Check for time condition met/unmet due to old libcurl impl

The 'problem' was found at CentOS 7, the libcurl implementation makes the 'If-Modified-Since' check at the client side. So, if the server responds with an HTTP OK (200) code but the dates don't match, the response content is ignored.

What's the problem? For us (HTTP client) the response looks ok and we take the download as correct, but the downloaded file doesn't have content, so when its read bad things happen (actually the error is logged and the fallback is to mark such repository as invalid and try the download from another repo, if such repo is available).

diff --git a/src/http/http.c b/src/http/http.c
index a3fdcd949dfb6b7bcd14c3b543112360f6b40e28..6f42cbf33f61672e2532f5114101a80982a4dd6c 100644 (file)
--- a/src/http/http.c
+++ b/src/http/http.c
@@ -7,6 +7,8 @@
 #include "file.h"
 #include "log.h"
 
+/* HTTP Response Code 200 (OK) */
+#define HTTP_OK                        200
 /* HTTP Response Code 304 (Not Modified) */
 #define HTTP_NOT_MODIFIED      304
 /* HTTP Response Code 400 (Bad Request) */
@@ -105,9 +107,10 @@ curl_err_string(struct http_handler *handler, CURLcode res)
  */
 static int
 http_fetch(struct http_handler *handler, char const *uri, long *response_code,
-    http_write_cb cb, void *arg)
+    long *cond_met, http_write_cb cb, void *arg)
 {
        CURLcode res;
+       long unmet = 0;
 
        handler->errbuf[0] = 0;
        curl_easy_setopt(handler->curl, CURLOPT_URL, uri);
@@ -117,8 +120,24 @@ http_fetch(struct http_handler *handler, char const *uri, long *response_code,
        pr_debug("Doing HTTP GET to '%s'.", uri);
        res = curl_easy_perform(handler->curl);
        curl_easy_getinfo(handler->curl, CURLINFO_RESPONSE_CODE, response_code);
-       if (res == CURLE_OK)
+       if (res == CURLE_OK) {
+               if (*response_code != HTTP_OK)
+                       return 0;
+               /*
+                * Scenario: Received an OK code, but the time condition wasn't
+                * actually met, handle this as a "Not Modified" code.
+                *
+                * This check is due to old libcurl versions, where the impl
+                * doesn't let us get the response content since the library
+                * does the time validation, resulting in "The requested
+                * document is not new enough".
+                */
+               res = curl_easy_getinfo(handler->curl, CURLINFO_CONDITION_UNMET,
+                   &unmet);
+               if (res == CURLE_OK && unmet == 1)
+                       *cond_met = 0;
                return 0;
+       }
 
        if (*response_code >= HTTP_BAD_REQUEST)
                return pr_err("Error requesting URL %s (received HTTP code %ld): %s",
@@ -136,13 +155,14 @@ http_easy_cleanup(struct http_handler *handler)
 
 static int
 __http_download_file(struct rpki_uri *uri, http_write_cb cb,
-    long *response_code, long ims_value)
+    long *response_code, long ims_value, long *cond_met)
 {
        struct http_handler handler;
        struct stat stat;
        FILE *out;
        int error;
 
+       *cond_met = 1;
        if (config_get_work_offline()) {
                response_code = 0; /* Not 200 code, but also not an error */
                return 0;
@@ -167,8 +187,8 @@ __http_download_file(struct rpki_uri *uri, http_write_cb cb,
                    CURL_TIMECOND_IFMODSINCE);
        }
 
-       error = http_fetch(&handler, uri_get_global(uri), response_code, cb,
-           out);
+       error = http_fetch(&handler, uri_get_global(uri), response_code,
+           cond_met, cb, out);
        http_easy_cleanup(&handler);
        file_close(out);
 
@@ -194,7 +214,8 @@ int
 http_download_file(struct rpki_uri *uri, http_write_cb cb)
 {
        long response = 0;
-       return __http_download_file(uri, cb, &response, 0);
+       long cond_met = 0;
+       return __http_download_file(uri, cb, &response, 0, &cond_met);
 }
 
 /*
@@ -213,14 +234,28 @@ int
 http_download_file_with_ims(struct rpki_uri *uri, http_write_cb cb, long value)
 {
        long response = 0;
+       long cond_met = 0;
        int error;
 
-       error = __http_download_file(uri, cb, &response, value);
+       error = __http_download_file(uri, cb, &response, value, &cond_met);
        if (error)
                return error;
 
        /* rfc7232#section-3.3:
         * "the origin server SHOULD generate a 304 (Not Modified) response"
         */
-       return response == HTTP_NOT_MODIFIED;
+       if (response == HTTP_NOT_MODIFIED)
+               return 1;
+
+       /*
+        * Got another HTTP response code (OK or error).
+        *
+        * Check if the time condition was met (in case of error is set as
+        * 'true'), if it wasn't, then do a regular request (no time condition).
+        */
+       if (cond_met)
+               return 0;
+
+       return __http_download_file(uri, cb, &response, 0, &cond_met);
+
 }