[confighttp] Apply MaxRequestBodySize to the result of a decompressed…

… body (open-telemetry#10289)

This change applies a restriction on the size of the decompressed
payload. Before this change, this is the result of the test added in
this PR:

```
--- FAIL: TestServerWithDecompression (0.03s)
    /home/jpkroehling/Projects/src/github.com/open-telemetry/opentelemetry-collector/config/confighttp/confighttp_test.go:1327:
        	Error Trace:	/home/jpkroehling/Projects/src/github.com/open-telemetry/opentelemetry-collector/config/confighttp/confighttp_test.go:1327
        	            				/usr/lib/golang/src/net/http/server.go:2166
        	            				/home/jpkroehling/Projects/src/github.com/open-telemetry/opentelemetry-collector/config/confighttp/compression.go:163
        	            				/home/jpkroehling/Projects/src/github.com/open-telemetry/opentelemetry-collector/config/confighttp/confighttp.go:455
        	            				/usr/lib/golang/src/net/http/server.go:2166
        	            				/home/jpkroehling/go/pkg/mod/go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp@v0.52.0/handler.go:212
        	            				/home/jpkroehling/go/pkg/mod/go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp@v0.52.0/handler.go:73
        	            				/usr/lib/golang/src/net/http/server.go:2166
        	            				/home/jpkroehling/Projects/src/github.com/open-telemetry/opentelemetry-collector/config/confighttp/clientinfohandler.go:26
        	            				/usr/lib/golang/src/net/http/server.go:3137
        	            				/usr/lib/golang/src/net/http/server.go:2039
        	            				/usr/lib/golang/src/runtime/asm_amd64.s:1695
        	Error:      	An error is expected but got nil.
        	Test:       	TestServerWithDecompression
    /home/jpkroehling/Projects/src/github.com/open-telemetry/opentelemetry-collector/config/confighttp/confighttp_test.go:1328:
        	Error Trace:	/home/jpkroehling/Projects/src/github.com/open-telemetry/opentelemetry-collector/config/confighttp/confighttp_test.go:1328
        	            				/usr/lib/golang/src/net/http/server.go:2166
        	            				/home/jpkroehling/Projects/src/github.com/open-telemetry/opentelemetry-collector/config/confighttp/compression.go:163
        	            				/home/jpkroehling/Projects/src/github.com/open-telemetry/opentelemetry-collector/config/confighttp/confighttp.go:455
        	            				/usr/lib/golang/src/net/http/server.go:2166
        	            				/home/jpkroehling/go/pkg/mod/go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp@v0.52.0/handler.go:212
        	            				/home/jpkroehling/go/pkg/mod/go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp@v0.52.0/handler.go:73
        	            				/usr/lib/golang/src/net/http/server.go:2166
        	            				/home/jpkroehling/Projects/src/github.com/open-telemetry/opentelemetry-collector/config/confighttp/clientinfohandler.go:26
        	            				/usr/lib/golang/src/net/http/server.go:3137
        	            				/usr/lib/golang/src/net/http/server.go:2039
        	            				/usr/lib/golang/src/runtime/asm_amd64.s:1695
        	Error:
        	Test:       	TestServerWithDecompression
    /home/jpkroehling/Projects/src/github.com/open-telemetry/opentelemetry-collector/config/confighttp/confighttp_test.go:1357:
        	Error Trace:	/home/jpkroehling/Projects/src/github.com/open-telemetry/opentelemetry-collector/config/confighttp/confighttp_test.go:1357
        	Error:      	Not equal:
        	            	expected: 200
        	            	actual  : 400
        	Test:       	TestServerWithDecompression
FAIL
FAIL	go.opentelemetry.io/collector/config/confighttp	0.036s
FAIL
```

Signed-off-by: Juraci Paixão Kröhling <juraci@kroehling.de>

---------

Signed-off-by: Juraci Paixão Kröhling <juraci@kroehling.de>

.chloggen/jpkroehling_set-maxrequestbodysize-to-compressed.yaml

@@ -0,0 +1,22 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: 'breaking'
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: confighttp
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Apply MaxRequestBodySize to the result of a decompressed body
+
+# One or more tracking issues or pull requests related to the change
+issues: [10289]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: |
+  When using compressed payloads, the Collector would verify only the size of the compressed payload. 
+  This change applies the same restriction to the decompressed content. As a security measure, a limit of 20 MiB was added, which makes this a breaking change. 
+  For most clients, this shouldn't be a problem, but if you often have payloads that decompress to more than 20 MiB, you might want to either configure your
+  client to send smaller batches (recommended), or increase the limit using the MaxRequestBodySize option.

config/confighttp/compression.go

@@ -67,24 +67,26 @@ func (r *compressRoundTripper) RoundTrip(req *http.Request) (*http.Response, err
 }
 
 type decompressor struct {
-	errHandler func(w http.ResponseWriter, r *http.Request, errorMsg string, statusCode int)
-	base       http.Handler
-	decoders   map[string]func(body io.ReadCloser) (io.ReadCloser, error)
+	errHandler         func(w http.ResponseWriter, r *http.Request, errorMsg string, statusCode int)
+	base               http.Handler
+	decoders           map[string]func(body io.ReadCloser) (io.ReadCloser, error)
+	maxRequestBodySize int64
 }
 
 // httpContentDecompressor offloads the task of handling compressed HTTP requests
 // by identifying the compression format in the "Content-Encoding" header and re-writing
 // request body so that the handlers further in the chain can work on decompressed data.
 // It supports gzip and deflate/zlib compression.
-func httpContentDecompressor(h http.Handler, eh func(w http.ResponseWriter, r *http.Request, errorMsg string, statusCode int), decoders map[string]func(body io.ReadCloser) (io.ReadCloser, error)) http.Handler {
+func httpContentDecompressor(h http.Handler, maxRequestBodySize int64, eh func(w http.ResponseWriter, r *http.Request, errorMsg string, statusCode int), decoders map[string]func(body io.ReadCloser) (io.ReadCloser, error)) http.Handler {
 	errHandler := defaultErrorHandler
 	if eh != nil {
 		errHandler = eh
 	}
 
 	d := &decompressor{
-		errHandler: errHandler,
-		base:       h,
+		maxRequestBodySize: maxRequestBodySize,
+		errHandler:         errHandler,
+		base:               h,
 		decoders: map[string]func(body io.ReadCloser) (io.ReadCloser, error){
 			"": func(io.ReadCloser) (io.ReadCloser, error) {
 				// Not a compressed payload. Nothing to do.
@@ -155,7 +157,7 @@ func (d *decompressor) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		// "Content-Length" is set to -1 as the size of the decompressed body is unknown.
 		r.Header.Del("Content-Length")
 		r.ContentLength = -1
-		r.Body = newBody
+		r.Body = http.MaxBytesReader(w, newBody, d.maxRequestBodySize)
 	}
 	d.base.ServeHTTP(w, r)
 }

config/confighttp/compression_test.go

@@ -134,7 +134,7 @@ func TestHTTPCustomDecompression(t *testing.T) {
 			return io.NopCloser(strings.NewReader("decompressed body")), nil
 		},
 	}
-	srv := httptest.NewServer(httpContentDecompressor(handler, defaultErrorHandler, decoders))
+	srv := httptest.NewServer(httpContentDecompressor(handler, defaultMaxRequestBodySize, defaultErrorHandler, decoders))
 
 	t.Cleanup(srv.Close)
 
@@ -253,7 +253,7 @@ func TestHTTPContentDecompressionHandler(t *testing.T) {
 				require.NoError(t, err, "failed to read request body: %v", err)
 				assert.EqualValues(t, testBody, string(body))
 				w.WriteHeader(http.StatusOK)
-			}), defaultErrorHandler, noDecoders))
+			}), defaultMaxRequestBodySize, defaultErrorHandler, noDecoders))
 			t.Cleanup(srv.Close)
 
 			req, err := http.NewRequest(http.MethodGet, srv.URL, tt.reqBody)

config/confighttp/confighttp.go

@@ -30,6 +30,7 @@ import (
 )
 
 const headerContentEncoding = "Content-Encoding"
+const defaultMaxRequestBodySize = 20 * 1024 * 1024 // 20MiB
 
 // ClientConfig defines settings for creating an HTTP client.
 type ClientConfig struct {
@@ -272,7 +273,7 @@ type ServerConfig struct {
 	// RateLimit for this receiver
 	RateLimit *RateLimit `mapstructure:"rate_limit"`
 
-	// MaxRequestBodySize sets the maximum request body size in bytes
+	// MaxRequestBodySize sets the maximum request body size in bytes. Default: 20MiB.
 	MaxRequestBodySize int64 `mapstructure:"max_request_body_size"`
 
 	// IncludeMetadata propagates the client metadata from the incoming requests to the downstream consumers
@@ -343,7 +344,11 @@ func (hss *ServerConfig) ToServer(_ context.Context, host component.Host, settin
 		o(serverOpts)
 	}
 
-	handler = httpContentDecompressor(handler, serverOpts.errHandler, serverOpts.decoders)
+	if hss.MaxRequestBodySize <= 0 {
+		hss.MaxRequestBodySize = defaultMaxRequestBodySize
+	}
+
+	handler = httpContentDecompressor(handler, hss.MaxRequestBodySize, serverOpts.errHandler, serverOpts.decoders)
 
 	if hss.MaxRequestBodySize > 0 {
 		handler = maxRequestBodySizeInterceptor(handler, hss.MaxRequestBodySize)

config/confighttp/confighttp_test.go

@@ -4,6 +4,7 @@
 package confighttp
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"fmt"
@@ -13,6 +14,7 @@ import (
 	"net/http/httptest"
 	"net/url"
 	"path/filepath"
+	"strings"
 	"testing"
 	"time"
 
@@ -1300,7 +1302,7 @@ func TestServerWithDecoder(t *testing.T) {
 	// test
 	response := &httptest.ResponseRecorder{}
 
-	req, err := http.NewRequest(http.MethodGet, srv.Addr, nil)
+	req, err := http.NewRequest(http.MethodGet, srv.Addr, bytes.NewBuffer([]byte("something")))
 	require.NoError(t, err, "Error creating request: %v", err)
 	req.Header.Set("Content-Encoding", "something-else")
 
@@ -1310,6 +1312,93 @@ func TestServerWithDecoder(t *testing.T) {
 
 }
 
+func TestServerWithDecompression(t *testing.T) {
+	// prepare
+	hss := ServerConfig{
+		MaxRequestBodySize: 1000, // 1 KB
+	}
+	body := []byte(strings.Repeat("a", 1000*1000)) // 1 MB
+
+	srv, err := hss.ToServer(
+		context.Background(),
+		componenttest.NewNopHost(),
+		componenttest.NewNopTelemetrySettings(),
+		http.HandlerFunc(func(resp http.ResponseWriter, req *http.Request) {
+			actualBody, err := io.ReadAll(req.Body)
+			assert.ErrorContains(t, err, "http: request body too large")
+			assert.Len(t, actualBody, 1000)
+
+			if err != nil {
+				resp.WriteHeader(http.StatusBadRequest)
+			} else {
+				resp.WriteHeader(http.StatusOK)
+			}
+		}),
+	)
+	require.NoError(t, err)
+
+	testSrv := httptest.NewServer(srv.Handler)
+	defer testSrv.Close()
+
+	req, err := http.NewRequest(http.MethodGet, testSrv.URL, compressZstd(t, body))
+	require.NoError(t, err, "Error creating request: %v", err)
+
+	req.Header.Set("Content-Encoding", "zstd")
+
+	// test
+	c := http.Client{}
+	resp, err := c.Do(req)
+	require.NoError(t, err, "Error sending request: %v", err)
+
+	_, err = io.ReadAll(resp.Body)
+	require.NoError(t, err, "Error reading response body: %v", err)
+
+	// verifications is done mostly within the test, but this is only a sanity check
+	// that we got into the test handler
+	assert.Equal(t, resp.StatusCode, http.StatusBadRequest)
+}
+
+func TestDefaultMaxRequestBodySize(t *testing.T) {
+	tests := []struct {
+		name     string
+		settings ServerConfig
+		expected int64
+	}{
+		{
+			name:     "default",
+			settings: ServerConfig{},
+			expected: defaultMaxRequestBodySize,
+		},
+		{
+			name:     "zero",
+			settings: ServerConfig{MaxRequestBodySize: 0},
+			expected: defaultMaxRequestBodySize,
+		},
+		{
+			name:     "negative",
+			settings: ServerConfig{MaxRequestBodySize: -1},
+			expected: defaultMaxRequestBodySize,
+		},
+		{
+			name:     "custom",
+			settings: ServerConfig{MaxRequestBodySize: 100},
+			expected: 100,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := tt.settings.ToServer(
+				context.Background(),
+				componenttest.NewNopHost(),
+				componenttest.NewNopTelemetrySettings(),
+				http.HandlerFunc(func(http.ResponseWriter, *http.Request) {}),
+			)
+			require.NoError(t, err)
+			assert.Equal(t, tt.expected, tt.settings.MaxRequestBodySize)
+		})
+	}
+}
+
 type mockHost struct {
 	component.Host
 	ext map[component.ID]component.Component