wget: correctly handle rare case when we get EAGAIN _on first_ read

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/networking/wget.c b/networking/wget.c
index f2d7daf2f886ce99bb472710c3ac5b5029f97d85..48688640a07f72fa22d8bb0c1f56e8a323d2dc75 100644 (file)
--- a/networking/wget.c
+++ b/networking/wget.c
@@ -487,6 +487,7 @@ static void NOINLINE retrieve_file_data(FILE *dfp, int output_fd)
                                        rdsz = (unsigned)G.content_len;
                                }
                        }
+
 #if ENABLE_FEATURE_WGET_STATUSBAR || ENABLE_FEATURE_WGET_TIMEOUT
 # if ENABLE_FEATURE_WGET_TIMEOUT
                        second_cnt = G.timeout_seconds;
@@ -497,22 +498,41 @@ static void NOINLINE retrieve_file_data(FILE *dfp, int output_fd)
 # if ENABLE_FEATURE_WGET_TIMEOUT
                                if (second_cnt != 0 && --second_cnt == 0) {
                                        progress_meter(PROGRESS_END);
-                                       bb_perror_msg_and_die("download timed out");
+                                       bb_error_msg_and_die("download timed out");
                                }
 # endif
                                /* Needed for "stalled" indicator */
                                progress_meter(PROGRESS_BUMP);
                        }
 #endif
+                       /* fread internally uses read loop, which in our case
+                        * is usually exited when we get EAGAIN.
+                        * In this case, libc sets error marker on the stream.
+                        * Need to clear it before next fread to avoid possible
+                        * rare false positive ferror below. Rare because usually
+                        * fread gets more than zero bytes, and we don't fall
+                        * into if (n <= 0) ...
+                        */
+                       clearerr(dfp);
+                       errno = 0;
                        n = fread(G.wget_buf, 1, rdsz, dfp);
+                       /* man fread:
+                        * If error occurs, or EOF is reached, the return value
+                        * is a short item count (or zero).
+                        * fread does not distinguish between EOF and error.
+                        */
                        if (n <= 0) {
-                               if (ferror(dfp)) {
-                                       /* perror will not work: ferror doesn't set errno */
-                                       bb_error_msg_and_die(bb_msg_read_error);
-                               }
-                               break;
+#if ENABLE_FEATURE_WGET_STATUSBAR || ENABLE_FEATURE_WGET_TIMEOUT
+                               if (errno == EAGAIN) /* poll lied, there is no data? */
+                                       continue; /* yes */
+#endif
+                               if (ferror(dfp))
+                                       bb_perror_msg_and_die(bb_msg_read_error);
+                               break; /* EOF, not error */
                        }
+
                        xwrite(output_fd, G.wget_buf, n);
+
 #if ENABLE_FEATURE_WGET_STATUSBAR
                        G.transferred += n;
                        progress_meter(PROGRESS_BUMP);