HTTP: Support templated TRACE responses

src/client_side_reply.cc

@@ -23,6 +23,7 @@
 #include "globals.h"
 #include "HeaderMangling.h"
 #include "http/Stream.h"
+#include "HttpHdrCc.h"
 #include "HttpHeaderTools.h"
 #include "HttpReply.h"
 #include "HttpRequest.h"
@@ -1002,12 +1003,18 @@ clientReplyContext::traceReply()
     triggerInitialStoreRead();
     http->storeEntry()->releaseRequest();
     http->storeEntry()->buffer();
-    MemBuf content;
-    content.init();
-    http->request->pack(&content, true /* hide authorization data */);
-    const HttpReplyPointer rep(new HttpReply);
-    rep->setHeaders(Http::scOkay, nullptr, "message/http", content.contentSize(), 0, squid_curtime);
-    rep->body.set(SBuf(content.buf, content.size));
+
+    ErrorState err(HTTP_TRACE_REPLY, Http::scOkay, http->request, http->al);
+    auto rep = err.BuildHttpReply();
+    // RFC 9110 specifies that TRACE response is not cacheable
+    // Reinforce that with explicit caching controls
+    HttpHdrCc cc;
+    cc.noStore(true);
+    cc.mustRevalidate(true);
+    cc.maxAge(0);
+    rep->putCc(cc);
+    // Reinforce that with explicit Expires for old HTTP/1.0 agents
+    rep->header.putTime(Http::HdrType::EXPIRES, squid_curtime);
     http->storeEntry()->replaceHttpReply(rep);
     http->storeEntry()->completeSuccessfully("traceReply() stored the entire response");
 }

src/error/forward.h

@@ -82,6 +82,9 @@ typedef enum {
     ERR_REQUEST_PARSE_TIMEOUT, // Aborts the connection instead of error page
     ERR_RELAY_REMOTE, // Sends server reply instead of error page
 
+    /* TRACE Response is optional, but SHOULD be equivalent to '%R\n' if sent */
+    HTTP_TRACE_REPLY,
+
     /* Cache Manager GUI can install a manager index/home page */
     MGR_INDEX,
 

src/errorpage.cc

@@ -381,12 +381,17 @@ TemplateFile::loadDefault()
     }
 #endif
 
-    /* test default location if failed (templates == English translation base templates) */
+    /** test default templates if failed (templates == English translation base templates) */
     if (!loaded()) {
         tryLoadTemplate("templates");
     }
 
-    /* giving up if failed */
+    /** test for any 'soft-coded' template available as default-if-none. */
+    if (!loaded()) {
+        tryInternalDefault();
+    }
+
+    /** giving up if failed. Will result in "Internal Error" production. */
     if (!loaded()) {
         debugs(1, (templateCode < TCP_RESET ? DBG_CRITICAL : 3), "WARNING: failed to find or read error text file " << templateName);
         template_.clear();
@@ -420,6 +425,26 @@ TemplateFile::tryLoadTemplate(const char *lang)
     return false;
 }
 
+void
+TemplateFile::tryInternalDefault()
+{
+    if (loaded())
+        return; // admin has provided a template.
+
+    // Default templates if no file is found.
+    static const std::list<std::pair<err_type, const SBuf>> SoftCodedErrors = {
+        { HTTP_TRACE_REPLY, SBuf("%R\n") }
+    };
+
+    for (const auto &m: SoftCodedErrors) {
+        if (m.first == templateCode) {
+            template_ = m.second;
+            wasLoaded = parse();
+            return;
+        }
+    }
+}
+
 bool
 TemplateFile::loadFromFile(const char *path)
 {

src/errorpage.h

@@ -329,6 +329,9 @@ class TemplateFile
      */
     bool tryLoadTemplate(const char *lang);
 
+    /// Try to load a built-in template, if none is configured.
+    void tryInternalDefault();
+
     SBuf template_; ///< raw template contents
     bool wasLoaded; ///< True if the template data read from disk without any problem
     String errLanguage; ///< The error language of the template.