Added streaming/IO support for MLI encoding and decoding

[Anushre20]

Description

This PR adds two new public functions to enable streaming/IO-based MLI encoding and decoding, making the library more suitable for real-world TCP socket implementations where data is read/written incrementally.

Changes

• EncodeWriter(w io.Writer, key string, length int) error - Encodes the MLI for the given key and length, writing directly to an io.Writer
• DecodeReader(r io.Reader, key string) (int, error) - Reads the MLI bytes from an io.Reader and returns the decoded message length
• Private helper mliSize(key string) int for internal size lookup
• Added io import

Motivation

The existing Encode/Decode API requires the full MLI byte slice upfront, which doesn't align well with streaming protocols like TCP where data arrives incrementally.

These new functions allow users to:

• Write MLI + message directly to a network connection in one flow
• Read MLI from a connection without pre-allocating byte slices
• Build cleaner ISO 8583 message framing over raw sockets

Example Usage

// Writer side
func writeMessage(w io.Writer, message []byte) error {
    if err := simplemli.EncodeWriter(w, simplemli.MLI2I, len(message)); err != nil {
        return err
    }
    _, err := w.Write(message)
    return err
}

// Reader side
func readMessage(r io.Reader) ([]byte, error) {
    length, err := simplemli.DecodeReader(r, simplemli.MLI2I)
    if err != nil {
        return nil, err
    }

    message := make([]byte, length)
    if _, err := io.ReadFull(r, message); err != nil {
        return nil, err
    }

    return message, nil
}

Testing

• All existing tests pass (32-bit and 64-bit)
• Added 14 new test cases covering:
  • Round-trip encode/decode via bytes.Buffer for all 7 MLI types
  • Error cases: invalid key, negative length, insufficient bytes, EOF
• Race detector: go test -race ./...
• Benchmarks unchanged (no performance regression)
• Code builds, vets, and formats cleanly

Backward Compatibility

✅ Fully backward compatible - no existing APIs modified, only new functions added

Checklist

• Tests pass (go test -race ./...)
• Code builds (go build ./...)
• Vet passes (go vet ./...)
• Formatted (gofmt -l .)
• No breaking changes
• Documentation in code comments

[CLAassistant]

All committers have signed the CLA.

[Anushre20]

hi @amisol @kranthipoturaju @apsivam
please review my pull request
thankyou

[madflojo]

Hello, thanks for the contribution.

We’ve intentionally kept I/O outside this library to keep its scope small and focused. Applications can combine the existing encoding and decoding functions with their own I/O and error handling.

Reader/writer helpers introduce additional decisions around partial reads and writes, error propagation, and recovery. We feel those decisions are better handled by the implementing applications.

[Anushre20]

@madflojo so do i close this repository ?

also , is there any issue or task i can work upon this repository as this would be really helpful for my practical learning ?