promdump: redact passwords if specified in the --url flag

Parsing the URL into a net/url object gets us password redaction for free. Added a variable "parsedURL" to hold the parsed URL so we don't have to parse it twice. This was a choice between global variable ick and copy and pasting code ick. I opted for the global since they're used all over the place already anyway.

Modified the "setupPromAPI" function to accept a URL instead of relying on the global "baseURL" string pointer. The Prometheus HTTP API still requires the URL to be passed in as a string, so the received URL is converted back into a string when instantiating the API.

Added a second handler to the flag logger that parses the URL flag into a URL object, saves the URL to the global variable "parsedURL", then prints the flag to the log with any password specified in the userinfo component of the URL redacted using parsedURL.Redacted().

Updated all instances where the URL is logged to use parsedURL.Redacted().

promdump/promdump.go

@@ -21,6 +21,7 @@ import (
 	"math"
 	"net"
 	"net/http"
+	"net/url"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -55,13 +56,16 @@ var (
 	defaultBaseUrl = fmt.Sprintf("http://%v:%v", defaultYbaHostname, defaultPromPort)
 
 	// Also see init() below for aliases
-	logToFile                = flag.Bool("log_to_file", true, "write log output to file")
-	logToStderr              = flag.Bool("log_to_console", true, "write log output to console (on standard error)")
-	logFilename              = flag.String("log_filename", "promdump.log", "if logging to disk is enabled, write logs to this file")
-	debugLogging             = flag.Bool("debug", false, "enable additional debug logging")
-	version                  = flag.Bool("version", false, "prints the promdump version and exits")
-	listUniverses            = flag.Bool("list_universes", false, "prints the list of Universes known to YBA and exits; requires a --yba_api_token")
+	logToFile     = flag.Bool("log_to_file", true, "write log output to file")
+	logToStderr   = flag.Bool("log_to_console", true, "write log output to console (on standard error)")
+	logFilename   = flag.String("log_filename", "promdump.log", "if logging to disk is enabled, write logs to this file")
+	debugLogging  = flag.Bool("debug", false, "enable additional debug logging")
+	version       = flag.Bool("version", false, "prints the promdump version and exits")
+	listUniverses = flag.Bool("list_universes", false, "prints the list of Universes known to YBA and exits; requires a --yba_api_token")
+	// The baseURL variable will report that it is unused because we're parsing the flag value directly into the
+	// parsedURL variable below.
 	baseURL                  = flag.String("url", defaultBaseUrl, "URL for Prometheus server API")
+	parsedURL                *url.URL
 	skipPromHostVerification = flag.Bool("skip_prometheus_host_verification", false, "bypasses TLS certificate verification for Prometheus queries (insecure)")
 	promApiTimeout           = flag.Duration("prometheus_api_timeout", 10, "the HTTP timeout to use for Prometheus API calls, in seconds (optional)")
 	startTime                = flag.String("start_time", "", "RFC3339 `timestamp` to start querying at (e.g. 2023-03-13T01:00:00-0100).")
@@ -650,7 +654,7 @@ func buildInstanceLabelString(instanceList string, nodeSet string) (string, erro
 	return instanceLabelString, nil
 }
 
-func setupPromAPI(ctx context.Context) (v1.API, error) {
+func setupPromAPI(ctx context.Context, promURL url.URL) (v1.API, error) {
 	tlsCc := &tls.Config{
 		InsecureSkipVerify: *skipPromHostVerification,
 	}
@@ -664,7 +668,7 @@ func setupPromAPI(ctx context.Context) (v1.API, error) {
 		Transport: tr,
 	}
 
-	apiClient, err := api.NewClient(api.Config{Address: *baseURL, Client: httpClient})
+	apiClient, err := api.NewClient(api.Config{Address: promURL.String(), Client: httpClient})
 	if err != nil {
 		return nil, fmt.Errorf("failed to create Prometheus API client: %w", err)
 	}
@@ -906,10 +910,24 @@ func main() {
 			}
 		}
 
+		// If this is the --url flag, it may have a password in it that we need to redact
+		if f.Name == "url" {
+			// parsedURL is global!! We don't want to have to parse in more than one place.
+			parsedURL, err = url.Parse(f.Value.String())
+			if err != nil {
+				logger.Printf("main: failed to parse flag '--url=%v' while logging flags: %v", f.Value, err)
+			}
+			_, err = flagString.WriteString(fmt.Sprintf(" --%s=%v", f.Name, parsedURL.Redacted()))
+			if err != nil {
+				logger.Printf("main: inexplicably failed to write while adding flag '--%s=%v' to flag logging string: %v", f.Name, parsedURL.Redacted(), err)
+			}
+			return
+		}
+
 		// If the flag name doesn't match any of the sensitive flags, we'll exit the for loop and log normally
 		_, err := flagString.WriteString(fmt.Sprintf(" --%s=%v", f.Name, f.Value))
 		if err != nil {
-			logger.Printf("main: inexplicably failed to write while adding flag '--%s=%v'' to flag logging string: %v", f.Name, f.Value, err)
+			logger.Printf("main: inexplicably failed to write while adding flag '--%s=%v' to flag logging string: %v", f.Name, f.Value, err)
 		}
 	})
 	// Write the complete flag string built by the string builder out to the log
@@ -1127,10 +1145,11 @@ func main() {
 		batchDur = periodDur
 	}
 
-	logger.Printf("main: Beginning metric collection against Prometheus endpoint '%v'", *baseURL)
+	// parsedURL is global! The URL is parsed from a string into an actual URL object during flag logging
+	logger.Printf("main: Beginning metric collection against Prometheus endpoint '%v'", parsedURL.Redacted())
 
 	ctx := context.Background()
-	promApi, err := setupPromAPI(ctx)
+	promApi, err := setupPromAPI(ctx, *parsedURL)
 	if err != nil {
 		logger.Fatalln("setupPromAPI: ", err)
 	}