Allow configuring compression level

Signed-off-by: Steffen Jaeckel <jaeckel-floss@eyet-services.de>

src/common.h

@@ -280,7 +280,8 @@ struct _xmpp_conn_t {
 
     struct {
         struct xmpp_compression *state;
-        int allowed, supported, dont_reset;
+        int allowed, dont_reset, level;
+        int supported;
     } compression;
 
     char *lang;

src/compression.c

@@ -227,7 +227,7 @@ int compression_init(xmpp_conn_t *conn)
 
     comp->compression.stream.next_out = comp->compression.buffer;
     comp->compression.stream.avail_out = STROPHE_COMPRESSION_BUFFER_SIZE;
-    int ret = deflateInit(&comp->compression.stream, Z_DEFAULT_COMPRESSION);
+    int ret = deflateInit(&comp->compression.stream, conn->compression.level);
     if (ret != Z_OK) {
         strophe_free_and_null(conn->ctx, comp->compression.buffer);
         conn->error = ret;

src/conn.c

@@ -167,6 +167,8 @@ xmpp_conn_t *xmpp_conn_new(xmpp_ctx_t *ctx)
         tls_clear_password_cache(conn);
         conn->password_retries = 1;
 
+        conn->compression.level = -1;
+
         conn->parser =
             parser_new(conn->ctx, _handle_stream_start, _handle_stream_end,
                        _handle_stream_stanza, conn);
@@ -348,6 +350,10 @@ int xmpp_conn_release(xmpp_conn_t *conn)
  *      In case the user enters the password manually it can be useful to
  *      directly retry if the decryption of the key file failed.
  *
+ * - \ref XMPP_SETTING_COMPRESSION_LEVEL
+ *      Set the compression level. \n
+ *      For zlib the valid range is `-1` to `9`.
+ *
  *  @param conn a   Strophe connection object
  *  @param setting  The setting that shall be configured
  *  @param value    The value, the settings should get
@@ -365,6 +371,9 @@ void xmpp_conn_set_int(xmpp_conn_t *conn,
         else
             conn->password_retries = value;
         break;
+    case XMPP_SETTING_COMPRESSION_LEVEL:
+        conn->compression.level = value;
+        break;
     default:
         strophe_warn(conn->ctx, "xmpp", "Invalid Int setting %d", setting);
         return;

strophe.h

@@ -389,6 +389,7 @@ typedef enum xmpp_conn_setting_t {
     /* Int values */
     XMPP_SETTING_PASSWORD_RETRIES = 0x40, /**< Number of retry attempts to
                                       decrypt a private key file. */
+    XMPP_SETTING_COMPRESSION_LEVEL,       /**< Compression level. */
 
     /* Pointer values */
     XMPP_SETTING_PASSWORD_CALLBACK_USERDATA = 0x80, /**< Userdata for password