added random_compress.nim to tests/

src/zippy/deflate.nim

@@ -449,7 +449,8 @@ func deflate*(src: seq[uint8]): seq[uint8] =
   b.data.setLen(
     b.data.len +
     (((hclen.int + 4) * 3 + 7) div 8) + # hclen rle
-    bitLensRle.len * 2
+    bitLensRle.len * 2 +
+    encoded.len
   )
 
   b.addBit(1)

tests/random_compress.nim

@@ -0,0 +1,28 @@
+import random, zippy
+
+randomize()
+
+# Generate random blobs of data containing runs of random lengths. Ensure
+# we can always compress this blob and that uncompressing the compressed
+# data matches the original blob.
+
+for i in 0 ..< 10000:
+  echo i
+
+  var
+    data: seq[uint8]
+    length = rand(100000)
+    i: int
+  data.setLen(length)
+  while i < length:
+    let
+      v = rand(255).uint8
+      runLength = min(rand(255), length - i)
+    for j in 0 ..< runLength:
+      data[i + j] = v
+    inc(i, runLength)
+
+  let
+    compressed = compress(data, dfGzip)
+    uncompressed = uncompress(compressed)
+  doAssert uncompressed == data