content_encoding: #error on too old zlib

The previous runtime check using strcmp() risks failing when zlib
reaches 1.10. While this instead changes the logic to a cruder
build-time instead of runtime, it avoids the 1.10 risk.

I verified that ZLIB_VERNUM has been provided since at least the 1.2.0.3
release.

1.2.0.4 was released on 10 August 2003.

Reported-by: Fay Stegerman
Closes #16202

diff --git a/lib/content_encoding.c b/lib/content_encoding.c
index d23f8cdb55784a1cff662a57c91f4064753a2c82..e365af61682e00a618bd8f2c2a1aeaf236eaf67c 100644 (file)
--- a/lib/content_encoding.c
+++ b/lib/content_encoding.c
@@ -69,6 +69,10 @@
 
 #ifdef HAVE_LIBZ
 
+#if !defined(ZLIB_VERNUM) || (ZLIB_VERNUM < 0x1204)
+#error "requires zlib 1.2.0.4 or newer"
+#endif
+
 typedef enum {
   ZLIB_UNINIT,               /* uninitialized */
   ZLIB_INIT,                 /* initialized */
@@ -309,24 +313,15 @@ static CURLcode gzip_do_init(struct Curl_easy *data,
 {
   struct zlib_writer *zp = (struct zlib_writer *) writer;
   z_stream *z = &zp->z;     /* zlib state structure */
-  const char *v = zlibVersion();
 
   /* Initialize zlib */
   z->zalloc = (alloc_func) zalloc_cb;
   z->zfree = (free_func) zfree_cb;
 
-  if(strcmp(v, "1.2.0.4") >= 0) {
-    /* zlib version >= 1.2.0.4 supports transparent gzip decompressing */
-    if(inflateInit2(z, MAX_WBITS + 32) != Z_OK) {
-      return process_zlib_error(data, z);
-    }
-    zp->zlib_init = ZLIB_INIT_GZIP; /* Transparent gzip decompress state */
-  }
-  else {
-    failf(data, "too old zlib version: %s", v);
-    return CURLE_FAILED_INIT;
-  }
+  if(inflateInit2(z, MAX_WBITS + 32) != Z_OK)
+    return process_zlib_error(data, z);
 
+  zp->zlib_init = ZLIB_INIT_GZIP; /* Transparent gzip decompress state */
   return CURLE_OK;
 }