Comment 1:

With some debugging prints:
chainHead=0 hashOffset=-2147188735 diff=2147188735
BAD i=2147188735 length=2 len(win)=58734
panic: runtime error: index out of range
goroutine 1 [running]:
compress/flate.(*compressor).findMatch(0x42191160, 0x7ffb7fff0000e46c,
0x1b9400000002, 0x2, 0x42179100, ...)
    /Users/rsc/g/go/src/pkg/compress/flate/deflate.go:160 +0x29c
compress/flate.(*compressor).deflate(0x42191160, 0x422bc400)
    /Users/rsc/g/go/src/pkg/compress/flate/deflate.go:270 +0x4ea
compress/flate.(*compressor).write(0x42191160, 0x422bcee8,
0x66e0000066e, 0x1156, 0x0, ...)
    /Users/rsc/g/go/src/pkg/compress/flate/deflate.go:363 +0x9f
compress/flate.(*Writer).Write(0x42191160, 0x422bc400, 0x115600001156,
0x100000001156, 0x0, ...)
    /Users/rsc/g/go/src/pkg/compress/flate/deflate.go:473 +0x54
compress/gzip.(*Writer).Write(0x421910b0, 0x422bc400, 0x115600001156,
0x115600001156, 0x0, ...)
    /Users/rsc/g/go/src/pkg/compress/gzip/gzip.go:190 +0x56c
main.main()
    /Users/rsc/Downloads/x.go:64 +0x9f8

Comment 2:

Thanks for the reproduction case. If I bound the arguments to findMatch the problem goes
away (diff below) but I am concerned that there are other wraparound bugs lurking.  I
will ask the person who wrote the code initially.
diff -r 7637a893613f src/pkg/compress/flate/deflate.go
--- a/src/pkg/compress/flate/deflate.go Tue May 29 14:37:41 2012 -0400
+++ b/src/pkg/compress/flate/deflate.go Tue May 29 15:43:15 2012 -0400
@@ -154,6 +154,9 @@
    minIndex := pos - windowSize
 
    for i := prevHead; tries > 0; tries-- {
+if i < 0 || i+1 >= len(win) || i+length >= len(win) || i+length < 0 {
+   print("BAD i=", i, " length=", length, " len(win)=", len(win), "\n")
+}
        if w0 == win[i] && w1 == win[i+1] && wEnd == win[i+length] {
            // The hash function ensures that if win[i] and win[i+1] match, win[i+2] matches
 
@@ -260,10 +263,11 @@
            minIndex = 0
        }
 
-       if d.chainHead-d.hashOffset >= minIndex &&
+       if off := d.chainHead-d.hashOffset; off >= minIndex && off < len(d.window) &&
            (d.fastSkipHashing != skipNever && lookahead > minMatchLength-1 ||
                d.fastSkipHashing == skipNever && lookahead > prevLength && prevLength < d.lazy) {
-           if newLength, newOffset, ok := d.findMatch(d.index, d.chainHead-d.hashOffset,
minMatchLength-1, lookahead); ok {
+if d.chainHead-d.hashOffset > 1<<29 { print("chainHead=", d.chainHead, "
hashOffset=", d.hashOffset, " diff=", off, "\n") }
+           if newLength, newOffset, ok := d.findMatch(d.index, off, minMatchLength-1,
lookahead); ok {
                d.length = newLength
                d.offset = newOffset
            }

Labels changed: added priority-later, removed priority-triage.

Status changed to Accepted.

Comment 3 by painted.now:

Just wanted to add that the problem persists in go version "go1.0.1", I only reported
the problem for go version "weekly.2012-03-27", sorry.

Comment 4:

No problem; I have reproduced this with the current tip.

Comment 5:

Reproduced. Started to work on this.

Comment 6:

The fix is on the review: http://golang.org/cl/6249067/
It's completely my fault.

Comment 7:

The fix is committed. Russ, should the bug be marked as closed?

Comment 8:

Yes, sorry. Usually we write "Fixes issue #3676." in the CL description and then it
closes automatically. I missed that that was missing.

Status changed to Fixed.