fetch: Add support for providing HTTP headers

I plan to use this in ignition-dracut to inject e.g. headers
from `/usr/lib/os-release`, so that a server (such as the
OpenShift 4 machine-config-operator server) can dispatch on them.

Author: cgwalters

internal/exec/engine.go

@@ -20,6 +20,9 @@ import (
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
+	"net/http"
+	"strings"
+
 	"net/url"
 	"os"
 	"time"
@@ -50,6 +53,7 @@ const (
 type Engine struct {
 	ConfigCache    string
 	FetchTimeout   time.Duration
+	FetchHeaders   []string
 	Logger         *log.Logger
 	Root           string
 	PlatformConfig platform.Config
@@ -272,7 +276,17 @@ func (e *Engine) fetchReferencedConfig(cfgRef types.ConfigReference) (types.Conf
 	if err != nil {
 		return types.Config{}, err
 	}
-	rawCfg, err := e.Fetcher.FetchToBuffer(*u, resource.FetchOptions{})
+	headers := make(http.Header)
+	for _, h := range e.FetchHeaders {
+		parts := strings.SplitN(h, "=", 2)
+		k := parts[0]
+		v := ""
+		if len(parts) > 1 {
+			v = parts[1]
+		}
+		headers.Add(k, v)
+	}
+	rawCfg, err := e.Fetcher.FetchToBuffer(*u, resource.FetchOptions{Headers: headers})
 	if err != nil {
 		return types.Config{}, err
 	}

internal/main.go

@@ -32,11 +32,23 @@ import (
 	"github.com/coreos/ignition/v2/internal/version"
 )
 
+type flagStringArray []string
+
+func (_ *flagStringArray) String() string {
+    return ""
+}
+
+func (a *flagStringArray) Set(value string) error {
+    *a = append(*a, value)
+    return nil
+}
+
 func main() {
 	flags := struct {
 		clearCache   bool
 		configCache  string
 		fetchTimeout time.Duration
+		fetchHeaders flagStringArray
 		platform     platform.Name
 		root         string
 		stage        stages.Name
@@ -47,6 +59,7 @@ func main() {
 	flag.BoolVar(&flags.clearCache, "clear-cache", false, "clear any cached config")
 	flag.StringVar(&flags.configCache, "config-cache", "/run/ignition.json", "where to cache the config")
 	flag.DurationVar(&flags.fetchTimeout, "fetch-timeout", exec.DefaultFetchTimeout, "initial duration for which to wait for config")
+	flag.Var(&flags.fetchHeaders, "fetch-header", "Include HTTP header for fetches")
 	flag.Var(&flags.platform, "platform", fmt.Sprintf("current platform. %v", platform.Names()))
 	flag.StringVar(&flags.root, "root", "/", "root of the filesystem")
 	flag.Var(&flags.stage, "stage", fmt.Sprintf("execution stage. %v", stages.Names()))
@@ -91,6 +104,7 @@ func main() {
 	engine := exec.Engine{
 		Root:           flags.root,
 		FetchTimeout:   flags.fetchTimeout,
+		FetchHeaders:   flags.fetchHeaders,
 		Logger:         &logger,
 		ConfigCache:    flags.configCache,
 		PlatformConfig: platformConfig,

internal/resource/url.go

@@ -68,6 +68,9 @@ type Fetcher struct {
 	// timeouts Ignition was configured to used will be ignored.
 	client *HttpClient
 
+	// headers is additional headers to include
+	headers []http.Header
+
 	// The AWS Session to use when fetching resources from S3. If left nil, the
 	// first S3 object that is fetched will initialize the field. This can be
 	// used to set credentials.