quiche: enable qlog output

quiche has the potential to log qlog files. To enable this, you must
build quiche with the qlog feature enabled `cargo build --features
qlog`. curl then passes a file descriptor to quiche, which takes
ownership of the file. The FD transfer only works on UNIX.

The convention is to enable logging when the QLOGDIR environment is
set. This should be a path to a folder where files are written with the
naming template <SCID>.qlog.

Co-authored-by: Lucas Pardue
Replaces #5337
Closes #5341

2 files changed, 43 insertions, 2 deletions

diff --git a/lib/dynbuf.h b/lib/dynbuf.h
index 427269c68..b4932b535 100644
--- a/lib/dynbuf.h
+++ b/lib/dynbuf.h
@@ -58,5 +58,5 @@ size_t Curl_dyn_len(const struct dynbuf *s);
 #define DYN_RTSP_REQ_HEADER (64*1024)
 #define DYN_TRAILERS        (64*1024)
 #define DYN_PROXY_CONNECT_HEADERS 16384
-
+#define DYN_QLOG_NAME       1024
 #endif
diff --git a/lib/vquic/quiche.c b/lib/vquic/quiche.c
index c40e5e937..38c0a0a3f 100644
--- a/lib/vquic/quiche.c
+++ b/lib/vquic/quiche.c
@@ -34,6 +34,10 @@
 #include "multiif.h"
 #include "connect.h"
 #include "strerror.h"
+#include "dynbuf.h"
+#ifdef HAVE_FCNTL_H
+#include <fcntl.h>
+#endif
 
 /* The last 3 #include files should be in this order */
 #include "curl_printf.h"
@@ -64,7 +68,6 @@ static CURLcode http_request(struct connectdata *conn, const void *mem,
 static Curl_recv h3_stream_recv;
 static Curl_send h3_stream_send;
 
-
 static int quiche_getsock(struct connectdata *conn, curl_socket_t *socks)
 {
   struct SingleRequest *k = &conn->data->req;
@@ -199,6 +202,44 @@ CURLcode Curl_quic_connect(struct connectdata *conn, curl_socket_t sockfd,
     return CURLE_OUT_OF_MEMORY;
   }
 
+  /* Known to not work on Windows */
+#if !defined(WIN32) && defined(HAVE_QUICHE_CONN_SET_QLOG_FD)
+#ifdef O_BINARY
+#define QLOGMODE O_WRONLY|O_CREAT|O_BINARY
+#else
+#define QLOGMODE O_WRONLY|O_CREAT
+#endif
+  {
+    const char *qlog_dir = getenv("QLOGDIR");
+    if(qlog_dir) {
+      struct dynbuf fname;
+      unsigned int i;
+      Curl_dyn_init(&fname, DYN_QLOG_NAME);
+      result = Curl_dyn_add(&fname, qlog_dir);
+      if(!result)
+        result = Curl_dyn_add(&fname, "/");
+      for(i = 0; (i < sizeof(qs->scid)) && !result; i++) {
+        char hex[3];
+        msnprintf(hex, 3, "%02x", qs->scid[i]);
+        result = Curl_dyn_add(&fname, hex);
+      }
+      if(!result)
+        result = Curl_dyn_add(&fname, ".qlog");
+
+      if(!result) {
+        int qlogfd = open(Curl_dyn_ptr(&fname), QLOGMODE,
+                          data->set.new_file_perms);
+        if(qlogfd != -1)
+          quiche_conn_set_qlog_fd(qs->conn, qlogfd,
+                                  "qlog title", "curl qlog");
+      }
+      Curl_dyn_free(&fname);
+      if(result)
+        return result;
+    }
+  }
+#endif
+
   result = flush_egress(conn, sockfd, qs);
   if(result)
     return result;