adb: don't divide by zero

If we stat a file and get a size of 0, and then successfully read bytes
from that file, we would previously divide by zero when calculating the
percentage completion of the file. This case happens either when we're
racing against something else writing to the file, or when we're pulling
magical files such as the ones in /dev/cpuctl/ that lie about their
size.

Bug: http://b/25925733
Change-Id: I980b9c14f44a1eb4a42bc8736c94fa6db06c08d1

1 files changed, 17 insertions, 4 deletions

diff --git a/adb/file_sync_client.cpp b/adb/file_sync_client.cpp
index e109e3eef4..c422b4f193 100644
--- a/adb/file_sync_client.cpp
+++ b/adb/file_sync_client.cpp
@@ -190,8 +190,15 @@ class SyncConnection {
 
             bytes_copied += ret;
 
-            int percentage = static_cast<int>(bytes_copied * 100 / total_size);
-            Printf("%s: %d%%", rpath, percentage);
+            if (total_size == 0) {
+                // This case can happen if we're racing against something that wrote to the file
+                // between our stat and our read, or if we're reading a magic file that lies about
+                // its size.
+                Printf("%s: ?%%", rpath);
+            } else {
+                int percentage = static_cast<int>(bytes_copied * 100 / total_size);
+                Printf("%s: %d%%", rpath, percentage);
+            }
         }
 
         adb_close(lfd);
@@ -458,8 +465,14 @@ static bool sync_recv(SyncConnection& sc, const char* rpath, const char* lpath)
 
         bytes_copied += msg.data.size;
 
-        int percentage = static_cast<int>(bytes_copied * 100 / size);
-        sc.Printf("%s: %d%%", rpath, percentage);
+        if (size == 0) {
+            // This case can happen if we're racing against something that wrote to the file between
+            // our stat and our read, or if we're reading a magic file that lies about its size.
+            sc.Printf("%s: ?%%", rpath);
+        } else {
+            int percentage = static_cast<int>(bytes_copied * 100 / size);
+            sc.Printf("%s: %d%%", rpath, percentage);
+        }
     }
 
     adb_close(lfd);