{}) {
+			if cfg.URL() != nil && cfg.URL().Scheme == "unix" {
+				c.Ui.Warn(fmt.Sprintf(format, a...))
+			}
+		}
 	}
 
 	// Opportunistically read from stdin and POST unless method has been
@@ -166,11 +170,13 @@ func (c *OperatorAPICommand) Run(args []string) int {
 		c.method = "GET"
 	}
 
+	// NewClient mutates or validates Config.Address, so call it to match
+	// the behavior of other commands. Typically these are called as a combination
+	// using c.Client(); however, we need access to the client configuration
+	// to build the corresponding curl output.
 	config := c.clientConfig()
+	apiC, err := api.NewClient(config)
 
-	// NewClient mutates or validates Config.Address, so call it to match
-	// the behavior of other commands.
-	_, err := api.NewClient(config)
 	if err != nil {
 		c.Ui.Error(fmt.Sprintf("Error initializing client: %v", err))
 		return 1
@@ -198,30 +204,21 @@ func (c *OperatorAPICommand) Run(args []string) int {
 		c.Ui.Output(out)
 		return 0
 	}
-
-	// Re-implement a big chunk of api/api.go since we don't export it.
-	client := cleanhttp.DefaultClient()
-	transport := client.Transport.(*http.Transport)
-	transport.TLSHandshakeTimeout = 10 * time.Second
-	transport.TLSClientConfig = &tls.Config{
-		MinVersion: tls.VersionTLS12,
-	}
-
-	if err := api.ConfigureTLS(client, config.TLSConfig); err != nil {
-		c.Ui.Error(fmt.Sprintf("Error configuring TLS: %v", err))
-		return 1
-	}
+	apiR := apiC.Raw()
 
 	setQueryParams(config, path)
-
-	verbose("> %s %s", c.method, path)
+	verboseSocket(config, fmt.Sprintf("* Trying %s...", config.URL().EscapedPath()))
 
 	req, err := http.NewRequest(c.method, path.String(), c.body)
 	if err != nil {
 		c.Ui.Error(fmt.Sprintf("Error making request: %v", err))
 		return 1
 	}
 
+	h := req.URL.Hostname()
+	verboseSocket(config, fmt.Sprintf("* Connected to %s (%s)", h, config.URL().EscapedPath()))
+	verbose("> %s %s %s", c.method, req.URL.Path, req.Proto)
+
 	// Set headers from command line
 	req.Header = headerFlags.headers
 
@@ -244,11 +241,11 @@ func (c *OperatorAPICommand) Run(args []string) int {
 			verbose("> %s: %s", k, v)
 		}
 	}
-
+	verbose(">")
 	verbose("* Sending request and receiving response...")
 
 	// Do the request!
-	resp, err := client.Do(req)
+	resp, err := apiR.Do(req)
 	if err != nil {
 		c.Ui.Error(fmt.Sprintf("Error performing request: %v", err))
 		return 1
@@ -310,14 +307,19 @@ func (c *OperatorAPICommand) apiToCurl(config *api.Config, headers http.Header,
 		parts = append(parts, "--verbose")
 	}
 
-	if c.method != "" {
+	// add method flags. Note: curl output complains about `-X GET`
+	if c.method != "" && c.method != http.MethodGet {
 		parts = append(parts, "-X "+c.method)
 	}
 
 	if c.body != nil {
 		parts = append(parts, "--data-binary @-")
 	}
 
+	if config.URL().EscapedPath() != "" {
+		parts = append(parts, fmt.Sprintf("--unix-socket %q", config.URL().EscapedPath()))
+	}
+
 	if config.TLSConfig != nil {
 		parts = tlsToCurl(parts, config.TLSConfig)
 
@@ -412,7 +414,9 @@ func pathToURL(config *api.Config, path string) (*url.URL, error) {
 
 	// If the scheme is missing from the path, it likely means the path is just
 	// the HTTP handler path. Attempt to infer this.
-	if !strings.HasPrefix(path, "http://") && !strings.HasPrefix(path, "https://") {
+	if !strings.HasPrefix(path, "http://") &&
+		!strings.HasPrefix(path, "https://") &&
+		!strings.HasPrefix(path, "unix://") {
 		scheme := "http"
 
 		// If the user has set any TLS configuration value, this is a good sign