Report a disk switch if the length of the file changed.

Currently, the logic for this doesn't re-detect the file type, and it may not work correctly with some 2mg files, but it should work in most cases.

driver.c

@@ -337,7 +337,18 @@ static Word DoRead(struct GSOSDP *dp) {
     enum NetDiskError err = DoHTTPRequest(sess, readStart, readEnd);
     if (err != OPERATION_SUCCESSFUL) {
         dp->transferCount = 0;
+        if (err == DIFFERENT_LENGTH) {
+            if ((sess->totalLength - sess->dataOffset) % BLOCK_SIZE != 0) {
                 return drvrIOError;
+            } else {
+                sess->dataLength = sess->totalLength - sess->dataOffset;
+                dp->dibPointer->blockCount = sess->dataLength / BLOCK_SIZE;
+                sess->expectedLength = sess->totalLength;
+                return drvrDiskSwitch;
+            }
+        } else {
+            return drvrIOError;
+        }
     }
     
     ReadStatus readStatus;

http.c

@@ -363,7 +363,9 @@ netRetry:
     }
     
     /* See if we got what we wanted */
-    if (sess->expectedLength != 0 && sess->totalLength != sess->expectedLength) {
+    if (sess->expectedLength == 0) {
+        sess->expectedLength = sess->totalLength;
+    } else if (sess->totalLength != sess->expectedLength) {
         result = DIFFERENT_LENGTH;
         goto errorReturn;
     }

netdiskerror.h

@@ -31,7 +31,7 @@ enum NetDiskError {
     UNSUPPORTED_HEADER_VALUE,
     REDIRECT_ERROR,
     NOT_DESIRED_CONTENT,
-    DIFFERENT_LENGTH, /* Might be considered successful later */
+    DIFFERENT_LENGTH,
     
     /* Error values of 4xx and 5xx mean we got the corresponding HTTP error */
     HTTP_ERROR = 400,