From 5c8d02efc158a55f1a495e11e97080f6a37efbc9 Mon Sep 17 00:00:00 2001
From: Istvan Bartha <106101+pityka@users.noreply.github.com>
Date: Thu, 4 Jun 2026 23:46:36 +0200
Subject: [PATCH] Gunzip block gzip files

Multiple gzip blocks concatenated form a valid gzip stream
---
 .../fs2/compression/CompressionPlatform.scala | 60 +++++++++++++------
 .../JvmNativeCompressionSuite.scala           | 25 ++++++++
 2 files changed, 66 insertions(+), 19 deletions(-)

diff --git a/core/jvm-native/src/main/scala/fs2/compression/CompressionPlatform.scala b/core/jvm-native/src/main/scala/fs2/compression/CompressionPlatform.scala
index 302f3d864f..6ba13f52a5 100644
--- a/core/jvm-native/src/main/scala/fs2/compression/CompressionPlatform.scala
+++ b/core/jvm-native/src/main/scala/fs2/compression/CompressionPlatform.scala
@@ -685,7 +685,7 @@ private[compression] trait CompressionCompanionPlatform
                           crc32 = Some(contentCrc32)
                         )(s).stream
                       )
-                      .through(_gunzip_validateTrailer(contentCrc32, inflater))
+                      .through(_gunzip_validateTrailer(inflateParams, contentCrc32, inflater))
                   )
                 )
               }
@@ -807,6 +807,7 @@ private[compression] trait CompressionCompanionPlatform
           else stream
 
       private def _gunzip_validateTrailer(
+          inflateParams: InflateParams,
           crc32: CRC32,
           inflater: Inflater
       ): Pipe[F, Byte, Byte] =
@@ -829,30 +830,51 @@ private[compression] trait CompressionCompanionPlatform
                   Pull.done
               } else Pull.raiseError(new ZipException("Failed to read trailer (1)"))
 
-            def streamUntilTrailer(last: Chunk[Byte]): Stream[F, Byte] => Pull[F, Byte, Unit] =
+            // RFC 1952 § 2.2: a gzip stream may concatenate multiple members.
+            def continueWithNextMember(s: Stream[F, Byte]): Pull[F, Byte, Unit] =
+              s.pull.uncons.flatMap {
+                case None               => Pull.done
+                case Some((next, rest)) =>
+                  (Stream.chunk(next) ++ rest)
+                    .through(gunzip(inflateParams))
+                    .flatMap(_.content)
+                    .pull
+                    .echo
+              }
+
+            def consumeTrailer(
+                buffered: Chunk[Byte],
+                rest: Stream[F, Byte]
+            ): Pull[F, Byte, Unit] =
+              if (buffered.size >= gzipTrailerBytes) {
+                val (trailer, afterTrailer) = buffered.splitAt(gzipTrailerBytes)
+                validateTrailer(trailer) >>
+                  continueWithNextMember(Stream.chunk(afterTrailer) ++ rest)
+              } else
+                rest.pull.uncons.flatMap {
+                  case Some((next, restRest)) => consumeTrailer(buffered ++ next, restRest)
+                  case None                   => validateTrailer(buffered)
+                }
+
+            def streamUntilTrailer(emitted: Long): Stream[F, Byte] => Pull[F, Byte, Unit] =
               _.pull.uncons
                 .flatMap {
                   case Some((next, rest)) =>
-                    if (inflater.finished())
-                      if (next.size >= gzipTrailerBytes)
-                        if (last.nonEmpty) Pull.output(last) >> streamUntilTrailer(next)(rest)
-                        else streamUntilTrailer(next)(rest)
-                      else
-                        streamUntilTrailer(last ++ next)(rest)
-                    else if (last.nonEmpty)
-                      Pull.output(last) >> Pull.output(next) >>
-                        streamUntilTrailer(Chunk.empty[Byte])(rest)
-                    else Pull.output(next) >> streamUntilTrailer(Chunk.empty[Byte])(rest)
+                    val contentRemaining = (inflater.getBytesWritten - emitted).max(0L).toInt
+                    val chunkIsAllContent = next.size <= contentRemaining
+                    val chunkStraddlesBoundary = !chunkIsAllContent && contentRemaining > 0
+                    if (chunkIsAllContent)
+                      Pull.output(next) >> streamUntilTrailer(emitted + next.size)(rest)
+                    else if (chunkStraddlesBoundary) {
+                      val (content, postContent) = next.splitAt(contentRemaining)
+                      Pull.output(content) >> consumeTrailer(postContent, rest)
+                    } else
+                      consumeTrailer(next, rest)
                   case None =>
-                    val preTrailerBytes = last.size - gzipTrailerBytes
-                    if (preTrailerBytes > 0)
-                      Pull.output(last.take(preTrailerBytes)) >>
-                        validateTrailer(last.drop(preTrailerBytes))
-                    else
-                      validateTrailer(last)
+                    Pull.raiseError(new ZipException("Failed to read trailer (1)"))
                 }
 
-            streamUntilTrailer(Chunk.empty[Byte])(stream)
+            streamUntilTrailer(0L)(stream)
           }.stream
 
       /** Like Stream.unconsN, but returns a chunk of elements that do not satisfy the predicate, splitting chunk as necessary.
diff --git a/core/jvm-native/src/test/scala/fs2/compression/JvmNativeCompressionSuite.scala b/core/jvm-native/src/test/scala/fs2/compression/JvmNativeCompressionSuite.scala
index c04b1157a4..960869eb22 100644
--- a/core/jvm-native/src/test/scala/fs2/compression/JvmNativeCompressionSuite.scala
+++ b/core/jvm-native/src/test/scala/fs2/compression/JvmNativeCompressionSuite.scala
@@ -22,6 +22,7 @@
 package fs2
 
 import cats.effect._
+import cats.syntax.traverse._
 import fs2.compression._
 import org.scalacheck.effect.PropF.forAllF
 
@@ -325,6 +326,30 @@ class JvmNativeCompressionSuite extends CompressionSuite {
       .assertEquals(expectedContent)
   }
 
+  test("gunzip handles concatenated gzip members (RFC 1952 § 2.2 / block gzip)") {
+    def gzipMember(s: String): IO[Chunk[Byte]] =
+      Stream
+        .chunk(Chunk.array(s.getBytes(StandardCharsets.UTF_8)))
+        .through(Compression[IO].gzip(8192))
+        .compile
+        .to(Chunk)
+
+    val parts = List("first member ", "second member ", "third member")
+    parts
+      .traverse(gzipMember)
+      .flatMap { members =>
+        Stream
+          .chunk(Chunk.concat(members))
+          .rechunkRandomlyWithSeed(0.1, 2)(System.nanoTime())
+          .through(Compression[IO].gunzip(8192))
+          .flatMap(_.content)
+          .compile
+          .toVector
+      }
+      .map(bytes => new String(bytes.toArray, StandardCharsets.UTF_8))
+      .assertEquals(parts.mkString)
+  }
+
   def toEncodableFileName(fileName: String): String =
     new String(
       fileName.replaceAll("\u0000", "_").getBytes(StandardCharsets.ISO_8859_1),