Make function documentation more clear about the negative offset value.

Improve error checking inside function and add comment about not updating the seek pointer when an offset of 0 is specified

2 files changed, 8 insertions, 7 deletions

diff --git a/indra/llcommon/llfile.cpp b/indra/llcommon/llfile.cpp
index 3e469111fa..a1d41cdf73 100755
--- a/indra/llcommon/llfile.cpp
+++ b/indra/llcommon/llfile.cpp
@@ -911,16 +911,16 @@ S64 LLFile::read(const std::string& filename, void* buf, S64 offset, S64 nbytes,
         std::ios_base::openmode omode = LLFile::in | LLFile::binary;
 
         LLFile file(filename, omode, ec);
-        if (file)
+        if (!ec && (bool)file)
         {
-            S64 bytes_read = 0;
             if (offset > 0)
             {
                 file.seek(offset, ec);
             }
+            // else (offset == 0) file was just opened and should already be at 0.
             if (!ec)
             {
-                bytes_read = file.read(buf, nbytes, ec);
+                S64 bytes_read = file.read(buf, nbytes, ec);
                 if (!ec)
                 {
                     return bytes_read;
@@ -961,16 +961,16 @@ S64 LLFile::write(const std::string& filename, const void* buf, S64 offset, S64
         }
 
         LLFile file(filename, omode, ec);
-        if (file)
+        if (!ec && (bool)file)
         {
-            S64 bytes_written = 0;
             if (offset > 0)
             {
                 file.seek(offset, ec);
             }
+            // else (offset == 0) we are not appending, file was just opened and should already be at 0.
             if (!ec)
             {
-                bytes_written = file.write(buf, nbytes, ec);
+                S64 bytes_written = file.write(buf, nbytes, ec);
                 if (!ec)
                 {
                     return bytes_written;
diff --git a/indra/llcommon/llfile.h b/indra/llcommon/llfile.h
index b007fcaf02..2c74c97d0b 100755
--- a/indra/llcommon/llfile.h
+++ b/indra/llcommon/llfile.h
@@ -343,7 +343,8 @@ public:
     /// write nBytes from the buffer into the file, starting at offset in the file
     static  S64     write(const std::string& filename, const void* buf, S64 offset, S64 nbytes);
     static  S64     write(const std::string& filename, const void* buf, S64 offset, S64 nbytes, std::error_code& ec);
-    ///< A negative offset will append the data to the end of the file
+    ///< If a negative offset is provided, the file is opened in append mode and the
+    ///  write will be appended to the end of the file.
     ///  @returns bytes written on success, or -1 on failure
 
     /// return the file stat structure for filename