1 files changed, 114 insertions, 0 deletions
diff --git a/core/src/main/java/org/spongycastle/asn1/StreamUtil.java b/core/src/main/java/org/spongycastle/asn1/StreamUtil.java
new file mode 100644
index 00000000..cf92c511
--- /dev/null
+++ b/core/src/main/java/org/spongycastle/asn1/StreamUtil.java
@@ -0,0 +1,114 @@
+package org.spongycastle.asn1;
+
+import java.io.ByteArrayInputStream;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.channels.FileChannel;
+
+class StreamUtil
+{
+    private static final long  MAX_MEMORY = Runtime.getRuntime().maxMemory();
+
+    /**
+     * Find out possible longest length...
+     *
+     * @param in input stream of interest
+     * @return length calculation or MAX_VALUE.
+     */
+    static int findLimit(InputStream in)
+    {
+        if (in instanceof LimitedInputStream)
+        {
+            return ((LimitedInputStream)in).getRemaining();
+        }
+        else if (in instanceof ASN1InputStream)
+        {
+            return ((ASN1InputStream)in).getLimit();
+        }
+        else if (in instanceof ByteArrayInputStream)
+        {
+            return ((ByteArrayInputStream)in).available();
+        }
+        else if (in instanceof FileInputStream)
+        {
+            try
+            {
+                FileChannel channel = ((FileInputStream)in).getChannel();
+                long  size = (channel != null) ? channel.size() : Integer.MAX_VALUE;
+
+                if (size < Integer.MAX_VALUE)
+                {
+                    return (int)size;
+                }
+            }
+            catch (IOException e)
+            {
+                // ignore - they'll find out soon enough!
+            }
+        }
+
+        if (MAX_MEMORY > Integer.MAX_VALUE)
+        {
+            return Integer.MAX_VALUE;
+        }
+
+        return (int)MAX_MEMORY;
+    }
+
+    static int calculateBodyLength(
+        int length)
+    {
+        int count = 1;
+
+        if (length > 127)
+        {
+            int size = 1;
+            int val = length;
+
+            while ((val >>>= 8) != 0)
+            {
+                size++;
+            }
+
+            for (int i = (size - 1) * 8; i >= 0; i -= 8)
+            {
+                count++;
+            }
+        }
+
+        return count;
+    }
+
+    static int calculateTagLength(int tagNo)
+        throws IOException
+    {
+        int length = 1;
+
+        if (tagNo >= 31)
+        {
+            if (tagNo < 128)
+            {
+                length++;
+            }
+            else
+            {
+                byte[] stack = new byte[5];
+                int pos = stack.length;
+
+                stack[--pos] = (byte)(tagNo & 0x7F);
+
+                do
+                {
+                    tagNo >>= 7;
+                    stack[--pos] = (byte)(tagNo & 0x7F | 0x80);
+                }
+                while (tagNo > 127);
+
+                length += stack.length - pos;
+            }
+        }
+
+        return length;
+    }
+}