https_client: log recoverable connection errors at INFO instead of WARNING

Follow-up to aarond10#210 (reset-timer fix). Submitted as a separate change since this is a logging-policy question rather than a behavior fix, and should not hold up the reset-timer fix if there is disagreement on log levels.

CURLE_OPERATION_TIMEDOUT, CURLE_HTTP2, CURLE_HTTP2_STREAM, CURLE_GOT_NOTHING, and CURLE_SEND_ERROR are all connection-reuse hiccups that the reset-timer path (see aarond10#210) already recovers from automatically without any user-visible impact. On resolvers whose edge cycles persistent connections periodically (observed with Quad9, not seen with Cloudflare), this is a routine, expected, self-healing condition - not a warning-worthy event - yet it was logged at WARNING twice per occurrence. On flash- and memory-constrained routers running at default verbosity, this produces a steady stream of log noise for a condition the proxy is already handling correctly on its own.

This logs the same information at INFO instead of WARNING specifically for the recoverable error codes above, matching the existing INFO-level "Client reset timer started" message already used for this recovery path. Genuinely unexpected failures are unchanged and still log at WARNING.

Tested on the same production router as aarond10#210 - confirmed curl-16 spam disappears from default-verbosity logs while the reset-timer recovery (and its own INFO-level messages, visible at raised verbosity) continues to function.

Author: MrObvious

src/https_client.c

@@ -347,6 +347,11 @@ static int https_fetch_ctx_process_response(https_client_t *client,
   long long_resp = 0;
   char *str_resp = NULL;
   int faulty_response = 1;
+  // Set for connection-reuse hiccups that the reset-timer path already
+  // recovers from automatically - these are routine, not warning-worthy,
+  // and logging them at WARNING just spams flash-constrained routers with
+  // an expected condition. Genuinely unexpected failures still log at WARNING.
+  int recoverable = 0;
 
   switch (curl_result_code) {
     case CURLE_OK:
@@ -363,11 +368,17 @@ static int https_fetch_ctx_process_response(https_client_t *client,
     case CURLE_SEND_ERROR:
       // These all indicate a stale/broken (often reused HTTP/2) connection,
       // not a one-off content error - same recovery path as a timeout.
+      recoverable = 1;
       if (!ev_is_active(&client->reset_timer)) {
         ILOG_REQ("Client reset timer started");
         ev_timer_start(client->loop, &client->reset_timer);
       }
-      __attribute__((fallthrough));
+      ILOG_REQ("curl request failed with %d: %s (recoverable, reset timer will recycle connection)",
+               curl_result_code, curl_easy_strerror(curl_result_code));
+      if (ctx->curl_errbuf[0] != 0) {
+        ILOG_REQ("curl error message: %s", ctx->curl_errbuf);
+      }
+      break;
     default:
       WLOG_REQ("curl request failed with %d: %s", curl_result_code, curl_easy_strerror(curl_result_code));
       if (ctx->curl_errbuf[0] != 0) {
@@ -385,8 +396,8 @@ static int https_fetch_ctx_process_response(https_client_t *client,
       curl_off_t uploaded_bytes = 0;
       if (curl_easy_getinfo(ctx->curl, CURLINFO_SIZE_UPLOAD_T, &uploaded_bytes) == CURLE_OK &&
           uploaded_bytes > 0) {
-        WLOG_REQ("Connecting and sending request to resolver was successful, "
-                 "but no response was sent back");
+        LOG(recoverable ? LOG_INFO : LOG_WARNING, "%04hX: Connecting and sending request to resolver was successful, "
+                 "but no response was sent back", ctx->id);
         if (client->opt->use_http_version == 1) {
           // for example Unbound DoH servers does not support HTTP/1.x, only HTTP/2
           WLOG("Resolver may not support current HTTP/%s protocol version",
@@ -398,7 +409,7 @@ static int https_fetch_ctx_process_response(https_client_t *client,
         // that have been opened a long time ago (if CURLOPT_MAXAGE_CONN can not be increased
         // it is 118 seconds)
         // also: when no internet connection, this floods the log for every failed request
-        WLOG_REQ("No response (probably connection has been closed or timed out)");
+        LOG(recoverable ? LOG_INFO : LOG_WARNING, "%04hX: No response (probably connection has been closed or timed out)", ctx->id);
       }
     } else {
       WLOG_REQ("curl response code: %d, content length: %zu", long_resp, ctx->buflen);