fix(files): 编辑器保存和打开也逐跳核对 SHA-256，途中变了的内容不写盘也不打开

cmd/felis/files.go

@@ -47,7 +47,7 @@ func cmdFiles(args []string, stdout, stderr io.Writer) int {
 	to := fs.String("to", "", "rename only: the destination path")
 	sourceURL := fs.String("source-url", "", "upload only: felis-api URL to fetch the bytes from")
 	size := fs.Int64("size", -1, "upload only: the byte count the fetched file must have")
-	sum := fs.String("sha256", "", "upload only: the SHA-256 (hex) the fetched file must have")
+	sum := fs.String("sha256", "", "write and upload: the SHA-256 (hex) the content or the fetched file must have")
 	overwrite := fs.Bool("overwrite", false, "upload and unzip: replace files already there")
 	if err := fs.Parse(args); err != nil {
 		return 2
@@ -70,12 +70,18 @@ func cmdFiles(args []string, stdout, stderr io.Writer) int {
 	// channel that must be a valid string.
 	switch *op {
 	case fileedit.OpWrite:
+		// The content's SHA-256 comes with it, so bytes that changed on the way
+		// to this Job are refused rather than written (Request.ContentSHA256).
+		if *sum == "" {
+			fmt.Fprintln(stderr, "felis files: a write needs --sha256")
+			return 2
+		}
 		content, err := fileedit.ContentFromEnv(os.LookupEnv)
 		if err != nil {
 			fmt.Fprintf(stderr, "felis files: %v\n", err)
 			return 2
 		}
-		req.Content = content
+		req.Content, req.ContentSHA256 = content, *sum
 	case fileedit.OpUpload:
 		token := os.Getenv(fileedit.UploadTokenEnv)
 		if *sourceURL == "" || token == "" {

cmd/felis/files_test.go

@@ -238,10 +238,11 @@ func TestCmdFilesUpload(t *testing.T) {
 
 func TestCmdFilesWrite(t *testing.T) {
 	root := t.TempDir()
-	args := []string{"--op", "write", "--path", "ops.json", "--worlds-root", root}
+	content := []byte("[]\r\n")
+	sum := sha256.Sum256(content)
+	args := []string{"--op", "write", "--path", "ops.json", "--worlds-root", root, "--sha256", hex.EncodeToString(sum[:])}
 
 	t.Run("reassembles the content parts", func(t *testing.T) {
-		content := []byte("[]\r\n")
 		t.Setenv(fileedit.ContentPartsEnv, "1")
 		t.Setenv(fileedit.ContentEnv+"_0", base64.StdEncoding.EncodeToString(content))
 		var stdout, stderr bytes.Buffer
@@ -261,13 +262,42 @@ func TestCmdFilesWrite(t *testing.T) {
 		t.Setenv(fileedit.ContentPartsEnv, "2")
 		t.Setenv(fileedit.ContentEnv+"_0", base64.StdEncoding.EncodeToString([]byte("x")))
 		var stdout, stderr bytes.Buffer
-		if code := cmdFiles([]string{"--op", "write", "--path", "new.txt", "--worlds-root", root}, &stdout, &stderr); code != 2 {
+		if code := cmdFiles([]string{"--op", "write", "--path", "new.txt", "--worlds-root", root, "--sha256", hex.EncodeToString(sum[:])}, &stdout, &stderr); code != 2 {
 			t.Fatalf("exit %d, want 2", code)
 		}
 		if _, err := os.Lstat(filepath.Join(root, "new.txt")); !os.IsNotExist(err) {
 			t.Fatalf("an incomplete spec wrote a file: %v", err)
 		}
 	})
+
+	// Without the content's SHA-256 the Job could not tell bytes changed on the
+	// way from the bytes felis-api sent.
+	t.Run("a write without its SHA-256 exits 2 and writes nothing", func(t *testing.T) {
+		t.Setenv(fileedit.ContentPartsEnv, "1")
+		t.Setenv(fileedit.ContentEnv+"_0", base64.StdEncoding.EncodeToString(content))
+		var stdout, stderr bytes.Buffer
+		if code := cmdFiles([]string{"--op", "write", "--path", "new.txt", "--worlds-root", root}, &stdout, &stderr); code != 2 {
+			t.Fatalf("exit %d, want 2", code)
+		}
+		if _, err := os.Lstat(filepath.Join(root, "new.txt")); !os.IsNotExist(err) {
+			t.Fatalf("a write without its SHA-256 wrote a file: %v", err)
+		}
+	})
+
+	t.Run("content that changed on the way is a result and writes nothing", func(t *testing.T) {
+		t.Setenv(fileedit.ContentPartsEnv, "1")
+		t.Setenv(fileedit.ContentEnv+"_0", base64.StdEncoding.EncodeToString([]byte("[]\n")))
+		var stdout, stderr bytes.Buffer
+		if code := cmdFiles([]string{"--op", "write", "--path", "new.txt", "--worlds-root", root, "--sha256", hex.EncodeToString(sum[:])}, &stdout, &stderr); code != 0 {
+			t.Fatalf("exit %d, stderr %q", code, stderr.String())
+		}
+		if res := filesResult(t, stdout.String()); res.Code != fileedit.CodeDigestMismatch {
+			t.Fatalf("result = %+v, want %s", res, fileedit.CodeDigestMismatch)
+		}
+		if _, err := os.Lstat(filepath.Join(root, "new.txt")); !os.IsNotExist(err) {
+			t.Fatalf("changed content wrote a file: %v", err)
+		}
+	})
 }
 
 // A caller-fault outcome is a successful run carrying a code, so felis-api can

docs/openapi.yaml

@@ -4615,7 +4615,7 @@ paths:
             application/json:
               schema:
                 type: object
-                required: [path, content, sha256]
+                required: [path, content, sha256, content_sha256]
                 properties:
                   path: { type: string }
                   content: { type: string, format: byte, description: Base64-encoded file bytes. }
@@ -4625,6 +4625,13 @@ paths:
                     description: >-
                       SHA-256 of the file as stored (before the rcon.password redaction in
                       server.properties). Send it back as expect_sha256 on the next write.
+                  content_sha256:
+                    type: string
+                    pattern: '^[0-9a-f]{64}$'
+                    description: >-
+                      SHA-256 of the decoded content as sent (after any redaction). A
+                      client that gets content hashing otherwise got it damaged on the
+                      way, and reads it again.
         '400':
           description: Missing path, invalid server name, or a path that escapes the world root.
           content:
@@ -4649,6 +4656,13 @@ paths:
           content:
             application/json:
               schema: { $ref: '#/components/schemas/Error' }
+        '502':
+          description: >-
+            The file's bytes do not hash to the digest the file Job sent with them
+            (read_damaged): they changed on the way to felis-api. Read it again.
+          content:
+            application/json:
+              schema: { $ref: '#/components/schemas/Error' }
         '503':
           $ref: '#/components/responses/ServiceUnavailable'
         '504':
@@ -4671,7 +4685,10 @@ paths:
         root is refused. The replacement is atomic (a synced temporary sibling renamed
         over the file, keeping its mode), so a failed write leaves the old file whole.
         With expect_sha256 the write lands only if the file still has that hash;
-        otherwise 409 file_changed. Audited as file.write.
+        otherwise 409 file_changed. content_sha256 is the SHA-256 of the content:
+        content that hashes otherwise changed on the way and is refused (400
+        digest_mismatch) before a Job starts, and the Job checks the bytes it received
+        the same way before writing. Audited as file.write.
       x-felis-face: [external]
       x-felis-tier: app
       security: [{ sessionCookie: [] }]
@@ -4688,9 +4705,16 @@ paths:
           application/json:
             schema:
               type: object
-              required: [content]
+              required: [content, content_sha256]
               properties:
                 content: { type: string, format: byte, description: Base64-encoded file bytes. }
+                content_sha256:
+                  type: string
+                  pattern: '^[0-9a-f]{64}$'
+                  description: >-
+                    The SHA-256 (lowercase hex) of the decoded content. Absent is 400
+                    digest_required, malformed 400 bad_digest, and content that does not
+                    hash to it 400 digest_mismatch; nothing is written.
                 expect_sha256:
                   type: string
                   pattern: '^[0-9a-f]{64}$'
@@ -4717,7 +4741,7 @@ paths:
                   status: { type: string, const: written }
                   sha256: { type: string, pattern: '^[0-9a-f]{64}$', description: SHA-256 of the bytes written. }
         '400':
-          description: Missing path, malformed body, invalid server name, or a path that escapes the world root.
+          description: Missing path, malformed body, invalid server name, or a path that escapes the world root (bad_request, bad_path), or content that came without its SHA-256 (digest_required), with a malformed one (bad_digest), or changed on the way (digest_mismatch).
           content:
             application/json:
               schema: { $ref: '#/components/schemas/Error' }

internal/api/handlers_files.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"crypto/sha256"
 	"encoding/base64"
+	"encoding/hex"
 	"errors"
 	"io"
 	"net/http"
@@ -78,8 +79,14 @@ type FileEditor interface {
 // nothing is at the path yet (409 file_exists otherwise), so it can never
 // truncate a file the caller did not know was there. The two cannot be combined —
 // one says the file exists, the other that it must not.
+//
+// ContentSHA256 is required: the SHA-256 (hex) of the decoded content, which
+// the caller computes over the bytes it means to write. Content that hashes
+// otherwise changed on the way and is refused (400 digest_mismatch) before a Job
+// starts; the Job checks the bytes it received the same way before it writes.
 type writeFileRequest struct {
 	Content       *[]byte `json:"content"`
+	ContentSHA256 string  `json:"content_sha256"`
 	ExpectSHA256  string  `json:"expect_sha256,omitempty"`
 	CreateOnly    bool    `json:"create_only,omitempty"`
 }
@@ -145,7 +152,12 @@ func (a *API) handleReadFile(w http.ResponseWriter, r *http.Request) {
 	if content == nil {
 		content = []byte{} // an empty file is "", never null
 	}
-	writeJSON(w, http.StatusOK, map[string]any{"path": path, "content": content, "sha256": sum})
+	// content_sha256 is of the bytes as sent (sha256 is of the file on disk,
+	// before any redaction), so the panel can tell a damaged read from the file.
+	got := sha256.Sum256(content)
+	writeJSON(w, http.StatusOK, map[string]any{
+		"path": path, "content": content, "sha256": sum, "content_sha256": hex.EncodeToString(got[:]),
+	})
 }
 
 // handleWriteFile serves PUT /api/v1/servers/{name}/file?path=… — replace a file's
@@ -201,6 +213,20 @@ func (a *API) handleWriteFile(w http.ResponseWriter, r *http.Request) {
 			"create_only and expect_sha256 cannot be combined"))
 		return
 	}
+	switch sum := sha256.Sum256(*body.Content); {
+	case body.ContentSHA256 == "":
+		writeError(w, r, newError(http.StatusBadRequest, "digest_required",
+			"send the SHA-256 of the content as content_sha256"))
+		return
+	case !sha256Hex.MatchString(body.ContentSHA256):
+		writeError(w, r, newError(http.StatusBadRequest, "bad_digest",
+			"content_sha256 must be the 64-digit lowercase hex SHA-256 of the content"))
+		return
+	case hex.EncodeToString(sum[:]) != body.ContentSHA256:
+		writeError(w, r, newError(http.StatusBadRequest, "digest_mismatch",
+			"the content that arrived does not hash to content_sha256, so it was changed on the way; send it again"))
+		return
+	}
 
 	// A write holds the world volume for its Job's lifetime (internal/maintenance);
 	// reads and listings do not. A read-only mount cannot hurt a server starting
@@ -633,6 +659,12 @@ func writeFileEditError(w http.ResponseWriter, r *http.Request, err error) {
 		writeError(w, r, newError(http.StatusInsufficientStorage, "volume_full", "%s", err.Error()))
 	case errors.Is(err, fileedit.ErrExists):
 		writeError(w, r, newError(http.StatusConflict, "file_exists", "%s", err.Error()))
+	case errors.Is(err, fileedit.ErrDigestMismatch):
+		// A write's content reached its Job changed; nothing was written.
+		writeError(w, r, newError(http.StatusBadRequest, "digest_mismatch", "%s", err.Error()))
+	case errors.Is(err, fileedit.ErrReadDamaged):
+		writeError(w, r, newError(http.StatusBadGateway, "read_damaged",
+			"the file's bytes changed on their way from the file Job; read it again"))
 	case errors.Is(err, context.DeadlineExceeded):
 		writeError(w, r, newError(http.StatusGatewayTimeout, "files_timeout",
 			"the file operation did not finish in time; retry shortly"))

internal/api/handlers_files_test.go

@@ -180,7 +180,7 @@ func TestFileEditorStoppedGate(t *testing.T) {
 	}{
 		{"list", "GET", "/api/v1/servers/survival/files?path=config", ""},
 		{"read", "GET", "/api/v1/servers/survival/file?path=server.properties", ""},
-		{"write", "PUT", "/api/v1/servers/survival/file?path=server.properties", `{"content":"aGk="}`},
+		{"write", "PUT", "/api/v1/servers/survival/file?path=server.properties", `{"content":"aGk=","content_sha256":"` + hiSum + `"}`},
 		{"mkdir", "POST", "/api/v1/servers/survival/files/mkdir?path=plugins", ""},
 		{"delete", "DELETE", "/api/v1/servers/survival/file?path=old.jar", ""},
 		{"rename", "POST", "/api/v1/servers/survival/files/rename?path=a.txt", `{"to":"b.txt"}`},
@@ -237,7 +237,7 @@ func TestFileEditorWorldVolumeGate(t *testing.T) {
 	}{
 		{"list", "GET", "/api/v1/servers/survival/files?path=config", ""},
 		{"read", "GET", "/api/v1/servers/survival/file?path=server.properties", ""},
-		{"write", "PUT", "/api/v1/servers/survival/file?path=server.properties", `{"content":"aGk="}`},
+		{"write", "PUT", "/api/v1/servers/survival/file?path=server.properties", `{"content":"aGk=","content_sha256":"` + hiSum + `"}`},
 		{"mkdir", "POST", "/api/v1/servers/survival/files/mkdir?path=plugins", ""},
 		{"delete", "DELETE", "/api/v1/servers/survival/file?path=old.jar", ""},
 		{"rename", "POST", "/api/v1/servers/survival/files/rename?path=a.txt", `{"to":"b.txt"}`},
@@ -278,7 +278,7 @@ func TestFileEditorAuthorization(t *testing.T) {
 	}{
 		{"list", "GET", "/api/v1/servers/survival/files", ""},
 		{"read", "GET", "/api/v1/servers/survival/file?path=server.properties", ""},
-		{"write", "PUT", "/api/v1/servers/survival/file?path=server.properties", `{"content":"aGk="}`},
+		{"write", "PUT", "/api/v1/servers/survival/file?path=server.properties", `{"content":"aGk=","content_sha256":"` + hiSum + `"}`},
 		{"mkdir", "POST", "/api/v1/servers/survival/files/mkdir?path=plugins", ""},
 		{"delete", "DELETE", "/api/v1/servers/survival/file?path=old.jar", ""},
 		{"rename", "POST", "/api/v1/servers/survival/files/rename?path=a.txt", `{"to":"b.txt"}`},
@@ -439,11 +439,14 @@ func TestFileEditorHandlers(t *testing.T) {
 			Path       string `json:"path"`
 			Content    []byte `json:"content"`
 			SHA256     string `json:"sha256"`
+			Content256 string `json:"content_sha256"`
 		}
 		if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
 			t.Fatalf("body not JSON: %v", err)
 		}
-		if resp.Path != "server.properties" || string(resp.Content) != "motd=hello\n" || resp.SHA256 != testSum {
+		// content_sha256 is of the bytes sent, so the panel can check what arrived.
+		if resp.Path != "server.properties" || string(resp.Content) != "motd=hello\n" || resp.SHA256 != testSum ||
+			resp.Content256 != hexSum([]byte("motd=hello\n")) {
 			t.Fatalf("unexpected response %+v (%q)", resp, resp.Content)
 		}
 	})
@@ -465,7 +468,7 @@ func TestFileEditorHandlers(t *testing.T) {
 		api.External = staticExternal{p: owner}
 
 		w := do(api.ExternalHandler(), "PUT", "/api/v1/servers/survival/file?path=server.properties",
-			`{"content":"bW90ZD1jaGFuZ2VkCg=="}`, jsonHeader)
+			`{"content":"bW90ZD1jaGFuZ2VkCg==","content_sha256":"`+hexSum([]byte("motd=changed\n"))+`"}`, jsonHeader)
 		if w.Code != http.StatusOK {
 			t.Fatalf("code = %d (%s)", w.Code, w.Body.String())
 		}
@@ -483,7 +486,7 @@ func TestFileEditorHandlers(t *testing.T) {
 		files.sum = strings.Repeat("b", 64)
 		api.External = staticExternal{p: owner}
 		w := do(api.ExternalHandler(), "PUT", "/api/v1/servers/survival/file?path=server.properties",
-			`{"content":"aGk=","expect_sha256":"`+testSum+`"}`, jsonHeader)
+			`{"content":"aGk=","content_sha256":"`+hiSum+`","expect_sha256":"`+testSum+`"}`, jsonHeader)
 		if w.Code != http.StatusOK {
 			t.Fatalf("code = %d (%s)", w.Code, w.Body.String())
 		}
@@ -516,7 +519,7 @@ func TestFileEditorHandlers(t *testing.T) {
 		files.err = fmt.Errorf("%w: server.properties has changed", fileedit.ErrConflict)
 		api.External = staticExternal{p: owner}
 		w := do(api.ExternalHandler(), "PUT", "/api/v1/servers/survival/file?path=server.properties",
-			`{"content":"aGk=","expect_sha256":"`+testSum+`"}`, jsonHeader)
+			`{"content":"aGk=","content_sha256":"`+hiSum+`","expect_sha256":"`+testSum+`"}`, jsonHeader)
 		if w.Code != http.StatusConflict || decodeErr(t, w) != "file_changed" {
 			t.Fatalf("code = %d body %s, want 409 file_changed", w.Code, w.Body.String())
 		}
@@ -577,7 +580,7 @@ func TestFileEditorHandlers(t *testing.T) {
 		api, _, _, files := mkFiles(t)
 		api.External = staticExternal{p: owner}
 		w := do(api.ExternalHandler(), "PUT", "/api/v1/servers/survival/file?path=server.properties",
-			`{"content":""}`, jsonHeader)
+			`{"content":"","content_sha256":"`+hexSum(nil)+`"}`, jsonHeader)
 		if w.Code != http.StatusOK {
 			t.Fatalf("code = %d, want 200 (%s)", w.Code, w.Body.String())
 		}
@@ -590,7 +593,8 @@ func TestFileEditorHandlers(t *testing.T) {
 	t.Run("a write at exactly the limit is allowed", func(t *testing.T) {
 		api, _, _, files := mkFiles(t)
 		api.External = staticExternal{p: owner}
-		body, err := json.Marshal(writeFileRequest{Content: bytesPtr(make([]byte, fileedit.MaxWriteBytes))})
+		content := make([]byte, fileedit.MaxWriteBytes)
+		body, err := json.Marshal(writeFileRequest{Content: &content, ContentSHA256: hexSum(content)})
 		if err != nil {
 			t.Fatalf("marshal: %v", err)
 		}
@@ -738,12 +742,12 @@ func TestFileManagerHandlers(t *testing.T) {
 		api, _, _, files := mkFiles(t)
 		api.External = staticExternal{p: owner}
 		w := do(api.ExternalHandler(), "PUT", "/api/v1/servers/survival/file?path=plugins/new.yml",
-			`{"content":"","create_only":true}`, jsonHeader)
+			`{"content":"","content_sha256":"`+hexSum(nil)+`","create_only":true}`, jsonHeader)
 		if w.Code != http.StatusOK || !files.gotCreateOnly || files.gotExpect != "" {
 			t.Fatalf("code = %d, createOnly = %v, expect = %q (%s)", w.Code, files.gotCreateOnly, files.gotExpect, w.Body.String())
 		}
 		w = do(api.ExternalHandler(), "PUT", "/api/v1/servers/survival/file?path=server.properties",
-			`{"content":"aGk="}`, jsonHeader)
+			`{"content":"aGk=","content_sha256":"`+hiSum+`"}`, jsonHeader)
 		if w.Code != http.StatusOK || files.gotCreateOnly {
 			t.Fatalf("a plain save: code = %d, createOnly = %v", w.Code, files.gotCreateOnly)
 		}
@@ -766,6 +770,58 @@ func contentDigestOf(body string) string {
 	return "sha-256=:" + base64.StdEncoding.EncodeToString(sum[:]) + ":"
 }
 
+// hexSum is the content_sha256 a client sends with a write of b; hiSum is that
+// of "hi" (aGk=).
+func hexSum(b []byte) string {
+	sum := sha256.Sum256(b)
+	return hex.EncodeToString(sum[:])
+}
+
+var hiSum = hexSum([]byte("hi"))
+
+// A write carries the SHA-256 of its content: one without it, with a malformed
+// one, or whose content hashes otherwise is refused before a Job starts, and a
+// Job that found the bytes it received changed answers the same way. None of
+// them is audited.
+func TestWriteFileChecksTheContentDigest(t *testing.T) {
+	owner := &Principal{UserID: "owner1", Email: "[email protected]", Role: "user"}
+	for _, tc := range []struct {
+		name string
+		body string
+		want string
+	}{
+		{"without a digest", `{"content":"aGk="}`, "digest_required"},
+		{"a malformed digest", `{"content":"aGk=","content_sha256":"` + strings.ToUpper(hiSum) + `"}`, "bad_digest"},
+		{"changed on the way", `{"content":"aGo=","content_sha256":"` + hiSum + `"}`, "digest_mismatch"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			api, repo, _, files := mkFiles(t)
+			api.External = staticExternal{p: owner}
+			w := do(api.ExternalHandler(), "PUT", "/api/v1/servers/survival/file?path=server.properties", tc.body, jsonHeader)
+			if w.Code != http.StatusBadRequest || decodeErr(t, w) != tc.want {
+				t.Fatalf("code = %d body %s, want 400 %s", w.Code, w.Body.String(), tc.want)
+			}
+			if files.calls != 0 || len(repo.audits) != 0 {
+				t.Fatalf("calls = %d audits = %+v, want no Job and no audit", files.calls, repo.audits)
+			}
+		})
+	}
+
+	t.Run("changed on the way to the Job", func(t *testing.T) {
+		api, repo, _, files := mkFiles(t)
+		files.err = fmt.Errorf("%w: the content hashes to 00 and was sent as 01", fileedit.ErrDigestMismatch)
+		api.External = staticExternal{p: owner}
+		w := do(api.ExternalHandler(), "PUT", "/api/v1/servers/survival/file?path=server.properties",
+			`{"content":"aGk=","content_sha256":"`+hiSum+`"}`, jsonHeader)
+		if w.Code != http.StatusBadRequest || decodeErr(t, w) != "digest_mismatch" {
+			t.Fatalf("code = %d body %s, want 400 digest_mismatch", w.Code, w.Body.String())
+		}
+		if files.calls != 1 || len(repo.audits) != 0 {
+			t.Fatalf("calls = %d audits = %+v, want the one Job and no audit", files.calls, repo.audits)
+		}
+	})
+}
+
 // doUpload sends an upload whose Content-Length is declared, not measured, the
 // way a client that streams or lies would send it. Its Content-Digest is that
 // of the body.
@@ -1063,6 +1119,7 @@ func TestFileEditorErrorMapping(t *testing.T) {
 		{"changed since read", fmt.Errorf("%w: nope", fileedit.ErrConflict), http.StatusConflict, "file_changed"},
 		{"volume full", fmt.Errorf("%w: nope", fileedit.ErrNoSpace), http.StatusInsufficientStorage, "volume_full"},
 		{"already there", fmt.Errorf("%w: nope", fileedit.ErrExists), http.StatusConflict, "file_exists"},
+		{"changed on the way from the Job", fmt.Errorf("%w: nope", fileedit.ErrReadDamaged), http.StatusBadGateway, "read_damaged"},
 		{"timeout", fmt.Errorf("waiting: %w", context.DeadlineExceeded), http.StatusGatewayTimeout, "files_timeout"},
 	}
 

internal/api/handlers_maintenance_test.go

@@ -107,7 +107,7 @@ func maintenanceOps(t *testing.T) (*API, *fakeCluster, []maintenanceOp) {
 		{"backup", maintenance.KindBackup, "POST", "/api/v1/servers/survival/backup", "",
 			func() int { return backuper.calls }},
 		{"file write", maintenance.KindFileWrite, "PUT", "/api/v1/servers/survival/file?path=server.properties",
-			`{"content":"aGk="}`, func() int { return files.calls }},
+			`{"content":"aGk=","content_sha256":"` + hiSum + `"}`, func() int { return files.calls }},
 		{"file mkdir", maintenance.KindFileWrite, "POST", "/api/v1/servers/survival/files/mkdir?path=plugins",
 			"", func() int { return files.calls }},
 		{"file delete", maintenance.KindFileWrite, "DELETE", "/api/v1/servers/survival/file?path=old.jar",

internal/fileedit/editor.go

@@ -77,6 +77,9 @@ var (
 	// ErrExists is a create, mkdir, rename or upload whose target is already
 	// there.
 	ErrExists = errors.New("fileedit: the target already exists")
+	// ErrReadDamaged is a read whose bytes do not hash to the digest the Job
+	// sent with them: they changed on the way to felis-api.
+	ErrReadDamaged = errors.New("fileedit: the file's bytes changed on their way from the file Job")
 )
 
 // Runner is the cluster-side half of a file operation. Run renders and creates
@@ -243,11 +246,17 @@ func (e *Editor) List(ctx context.Context, server, path string) (Listing, error)
 
 // Read returns a file's bytes, resolved under the server's world root, and the
 // SHA-256 of the file as it is on disk — the value to hand back as Write's expect.
+// Bytes that do not hash to the digest the Job computed over what it sent
+// (Result.ContentSHA256) are ErrReadDamaged: an editor that saves back a
+// damaged read would write the damage.
 func (e *Editor) Read(ctx context.Context, server, path string) ([]byte, string, error) {
 	res, err := e.run(ctx, server, JobParams{Op: OpRead, Path: path})
 	if err != nil {
 		return nil, "", err
 	}
+	if got := digest(res.Content); got != res.ContentSHA256 {
+		return nil, "", fmt.Errorf("%w: they hash to %s, sent as %q", ErrReadDamaged, got, res.ContentSHA256)
+	}
 	// A zero-length file unmarshals Content as nil, which is a legitimate result,
 	// not an error — normalise so the caller never has to distinguish nil from empty.
 	if res.Content == nil {
@@ -457,6 +466,8 @@ func resultError(res Result) error {
 		return fmt.Errorf("%w: %s", ErrNoSpace, res.Error)
 	case CodeExists:
 		return fmt.Errorf("%w: %s", ErrExists, res.Error)
+	case CodeDigestMismatch:
+		return fmt.Errorf("%w: %s", ErrDigestMismatch, res.Error)
 	default:
 		return fmt.Errorf("fileedit: file operation failed (%s): %s", res.Code, res.Error)
 	}

internal/fileedit/editor_test.go

@@ -2,6 +2,7 @@ package fileedit
 
 import (
 	"context"
+	"encoding/hex"
 	"encoding/json"
 	"errors"
 	"testing"
@@ -79,7 +80,7 @@ func TestEditorRendersParams(t *testing.T) {
 	})
 
 	t.Run("read", func(t *testing.T) {
-		r := &fakeRunner{payload: mustPayload(t, Result{Content: []byte("motd=hi\n"), SHA256: "abc"})}
+		r := &fakeRunner{payload: mustPayload(t, Result{Content: []byte("motd=hi\n"), SHA256: "abc", ContentSHA256: hex.EncodeToString(sumOf("motd=hi\n"))})}
 		e := &Editor{Runner: r, Config: Config{Image: "img"}}
 
 		got, sum, err := e.Read(context.Background(), "survival", "server.properties")
@@ -162,7 +163,7 @@ func TestEditorRendersParams(t *testing.T) {
 // every time. If it ever cached one, two operations would collide on a name
 // felis-api has no permission to delete.
 func TestEditorMintsAFreshOpID(t *testing.T) {
-	r := &fakeRunner{payload: mustPayload(t, Result{})}
+	r := &fakeRunner{payload: mustPayload(t, Result{ContentSHA256: hex.EncodeToString(sumOf(""))})}
 	e := &Editor{Runner: r, Config: Config{Image: "img"}}
 
 	for range 3 {
@@ -198,6 +199,7 @@ func TestEditorMapsResultCodes(t *testing.T) {
 		{"changed since read", CodeConflict, ErrConflict},
 		{"volume full", CodeNoSpace, ErrNoSpace},
 		{"already there", CodeExists, ErrExists},
+		{"changed on the way", CodeDigestMismatch, ErrDigestMismatch},
 	}
 	for _, tc := range cases {
 		t.Run(tc.name, func(t *testing.T) {
@@ -251,11 +253,33 @@ func TestEditorRefusesOversizedWriteBeforeTheCluster(t *testing.T) {
 	}
 }
 
+// A read whose bytes do not hash to the digest the Job sent with them changed
+// on the way, and none of them is handed on: an editor saving a damaged read
+// would write the damage back.
+func TestEditorReadRefusesBytesChangedOnTheWay(t *testing.T) {
+	for _, tc := range []struct {
+		name string
+		sent string
+	}{
+		{"hashed otherwise", hex.EncodeToString(sumOf("motd=hi\n"))},
+		{"with no digest", ""},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			r := &fakeRunner{payload: mustPayload(t, Result{Content: []byte("motd=ho\n"), SHA256: "abc", ContentSHA256: tc.sent})}
+			e := &Editor{Runner: r, Config: Config{Image: "img"}}
+			got, sum, err := e.Read(context.Background(), "survival", "server.properties")
+			if !errors.Is(err, ErrReadDamaged) || got != nil || sum != "" {
+				t.Fatalf("Read = %q, %q, %v; want nothing and ErrReadDamaged", got, sum, err)
+			}
+		})
+	}
+}
+
 // TestEditorNormalisesEmptyResults pins that "nothing there" is a success, not a
 // nil surprise: an empty directory lists as [] and a zero-length file reads as
 // empty bytes, so no caller has to distinguish nil from empty.
 func TestEditorNormalisesEmptyResults(t *testing.T) {
-	r := &fakeRunner{payload: mustPayload(t, Result{})}
+	r := &fakeRunner{payload: mustPayload(t, Result{ContentSHA256: hex.EncodeToString(sumOf(""))})}
 	e := &Editor{Runner: r, Config: Config{Image: "img"}}
 
 	ls, err := e.List(context.Background(), "survival", "empty")

internal/fileedit/exec.go

@@ -84,6 +84,10 @@ const (
 	// there. None of them replaces anything unless told to (an upload's
 	// Overwrite), so a name collision is reported rather than resolved.
 	CodeExists = "exists"
+	// CodeDigestMismatch is a write whose bytes do not hash to the SHA-256
+	// felis-api computed over them (Request.ContentSHA256): they changed on the
+	// way to the Job, and nothing was written.
+	CodeDigestMismatch = "digest_mismatch"
 )
 
 // ResultPrefix marks the single stdout line carrying the JSON Result. The Job's
@@ -186,6 +190,10 @@ type Result struct {
 	// conflict, the file as it is now. A client hands it back as the expected
 	// hash of its next write (see write).
 	SHA256 string `json:"sha256,omitempty"`
+	// ContentSHA256 is, after a read, the hex digest of Content as handed out
+	// (after any redaction), so felis-api can tell the bytes it got from the
+	// bytes this Job sent (Editor.Read).
+	ContentSHA256 string `json:"content_sha256,omitempty"`
 
 	// Conflicts lists, relative to the root and sorted, the existing files an
 	// unzip would replace: the first of them, up to MaxConflicts and 8 KiB of
@@ -213,9 +221,11 @@ type Request struct {
 	To string
 	// Content and Expect are a write's bytes and precondition: when Expect is
 	// non-empty, the write lands only if the file's current SHA-256 (hex) equals
-	// it.
+	// it. ContentSHA256, when set, is the SHA-256 (hex) felis-api computed over
+	// Content; bytes that hash otherwise are not written (CodeDigestMismatch).
 	Content       []byte
 	Expect        string
+	ContentSHA256 string
 	// CreateOnly makes a write refuse a path that already exists. It is the
 	// panel's "new file", which must never truncate a file it did not know was
 	// there.
@@ -295,7 +305,7 @@ func Execute(root string, req Request) (Result, error) {
 	case OpRead:
 		return read(r, path), nil
 	case OpWrite:
-		return write(r, path, req.Content, req.Expect, req.CreateOnly), nil
+		return write(r, path, req.Content, req.ContentSHA256, req.Expect, req.CreateOnly), nil
 	case OpMkdir:
 		return mkdir(r, path), nil
 	case OpDelete:
@@ -432,7 +442,7 @@ func read(r *os.Root, name string) Result {
 	if redact {
 		content = RedactProps(b)
 	}
-	return Result{Content: content, SHA256: digest(b)}
+	return Result{Content: content, SHA256: digest(b), ContentSHA256: digest(content)}
 }
 
 // propsPath is the server's main config file, and rconPasswordKey the one line in
@@ -492,7 +502,17 @@ func redactSecretProps(name string, content []byte) []byte {
 // being overwritten, which is how two people editing the same file find out.
 // The world lock (internal/maintenance) already serialises writes, so the check
 // and the rename cannot interleave with another write.
-func write(r *os.Root, name string, content []byte, expect string, createOnly bool) Result {
+//
+// sum, when set, is the SHA-256 felis-api computed over content before handing
+// it to the Job: content that hashes otherwise changed on the way, and is
+// refused with CodeDigestMismatch before anything is touched.
+func write(r *os.Root, name string, content []byte, sum, expect string, createOnly bool) Result {
+	if sum != "" {
+		if got := digest(content); got != sum {
+			return Result{Code: CodeDigestMismatch, Error: fmt.Sprintf(
+				"the content hashes to %s and was sent as %s; nothing was written", got, sum)}
+		}
+	}
 	if len(content) > MaxWriteBytes {
 		// Defence in depth: felis-api already refuses an oversized write with a 413
 		// before rendering the Job. Re-checking here keeps the ceiling true even if

internal/fileedit/exec_test.go

@@ -435,6 +435,11 @@ func TestReadRedactsRconPassword(t *testing.T) {
 	if sum := sha256.Sum256([]byte(props)); res.SHA256 != hex.EncodeToString(sum[:]) {
 		t.Fatalf("sha256 = %s, want the hash of the file as stored", res.SHA256)
 	}
+	// The content digest is of the copy handed out, so the bytes that arrive
+	// can be checked against it.
+	if sum := sha256.Sum256(res.Content); res.ContentSHA256 != hex.EncodeToString(sum[:]) || res.ContentSHA256 == res.SHA256 {
+		t.Fatalf("content_sha256 = %s, want the hash of the redacted copy (%x), apart from sha256 %s", res.ContentSHA256, sum, res.SHA256)
+	}
 	got := string(res.Content)
 	if strings.Contains(got, "hunter2") {
 		t.Fatalf("read returned the RCON password (spec §286):\n%s", got)
@@ -633,6 +638,34 @@ func TestWriteDetectsConcurrentChange(t *testing.T) {
 	}
 }
 
+// TestWriteChecksTheContentDigest: a write lands only bytes that hash to the
+// SHA-256 felis-api sent with them; bytes changed on the way touch nothing.
+func TestWriteChecksTheContentDigest(t *testing.T) {
+	root, _ := worldRoot(t)
+	props := filepath.Join(root, "server.properties")
+	if err := os.WriteFile(props, []byte("motd=hello\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	sent := sha256.Sum256([]byte("motd=mine\n"))
+	req := Request{Op: OpWrite, Path: "server.properties", Content: []byte("motd=mint\n"), ContentSHA256: hex.EncodeToString(sent[:])}
+	res, err := Execute(root, req)
+	if err != nil || res.Code != CodeDigestMismatch {
+		t.Fatalf("changed write = %+v, %v; want %s", res, err, CodeDigestMismatch)
+	}
+	if b, _ := os.ReadFile(props); string(b) != "motd=hello\n" {
+		t.Fatalf("a changed write replaced the file with %q", b)
+	}
+	assertNoTemporaries(t, root)
+
+	req.Content = []byte("motd=mine\n")
+	if res, err := Execute(root, req); err != nil || res.Code != "" {
+		t.Fatalf("write as sent = %+v, %v", res, err)
+	}
+	if b, _ := os.ReadFile(props); string(b) != "motd=mine\n" {
+		t.Fatalf("on disk %q, want the bytes as sent", b)
+	}
+}
+
 func assertNoTemporaries(t *testing.T, dir string) {
 	t.Helper()
 	des, err := os.ReadDir(dir)

internal/fileedit/jobspec.go

@@ -195,6 +195,9 @@ func FilesJob(p JobParams) (*batchv1.Job, error) {
 	// secret, so it rides argv; only the content itself needs the env channel.
 	switch p.Op {
 	case OpWrite:
+		// The content's own SHA-256 goes beside it, so the Job writes only the
+		// bytes felis-api handed over (Request.ContentSHA256).
+		args = append(args, "--sha256", digest(p.Content))
 		if p.Expect != "" {
 			args = append(args, "--expect-sha256", p.Expect)
 		}

internal/fileedit/jobspec_test.go

@@ -2,7 +2,9 @@ package fileedit
 
 import (
 	"bytes"
+	"crypto/sha256"
 	"encoding/base64"
+	"encoding/hex"
 	"slices"
 	"strconv"
 	"strings"
@@ -274,6 +276,12 @@ func TestFilesJobContentEnv(t *testing.T) {
 		if strings.Contains(strings.Join(job.Spec.Template.Spec.Containers[0].Args, " "), "motd=hello") {
 			t.Fatal("content must not appear in the container arguments")
 		}
+		// Its SHA-256 does, so the Job writes only the bytes felis-api handed over.
+		sum := sha256.Sum256(p.Content)
+		args := job.Spec.Template.Spec.Containers[0].Args
+		if i := slices.Index(args, "--sha256"); i < 0 || i+1 >= len(args) || args[i+1] != hex.EncodeToString(sum[:]) {
+			t.Fatalf("args %q, want --sha256 %x", args, sum)
+		}
 	})
 
 	// execve refuses one environment string over 128 KiB and the container never
@@ -353,7 +361,8 @@ func TestFilesJobOpArgs(t *testing.T) {
 
 	create := testParams(OpWrite)
 	create.CreateOnly = true
-	if got := args(create); !slices.Equal(got, []string{"--create-only"}) {
+	// The content (none here) goes with its SHA-256.
+	if got := args(create); !slices.Equal(got, []string{"--sha256", "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855", "--create-only"}) {
 		t.Errorf("create-only write args = %v", got)
 	}
 	readCreate := testParams(OpRead)

panel/src/i18n/resources/en-US/errors.json

@@ -72,9 +72,10 @@
   "upload_incomplete": "The upload stopped before the whole file arrived, so nothing was changed. Try again.",
   "length_required": "The upload did not say how large it is, so it was refused. Upload it again from the panel.",
   "digest_mismatch": "The file was changed on its way to the server, so it was refused and nothing was written. Try again.",
-  "digest_required": "The upload came without a checksum, so it was refused. Reload the panel and upload it again.",
-  "bad_digest": "The upload's checksum was malformed, so it was refused. Reload the panel and upload it again.",
+  "digest_required": "The request came without a checksum, so it was refused. Reload the panel and try again.",
+  "bad_digest": "The request's checksum was malformed, so it was refused. Reload the panel and try again.",
   "file_unreadable": "The file could not be read: it was changed, moved or deleted after it was picked. Pick it again and upload.",
+  "read_damaged": "The file arrived damaged, so it was not opened: saving it would write the damage back. Open it again.",
   "upload_not_found": "This upload is gone: it was cancelled, already landed, sat idle for 6 hours, or the panel service restarted. Upload the file again.",
   "too_many_uploads": "You already have 4 large uploads in progress. Wait for one to finish, or cancel one, and try again.",
   "op_lost": "The operation's progress can no longer be read. Refresh the list to see whether the file landed.",

panel/src/i18n/resources/zh-CN/errors.json

@@ -72,9 +72,10 @@
   "upload_incomplete": "文件还没传完上传就中断了，什么都没有改动。请重试。",
   "length_required": "这次上传没有声明文件大小，被拒绝了。请从面板重新上传。",
   "digest_mismatch": "文件在传输途中被改动了，服务器已拒收，什么都没有写入。请重试。",
-  "digest_required": "这次上传没有附带校验值，被拒绝了。请刷新面板后重新上传。",
-  "bad_digest": "这次上传附带的校验值格式不对，被拒绝了。请刷新面板后重新上传。",
+  "digest_required": "这次请求没有附带校验值，被拒绝了。请刷新面板后再试。",
+  "bad_digest": "这次请求附带的校验值格式不对，被拒绝了。请刷新面板后再试。",
   "file_unreadable": "读不出这个文件：它在选中之后被改动、移走或删除了。请重新选择文件再上传。",
+  "read_damaged": "文件传过来时损坏了，所以没有打开：保存它会把损坏写回去。请重新打开。",
   "upload_not_found": "这次分片上传已经不在了（取消过、已经写入、闲置超过 6 小时，或者面板服务重启过）。请重新上传。",
   "too_many_uploads": "你同时进行的大文件上传已经有 4 个了。等其中一个完成，或者取消一个再试。",
   "op_lost": "看不到这次操作的进度了。刷新列表看看文件有没有写入。",

panel/src/lib/api.test.ts

@@ -1,4 +1,7 @@
 import { createHash } from "node:crypto";
+
+// hexOf is the SHA-256 (hex) of the bytes a file editor call carries.
+const hexOf = (bytes: string | Uint8Array) => createHash("sha256").update(bytes).digest("hex");
 import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
 
 // Pin the GET /me wire shape. is_admin crosses an untyped fetch().json() boundary
@@ -853,15 +856,29 @@ describe("image whitelist and builds wire shapes", () => {
     });
 
     it("readServerFile GETs /servers/{name}/file and passes base64 through", async () => {
-      const fetchSpy = fakeFetch({ path: "world/level.dat", content: "AAEC" });
+      const content_sha256 = hexOf(new Uint8Array([0, 1, 2]));
+      const fetchSpy = fakeFetch({ path: "world/level.dat", content: "AAEC", sha256: "a".repeat(64), content_sha256 });
       vi.stubGlobal("fetch", fetchSpy);
       const res = await api.readServerFile("survival", "world/level.dat");
-      expect(res.content).toBe("AAEC");
+      expect(res).toEqual({ path: "world/level.dat", content: "AAEC", sha256: "a".repeat(64), content_sha256 });
       const [url, opts] = (fetchSpy as unknown as ReturnType<typeof vi.fn>).mock.calls[0];
       expect(String(url)).toBe("/servers/survival/file?path=world%2Flevel.dat");
       expect((opts as RequestInit).method).toBe("GET");
     });
 
+    // An editor that opened a damaged read would save the damage back.
+    it.each([
+      ["hash otherwise", "AAED"],
+      ["are not base64 at all", "AA=E"],
+    ])("readServerFile refuses content whose bytes %s", async (_, content) => {
+      vi.stubGlobal(
+        "fetch",
+        fakeFetch({ path: "world/level.dat", content, sha256: "a".repeat(64), content_sha256: hexOf(new Uint8Array([0, 1, 2])) }),
+      );
+      await expect(api.readServerFile("survival", "world/level.dat")).rejects.toMatchObject({ code: "read_damaged" });
+      expect(humanizeError({ code: "read_damaged" })).toMatch(/arrived damaged/);
+    });
+
     it("writeServerFile PUTs {content} — an explicit \"\" is a deliberate truncate, not an omitted field", async () => {
       const fetchSpy = fakeFetch({ path: "a.txt", status: "written" });
       vi.stubGlobal("fetch", fetchSpy);
@@ -870,7 +887,7 @@ describe("image whitelist and builds wire shapes", () => {
       const [url, opts] = (fetchSpy as unknown as ReturnType<typeof vi.fn>).mock.calls[0];
       expect(String(url)).toBe("/servers/survival/file?path=a.txt");
       expect((opts as RequestInit).method).toBe("PUT");
-      expect((opts as RequestInit).body).toBe(JSON.stringify({ content: "" }));
+      expect((opts as RequestInit).body).toBe(JSON.stringify({ content: "", content_sha256: hexOf("") }));
     });
 
     it("writeServerFile sends the hash the read returned as expect_sha256", async () => {
@@ -880,7 +897,7 @@ describe("image whitelist and builds wire shapes", () => {
       expect(res.sha256).toBe("b".repeat(64));
       const [, opts] = (fetchSpy as unknown as ReturnType<typeof vi.fn>).mock.calls[0];
       expect((opts as RequestInit).body).toBe(
-        JSON.stringify({ content: "aGk=", expect_sha256: "a".repeat(64) }),
+        JSON.stringify({ content: "aGk=", content_sha256: hexOf("hi"), expect_sha256: "a".repeat(64) }),
       );
     });
   });
@@ -1372,7 +1389,7 @@ describe("server file manager wire shapes", () => {
     const [url, opts] = sent(fetchSpy);
     expect(url).toBe("/servers/survival/file?path=plugins%2Fnew.yml");
     expect(opts.method).toBe("PUT");
-    expect(opts.body).toBe(JSON.stringify({ content: "", create_only: true }));
+    expect(opts.body).toBe(JSON.stringify({ content: "", content_sha256: hexOf(""), create_only: true }));
   });
 
   it("deleteServerFile DELETEs /servers/{name}/file with no body", async () => {

panel/src/lib/api.ts

@@ -45,7 +45,7 @@ import type {
   UpdateReport,
 } from "./types";
 import { loadConfig } from "./config";
-import { sha256Of } from "./digest";
+import { base64Sha256, sha256Of } from "./digest";
 import i18next from "i18next";
 
 // Typed client for the felis-api external face (spec §7). Credentials are sent so
@@ -768,31 +768,49 @@ export const api = rejectingSync({
   // readServerFile returns one file's bytes (base64) and the sha256 of the file
   // as stored. A file over the read ceiling is a 413, never a silent truncation,
   // because a later save of a truncated body would destroy the rest of the file.
-  readServerFile: (name: string, path: string) =>
-    request<{ path: string; content: string; sha256: string }>(
+  // The content must hash to content_sha256, the digest of the bytes as sent: a
+  // read damaged on the way is refused (read_damaged) rather than opened, since
+  // saving it would write the damage back.
+  readServerFile: async (name: string, path: string) => {
+    const r = await request<{ path: string; content: string; sha256: string; content_sha256: string }>(
       "GET",
       urlPath`/servers/${name}/file` + `?path=${encodeURIComponent(path)}`,
-    ),
+    );
+    let got = "";
+    try {
+      got = await base64Sha256(r.content);
+    } catch {
+      /* not base64 at all: damaged too */
+    }
+    if (got !== r.content_sha256) throw clientError("read_damaged");
+    return r;
+  },
 
   // writeServerFile atomically replaces a file's contents (creating it if
   // absent). Sending an explicit "" is a deliberate truncate; the wire field is
   // required, but that is enforced by the caller (this method always sends one).
   // With expectSha256 (the hash the read returned) a file someone changed since
   // is refused with 409 file_changed; without it the write is unconditional.
-  writeServerFile: (name: string, path: string, content: string, expectSha256?: string) =>
+  // The content goes with its SHA-256 (content_sha256), so content changed on
+  // the way is refused (digest_mismatch) and nothing is written.
+  writeServerFile: async (name: string, path: string, content: string, expectSha256?: string) =>
     request<{ path: string; status: string; sha256: string }>(
       "PUT",
       urlPath`/servers/${name}/file` + `?path=${encodeURIComponent(path)}`,
-      expectSha256 ? { content, expect_sha256: expectSha256 } : { content },
+      {
+        content,
+        content_sha256: await base64Sha256(content),
+        ...(expectSha256 ? { expect_sha256: expectSha256 } : {}),
+      },
     ),
 
   // createServerFile makes a new file with content, and only if nothing is at the
   // path yet: something that appeared meanwhile is 409 file_exists, never replaced.
-  createServerFile: (name: string, path: string, content: string) =>
+  createServerFile: async (name: string, path: string, content: string) =>
     request<{ path: string; status: string; sha256: string }>(
       "PUT",
       urlPath`/servers/${name}/file` + `?path=${encodeURIComponent(path)}`,
-      { content, create_only: true },
+      { content, content_sha256: await base64Sha256(content), create_only: true },
     ),
 
   // deleteServerFile deletes a file, a link (never what it names) or a folder with
@@ -1388,6 +1406,9 @@ export function humanizeError(e: unknown): string {
       return t("bad_digest");
     case "file_unreadable":
       return t("file_unreadable");
+    // A file opened in the editor whose bytes arrived damaged (readServerFile).
+    case "read_damaged":
+      return t("read_damaged");
     // An upload sent in parts: the session is gone (cancelled, landed, idle for
     // 6 hours, or felis-api restarted), or the account holds four already.
     case "upload_not_found":

panel/src/lib/digest.ts

@@ -22,3 +22,13 @@ export async function sha256Of(blob: Blob): Promise<{ hex: string; header: strin
   }
   return { hex, header: `sha-256=:${btoa(bin)}:` };
 }
+
+// base64Sha256 answers the hex SHA-256 of the bytes b64 encodes: the file
+// editor's content_sha256, which a save sends with its content and a read is
+// checked against. A string that is not base64 throws.
+export async function base64Sha256(b64: string): Promise<string> {
+  const bin = atob(b64);
+  const bytes = new Uint8Array(bin.length);
+  for (let i = 0; i < bin.length; i++) bytes[i] = bin.charCodeAt(i);
+  return (await sha256Of(new Blob([bytes]))).hex;
+}

panel/src/lib/openapi.gen.ts

@@ -1412,7 +1412,7 @@ export interface paths {
         get: operations["readServerFile"];
         /**
          * Write a file in a server's world volume (owner-or-admin; server must be stopped).
-         * @description Replaces a file's contents, creating the file if absent but never creating its parent directories. Content is base64 so arbitrary bytes (CRLF endings, a BOM) survive intact. Writes are capped at 256 KiB — the Job spec carries the content, and etcd bounds the object — so a larger body is 413. Same stopped-gate and os.Root containment as the read; a write through a symlink leaving the world root is refused. The replacement is atomic (a synced temporary sibling renamed over the file, keeping its mode), so a failed write leaves the old file whole. With expect_sha256 the write lands only if the file still has that hash; otherwise 409 file_changed. Audited as file.write.
+         * @description Replaces a file's contents, creating the file if absent but never creating its parent directories. Content is base64 so arbitrary bytes (CRLF endings, a BOM) survive intact. Writes are capped at 256 KiB — the Job spec carries the content, and etcd bounds the object — so a larger body is 413. Same stopped-gate and os.Root containment as the read; a write through a symlink leaving the world root is refused. The replacement is atomic (a synced temporary sibling renamed over the file, keeping its mode), so a failed write leaves the old file whole. With expect_sha256 the write lands only if the file still has that hash; otherwise 409 file_changed. content_sha256 is the SHA-256 of the content: content that hashes otherwise changed on the way and is refused (400 digest_mismatch) before a Job starts, and the Job checks the bytes it received the same way before writing. Audited as file.write.
          */
         put: operations["writeServerFile"];
         post?: never;
@@ -6921,6 +6921,8 @@ export interface operations {
                         content: string;
                         /** @description SHA-256 of the file as stored (before the rcon.password redaction in server.properties). Send it back as expect_sha256 on the next write. */
                         sha256: string;
+                        /** @description SHA-256 of the decoded content as sent (after any redaction). A client that gets content hashing otherwise got it damaged on the way, and reads it again. */
+                        content_sha256: string;
                     };
                 };
             };
@@ -6962,6 +6964,15 @@ export interface operations {
                     "application/json": components["schemas"]["Error"];
                 };
             };
+            /** @description The file's bytes do not hash to the digest the file Job sent with them (read_damaged): they changed on the way to felis-api. Read it again. */
+            502: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["Error"];
+                };
+            };
             503: components["responses"]["ServiceUnavailable"];
             /** @description The file Job did not finish in time; retry. */
             504: {
@@ -6995,6 +7006,8 @@ export interface operations {
                      * @description Base64-encoded file bytes.
                      */
                     content: string;
+                    /** @description The SHA-256 (lowercase hex) of the decoded content. Absent is 400 digest_required, malformed 400 bad_digest, and content that does not hash to it 400 digest_mismatch; nothing is written. */
+                    content_sha256: string;
                     /** @description The sha256 a read returned. When present, the write is refused with 409 file_changed if the file has changed (or been deleted) since. Omit it to write unconditionally. */
                     expect_sha256?: string;
                     /** @description true writes only if nothing is at the path yet (409 file_exists otherwise), for making a new file without replacing one that appeared meanwhile. Cannot be combined with expect_sha256. */
@@ -7018,7 +7031,7 @@ export interface operations {
                     };
                 };
             };
-            /** @description Missing path, malformed body, invalid server name, or a path that escapes the world root. */
+            /** @description Missing path, malformed body, invalid server name, or a path that escapes the world root (bad_request, bad_path), or content that came without its SHA-256 (digest_required), with a malformed one (bad_digest), or changed on the way (digest_mismatch). */
             400: {
                 headers: {
                     [name: string]: unknown;