fix(pdf-server): one bad form field no longer aborts saving the rest

#577 dropped the per-field try/catch in buildAnnotatedPdfBytes when it
swapped to type-dispatch, so the first field whose pdf-lib write throws
(max-length text, missing /Yes appearance, radio buttonValue mapping to
neither label nor index, ...) bubbled to the outer catch and silently
dropped every subsequent field. Compounded by getAnnotatedPdfBytes
passing every baseline field, so even an untouched problematic field in
the PDF poisoned the whole save.

- Re-wrap each field write in its own try/catch (warn + continue).
- getAnnotatedPdfBytes now only sends fields whose value differs from
  baseline (still includes explicit ''/false sentinels for cleared
  fields so pdf-lib overwrites the original /V).
- Regression test: a maxLength=2 text field fed a long string, followed
  by a normal field; assert the second one still lands.

Author: ochafik

examples/pdf-server/src/mcp-app.ts

@@ -2971,15 +2971,23 @@ async function getAnnotatedPdfBytes(): Promise<Uint8Array> {
     }
   }
 
-  // buildAnnotatedPdfBytes gates on formFields.size > 0 and only writes
-  // entries present in the map. After clearAllItems() the map is empty →
-  // zero setText/uncheck calls → pdf-lib leaves original /V intact →
-  // the "stripped PDF" we promised keeps all its form data. To actually
-  // clear, send an explicit sentinel for every baseline field the user
-  // dropped: "" for text, false for checkbox (matching baseline type).
-  const formFieldsOut = new Map(formFieldValues);
+  // Only write fields that actually changed vs. what's already in the PDF.
+  // Unchanged fields are no-ops at best, and at worst trip pdf-lib edge
+  // cases (max-length text, missing /Yes appearance, …) on fields the user
+  // never touched — which, before the per-field catch in
+  // buildAnnotatedPdfBytes, aborted every subsequent field.
+  //
+  // Fields the user cleared (present in baseline, absent from formFieldValues
+  // after clearAllItems()) still need an explicit "" / false so pdf-lib
+  // overwrites the original /V instead of leaving it intact.
+  const formFieldsOut = new Map<string, string | boolean>();
+  for (const [name, value] of formFieldValues) {
+    if (pdfBaselineFormValues.get(name) !== value) {
+      formFieldsOut.set(name, value);
+    }
+  }
   for (const [name, baselineValue] of pdfBaselineFormValues) {
-    if (!formFieldsOut.has(name)) {
+    if (!formFieldValues.has(name)) {
       formFieldsOut.set(name, typeof baselineValue === "boolean" ? false : "");
     }
   }

examples/pdf-server/src/pdf-annotations.test.ts

@@ -1105,6 +1105,34 @@ describe("buildAnnotatedPdfBytes", () => {
       const form = (await PDFDocument.load(out)).getForm();
       expect(form.getTextField("name").getText()).toBe("kept");
     });
+
+    it("a field that throws on write does not abort subsequent fields", async () => {
+      // Regression for #577: the per-field try/catch was dropped, so the
+      // first throwing field bubbled to the outer catch and silently dropped
+      // every field after it. setText() throws when value exceeds maxLength.
+      const doc = await PDFDocument.create();
+      const page = doc.addPage([612, 792]);
+      const form = doc.getForm();
+      const limited = form.createTextField("limited");
+      limited.setMaxLength(2);
+      limited.addToPage(page, { x: 10, y: 700 });
+      form.createTextField("after").addToPage(page, { x: 10, y: 660 });
+      const fixture = await doc.save();
+
+      const out = await buildAnnotatedPdfBytes(
+        fixture,
+        [],
+        new Map<string, string | boolean>([
+          ["limited", "way too long"], // throws
+          ["after", "kept"],
+        ]),
+      );
+
+      const saved = (await PDFDocument.load(out)).getForm();
+      expect(saved.getTextField("after").getText()).toBe("kept");
+      // The throwing field is left at whatever pdf-lib could do with it —
+      // we only assert it didn't poison "after".
+    });
   });
 });
 

examples/pdf-server/src/pdf-annotations.ts

@@ -22,6 +22,7 @@ import {
   PDFCheckBox,
   PDFDropdown,
   PDFRadioGroup,
+  type PDFForm,
 } from "pdf-lib";
 
 // =============================================================================
@@ -815,44 +816,58 @@ export async function buildAnnotatedPdfBytes(
   await addAnnotationDicts(pdfDoc, annotations);
 
   // Apply form fills. Dispatch on actual field type — getTextField(name) throws
-  // for dropdowns/radios, so the old try/catch silently dropped those on save.
+  // for dropdowns/radios, so we look up the generic field and instanceof it.
+  // Each field is wrapped in its own try/catch: pdf-lib can throw on
+  // length-constrained text, radios whose buttonValue maps to neither label
+  // nor index, checkboxes missing a /Yes appearance, etc. One bad field must
+  // not abort the rest of the loop (regressed in #577 when the inner catch
+  // was dropped along with the type-specific getters).
   if (formFields.size > 0) {
+    let form: PDFForm | undefined;
     try {
-      const form = pdfDoc.getForm();
+      form = pdfDoc.getForm();
+    } catch {
+      // No AcroForm in this PDF
+    }
+    if (form) {
       for (const [name, value] of formFields) {
-        const field = form.getFieldMaybe(name);
-        if (!field) continue;
-
-        if (field instanceof PDFCheckBox) {
-          if (value) field.check();
-          else field.uncheck();
-        } else if (field instanceof PDFRadioGroup) {
-          // The viewer stores pdf.js's buttonValue, which for PDFs with an
-          // /Opt array is a numeric index ("0","1","2") rather than the
-          // option label pdf-lib's select() expects. Try the label first,
-          // then fall back to indexing into getOptions().
-          const opts = field.getOptions();
-          const s = String(value);
-          if (opts.includes(s)) {
-            field.select(s);
-          } else {
-            const idx = Number(s);
-            if (Number.isInteger(idx) && idx >= 0 && idx < opts.length) {
-              field.select(opts[idx]);
+        try {
+          const field = form.getFieldMaybe(name);
+          if (!field) continue;
+
+          if (field instanceof PDFCheckBox) {
+            if (value) field.check();
+            else field.uncheck();
+          } else if (field instanceof PDFRadioGroup) {
+            // The viewer stores pdf.js's buttonValue, which for PDFs with an
+            // /Opt array is a numeric index ("0","1","2") rather than the
+            // option label pdf-lib's select() expects. Try the label first,
+            // then fall back to indexing into getOptions().
+            const opts = field.getOptions();
+            const s = String(value);
+            if (opts.includes(s)) {
+              field.select(s);
+            } else {
+              const idx = Number(s);
+              if (Number.isInteger(idx) && idx >= 0 && idx < opts.length) {
+                field.select(opts[idx]);
+              }
+              // else: value is neither label nor index — leave unset
             }
-            // else: value is neither label nor index — leave unset
+          } else if (field instanceof PDFDropdown) {
+            // select() auto-enables edit mode for values outside getOptions(),
+            // so this works for both enumerated and free-text combos.
+            field.select(String(value));
+          } else if (field instanceof PDFTextField) {
+            field.setText(String(value));
           }
-        } else if (field instanceof PDFDropdown) {
-          // select() auto-enables edit mode for values outside getOptions(),
-          // so this works for both enumerated and free-text combos.
-          field.select(String(value));
-        } else if (field instanceof PDFTextField) {
-          field.setText(String(value));
+          // PDFButton, PDFOptionList, PDFSignature: no fill_form support yet
+        } catch (err) {
+          // Skip this field; carry on with the rest. Surfacing per-field
+          // failures is the caller's job (see fill_form result), not save's.
+          console.warn(`buildAnnotatedPdfBytes: skipped field "${name}":`, err);
         }
-        // PDFButton, PDFOptionList, PDFSignature: no fill_form support yet
       }
-    } catch {
-      // pdfDoc.getForm() throws if the PDF has no AcroForm
     }
   }