feat(compress): Decode brotli and zstd response bodies

README.md

@@ -377,15 +377,15 @@ itself, and leaves the rest of the run intact:
 
 ```console
 $ http-assert --assert-body '"status":"success"' https://cdn.example.com/
-- body: response is br-encoded and was not decoded: no decoder for "br"; gzip and deflate are supported
+- body: response is compress-encoded and was not decoded: no decoder for "compress"; br, deflate, gzip, zstd are supported
 
 $ http-assert --assert-ok https://cdn.example.com/
 [+] PASSED 38ms
 ```
 
-Brotli (`br`) and zstd are the encodings this covers in practice. Neither is
-supported yet: [#77](https://github.com/korya/http-assert/issues/77) tracks
-brotli and [#78](https://github.com/korya/http-assert/issues/78) tracks zstd.
+gzip, deflate, brotli (`br`) and zstd are decoded. Brotli and zstd each cost a
+dependency, which is why they are named here rather than assumed: they are what
+CDNs actually serve, and a body assertion against one is the ordinary case.
 
 A header that claims an encoding the body does not have is treated the same
 way. Reading those bytes as plain text would be its own silent corruption.
@@ -604,7 +604,7 @@ a tool whose job is checking. This is the complete list:
 | `-d @file` | reads the file | sends the literal string `@file` |
 | `-d` repeated | values joined with `&` | rejected, exit `71` |
 | `--retry` | transport errors and a fixed set of transient statuses, exponential backoff | any failed attempt, assertion failures included, fixed delay |
-| Response decompression | opt-in via `--compressed` | always: gzip and deflate are decoded before assertions run |
+| Response decompression | opt-in via `--compressed` | always: gzip, deflate, br and zstd are decoded before assertions run |
 | Pointing at a backend | `--resolve host:port:addr` takes an address | `--maphost 'host:port=dst[:port]'` takes a hostname or an address |
 
 ## License

assertions_test.go

@@ -729,8 +729,8 @@ func Test_AssertionCheckSeparatesFailureFromError(t *testing.T) {
 
 	t.Run("an undecodable body is an error, not a Failure", func(t *testing.T) {
 		res := &httpResponse{
-			Encoding:  "br",
-			DecodeErr: errors.New(`no decoder for "br"`),
+			Encoding:  "compress",
+			DecodeErr: errors.New(`no decoder for "compress"`),
 		}
 
 		for name, a := range map[string]Assertion{
@@ -755,8 +755,8 @@ func Test_AssertionCheckSeparatesFailureFromError(t *testing.T) {
 	t.Run("a status assertion is unaffected by an undecodable body", func(t *testing.T) {
 		res := &httpResponse{
 			Response:  &http.Response{StatusCode: 200, Status: "200 OK"},
-			Encoding:  "br",
-			DecodeErr: errors.New(`no decoder for "br"`),
+			Encoding:  "compress",
+			DecodeErr: errors.New(`no decoder for "compress"`),
 		}
 
 		f, err := AssertStatusOK().Check(res)

compression_test.go

@@ -145,10 +145,10 @@ func Test_decodeBody(t *testing.T) {
 		},
 		{
 			Name:         "an encoding with no decoder here",
-			Enc:          "br",
-			Body:         []byte{0x1b, 0x13, 0x00},
+			Enc:          "compress",
+			Body:         []byte("payload"),
 			WantErr:      true,
-			WantEncoding: "br",
+			WantEncoding: "compress",
 		},
 		{
 			// The header claims gzip and the bytes are not. Silently asserting
@@ -246,11 +246,11 @@ func Test_bodyOf(t *testing.T) {
 	})
 
 	t.Run("an undecoded body is refused, and says why", func(t *testing.T) {
-		res := encoded("br", []byte{0x1b, 0x13, 0x00})
+		res := encoded("compress", []byte("payload"))
 		res.decodeBody()
 
 		_, err := bodyOf(res)
-		checkErrMatch(t, "bodyOf", err, `^body: response is br-encoded and was not decoded: `)
+		checkErrMatch(t, "bodyOf", err, `^body: response is compress-encoded and was not decoded: `)
 	})
 }
 
@@ -275,10 +275,10 @@ func Test_bodyAssertionsRefuseAnEncodedBody(t *testing.T) {
 
 	for name, a := range assertions {
 		t.Run(name, func(t *testing.T) {
-			res := encoded("br", []byte{0x1b, 0x13, 0x00})
+			res := encoded("compress", []byte("payload"))
 			res.decodeBody()
 
-			checkErrMatch(t, name, check(a, res), `^body: response is br-encoded and was not decoded: `)
+			checkErrMatch(t, name, check(a, res), `^body: response is compress-encoded and was not decoded: `)
 		})
 	}
 }

e2e_compression_test.go

@@ -111,28 +111,74 @@ func TestE2ECompressionHeadersSurvive(t *testing.T) {
 	})
 }
 
+// TestE2ECompressionBrotliZstd covers the two codings that cost a dependency.
+//
+// Both are what CDNs actually serve, so a body assertion against one is the
+// ordinary case rather than an exotic one (#77, #78).
+func TestE2ECompressionBrotliZstd(t *testing.T) {
+	for path, coding := range map[string]string{"/brotli": "br", "/zstd": "zstd"} {
+		t.Run(coding+" is decoded before the body assertions run", func(t *testing.T) {
+			assertExit(t, run(t, nil, "--assert-body", `"status":"success"`, url(path)), exitOK)
+			assertExit(t, run(t, nil, "--assert-body-eq", `{"status":"success"}`, url(path)), exitOK)
+		})
+
+		t.Run(coding+" decodes for --assert-jq too", func(t *testing.T) {
+			assertExit(t, run(t, nil, "--assert-jq", `.status == "success"`, url(path)), exitOK)
+		})
+
+		// Decoding must not rewrite what the response said about itself: the
+		// point of decoding by hand is to assert on the payload and on the
+		// Content-Encoding at the same time.
+		t.Run(coding+" is still reported as the encoding that arrived", func(t *testing.T) {
+			r := run(t, nil,
+				"--assert-header-eq", "Content-Encoding: "+coding,
+				"--assert-body", `"status":"success"`, url(path))
+			assertExit(t, r, exitOK)
+		})
+	}
+
+	// A decoder makes this failure reachable for br at all; without one the
+	// body never got as far as being malformed.
+	t.Run("a body that claims br and is not br fails the body assertions", func(t *testing.T) {
+		r := run(t, nil, "--assert-body", `"status":"success"`, url("/brotli-corrupt"))
+		assertExit(t, r, exitAssertFail)
+		assertContains(t, r, "body: response is br-encoded and was not decoded")
+	})
+
+	t.Run("a status check is unaffected by a corrupt br body", func(t *testing.T) {
+		assertExit(t, run(t, nil, "--assert-ok", url("/brotli-corrupt")), exitOK)
+	})
+}
+
 // TestE2ECompressionUndecodable covers an encoding with no decoder here.
 //
 // The response still has a status and headers worth asserting on, so only the
 // body assertions refuse. Failing the whole run would be simpler and would
-// break a status check against any CDN serving brotli.
+// break a status check against any CDN serving a coding this does not know.
 func TestE2ECompressionUndecodable(t *testing.T) {
 	t.Run("a status check is unaffected", func(t *testing.T) {
-		assertExit(t, run(t, nil, "--assert-ok", url("/brotli")), exitOK)
+		assertExit(t, run(t, nil, "--assert-ok", url("/unsupported")), exitOK)
 	})
 
 	t.Run("a header check is unaffected", func(t *testing.T) {
-		r := run(t, nil, "--assert-header-eq", "Content-Encoding: br", url("/brotli"))
+		r := run(t, nil, "--assert-header-eq", "Content-Encoding: compress", url("/unsupported"))
 		assertExit(t, r, exitOK)
 	})
 
 	t.Run("a body check refuses, and names the encoding", func(t *testing.T) {
-		r := run(t, nil, "--assert-body", `"status":"success"`, url("/brotli"))
+		r := run(t, nil, "--assert-body", `"status":"success"`, url("/unsupported"))
 		assertExit(t, r, exitAssertFail)
-		assertContains(t, r, "body: response is br-encoded and was not decoded")
-		assertContains(t, r, "no decoder for \"br\"")
+		assertContains(t, r, "body: response is compress-encoded and was not decoded")
+		assertContains(t, r, "no decoder for \"compress\"")
 		// The old failure was a bare hex dump with nothing explaining it.
-		assertContains(t, r, "<< Payload is br-encoded and was not decoded >>")
+		assertContains(t, r, "<< Payload is compress-encoded and was not decoded >>")
+	})
+
+	// The list in the failure is derived from the decoder map, so a coding
+	// added without updating the message is not possible.
+	t.Run("it names what it does support", func(t *testing.T) {
+		r := run(t, nil, "--assert-body", `"status":"success"`, url("/unsupported"))
+		assertContains(t, r, "br, deflate, gzip, zstd are supported")
 	})
 
 	// A header claiming an encoding the body does not have. Treating those

e2e_jq_test.go

@@ -177,9 +177,9 @@ func TestE2EAssertJQBodyProblems(t *testing.T) {
 
 	// An encoding nothing can decode reports the encoding, not invalid JSON.
 	t.Run("a body still encoded", func(t *testing.T) {
-		r := run(t, nil, "--assert-jq", `. == 1`, url("/brotli"))
+		r := run(t, nil, "--assert-jq", `. == 1`, url("/unsupported"))
 		assertExit(t, r, exitAssertFail)
-		assertContains(t, r, "body: response is br-encoded")
+		assertContains(t, r, "body: response is compress-encoded")
 	})
 
 	// A query yielding nothing has checked nothing, so it must not pass.

e2e_server_test.go

@@ -1,6 +1,7 @@
 package main_test
 
 import (
+	"bytes"
 	"compress/flate"
 	"compress/gzip"
 	"compress/zlib"
@@ -17,6 +18,9 @@ import (
 	"sync/atomic"
 	"testing"
 	"time"
+
+	"github.com/andybalholm/brotli"
+	"github.com/klauspost/compress/zstd"
 )
 
 // The e2e suite talks to two real servers started once per test run: a plain
@@ -267,11 +271,39 @@ func testHandler() http.Handler {
 		_ = zw.Close()
 	})
 
-	// An encoding with no decoder here. Brotli is the realistic case; the bytes
-	// are not real brotli because nothing in the suite could produce them, and
-	// the CLI never gets far enough to care.
 	mux.HandleFunc("/brotli", func(w http.ResponseWriter, _ *http.Request) {
-		write(w, http.StatusOK, []byte{0x1b, 0x13, 0x00, 0x00, 0xa4, 0xb0, 0xb2},
+		var buf bytes.Buffer
+		bw := brotli.NewWriter(&buf)
+		_, _ = bw.Write([]byte(`{"status":"success"}`))
+		_ = bw.Close()
+		write(w, http.StatusOK, buf.Bytes(), http.Header{"Content-Encoding": {"br"}})
+	})
+
+	mux.HandleFunc("/zstd", func(w http.ResponseWriter, _ *http.Request) {
+		var buf bytes.Buffer
+		zw, err := zstd.NewWriter(&buf)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+		_, _ = zw.Write([]byte(`{"status":"success"}`))
+		_ = zw.Close()
+		write(w, http.StatusOK, buf.Bytes(), http.Header{"Content-Encoding": {"zstd"}})
+	})
+
+	// An encoding with no decoder here, and the one place the suite needs a
+	// coding that will stay unsupported. RFC 9110 still registers `compress`
+	// (LZW), and effectively nothing serves it -- unlike br and zstd, which
+	// were the realistic examples right up until they were implemented.
+	mux.HandleFunc("/unsupported", func(w http.ResponseWriter, _ *http.Request) {
+		write(w, http.StatusOK, []byte(`{"status":"success"}`),
+			http.Header{"Content-Encoding": {"compress"}})
+	})
+
+	// Claims brotli and is not brotli. gzip-corrupt covers the same class, but
+	// only since br gained a decoder can a br body fail this way at all.
+	mux.HandleFunc("/brotli-corrupt", func(w http.ResponseWriter, _ *http.Request) {
+		write(w, http.StatusOK, []byte(`{"status":"success"}`),
 			http.Header{"Content-Encoding": {"br"}})
 	})
 

go.mod

@@ -5,7 +5,9 @@ go 1.26
 toolchain go1.26.5
 
 require (
+	github.com/andybalholm/brotli v1.2.2
 	github.com/itchyny/gojq v0.12.19
+	github.com/klauspost/compress v1.19.2
 	github.com/spf13/cobra v1.10.2
 	github.com/spf13/pflag v1.0.10
 )

go.sum

@@ -1,15 +1,21 @@
+github.com/andybalholm/brotli v1.2.2 h1:HzTuoo2ErYQqf5qvcJInB8uvqSVxRttzkFexPWtnceM=
+github.com/andybalholm/brotli v1.2.2/go.mod h1:rzTDkvFWvIrjDXZHkuS16NPggd91W3kUSvPlQ1pLaKY=
 github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=
 github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
 github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
 github.com/itchyny/gojq v0.12.19 h1:ttXA0XCLEMoaLOz5lSeFOZ6u6Q3QxmG46vfgI4O0DEs=
 github.com/itchyny/gojq v0.12.19/go.mod h1:5galtVPDywX8SPSOrqjGxkBeDhSxEW1gSxoy7tn1iZY=
 github.com/itchyny/timefmt-go v0.1.8 h1:1YEo1JvfXeAHKdjelbYr/uCuhkybaHCeTkH8Bo791OI=
 github.com/itchyny/timefmt-go v0.1.8/go.mod h1:5E46Q+zj7vbTgWY8o5YkMeYb4I6GeWLFnetPy5oBrAI=
+github.com/klauspost/compress v1.19.2 h1:hMRETovs/pu/dVWN7zIT1PGG8t509MwT6bO7XSi26R8=
+github.com/klauspost/compress v1.19.2/go.mod h1:cwPg85FWrGar70rWktvGQj8/hthj3wpl0PGDogxkrSQ=
 github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
 github.com/spf13/cobra v1.10.2 h1:DMTTonx5m65Ic0GOoRY2c16WCbHxOOw6xxezuLaBpcU=
 github.com/spf13/cobra v1.10.2/go.mod h1:7C1pvHqHw5A4vrJfjNwvOdzYu0Gml16OCs2GRiTUUS4=
 github.com/spf13/pflag v1.0.9/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
 github.com/spf13/pflag v1.0.10 h1:4EBh2KAYBwaONj6b2Ye1GiHfwjqyROoF4RwYO+vPwFk=
 github.com/spf13/pflag v1.0.10/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+github.com/xyproto/randomstring v1.0.5 h1:YtlWPoRdgMu3NZtP45drfy1GKoojuR7hmRcnhZqKjWU=
+github.com/xyproto/randomstring v1.0.5/go.mod h1:rgmS5DeNXLivK7YprL0pY+lTuhNQW3iGxZ18UQApw/E=
 go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=

jq_test.go

@@ -286,10 +286,10 @@ func Test_decodeJSON_parsesOnce(t *testing.T) {
 	// the reader would otherwise go looking for a malformed payload (#27).
 	t.Run("an undecoded body reports the encoding", func(t *testing.T) {
 		enc := jqResponse(jqDoc)
-		enc.Encoding = "br"
-		enc.DecodeErr = errors.New("no decoder for \"br\"")
+		enc.Encoding = "compress"
+		enc.DecodeErr = errors.New("no decoder for \"compress\"")
 
 		_, err := enc.decodeJSON()
-		checkErrMatch(t, "decodeJSON", err, `^body: response is br-encoded`)
+		checkErrMatch(t, "decodeJSON", err, `^body: response is compress-encoded`)
 	})
 }

main.go

@@ -76,9 +76,9 @@
 // # Compression
 //
 // A compressed body is decoded before the assertions run, so --assert-body and
-// friends always see the payload. gzip and deflate are understood; an encoding
-// nothing here can remove fails the body assertions by name and leaves every
-// other assertion alone.
+// friends always see the payload. gzip, deflate, br and zstd are understood; an
+// encoding nothing here can remove fails the body assertions by name and leaves
+// every other assertion alone.
 //
 // The request advertises no Accept-Encoding of its own, and the response
 // headers are reported exactly as they arrived. net/http would decode only
@@ -107,6 +107,8 @@ import (
 	"strings"
 	"time"
 
+	"github.com/andybalholm/brotli"
+	"github.com/klauspost/compress/zstd"
 	"github.com/spf13/cobra"
 	"github.com/spf13/pflag"
 )
@@ -187,9 +189,10 @@ Retries:
 
 Compression:
   A compressed body is decoded before the assertions run, so --assert-body and
-  the other body assertions always see the payload. gzip and deflate are
-  understood; an encoding with no decoder here fails the body assertions by
-  name and leaves --assert-ok, --assert-status and --assert-header* alone.
+  the other body assertions always see the payload. gzip, deflate, br (brotli)
+  and zstd are understood; an encoding with no decoder here fails the body
+  assertions by name and leaves --assert-ok, --assert-status and
+  --assert-header* alone.
 
   Nothing is advertised in Accept-Encoding unless -H says so, and the response
   headers are reported exactly as they arrived -- so a body can be asserted on
@@ -1239,6 +1242,15 @@ func (r *httpResponse) decodeJSON() (any, error) {
 var decoders = map[string]func([]byte) ([]byte, error){
 	"gzip":    decodeGzip,
 	"deflate": decodeDeflate,
+	"br":      decodeBrotli,
+	"zstd":    decodeZstd,
+}
+
+// supportedCodings names the decoders in a stable order, so the failure for an
+// encoding with no decoder can say what it does have without drifting from the
+// map as it grows.
+func supportedCodings() string {
+	return strings.Join(slices.Sorted(maps.Keys(decoders)), ", ")
 }
 
 // decodeBody removes the Content-Encoding from BodyBytes, leaving every header
@@ -1263,7 +1275,7 @@ func (r *httpResponse) decodeBody() {
 	default:
 		decode, ok := decoders[enc]
 		if !ok {
-			r.DecodeErr = fmt.Errorf("no decoder for %q; gzip and deflate are supported", r.Encoding)
+			r.DecodeErr = fmt.Errorf("no decoder for %q; %s are supported", r.Encoding, supportedCodings())
 			return
 		}
 
@@ -1276,6 +1288,27 @@ func (r *httpResponse) decodeBody() {
 	}
 }
 
+// decodeBrotli removes a brotli coding. There is no brotli in the standard
+// library, which is the whole reason this took a dependency; andybalholm/brotli
+// is pure Go and brings nothing else with it.
+func decodeBrotli(b []byte) ([]byte, error) {
+	return io.ReadAll(brotli.NewReader(bytes.NewReader(b)))
+}
+
+// decodeZstd removes a zstd coding (RFC 8878).
+//
+// klauspost/compress is a large repository, but only the zstd package links
+// into the binary, so the cost is the decoder rather than the library.
+func decodeZstd(b []byte) ([]byte, error) {
+	zr, err := zstd.NewReader(bytes.NewReader(b))
+	if err != nil {
+		return nil, err
+	}
+	defer zr.Close()
+
+	return io.ReadAll(zr)
+}
+
 func decodeGzip(b []byte) ([]byte, error) {
 	zr, err := gzip.NewReader(bytes.NewReader(b))
 	if err != nil {