What causes "file not open for reading" in gofr-dev/gofr?

Reopen the file in read mode (or read+write flags if supported by the adapter) before calling Read/ReadAll.

errFileNotOpenForReading

errFileNotOpenForReading

Error message

file not open for reading

What it means

A sentinel error from the common file layer: the file handle was opened without read intent (openFlags lacked read), so Read/ReadAll refuse to operate. It prevents silently reading an empty stream from a write-only handle.

Source

Thrown at pkg/gofr/datasource/file/common_file.go:18

package file

import (
	"context"
	"errors"
	"fmt"
	"io"
	"os"
	"strings"
	"time"

	"gofr.dev/pkg/gofr/datasource"
)

// Error variables for common file operations.
var (
	// errFileNotOpenForReading is returned when attempting to read from a file that wasn't opened for reading.
	errFileNotOpenForReading = errors.New("file not open for reading")

	// errFileNotOpenForWriting is returned when attempting to write to a file that wasn't opened for writing.
	errFileNotOpenForWriting = errors.New("file not open for writing")

	// errWriteAtNotSupported is returned when WriteAt is called on cloud storage.
	errWriteAtNotSupported = errors.New("WriteAt not supported for cloud storage")

	// errWriterNil is returned when NewWriter returns nil.
	errWriterNil = errors.New("NewWriter returned nil")
)

// File permission constants.
const (
	// DefaultFileMode is the standard file permission (0644 = rw-r--r--).
	DefaultFileMode os.FileMode = 0644

	// DefaultDirMode is the standard directory permission (0755 = rwxr-xr-x).
	DefaultDirMode os.FileMode = 0755

View on GitHub (pinned to 187eb24962)

Solutions

Reopen the file in read mode (or read+write flags if supported by the adapter) before calling Read/ReadAll.
Check the file's open mode / read flag before reading, and fail fast with a clear message.
Use WriteAt/Write for output handles and a separate Open() call for reading back content.

Example fix

// before
f, _ := store.Create(ctx, "out.txt")
f.ReadAll(ctx) // error: file not open for reading
// after
f, _ := store.Open(ctx, "out.txt")
data, err := f.ReadAll(ctx)

Defensive patterns

Strategy: validation

Validate before calling

func canRead(f interface{ Read(context.Context, []byte) (int, error) }, openedForRead bool) error {
    if !openedForRead {
        return errors.New("handle not opened for reading: reopen via Open() before Read/ReadAll")
    }
    return nil
}

Try / catch

data, err := f.ReadAll(ctx)
if err != nil && errors.Is(err, datasource.ErrFileNotOpenForReading) {
    f, err = store.Open(ctx, path) // reopen in read mode
    if err != nil { return err }
    data, err = f.ReadAll(ctx)
}

Prevention

Open with read intent (Open) whenever you plan to call Read/ReadAll.
Treat Create/Append handles as write-only in this abstraction.
Track the open mode alongside handles and assert before read calls.
After writes, close and reopen the file to read content back.

When it happens

Trigger: Calling Read or ReadAll on a file obtained via Create/AppendMode or opened with write-only flags in common_file.go, rather than via an Open/read-enabled handle.

Common situations: Opening a cloud file for append/write then trying to read back what was written without reopening; Copy-on-write patterns forgetting to reopen with read; misunderstanding that write-mode handles in this abstraction don't also grant read.

Related errors

AI-assisted analysis of gofr-dev/gofr@187eb24962 (2026-09-01). Data as JSON: /api/errors/ece0f8d9a4e31cc9. Report an issue: GitHub.