From ed202f73ddbaad81fefbc3aef53eba88e4488014 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mateusz=20=C5=81oskot?= <mateusz@loskot.net>
Date: Sat, 21 Sep 2024 20:52:46 +0200
Subject: [PATCH] Discover HTTPBIN_ env vars at process startup, not per
 request
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Signed-off-by: Mateusz Łoskot <mateusz@loskot.net>
---
 httpbin/cmd/cmd.go  | 10 ++++++++++
 httpbin/handlers.go | 12 +-----------
 httpbin/httpbin.go  |  4 ++++
 httpbin/options.go  |  8 ++++++++
 4 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/httpbin/cmd/cmd.go b/httpbin/cmd/cmd.go
index 08a98465..9fa3a10e 100644
--- a/httpbin/cmd/cmd.go
+++ b/httpbin/cmd/cmd.go
@@ -74,10 +74,20 @@ func mainImpl(args []string, getEnv func(string) string, getHostname func() (str
 		logger = slog.New(handler)
 	}
 
+	env := make(map[string]string)
+	for _, e := range os.Environ() {
+		v := strings.SplitN(e, "=", 2)
+		if !strings.HasPrefix(v[0], "HTTPBIN_") {
+			continue
+		}
+		env[v[0]] = v[1]
+	}
+
 	opts := []httpbin.OptionFunc{
 		httpbin.WithMaxBodySize(cfg.MaxBodySize),
 		httpbin.WithMaxDuration(cfg.MaxDuration),
 		httpbin.WithObserver(httpbin.StdLogObserver(logger)),
+		httpbin.WithEnv(env),
 		httpbin.WithExcludeHeaders(cfg.ExcludeHeaders),
 	}
 	if cfg.Prefix != "" {
diff --git a/httpbin/handlers.go b/httpbin/handlers.go
index 8342f9df..fbd3d46b 100644
--- a/httpbin/handlers.go
+++ b/httpbin/handlers.go
@@ -11,7 +11,6 @@ import (
 	"net/http"
 	"net/http/httputil"
 	"net/url"
-	"os"
 	"strconv"
 	"strings"
 	"time"
@@ -38,17 +37,8 @@ func (h *HTTPBin) Index(w http.ResponseWriter, r *http.Request) {
 
 // Env - returns environment variables with HTTPBIN_ prefix, if any pre-configured by operator
 func (h *HTTPBin) Env(w http.ResponseWriter, _ *http.Request) {
-	variables := make(map[string]string)
-	for _, e := range os.Environ() {
-		v := strings.SplitN(e, "=", 2)
-		if !strings.HasPrefix(v[0], "HTTPBIN_") {
-			continue
-		}
-		variables[v[0]] = v[1]
-	}
-
 	writeJSON(http.StatusOK, w, &envResponse{
-		Env: variables,
+		Env: h.env,
 	})
 }
 
diff --git a/httpbin/httpbin.go b/httpbin/httpbin.go
index 3dfc99f7..7c60924a 100644
--- a/httpbin/httpbin.go
+++ b/httpbin/httpbin.go
@@ -57,6 +57,10 @@ type HTTPBin struct {
 	// Set of hosts to which the /redirect-to endpoint will allow redirects
 	AllowedRedirectDomains map[string]struct{}
 
+	// The operator-controlled environment variables filtered from
+	// the process environment, based on named HTTPBIN_ prefix.
+	env map[string]string
+
 	// Pre-computed error message for the /redirect-to endpoint, based on
 	// -allowed-redirect-domains/ALLOWED_REDIRECT_DOMAINS
 	forbiddenRedirectError string
diff --git a/httpbin/options.go b/httpbin/options.go
index e697a1c1..15f60904 100644
--- a/httpbin/options.go
+++ b/httpbin/options.go
@@ -46,6 +46,14 @@ func WithObserver(o Observer) OptionFunc {
 	}
 }
 
+// WithEnv sets the HTTPBIN_-prefixed environment variables reported
+// by the /env endpoint.
+func WithEnv(env map[string]string) OptionFunc {
+	return func(h *HTTPBin) {
+		h.env = env
+	}
+}
+
 // WithExcludeHeaders sets the headers to exclude in outgoing responses, to
 // prevent possible information leakage.
 func WithExcludeHeaders(excludeHeaders string) OptionFunc {