feat: add partial update support (#331)

Co-authored-by: Henrique Dias <[email protected]>

.github/workflows/build.yml

@@ -12,7 +12,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
       - uses: actions/setup-go@v6
         with:
           go-version: "1.26.x"

.github/workflows/docker.yml

@@ -18,7 +18,7 @@ jobs:
       id-token: write
     steps:
       - name: Check out the repo
-        uses: actions/checkout@v6
+        uses: actions/checkout@v7
 
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v4

.github/workflows/lint.yml

@@ -12,7 +12,7 @@ jobs:
   lint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
       - uses: actions/setup-go@v6
         with:
           go-version: "1.26.x"

.github/workflows/releaser.yml

@@ -12,7 +12,7 @@ jobs:
   goreleaser:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
         with:
           fetch-depth: 0
       - uses: actions/setup-go@v6

.github/workflows/test.yml

@@ -13,7 +13,7 @@ jobs:
     name: test
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
       - uses: actions/setup-go@v6
         with:
           go-version: "1.26.x"

README.md

@@ -60,6 +60,19 @@ the log.
 --name webdav \
 ```
 
+### Partial updates
+
+This server supports partial file updates compatible with SabreDAV's `PATCH` extension. This is not an official WebDAV specification. Requests must use the `application/x-sabredav-partialupdate` content type, include `Content-Length`, and provide the target range in `X-Update-Range`.
+
+Supported `X-Update-Range` values are:
+
+- `bytes=start-end`
+- `bytes=start-`
+- `bytes=-N`
+- `append`
+
+For clients that use it, the server also supports partial `PUT` requests with `Content-Range`, for example `Content-Range: bytes 6-8/*`. This is an extra compatibility path and should be treated as a client/server agreement.
+
 ## Configuration
 
 The configuration can be provided as a YAML, JSON or TOML file. Below is an example of a YAML configuration file with 
@@ -136,6 +149,7 @@ cors:
   allowed_headers:
     - Authorization
     - Content-Type
+    - Content-Range
     - Depth
     - Destination
     - If
@@ -143,6 +157,7 @@ cors:
     - Overwrite
     - TimeOut
     - Translate
+    - X-Update-Range
   allowed_methods:
     - COPY
     - DELETE
@@ -153,6 +168,7 @@ cors:
     - MKCOL
     - MOVE
     - OPTIONS
+    - PATCH
     - POST
     - PROPFIND
     - PROPPATCH

go.mod

@@ -12,9 +12,9 @@ require (
 	github.com/stretchr/testify v1.11.1
 	github.com/studio-b12/gowebdav v0.12.0
 	go.uber.org/zap v1.28.0
-	golang.org/x/crypto v0.52.0
-	golang.org/x/crypto/x509roots/fallback v0.0.0-20260602072539-e2ffffe738fb
-	golang.org/x/net v0.55.0
+	golang.org/x/crypto v0.53.0
+	golang.org/x/crypto/x509roots/fallback v0.0.0-20260626155920-5b7f84159940
+	golang.org/x/net v0.56.0
 )
 
 require (
@@ -30,7 +30,7 @@ require (
 	github.com/subosito/gotenv v1.6.0 // indirect
 	go.uber.org/multierr v1.11.0 // indirect
 	go.yaml.in/yaml/v3 v3.0.4 // indirect
-	golang.org/x/sys v0.45.0 // indirect
-	golang.org/x/text v0.37.0 // indirect
+	golang.org/x/sys v0.46.0 // indirect
+	golang.org/x/text v0.38.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -55,16 +55,16 @@ go.uber.org/zap v1.28.0 h1:IZzaP1Fv73/T/pBMLk4VutPl36uNC+OSUh3JLG3FIjo=
 go.uber.org/zap v1.28.0/go.mod h1:rDLpOi171uODNm/mxFcuYWxDsqWSAVkFdX4XojSKg/Q=
 go.yaml.in/yaml/v3 v3.0.4 h1:tfq32ie2Jv2UxXFdLJdh3jXuOzWiL1fo0bu/FbuKpbc=
 go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
-golang.org/x/crypto v0.52.0 h1:RMs7fP2rXdep0CftQlK8Uf+kibLm7qkCcradZWYz988=
-golang.org/x/crypto v0.52.0/go.mod h1:1QgfPxDqh0T2M/elOJtp9RvuR95kVjir0e6/BvEmGbc=
-golang.org/x/crypto/x509roots/fallback v0.0.0-20260602072539-e2ffffe738fb h1:CwwbfJyWu/4JFx3SUseZXBthp02ezLIBochvBIBfwr8=
-golang.org/x/crypto/x509roots/fallback v0.0.0-20260602072539-e2ffffe738fb/go.mod h1:+UoQFNBq2p2wO+Q6ddVtYc25GZ6VNdOMyyrd4nrqrKs=
-golang.org/x/net v0.55.0 h1:bcvxaJn3e1U6InsFWt1JUq1aSjnRxLzT2rtD2KfkDF8=
-golang.org/x/net v0.55.0/go.mod h1:L5U2KuzuOe1lY7Z+aWVIKK6qEeJXnXV9yzGA+WCHJww=
-golang.org/x/sys v0.45.0 h1:dO4czNzziLiiXplLQgBCEpCvXQ3dnkn0SdaZSYdQ+FY=
-golang.org/x/sys v0.45.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
-golang.org/x/text v0.37.0 h1:Cqjiwd9eSg8e0QAkyCaQTNHFIIzWtidPahFWR83rTrc=
-golang.org/x/text v0.37.0/go.mod h1:a5sjxXGs9hsn/AJVwuElvCAo9v8QYLzvavO5z2PiM38=
+golang.org/x/crypto v0.53.0 h1:QZ4Muo8THX6CizN2vPPd5fBGHyogrdK9fG4wLPFUsto=
+golang.org/x/crypto v0.53.0/go.mod h1:DNLU434OwVakk9PzuwV8w62mAJpRJL3vsgcfp4Qnsio=
+golang.org/x/crypto/x509roots/fallback v0.0.0-20260626155920-5b7f84159940 h1:WD+hrfJy2TRwCU7dnWiqw/dGb9jNdEzy2uR+jtpYJYk=
+golang.org/x/crypto/x509roots/fallback v0.0.0-20260626155920-5b7f84159940/go.mod h1:+UoQFNBq2p2wO+Q6ddVtYc25GZ6VNdOMyyrd4nrqrKs=
+golang.org/x/net v0.56.0 h1:Rw8j/hFzGvJUZwNBXnAtf5sVDVt+65SK2C7IxCxZt5o=
+golang.org/x/net v0.56.0/go.mod h1:D3Ku6r+V6JROoZK144D2XfMHFcMq/0zSfLelVTCFKec=
+golang.org/x/sys v0.46.0 h1:noSf2Fq6F8DBgS+LysIkx7rIExoNHJsxOAtPp4rthXw=
+golang.org/x/sys v0.46.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
+golang.org/x/text v0.38.0 h1:sXmwo9DwP3OK9EZ7PqAdaooSGozfl/3a6/xJcbzPRhE=
+golang.org/x/text v0.38.0/go.mod h1:YXZt3QhHUKYT53r2lLKFIVi6Ao1jdzrTR/KQ09qyxF4=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 h1:YR8cESwS4TdDjEe65xsg0ogRM/Nc3DYOhEAlW+xobZo=
 gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=

lib/config.go

@@ -87,8 +87,8 @@ func ParseConfig(filename string, flags *pflag.FlagSet) (*Config, error) {
 	v.SetDefault("Log.Outputs", []string{"stderr"})
 	v.SetDefault("Log.Colors", true)
 	v.SetDefault("CORS.Allowed_Hosts", []string{"*"})
-	v.SetDefault("CORS.Allowed_Headers", []string{"Authorization", "Content-Type", "Depth", "Destination", "If", "Lock-Token", "Overwrite"})
-	v.SetDefault("CORS.Allowed_Methods", []string{"COPY", "DELETE", "GET", "HEAD", "LOCK", "MKCOL", "MOVE", "OPTIONS", "POST", "PROPFIND", "PROPPATCH", "PUT", "UNLOCK"})
+	v.SetDefault("CORS.Allowed_Headers", []string{"Authorization", "Content-Type", "Content-Range", "Depth", "Destination", "If", "Lock-Token", "Overwrite", "X-Update-Range"})
+	v.SetDefault("CORS.Allowed_Methods", []string{"COPY", "DELETE", "GET", "HEAD", "LOCK", "MKCOL", "MOVE", "OPTIONS", "PATCH", "POST", "PROPFIND", "PROPPATCH", "PUT", "UNLOCK"})
 
 	// Read and unmarshal configuration
 	err := v.ReadInConfig()

lib/config_test.go

@@ -52,8 +52,8 @@ func TestConfigDefaults(t *testing.T) {
 	require.Equal(t, dir, cfg.Directory)
 
 	require.EqualValues(t, []string{"*"}, cfg.CORS.AllowedHosts)
-	require.EqualValues(t, []string{"Authorization", "Content-Type", "Depth", "Destination", "If", "Lock-Token", "Overwrite"}, cfg.CORS.AllowedHeaders)
-	require.EqualValues(t, []string{"COPY", "DELETE", "GET", "HEAD", "LOCK", "MKCOL", "MOVE", "OPTIONS", "POST", "PROPFIND", "PROPPATCH", "PUT", "UNLOCK"}, cfg.CORS.AllowedMethods)
+	require.EqualValues(t, []string{"Authorization", "Content-Type", "Content-Range", "Depth", "Destination", "If", "Lock-Token", "Overwrite", "X-Update-Range"}, cfg.CORS.AllowedHeaders)
+	require.EqualValues(t, []string{"COPY", "DELETE", "GET", "HEAD", "LOCK", "MKCOL", "MOVE", "OPTIONS", "PATCH", "POST", "PROPFIND", "PROPPATCH", "PUT", "UNLOCK"}, cfg.CORS.AllowedMethods)
 }
 
 func TestConfigCascade(t *testing.T) {

lib/handler.go

@@ -176,6 +176,16 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
+	if r.Method == "OPTIONS" {
+		user.handleOptions(w, r, req.path)
+		return
+	}
+
+	if r.Method == "PATCH" || (r.Method == "PUT" && r.Header.Get("Content-Range") != "") {
+		user.handlePartialUpdate(w, r, req.path)
+		return
+	}
+
 	// Runs the WebDAV.
 	user.ServeHTTP(w, r)
 }

lib/handler_test.go

@@ -2,10 +2,13 @@ package lib
 
 import (
 	"fmt"
+	"io"
+	"net/http"
 	"net/http/httptest"
 	"os"
 	"path/filepath"
 	"sort"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -82,6 +85,404 @@ func TestServerDefaults(t *testing.T) {
 	require.ErrorContains(t, client.Write("/foo.txt", []byte("hello world 2"), 0666), "403")
 }
 
+func TestServerPartialUpdateOptions(t *testing.T) {
+	t.Parallel()
+
+	dir := makeTestDirectory(t, map[string][]byte{
+		"foo.txt": []byte("hello world"),
+	})
+	srv := makeTestServer(t, "directory: "+dir+"\npermissions: CRUD")
+	defer srv.Close()
+
+	req, err := http.NewRequest(http.MethodOptions, srv.URL+"/foo.txt", nil)
+	require.NoError(t, err)
+	resp, err := http.DefaultClient.Do(req)
+	require.NoError(t, err)
+	defer func() { _ = resp.Body.Close() }()
+
+	require.Equal(t, http.StatusOK, resp.StatusCode)
+	require.Contains(t, resp.Header.Get("DAV"), "sabredav-partialupdate")
+	require.Contains(t, resp.Header.Get("Allow"), "PATCH")
+	require.Equal(t, partialUpdateContentType, resp.Header.Get("Accept-Patch"))
+}
+
+func TestServerPatchPartialUpdate(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name        string
+		initialData string
+		body        string
+		updateRange string
+		wantData    string
+	}{{
+		name:        "start",
+		initialData: "hello world",
+		body:        "DAV",
+		updateRange: "bytes=6-",
+		wantData:    "hello DAVld",
+	}, {
+		name:        "suffix",
+		initialData: "hello world",
+		body:        "DAV",
+		updateRange: "bytes=-5",
+		wantData:    "hello DAVld",
+	}, {
+		name:        "append",
+		initialData: "hello",
+		body:        " world",
+		updateRange: "append",
+		wantData:    "hello world",
+	}, {
+		name:        "suffix_zero",
+		initialData: "hello",
+		body:        " world",
+		updateRange: "bytes=-0",
+		wantData:    "hello world",
+	}}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			dir := makeTestDirectory(t, map[string][]byte{
+				"foo.txt": []byte(tc.initialData),
+			})
+			srv := makeTestServer(t, "directory: "+dir+"\npermissions: CRUD")
+			defer srv.Close()
+
+			req, err := http.NewRequest("PATCH", srv.URL+"/foo.txt", strings.NewReader(tc.body))
+			require.NoError(t, err)
+			req.Header.Set("Content-Type", partialUpdateContentType)
+			req.Header.Set("X-Update-Range", tc.updateRange)
+			resp, err := http.DefaultClient.Do(req)
+			require.NoError(t, err)
+			defer func() { _ = resp.Body.Close() }()
+
+			require.Equal(t, http.StatusNoContent, resp.StatusCode)
+			data, err := os.ReadFile(filepath.Join(dir, "foo.txt"))
+			require.NoError(t, err)
+			require.Equal(t, tc.wantData, string(data))
+		})
+	}
+}
+
+func TestServerPatchPartialUpdateCreatesSparseFile(t *testing.T) {
+	t.Parallel()
+
+	dir := makeTestDirectory(t, nil)
+	srv := makeTestServer(t, "directory: "+dir+"\npermissions: CRUD")
+	defer srv.Close()
+
+	req, err := http.NewRequest("PATCH", srv.URL+"/new.bin", strings.NewReader("x"))
+	require.NoError(t, err)
+	req.Header.Set("Content-Type", partialUpdateContentType)
+	req.Header.Set("X-Update-Range", "bytes=3-")
+	resp, err := http.DefaultClient.Do(req)
+	require.NoError(t, err)
+	defer func() { _ = resp.Body.Close() }()
+
+	require.Equal(t, http.StatusCreated, resp.StatusCode)
+	data, err := os.ReadFile(filepath.Join(dir, "new.bin"))
+	require.NoError(t, err)
+	require.Equal(t, []byte{0, 0, 0, 'x'}, data)
+}
+
+func TestServerPutContentRangePartialUpdate(t *testing.T) {
+	t.Parallel()
+
+	dir := makeTestDirectory(t, map[string][]byte{
+		"foo.txt": []byte("hello world"),
+	})
+	srv := makeTestServer(t, "directory: "+dir+"\npermissions: CRUD")
+	defer srv.Close()
+
+	req, err := http.NewRequest(http.MethodPut, srv.URL+"/foo.txt", strings.NewReader("DAV"))
+	require.NoError(t, err)
+	req.Header.Set("Content-Range", "bytes 6-8/*")
+	resp, err := http.DefaultClient.Do(req)
+	require.NoError(t, err)
+	defer func() { _ = resp.Body.Close() }()
+	_, _ = io.Copy(io.Discard, resp.Body)
+
+	require.Equal(t, http.StatusNoContent, resp.StatusCode)
+	data, err := os.ReadFile(filepath.Join(dir, "foo.txt"))
+	require.NoError(t, err)
+	require.Equal(t, "hello DAVld", string(data))
+}
+
+func TestServerPartialUpdateErrors(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name          string
+		method        string
+		body          string
+		contentLength int64
+		path          string
+		headerName    string
+		updateRange   string
+		contentRange  string
+		wantStatus    int
+	}{{
+		name:          "patch_missing_content_length",
+		method:        "PATCH",
+		body:          "DAV",
+		contentLength: -1,
+		updateRange:   "bytes=6-8",
+		wantStatus:    http.StatusLengthRequired,
+	}, {
+		name:        "patch_invalid_range",
+		method:      "PATCH",
+		body:        "DAV",
+		updateRange: "bytes=8-6",
+		wantStatus:  http.StatusRequestedRangeNotSatisfiable,
+	}, {
+		name:        "patch_length_mismatch",
+		method:      "PATCH",
+		body:        "TOOLONG",
+		updateRange: "bytes=6-8",
+		wantStatus:  http.StatusRequestedRangeNotSatisfiable,
+	}, {
+		name:          "put_content_range_length_mismatch",
+		method:        http.MethodPut,
+		body:          "TOOLONG",
+		contentLength: -1,
+		contentRange:  "bytes 6-8/*",
+		wantStatus:    http.StatusRequestedRangeNotSatisfiable,
+	}, {
+		name:        "if_none_match",
+		method:      "PATCH",
+		body:        "DAV",
+		headerName:  "If-None-Match",
+		updateRange: "bytes=0-2",
+		wantStatus:  http.StatusPreconditionFailed,
+	}, {
+		name:        "if_match",
+		method:      "PATCH",
+		path:        "/missing.txt",
+		body:        "DAV",
+		headerName:  "If-Match",
+		updateRange: "bytes=0-2",
+		wantStatus:  http.StatusPreconditionFailed,
+	}}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			dir := makeTestDirectory(t, map[string][]byte{
+				"foo.txt": []byte("hello world"),
+			})
+			srv := makeTestServer(t, "directory: "+dir+"\npermissions: CRUD")
+			defer srv.Close()
+
+			var body io.Reader = strings.NewReader(tc.body)
+			if tc.contentLength < 0 {
+				body = io.NopCloser(strings.NewReader(tc.body))
+			}
+			path := tc.path
+			if path == "" {
+				path = "/foo.txt"
+			}
+			req, err := http.NewRequest(tc.method, srv.URL+path, body)
+			require.NoError(t, err)
+			if tc.contentLength < 0 {
+				req.ContentLength = tc.contentLength
+			}
+			if tc.method == "PATCH" {
+				req.Header.Set("Content-Type", partialUpdateContentType)
+				req.Header.Set("X-Update-Range", tc.updateRange)
+			}
+			if tc.contentRange != "" {
+				req.Header.Set("Content-Range", tc.contentRange)
+			}
+			if tc.headerName != "" {
+				req.Header.Set(tc.headerName, "*")
+			}
+			resp, err := http.DefaultClient.Do(req)
+			require.NoError(t, err)
+			defer func() { _ = resp.Body.Close() }()
+
+			require.Equal(t, tc.wantStatus, resp.StatusCode)
+			data, err := os.ReadFile(filepath.Join(dir, "foo.txt"))
+			require.NoError(t, err)
+			require.Equal(t, "hello world", string(data))
+		})
+	}
+}
+
+func TestServerPartialUpdateETagPreconditions(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name         string
+		method       string
+		headerName   string
+		headerValue  func(string) string
+		contentRange string
+		wantStatus   int
+		wantData     string
+	}{{
+		name:        "if_match_matches",
+		method:      "PATCH",
+		headerName:  "If-Match",
+		headerValue: func(etag string) string { return etag },
+		wantStatus:  http.StatusNoContent,
+		wantData:    "hello DAVld",
+	}, {
+		name:        "if_match_mismatch",
+		method:      "PATCH",
+		headerName:  "If-Match",
+		headerValue: func(string) string { return `"definitely-wrong"` },
+		wantStatus:  http.StatusPreconditionFailed,
+		wantData:    "hello world",
+	}, {
+		name:        "if_match_list_matches",
+		method:      "PATCH",
+		headerName:  "If-Match",
+		headerValue: func(etag string) string { return `"definitely-wrong", ` + etag },
+		wantStatus:  http.StatusNoContent,
+		wantData:    "hello DAVld",
+	}, {
+		name:        "if_none_match_matches",
+		method:      "PATCH",
+		headerName:  "If-None-Match",
+		headerValue: func(etag string) string { return etag },
+		wantStatus:  http.StatusPreconditionFailed,
+		wantData:    "hello world",
+	}, {
+		name:        "if_none_match_mismatch",
+		method:      "PATCH",
+		headerName:  "If-None-Match",
+		headerValue: func(string) string { return `"definitely-wrong"` },
+		wantStatus:  http.StatusNoContent,
+		wantData:    "hello DAVld",
+	}, {
+		name:         "put_content_range_if_match_mismatch",
+		method:       http.MethodPut,
+		headerName:   "If-Match",
+		headerValue:  func(string) string { return `"definitely-wrong"` },
+		contentRange: "bytes 6-8/*",
+		wantStatus:   http.StatusPreconditionFailed,
+		wantData:     "hello world",
+	}}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			dir := makeTestDirectory(t, map[string][]byte{
+				"foo.txt": []byte("hello world"),
+			})
+			srv := makeTestServer(t, "directory: "+dir+"\npermissions: CRUD")
+			defer srv.Close()
+
+			req, err := http.NewRequest(http.MethodHead, srv.URL+"/foo.txt", nil)
+			require.NoError(t, err)
+			resp, err := http.DefaultClient.Do(req)
+			require.NoError(t, err)
+			_ = resp.Body.Close()
+			require.Equal(t, http.StatusOK, resp.StatusCode)
+			etag := resp.Header.Get("ETag")
+			require.NotEmpty(t, etag)
+
+			req, err = http.NewRequest(tc.method, srv.URL+"/foo.txt", strings.NewReader("DAV"))
+			require.NoError(t, err)
+			if tc.method == "PATCH" {
+				req.Header.Set("Content-Type", partialUpdateContentType)
+				req.Header.Set("X-Update-Range", "bytes=6-8")
+			}
+			if tc.contentRange != "" {
+				req.Header.Set("Content-Range", tc.contentRange)
+			}
+			req.Header.Set(tc.headerName, tc.headerValue(etag))
+			resp, err = http.DefaultClient.Do(req)
+			require.NoError(t, err)
+			defer func() { _ = resp.Body.Close() }()
+
+			require.Equal(t, tc.wantStatus, resp.StatusCode)
+			data, err := os.ReadFile(filepath.Join(dir, "foo.txt"))
+			require.NoError(t, err)
+			require.Equal(t, tc.wantData, string(data))
+		})
+	}
+}
+
+func TestServerPartialUpdateHonorsLocks(t *testing.T) {
+	t.Parallel()
+
+	const createLockBody = `<?xml version="1.0" encoding="utf-8" ?>
+		<D:lockinfo xmlns:D='DAV:'>
+			<D:lockscope><D:exclusive/></D:lockscope>
+			<D:locktype><D:write/></D:locktype>
+			<D:owner>test</D:owner>
+		</D:lockinfo>`
+
+	testCases := []struct {
+		name     string
+		lockPath string
+		depth    string
+		ifPath   string
+	}{{
+		name:     "file",
+		lockPath: "/foo.txt",
+		depth:    "0",
+		ifPath:   "/foo.txt",
+	}, {
+		name:     "root",
+		lockPath: "/",
+		depth:    "infinity",
+		ifPath:   "/",
+	}}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			dir := makeTestDirectory(t, map[string][]byte{
+				"foo.txt": []byte("hello world"),
+			})
+			srv := makeTestServer(t, "directory: "+dir+"\npermissions: CRUD")
+			defer srv.Close()
+
+			req, err := http.NewRequest("LOCK", srv.URL+tc.lockPath, strings.NewReader(createLockBody))
+			require.NoError(t, err)
+			req.Header.Set("Content-Type", "application/xml")
+			req.Header.Set("Depth", tc.depth)
+			resp, err := http.DefaultClient.Do(req)
+			require.NoError(t, err)
+			defer func() { _ = resp.Body.Close() }()
+			_, _ = io.Copy(io.Discard, resp.Body)
+			require.Equal(t, http.StatusOK, resp.StatusCode)
+			lockToken := resp.Header.Get("Lock-Token")
+
+			req, err = http.NewRequest("PATCH", srv.URL+"/foo.txt", strings.NewReader("DAV"))
+			require.NoError(t, err)
+			req.Header.Set("Content-Type", partialUpdateContentType)
+			req.Header.Set("X-Update-Range", "bytes=6-8")
+			resp, err = http.DefaultClient.Do(req)
+			require.NoError(t, err)
+			defer func() { _ = resp.Body.Close() }()
+			require.Equal(t, 423, resp.StatusCode)
+
+			req, err = http.NewRequest("PATCH", srv.URL+"/foo.txt", strings.NewReader("DAV"))
+			require.NoError(t, err)
+			req.Header.Set("Content-Type", partialUpdateContentType)
+			req.Header.Set("X-Update-Range", "bytes=6-8")
+			req.Header.Set("If", fmt.Sprintf("<%s%s> (%s)", srv.URL, tc.ifPath, lockToken))
+			resp, err = http.DefaultClient.Do(req)
+			require.NoError(t, err)
+			defer func() { _ = resp.Body.Close() }()
+			require.Equal(t, http.StatusNoContent, resp.StatusCode)
+
+			data, err := os.ReadFile(filepath.Join(dir, "foo.txt"))
+			require.NoError(t, err)
+			require.Equal(t, "hello DAVld", string(data))
+		})
+	}
+}
+
 func TestServerListingCharacters(t *testing.T) {
 	t.Parallel()
 

lib/partial_update.go

@@ -0,0 +1,526 @@
+package lib
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"mime"
+	"net/http"
+	"net/url"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+
+	"golang.org/x/net/webdav"
+)
+
+const partialUpdateContentType = "application/x-sabredav-partialupdate"
+
+type updateRange struct {
+	offset int64
+	end    int64
+	hasEnd bool
+	append bool
+}
+
+type partialUpdateError struct {
+	status int
+	err    error
+}
+
+func (e partialUpdateError) Error() string {
+	return e.err.Error()
+}
+
+func newPartialUpdateError(status int, message string) error {
+	return partialUpdateError{status: status, err: errors.New(message)}
+}
+
+func writePartialUpdateError(w http.ResponseWriter, err error, fallbackStatus int) {
+	var httpErr partialUpdateError
+	if errors.As(err, &httpErr) {
+		fallbackStatus = httpErr.status
+	}
+	http.Error(w, err.Error(), fallbackStatus)
+}
+
+func (u *handlerUser) handleOptions(w http.ResponseWriter, r *http.Request, reqPath string) {
+	allow := "OPTIONS, LOCK, PUT, MKCOL, PATCH"
+	if fi, err := u.FileSystem.Stat(r.Context(), reqPath); err == nil {
+		if fi.IsDir() {
+			allow = "OPTIONS, LOCK, DELETE, PROPPATCH, COPY, MOVE, UNLOCK, PROPFIND"
+		} else {
+			allow = "OPTIONS, LOCK, GET, HEAD, POST, DELETE, PROPPATCH, COPY, MOVE, UNLOCK, PROPFIND, PUT, PATCH"
+		}
+	}
+
+	w.Header().Set("Allow", allow)
+	w.Header().Set("DAV", "1, 2, sabredav-partialupdate")
+	w.Header().Set("MS-Author-Via", "DAV")
+	w.Header().Set("Accept-Patch", partialUpdateContentType)
+	w.WriteHeader(http.StatusOK)
+}
+
+func (u *handlerUser) handlePartialUpdate(w http.ResponseWriter, r *http.Request, reqPath string) {
+	contentRange := r.Header.Get("Content-Range")
+	isContentRangePut := r.Method == "PUT" && contentRange != ""
+
+	var (
+		updateRange updateRange
+		err         error
+	)
+	if isContentRangePut {
+		updateRange, err = parseContentRange(contentRange)
+	} else {
+		if err := checkPartialUpdateContentType(r.Header.Get("Content-Type")); err != nil {
+			http.Error(w, err.Error(), http.StatusUnsupportedMediaType)
+			return
+		}
+		updateRange, err = parseUpdateRange(r.Header.Get("X-Update-Range"))
+	}
+	if err != nil {
+		writePartialUpdateError(w, err, http.StatusBadRequest)
+		return
+	}
+	if r.Method == "PATCH" && r.ContentLength < 0 {
+		http.Error(w, "missing content length", http.StatusLengthRequired)
+		return
+	}
+
+	release, status, err := u.confirmPartialUpdateLocks(r, reqPath)
+	if err != nil {
+		http.Error(w, err.Error(), status)
+		return
+	}
+	defer release()
+
+	ctx := r.Context()
+	fi, statErr := u.FileSystem.Stat(ctx, reqPath)
+	exists := statErr == nil
+	if statErr != nil && !os.IsNotExist(statErr) {
+		http.Error(w, statErr.Error(), http.StatusMethodNotAllowed)
+		return
+	}
+	if exists && fi.IsDir() {
+		http.Error(w, "cannot update a collection", http.StatusMethodNotAllowed)
+		return
+	}
+
+	etag, status, err := u.checkPartialUpdatePreconditions(r, exists, fi)
+	if err != nil {
+		if etag != "" {
+			w.Header().Set("ETag", etag)
+		}
+		http.Error(w, err.Error(), status)
+		return
+	}
+
+	currentSize := int64(0)
+	if exists {
+		currentSize = fi.Size()
+	}
+	if updateRange.append {
+		updateRange.offset = currentSize
+	} else if updateRange.offset < 0 {
+		updateRange.offset += currentSize
+		if updateRange.offset < 0 {
+			updateRange.offset = 0
+		}
+	}
+
+	if updateRange.hasEnd {
+		expected := updateRange.end - updateRange.offset + 1
+		if expected < 0 {
+			http.Error(w, "invalid byte range", http.StatusRequestedRangeNotSatisfiable)
+			return
+		}
+		if r.ContentLength >= 0 && r.ContentLength != expected {
+			http.Error(w, "content length does not match byte range", http.StatusRequestedRangeNotSatisfiable)
+			return
+		}
+	}
+
+	body := io.Reader(r.Body)
+	var cleanup func()
+	if updateRange.hasEnd {
+		body, cleanup, err = spoolBoundedBody(r.Body, updateRange.end-updateRange.offset+1)
+		if err != nil {
+			writePartialUpdateError(w, err, http.StatusMethodNotAllowed)
+			return
+		}
+		defer cleanup()
+	}
+
+	flag := os.O_RDWR
+	if !exists {
+		flag |= os.O_CREATE
+	}
+	f, err := u.FileSystem.OpenFile(ctx, reqPath, flag, 0666)
+	if err != nil {
+		if os.IsNotExist(err) {
+			http.Error(w, err.Error(), http.StatusConflict)
+			return
+		}
+		http.Error(w, err.Error(), http.StatusNotFound)
+		return
+	}
+	defer func() { _ = f.Close() }()
+
+	if _, err := f.Seek(updateRange.offset, io.SeekStart); err != nil {
+		http.Error(w, err.Error(), http.StatusMethodNotAllowed)
+		return
+	}
+	if _, err := io.Copy(f, body); err != nil {
+		http.Error(w, err.Error(), http.StatusMethodNotAllowed)
+		return
+	}
+
+	if !exists {
+		w.WriteHeader(http.StatusCreated)
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}
+
+func checkPartialUpdateContentType(contentType string) error {
+	if contentType == "" {
+		return errors.New("missing content type")
+	}
+	mediaType, _, err := mime.ParseMediaType(contentType)
+	if err != nil {
+		return err
+	}
+	if mediaType != partialUpdateContentType {
+		return fmt.Errorf("unsupported content type %q", mediaType)
+	}
+	return nil
+}
+
+func (u *handlerUser) checkPartialUpdatePreconditions(r *http.Request, exists bool, fi os.FileInfo) (etag string, status int, err error) {
+	ifMatch := r.Header.Get("If-Match")
+	ifNoneMatch := r.Header.Get("If-None-Match")
+	if ifMatch == "" && ifNoneMatch == "" {
+		return "", 0, nil
+	}
+
+	if ifMatch != "" && !exists {
+		return "", http.StatusPreconditionFailed, errors.New("resource does not exist")
+	}
+
+	if exists {
+		etag, err = findPartialETag(r.Context(), fi)
+		if err != nil {
+			return "", http.StatusInternalServerError, err
+		}
+	}
+
+	if ifMatch != "" && !partialETagHeaderMatches(ifMatch, etag, exists) {
+		return etag, http.StatusPreconditionFailed, errors.New("etag does not match")
+	}
+
+	if ifNoneMatch != "" && exists && partialETagHeaderMatches(ifNoneMatch, etag, true) {
+		return etag, http.StatusPreconditionFailed, errors.New("etag matches")
+	}
+
+	return etag, 0, nil
+}
+
+func findPartialETag(ctx context.Context, fi os.FileInfo) (string, error) {
+	if etager, ok := fi.(webdav.ETager); ok {
+		etag, err := etager.ETag(ctx)
+		if !errors.Is(err, webdav.ErrNotImplemented) {
+			return etag, err
+		}
+	}
+	return fmt.Sprintf(`"%x%x"`, fi.ModTime().UnixNano(), fi.Size()), nil
+}
+
+func partialETagHeaderMatches(header, etag string, exists bool) bool {
+	for _, item := range strings.Split(header, ",") {
+		item = strings.TrimSpace(item)
+		if item == "*" {
+			return exists
+		}
+		if item == etag || strings.ReplaceAll(item, `\"`, `"`) == etag {
+			return true
+		}
+	}
+	return false
+}
+
+func parseUpdateRange(header string) (updateRange, error) {
+	if header == "" {
+		return updateRange{}, errors.New("missing X-Update-Range header")
+	}
+	if header == "append" {
+		return updateRange{append: true}, nil
+	}
+	if !strings.HasPrefix(header, "bytes=") {
+		return updateRange{}, errors.New("invalid X-Update-Range header")
+	}
+	return parseByteRange(strings.TrimPrefix(header, "bytes="), true)
+}
+
+func parseContentRange(header string) (updateRange, error) {
+	if !strings.HasPrefix(header, "bytes ") {
+		return updateRange{}, errors.New("invalid Content-Range header")
+	}
+	spec, _, ok := strings.Cut(strings.TrimPrefix(header, "bytes "), "/")
+	if !ok {
+		return updateRange{}, errors.New("invalid Content-Range header")
+	}
+	return parseByteRange(spec, false)
+}
+
+func parseByteRange(spec string, allowNegativeStart bool) (updateRange, error) {
+	if strings.HasPrefix(spec, "-") {
+		if !allowNegativeStart {
+			return updateRange{}, errors.New("invalid byte range start")
+		}
+		start, err := strconv.ParseInt(strings.TrimPrefix(spec, "-"), 10, 64)
+		if err != nil || start < 0 {
+			return updateRange{}, errors.New("invalid byte range start")
+		}
+		if start == 0 {
+			return updateRange{append: true}, nil
+		}
+		return updateRange{offset: -start}, nil
+	}
+
+	startText, endText, ok := strings.Cut(spec, "-")
+	if !ok || startText == "" {
+		return updateRange{}, errors.New("invalid byte range")
+	}
+
+	start, err := strconv.ParseInt(startText, 10, 64)
+	if err != nil {
+		return updateRange{}, errors.New("invalid byte range start")
+	}
+	if start < 0 && !allowNegativeStart {
+		return updateRange{}, errors.New("invalid byte range start")
+	}
+
+	r := updateRange{offset: start}
+	if endText == "" {
+		return r, nil
+	}
+	if start < 0 {
+		return updateRange{}, errors.New("negative byte range cannot include an end")
+	}
+
+	end, err := strconv.ParseInt(endText, 10, 64)
+	if err != nil {
+		return updateRange{}, errors.New("invalid byte range end")
+	}
+	if end < start {
+		return updateRange{}, newPartialUpdateError(http.StatusRequestedRangeNotSatisfiable, "invalid byte range")
+	}
+	r.end = end
+	r.hasEnd = true
+	return r, nil
+}
+
+func spoolBoundedBody(body io.Reader, expected int64) (io.Reader, func(), error) {
+	tmp, err := os.CreateTemp("", "webdav-partial-update-*")
+	if err != nil {
+		return nil, nil, err
+	}
+	cleanup := func() {
+		name := tmp.Name()
+		_ = tmp.Close()
+		_ = os.Remove(name)
+	}
+	cleanupOnError := true
+	defer func() {
+		if cleanupOnError {
+			cleanup()
+		}
+	}()
+
+	n, err := io.Copy(tmp, io.LimitReader(body, expected+1))
+	if err != nil {
+		return nil, nil, err
+	}
+	if n != expected {
+		return nil, nil, newPartialUpdateError(http.StatusRequestedRangeNotSatisfiable, "body length does not match byte range")
+	}
+
+	if _, err := tmp.Seek(0, io.SeekStart); err != nil {
+		return nil, nil, err
+	}
+	cleanupOnError = false
+	return tmp, cleanup, nil
+}
+
+// confirmPartialUpdateLocks mirrors the unexported confirmLocks helper from
+// golang.org/x/net/webdav so that partial updates honor WebDAV locks the same
+// way regular PUT requests do. Keep it in sync if the upstream behavior changes.
+func (u *handlerUser) confirmPartialUpdateLocks(r *http.Request, src string) (release func(), status int, err error) {
+	hdr := r.Header.Get("If")
+	if hdr == "" {
+		now := time.Now()
+		token, err := u.LockSystem.Create(now, webdav.LockDetails{
+			Root:      src,
+			Duration:  -1,
+			ZeroDepth: true,
+		})
+		if err != nil {
+			if errors.Is(err, webdav.ErrLocked) {
+				return nil, webdav.StatusLocked, err
+			}
+			return nil, http.StatusInternalServerError, err
+		}
+		return func() {
+			_ = u.LockSystem.Unlock(now, token)
+		}, 0, nil
+	}
+
+	ifLists, ok := parsePartialIfHeader(hdr)
+	if !ok {
+		return nil, http.StatusBadRequest, errors.New("webdav: invalid If header")
+	}
+	for _, l := range ifLists {
+		lsrc := l.resourceTag
+		if lsrc == "" {
+			lsrc = src
+		} else {
+			parsedURL, err := url.Parse(lsrc)
+			if err != nil {
+				continue
+			}
+			if parsedURL.Host != r.Host {
+				continue
+			}
+			lsrc, err = stripPartialPrefix(parsedURL.Path, u.Prefix)
+			if err != nil {
+				return nil, http.StatusNotFound, err
+			}
+			if lsrc == "" {
+				lsrc = src
+			}
+		}
+		release, err = u.LockSystem.Confirm(time.Now(), lsrc, "", l.conditions...)
+		if errors.Is(err, webdav.ErrConfirmationFailed) {
+			continue
+		}
+		if err != nil {
+			return nil, http.StatusInternalServerError, err
+		}
+		return release, 0, nil
+	}
+	return nil, http.StatusPreconditionFailed, webdav.ErrLocked
+}
+
+type partialIfList struct {
+	resourceTag string
+	conditions  []webdav.Condition
+}
+
+// parsePartialIfHeader, parsePartialIfConditions and cutPartialIfToken
+// reimplement the unexported If-header parser from golang.org/x/net/webdav,
+// which is not accessible from outside that package. Keep them in sync with the
+// upstream parseIfHeader if it changes.
+func parsePartialIfHeader(header string) ([]partialIfList, bool) {
+	s := strings.TrimSpace(header)
+	tagged := strings.HasPrefix(s, "<")
+	var lists []partialIfList
+	for s != "" {
+		resourceTag := ""
+		if strings.HasPrefix(s, "<") {
+			if !tagged {
+				return nil, false
+			}
+			var ok bool
+			resourceTag, s, ok = cutPartialIfToken(s, '<', '>')
+			if !ok {
+				return nil, false
+			}
+			s = strings.TrimSpace(s)
+			if !strings.HasPrefix(s, "(") {
+				return nil, false
+			}
+		}
+		for strings.HasPrefix(s, "(") {
+			body, rest, ok := cutPartialIfToken(s, '(', ')')
+			if !ok {
+				return nil, false
+			}
+			conditions, ok := parsePartialIfConditions(body)
+			if !ok {
+				return nil, false
+			}
+			lists = append(lists, partialIfList{resourceTag: resourceTag, conditions: conditions})
+			s = strings.TrimSpace(rest)
+		}
+		if s != "" && !strings.HasPrefix(s, "<") {
+			return nil, false
+		}
+	}
+	return lists, len(lists) > 0
+}
+
+func parsePartialIfConditions(s string) ([]webdav.Condition, bool) {
+	var conditions []webdav.Condition
+	for {
+		s = strings.TrimSpace(s)
+		if s == "" {
+			return conditions, len(conditions) > 0
+		}
+		not := false
+		if strings.HasPrefix(s, "Not ") || strings.HasPrefix(s, "Not\t") {
+			not = true
+			s = strings.TrimSpace(s[3:])
+		}
+		if s == "" {
+			return nil, false
+		}
+		var token string
+		switch s[0] {
+		case '<':
+			var ok bool
+			token, s, ok = cutPartialIfToken(s, '<', '>')
+			if !ok {
+				return nil, false
+			}
+			conditions = append(conditions, webdav.Condition{Not: not, Token: token})
+		case '[':
+			var ok bool
+			token, s, ok = cutPartialIfToken(s, '[', ']')
+			if !ok {
+				return nil, false
+			}
+			conditions = append(conditions, webdav.Condition{Not: not, ETag: token})
+		default:
+			i := strings.IndexAny(s, " \t")
+			if i < 0 {
+				token, s = s, ""
+			} else {
+				token, s = s[:i], s[i:]
+			}
+			if token == "" || strings.ContainsAny(token, "()<>[]") {
+				return nil, false
+			}
+			conditions = append(conditions, webdav.Condition{Not: not, Token: token})
+		}
+	}
+}
+
+func cutPartialIfToken(s string, open, close byte) (string, string, bool) {
+	if s == "" || s[0] != open {
+		return "", "", false
+	}
+	token, rest, ok := strings.Cut(s[1:], string(close))
+	return token, rest, ok
+}
+
+func stripPartialPrefix(p, prefix string) (string, error) {
+	if prefix == "" {
+		return p, nil
+	}
+	if stripped := strings.TrimPrefix(p, prefix); len(stripped) < len(p) {
+		return stripped, nil
+	}
+	return "", errors.New("webdav: prefix mismatch")
+}

lib/permissions.go

@@ -152,7 +152,7 @@ func (p Permissions) Allowed(r *request, fileExists func(string) bool) bool {
 		return p.Create
 	case "PROPPATCH":
 		return p.Update
-	case "PUT":
+	case "PUT", "PATCH":
 		if fileExists(r.path) {
 			return p.Update
 		} else {