What causes "Writing file's '%s' content error" in OpenFeign/feign?

Verify the file exists and is readable before adding it to the multipart request

OpenFeign/feign · error · EncodeException

Writing file's ' ' content error

Error message

Writing file's '%s' content error

What it means

In SingleFileWriter.write (feign-form), the multipart writer fails while streaming the content of a java.io.File into the form output. The file was opened with FileInputStream but an IOException occurred during reading or writing (typical causes: file deleted or unreadable after metadata was written, disk/pipe I/O failure). The exception is rethrown as an EncodeException carrying the file name, so multipart encoding of the request aborts.

Solutions

Verify the file exists and is readable before adding it to the multipart request
Check disk space and output stream health if the read itself is failing
Log/inspect the wrapped IOException cause for the root filesystem error
Copy the file to a stable temporary location before encoding if it may change mid-write

Example fix

// before
client.upload(new File("/tmp/report.pdf"));
// after
File f = new File("/tmp/report.pdf");
if (!f.isFile() || !f.canRead()) throw new IllegalStateException("unreadable file: " + f);
client.upload(f);

Defensive patterns

Strategy: validation

Validate before calling

static void requireReadable(File f) {
  if (f == null || !f.isFile() || !f.canRead())
    throw new IllegalArgumentException("file missing or unreadable: " + f);
}

Try / catch

try {
  client.upload(file);
} catch (EncodeException e) {
  if (e.getMessage().contains("content error")) {
    throw new UncheckedIOException((IOException) e.getCause());
  }
  throw e;
}

Prevention

Validate file existence/readability just before encoding
Avoid encoding files on volatile storage or that another process may replace
Prefer in-memory byte[] or a stable InputStream for uploads

When it happens

Trigger: write() called while encoding a single-file multipart part and the InputStream read fails (file missing, unreadable, closed) or the output stream write fails mid-copy.

Common situations: Encoding a java.io.File that was deleted or moved after the request was built; permission issues on the file; network-backed streams that fail mid-read.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

AI-assisted analysis of OpenFeign/feign@e2a1e27560 (2026-09-10). Data as JSON: /api/errors/9277ccdead0b4312. Report an issue: GitHub.

Appendix: source

Thrown at form/src/main/java/feign/form/multipart/SingleFileWriter.java:51

  public boolean isApplicable(Object value) {
    return value instanceof File;
  }

  @Override
  protected void write(Output output, String key, Object value) throws EncodeException {
    val file = (File) value;
    writeFileMetadata(output, key, file.getName(), null);

    try (InputStream input = new FileInputStream(file)) {
      val buf = new byte[4096];
      int length = input.read(buf);
      while (length > 0) {
        output.write(buf, 0, length);
        length = input.read(buf);
      }
    } catch (IOException ex) {
      val message = String.format("Writing file's '%s' content error", file.getName());
      throw new EncodeException(message, ex);
    }
  }
}

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