[GitHub] [commons-compress] bodewig commented on a change in pull request #85: COMPRESS-497 Handle missing endheader offset

[GitBox <gi...@apache.org>]

bodewig commented on a change in pull request #85: COMPRESS-497 Handle missing endheader offset
URL: https://github.com/apache/commons-compress/pull/85#discussion_r341814277
 
 

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 File path: src/main/java/org/apache/commons/compress/archivers/sevenz/SevenZFile.java
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 @@ -441,17 +441,81 @@ private Archive readHeaders(final byte[] password) throws IOException {
                     archiveVersionMajor, archiveVersionMinor));
         }
 
+        boolean headerLooksValid = false;  // See https://www.7-zip.org/recover.html - "There is no correct End Header at the end of archive"
         final long startHeaderCrc = 0xffffFFFFL & buf.getInt();
-        final StartHeader startHeader = readStartHeader(startHeaderCrc);
+        if (startHeaderCrc == 0) {
+            // This is an indication of a corrupt header - peek the next 20 bytes
+            long currentPosition = channel.position();
+            ByteBuffer peekBuf = ByteBuffer.allocate(20);
+            readFully(peekBuf);
+            channel.position(currentPosition);
+            // Header invalid if all data is 0
+            while (peekBuf.hasRemaining()) {
+                if (peekBuf.get()!=0) {
+                    headerLooksValid = true;
+                    break;
+                }
+            }
+        } else {
+            headerLooksValid = true;
+        }
+
+        if (headerLooksValid) {
+            final StartHeader startHeader = readStartHeader(startHeaderCrc);
+            return initializeArchive(startHeader, password, true);
+        } else {
+            // No valid header found - probably first file of multipart archive was removed too early. Scan for end header.
 
 Review comment:
   Could you please extract the block starting here into a new method?

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