SSL: support for compressed server certificates with OpenSSL.

The ssl_certificate_compression directive allows to send compressed
server certificates.  In OpenSSL, they are pre-compressed on startup.
To simplify configuration, the SSL_OP_NO_TX_CERTIFICATE_COMPRESSION
option is automatically cleared if certificates were pre-compressed.

SSL_CTX_compress_certs() may return an error in legitimate cases,
e.g., when none of compression algorithms is available or if the
resulting compressed size is larger than the original one, thus it
is silently ignored.

Certificate compression is supported in Chrome with brotli only,
in Safari with zlib only, and in Firefox with all listed algorithms.
It is supported since Ubuntu 24.10, which has OpenSSL with enabled
zlib and zstd support.

The actual list of algorithms supported in OpenSSL depends on how
the library was configured; it can be brotli, zlib, zstd as listed
in RFC 8879.

2 files changed, 19 insertions, 0 deletions

diff --git a/src/stream/ngx_stream_ssl_module.c b/src/stream/ngx_stream_ssl_module.c
index 2f1b99624..7ce1175f1 100644
--- a/src/stream/ngx_stream_ssl_module.c
+++ b/src/stream/ngx_stream_ssl_module.c
@@ -133,6 +133,13 @@ static ngx_command_t  ngx_stream_ssl_commands[] = {
       0,
       NULL },
 
+    { ngx_string("ssl_certificate_compression"),
+      NGX_STREAM_MAIN_CONF|NGX_STREAM_SRV_CONF|NGX_CONF_FLAG,
+      ngx_conf_set_flag_slot,
+      NGX_STREAM_SRV_CONF_OFFSET,
+      offsetof(ngx_stream_ssl_srv_conf_t, certificate_compression),
+      NULL },
+
     { ngx_string("ssl_dhparam"),
       NGX_STREAM_MAIN_CONF|NGX_STREAM_SRV_CONF|NGX_CONF_TAKE1,
       ngx_conf_set_str_slot,
@@ -881,6 +888,7 @@ ngx_stream_ssl_create_srv_conf(ngx_conf_t *cf)
     sscf->passwords = NGX_CONF_UNSET_PTR;
     sscf->conf_commands = NGX_CONF_UNSET_PTR;
     sscf->prefer_server_ciphers = NGX_CONF_UNSET;
+    sscf->certificate_compression = NGX_CONF_UNSET;
     sscf->reject_handshake = NGX_CONF_UNSET;
     sscf->verify = NGX_CONF_UNSET_UINT;
     sscf->verify_depth = NGX_CONF_UNSET_UINT;
@@ -914,6 +922,9 @@ ngx_stream_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
     ngx_conf_merge_value(conf->prefer_server_ciphers,
                          prev->prefer_server_ciphers, 0);
 
+    ngx_conf_merge_value(conf->certificate_compression,
+                         prev->certificate_compression, 0);
+
     ngx_conf_merge_value(conf->reject_handshake, prev->reject_handshake, 0);
 
     ngx_conf_merge_bitmask_value(conf->protocols, prev->protocols,
@@ -1039,6 +1050,13 @@ ngx_stream_ssl_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child)
         {
             return NGX_CONF_ERROR;
         }
+
+        if (ngx_ssl_certificate_compression(cf, &conf->ssl,
+                                            conf->certificate_compression)
+            != NGX_OK)
+        {
+            return NGX_CONF_ERROR;
+        }
     }
 
     if (conf->verify) {
diff --git a/src/stream/ngx_stream_ssl_module.h b/src/stream/ngx_stream_ssl_module.h
index ffa03a6f3..31f138cfd 100644
--- a/src/stream/ngx_stream_ssl_module.h
+++ b/src/stream/ngx_stream_ssl_module.h
@@ -18,6 +18,7 @@ typedef struct {
     ngx_msec_t        handshake_timeout;
 
     ngx_flag_t        prefer_server_ciphers;
+    ngx_flag_t        certificate_compression;
     ngx_flag_t        reject_handshake;
 
     ngx_ssl_t         ssl;