From 49e36679c5d9f81898ee87dcaf80dbda59e8ea7f Mon Sep 17 00:00:00 2001
From: Evan Jones <evan.jones@datadoghq.com>
Date: Wed, 7 Jul 2021 16:40:42 -0400
Subject: [PATCH 1/2] zstd.go: Set ZSTD_LEGACY_SUPPORT=4 to decompress legacy
 payloads

The compressed output format was finalized with zstd version 0.8. To
support decompression of previous versions, set the macro
ZSTD_LEGACY_SUPPORT=4, which matches the documented default for the
zstd command line tool:

https://github.com/facebook/zstd/blob/dev/programs/README.md

This made the compiled library about 20 kiB larger, but will allow
this to be used with really old zstd payloads.

.circleci/config.yml: Do not test with different versions of this
macro, since the tests now include a check that it can decompress
old payloads.
---
 .circleci/config.yml |  9 ---------
 zstd.go              |  5 +++++
 zstd_test.go         | 25 +++++++++++++++++++++++++
 3 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/.circleci/config.yml b/.circleci/config.yml
index 3f54a9c..9a93946 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -41,15 +41,6 @@ jobs:
       - run: 'unzip mr.zip'
       - run: 'go build'
       - run: 'PAYLOAD=`pwd`/mr GODEBUG=efence=1 go test -v'
-  "golang-zstd-legacy-support":
-    docker:
-      - image: circleci/golang:latest
-    steps:
-      - checkout
-      - run: 'wget https://github.com/DataDog/zstd/files/2246767/mr.zip'
-      - run: 'unzip mr.zip'
-      - run: 'CGO_CFLAGS="-DZSTD_LEGACY_SUPPORT=1" go build'
-      - run: 'PAYLOAD=`pwd`/mr CGO_CFLAGS="-DZSTD_LEGACY_SUPPORT=1" go test -v'
   "golang-i386":
     docker:
       - image: 32bit/ubuntu:16.04
diff --git a/zstd.go b/zstd.go
index 634ed65..a86eef5 100644
--- a/zstd.go
+++ b/zstd.go
@@ -1,6 +1,11 @@
 package zstd
 
 /*
+// support decoding of "legacy" zstd payloads from versions [0.4, 0.8], matching the
+// default configuration of the zstd command line tool:
+// https://github.com/facebook/zstd/blob/dev/programs/README.md
+#cgo CFLAGS: -DZSTD_LEGACY_SUPPORT=4
+
 #define ZSTD_STATIC_LINKING_ONLY
 #include "zstd.h"
 */
diff --git a/zstd_test.go b/zstd_test.go
index e5bb2d2..399b69a 100644
--- a/zstd_test.go
+++ b/zstd_test.go
@@ -6,6 +6,8 @@ import (
 	"fmt"
 	"io/ioutil"
 	"os"
+	"strconv"
+	"strings"
 	"testing"
 )
 
@@ -259,6 +261,29 @@ func TestRealPayload(t *testing.T) {
 	}
 }
 
+func TestLegacy(t *testing.T) {
+	// payloads compressed with zstd v0.5
+	// needs ZSTD_LEGACY_SUPPORT=5 or less
+	testCases := []struct {
+		input    string
+		expected string
+	}{
+		{"%\xb5/\xfd\x00@\x00\x1bcompressed with legacy zstd\xc0\x00\x00", "compressed with legacy zstd"},
+		{"%\xb5/\xfd\x00\x00\x00A\x11\x007\x14\xb0\xb5\x01@\x1aR\xb6iI7[FH\x022u\xe0O-\x18\xe3G\x9e2\xab\xd9\xea\xca7؊\xee\x884\xbf\xe7\xdc\xe4@\xe1-\x9e\xac\xf0\xf2\x86\x0f\xf1r\xbb7\b\x81Z\x01\x00\x01\x00\xdf`\xfe\xc0\x00\x00", "compressed with legacy zstd"},
+	}
+	for i, testCase := range testCases {
+		t.Run(strconv.Itoa(i), func(t *testing.T) {
+			out, err := Decompress(nil, []byte(testCase.input))
+			if err != nil {
+				t.Fatal(err)
+			}
+			if !strings.Contains(string(out), testCase.expected) {
+				t.Errorf("expected to find %#v; output=%#v", testCase.expected, string(out))
+			}
+		})
+	}
+}
+
 func BenchmarkCompression(b *testing.B) {
 	if raw == nil {
 		b.Fatal(ErrNoPayloadEnv)

From 791d5e3e96fb64a7f922bab0590d52d4ef8611bc Mon Sep 17 00:00:00 2001
From: Dmytro Milinevskyi <dmytro.milinevskyi@datadoghq.com>
Date: Wed, 16 Mar 2022 13:39:31 +0100
Subject: [PATCH 2/2] ci:circle: remove golang-zstd-legacy-support from the
 workflows

---
 .circleci/config.yml | 1 -
 1 file changed, 1 deletion(-)

diff --git a/.circleci/config.yml b/.circleci/config.yml
index 5a4f907..f341c3c 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -109,4 +109,3 @@ workflows:
       - "golang-efence"
       - "golang-efence-external-libzstd"
       - "golang-i386"
-      - "golang-zstd-legacy-support"