From b89ec523c123a31a41a2f35ff58b84e6b17161d0 Mon Sep 17 00:00:00 2001
From: Andreas Fankhauser hiddenalpha.ch
Date: Thu, 29 Dec 2022 23:07:01 +0100
Subject: Add ConcatInputStream

---
 .../xtra4j/octetstream/ConcatInputStream.java      | 97 ++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 xtra4j-misc/src/main/java/ch/hiddenalpha/xtra4j/octetstream/ConcatInputStream.java

diff --git a/xtra4j-misc/src/main/java/ch/hiddenalpha/xtra4j/octetstream/ConcatInputStream.java b/xtra4j-misc/src/main/java/ch/hiddenalpha/xtra4j/octetstream/ConcatInputStream.java
new file mode 100644
index 0000000..7ed8754
--- /dev/null
+++ b/xtra4j-misc/src/main/java/ch/hiddenalpha/xtra4j/octetstream/ConcatInputStream.java
@@ -0,0 +1,97 @@
+package ch.hiddenalpha.xtra4j.octetstream;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+
+/**
+ * Concatenates multiple {@link InputStream}s into one stream.
+ */
+public class ConcatInputStream extends InputStream {
+
+    private InputStream[] sources;
+    private int iSrc;
+
+    public ConcatInputStream( InputStream... sources ){
+        assert sources != null;
+        this.sources = sources;
+        this.iSrc = 0;
+    }
+
+    @Override
+    public int read( byte[] b, int off, int len ) throws IOException {
+        int copied = 0;
+        while( true ){
+            if( copied == len ){ // Request fully served
+                return len; }
+            if( isEof() ){
+                return (copied == 0) ? -1 : copied; }
+            InputStream src = sources[iSrc];
+            int readLen = src.read(b, off + copied, len - copied);
+            if( readLen < 0 ){
+                assert readLen == -1 : "Streams MUST NOT return negative values other than -1";
+                // Source drained. Continue read with next source.
+                shiftToNextSource();
+                continue;
+            }
+            copied += readLen;
+        }
+    }
+
+    @Override
+    public int read() throws IOException {
+        while( !isEof() ){
+            InputStream src = sources[iSrc];
+            int read = src.read();
+            assert read >= -1 : "Streams MUST NOT return negative values other than -1";
+            if( read == -1 ){
+                shiftToNextSource();
+                continue; // Try reading from next source.
+            }
+            return read;
+        }
+        return -1; // No more sources. We're done.
+    }
+
+    @Override
+    public void close() throws IOException {
+        // Close all remaining sources.
+        Exception firstException = null;
+        for( int i = iSrc ; i < sources.length ; ++i ){
+            try{
+                sources[i].close();
+            }catch( IOException|RuntimeException ex ){
+                if( firstException == null ){
+                    // Track the exception. But we have to close the
+                    // remaining streams regardless of early exceptions.
+                    firstException = ex;
+                }else if( firstException != ex ){
+                    firstException.addSuppressed(ex);
+                }
+            }
+        }
+        sources = null; // GC is not a magician. So tell him what we know.
+        // Bubble exception if we had any.
+        if( firstException instanceof RuntimeException ){
+            throw (RuntimeException)firstException;
+        }else if( firstException != null ){
+            throw (IOException)firstException;
+        }
+    }
+
+    private void shiftToNextSource() throws IOException {
+        if( !isEof() ){
+            InputStream oldSrc = sources[iSrc];
+            sources[iSrc] = null;
+            iSrc += 1;
+            // Calling close as last step to prevent trouble with our
+            // state as callee potentially could throw.
+            oldSrc.close();
+        }
+    }
+
+    private boolean isEof() {
+        return iSrc >= sources.length;
+    }
+
+}
-- 
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