czSocket

Single-file VB6 UserControl for TCP, TLS/HTTPS, HTTP, and WebSocket (WS/WSS).

Zero external dependencies. Drop one .ctl file into your project — done.

Features

TCP/UDP — Client and server with async I/O
TLS/HTTPS — Native Windows Schannel (SSPI), TLS 1.0–1.3, client and server
HTTP — GET, POST, PUT, DELETE with response parsing (chunked + Content-Length)
WebSocket — Full RFC 6455: text, binary, ping/pong, close handshake
File Transfer — Streaming upload (multipart, 64KB chunks), streaming download (save to disk), chunked send
Resume Support — Pause/resume downloads with HTTP Range header
Progress Tracking — Real-time speed (bytes/sec) and ETA for all transfers
Auto-Retry — Configurable retry on connection failures
Universal API — One set of methods auto-detects protocol from URL scheme
Zero Dependencies — Uses only built-in Windows DLLs
Minimum OS — Windows 7

Quick Start

1. Add to your VB6 project

Copy czSocket.ctl into your project folder, then in VB6:

Project → Add User Control → Existing → czSocket.ctl

Place czSocket1 on your form. That's it.

2. Use it

' TCP
czSocket1.Connect "example.com", 80

' HTTPS (auto-TLS)
czSocket1.Request "GET", "https://jsonplaceholder.typicode.com/posts/1"

' WebSocket (auto from URL)
czSocket1.Connect "wss://ws.postman-echo.com/raw"

Universal API

czSocket auto-detects the protocol from the URL scheme. You don't need to remember which method to call — the same methods work for all protocols.

Methods

Method	Description
`Connect host, [port]`	Connect to host. Auto-detects `ws://`, `wss://`, `http://`, `https://`
`SendData data`	Send string or byte array. Auto: WS frame or raw TCP
`SendFile path, [chunkSize]`	Send file from disk in chunks. Auto: WS binary frames or raw TCP
`Download url, savePath, [headers], [resumeFrom]`	Download file via HTTP/HTTPS. Optional resume from byte offset
`Upload url, filePath, [field]`	Stream upload file via HTTP POST multipart (64KB chunks, non-blocking)
`Request method, url, [body]`	Send HTTP/HTTPS request (GET, POST, PUT, etc.)
`Ping [data]`	Send WebSocket ping frame
`Disconnect`	Close connection. Auto: WS graceful close + TCP close
`Listen`	Start listening for incoming connections (server)
`Accept requestID`	Accept incoming connection
`Bind [port], [ip]`	Bind to local port
`GetData data, [type], [maxLen]`	Retrieve received data
`PeekData data, [type], [maxLen]`	Peek at received data without consuming

Events

Event	When
`Connect()`	Connection established (TCP, TLS handshake, or WS handshake)
`DataArrival(bytesTotal)`	Raw data available (TCP/UDP mode)
`Response(Status, ContentType, Body, Headers)`	HTTP response received. In download mode, `Body` = saved file path
`Progress(BytesSent, BytesTotal, BytesPerSec, SecondsRemaining)`	Transfer progress with speed and ETA
`Receive(Data, IsBinary)`	WebSocket message received
`Disconnected(Code, Reason)`	Connection closed (TCP: Code=0, WS: close code)
`ConnectionRequest(requestID)`	Incoming connection on server
`SendProgress(bytesSent, bytesRemaining)`	Buffer send progress
`SendComplete()`	All queued/chunked data sent
`Error(Number, Description, ...)`	Socket or TLS error

Properties

Property	Type	Access	Description
`RemoteHost`	String	R/W	Remote host name or IP
`RemotePort`	Long	R/W	Remote port number
`RemoteHostIP`	String	R	Resolved remote IP address
`LocalPort`	Long	R/W	Local port for Bind/Listen
`LocalHostName`	String	R	Local machine name
`LocalIP`	String	R	Local IP address
`Protocol`	Enum	R/W	`sckTCPProtocol` / `sckUDPProtocol` / `sckTLSProtocol`
`State`	Enum	R	Current socket state
`SocketHandle`	Long	R	Raw WinSock handle
`Timeout`	Long	R/W	Connection timeout (ms)
`StatusCode`	Long	R	Last HTTP response status code
`ReadyState`	Long	R	WebSocket state (0=None, 1=Connecting, 2=Open, 3=Closing)
`SockOpt`	Long	R/W	Raw socket options

Examples

Raw TCP (Classic Winsock Replacement)

Private Sub Form_Load()
    czSocket1.Connect "example.com", 80
End Sub

Private Sub czSocket1_Connect()
    czSocket1.SendData "GET / HTTP/1.1" & vbCrLf & _
        "Host: example.com" & vbCrLf & _
        "Connection: close" & vbCrLf & vbCrLf
End Sub

Private Sub czSocket1_DataArrival(ByVal bytesTotal As Long)
    Dim s As String
    czSocket1.GetData s
    txtOutput.Text = txtOutput.Text & s
End Sub

HTTPS JSON API

Private Sub btnFetch_Click()
    czSocket1.Request "GET", "https://jsonplaceholder.typicode.com/posts/1"
End Sub

Private Sub czSocket1_Response(ByVal Status As Long, ByVal ContentType As String, _
    Body As String, Headers As String)
    Debug.Print "Status: " & Status
    Debug.Print "Body: " & Body
End Sub

WebSocket

Private Sub Form_Load()
    ' Connect auto-detects wss:// → WebSocket + TLS
    czSocket1.Connect "wss://ws.postman-echo.com/raw"
End Sub

Private Sub czSocket1_Connect()
    ' SendData auto-detects WebSocket → sends as WS text frame
    czSocket1.SendData "Hello, WebSocket!"
End Sub

Private Sub czSocket1_Receive(ByVal Data As String, ByVal IsBinary As Boolean)
    MsgBox "Received: " & Data
End Sub

Private Sub czSocket1_Disconnected(ByVal Code As Long, ByVal Reason As String)
    Debug.Print "Disconnected: " & Code & " " & Reason
End Sub

Web3 / JSON-RPC

' Via HTTPS
Private Sub btnGetBlock_Click()
    Dim body As String
    body = "{""jsonrpc"":""2.0"",""method"":""eth_blockNumber"",""params"":[],""id"":1}"
    czSocket1.Request "POST", "https://mainnet.infura.io/v3/YOUR_KEY", body
End Sub

' Via WebSocket (real-time subscription)
Private Sub btnSubscribe_Click()
    czSocket1.Connect "wss://mainnet.infura.io/ws/v3/YOUR_KEY"
End Sub

Private Sub czSocket1_Connect()
    czSocket1.SendData "{""jsonrpc"":""2.0"",""method"":""eth_subscribe""," & _
        """params"":[""newHeads""],""id"":1}"
End Sub

Private Sub czSocket1_Receive(ByVal Data As String, ByVal IsBinary As Boolean)
    Debug.Print "New block: " & Data
End Sub

Download File with Progress

Private Sub btnDownload_Click()
    czSocket1.Download "https://example.com/largefile.zip", "C:\Downloads\largefile.zip"
End Sub

Private Sub czSocket1_Progress(ByVal BytesSent As Long, ByVal BytesTotal As Long, _
    ByVal BytesPerSec As Long, ByVal SecondsRemaining As Long)
    Dim pct As Long
    If BytesTotal > 0 Then pct = (BytesSent * 100) / BytesTotal
    ProgressBar1.Value = pct
    
    Dim speed As String
    If BytesPerSec > 1048576 Then
        speed = Format$(BytesPerSec / 1048576, "0.0") & " MB/s"
    ElseIf BytesPerSec > 1024 Then
        speed = Format$(BytesPerSec / 1024, "0.0") & " KB/s"
    Else
        speed = BytesPerSec & " B/s"
    End If
    
    lblStatus.Caption = pct & "% | " & speed & " | ETA: " & SecondsRemaining & "s"
End Sub

Private Sub czSocket1_Response(ByVal Status As Long, ByVal ContentType As String, _
    Body As String, Headers As String)
    MsgBox "Download complete: " & Body  ' Body = saved file path
End Sub

Resume Download (Pause/Resume)

Dim lBytesDownloaded As Long

' Pause: disconnect and remember bytes
Private Sub btnPause_Click()
    lBytesDownloaded = m_lCurrentBytes
    czSocket1.Disconnect
End Sub

' Resume: use ResumeFrom parameter with Range header
Private Sub btnResume_Click()
    czSocket1.Download "https://example.com/largefile.zip", _
                       "C:\Downloads\largefile.zip", , lBytesDownloaded
End Sub

Upload File

Private Sub btnUpload_Click()
    czSocket1.Upload "https://api.example.com/upload", "C:\Photos\photo.jpg"
End Sub

Private Sub czSocket1_Progress(ByVal BytesSent As Long, ByVal BytesTotal As Long, _
    ByVal BytesPerSec As Long, ByVal SecondsRemaining As Long)
    lblStatus.Caption = "Uploading: " & Format$(BytesSent / BytesTotal * 100, "0.0") & _
        "%  " & Format$(BytesPerSec / 1048576, "0.0") & " MB/s"
End Sub

Private Sub czSocket1_Response(ByVal Status As Long, ByVal ContentType As String, _
    Body As String, Headers As String)
    If Status = 200 Then
        MsgBox "Upload successful!"
    Else
        MsgBox "Upload failed: " & Status
    End If
End Sub

Send Large File via WebSocket

Private Sub btnSend_Click()
    czSocket1.Connect "wss://fileserver.example.com/upload"
End Sub

Private Sub czSocket1_Connect()
    ' SendFile auto-detects WS mode → sends as binary frames
    czSocket1.SendFile "C:\Videos\video.mp4", 65536  ' 64KB chunks
End Sub

Private Sub czSocket1_Progress(ByVal BytesSent As Long, ByVal BytesTotal As Long, _
    ByVal BytesPerSec As Long, ByVal SecondsRemaining As Long)
    lblProgress.Caption = Format$(BytesSent / 1048576, "0.0") & " / " & _
        Format$(BytesTotal / 1048576, "0.0") & " MB"
End Sub

Private Sub czSocket1_SendComplete()
    MsgBox "File sent!"
End Sub

TCP Server

Private Sub Form_Load()
    czSocket1.LocalPort = 8080
    czSocket1.Listen
End Sub

Private Sub czSocket1_ConnectionRequest(ByVal requestID As Long)
    czSocket1.Disconnect
    czSocket1.Accept requestID
End Sub

Private Sub czSocket1_DataArrival(ByVal bytesTotal As Long)
    Dim s As String
    czSocket1.GetData s
    czSocket1.SendData "Echo: " & s
End Sub

HTTPS Server (TLS)

' Uses two czSocket controls: czServer (listener) + czClient (accepted)
Private Sub Form_Load()
    czServer.LocalPort = 8443
    czServer.Listen App.Path & "\server.pfx", "password"
End Sub

Private Sub czServer_ConnectionRequest(ByVal requestID As Long)
    czClient.Disconnect
    czClient.Accept requestID  ' TLS handshake is automatic
End Sub

Private Sub czClient_Connect()
    ' TLS handshake complete — client is ready
End Sub

Private Sub czClient_DataArrival(ByVal bytesTotal As Long)
    Dim s As String
    czClient.GetData s
    ' Send HTTP response
    Dim resp As String
    resp = "HTTP/1.1 200 OK" & vbCrLf & _
           "Content-Type: text/plain" & vbCrLf & _
           "Content-Length: 13" & vbCrLf & _
           "Connection: close" & vbCrLf & vbCrLf & _
           "Hello, World!"
    czClient.SendData resp
End Sub

Private Sub czClient_SendComplete()
    czClient.Disconnect
End Sub

Auto-Detection Logic

URL Scheme          →  Protocol Mode
─────────────────────────────────────
wss://...           →  WebSocket + TLS
ws://...            →  WebSocket
https://...         →  TCP + TLS
http://...          →  TCP
host, port          →  Raw TCP (backward compatible)

Method              →  Behavior When WS is Open
─────────────────────────────────────
SendData "text"     →  WS text frame
SendData bytes()    →  WS binary frame
SendFile "path"     →  WS binary frames (chunked)
Disconnect          →  WS close frame + TCP close

Architecture

┌─────────────────────────────────────────┐
│           czSocket.ctl (Single File)    │
├─────────────────────────────────────────┤
│  Universal API Layer                    │
│  Connect / SendData / SendFile /        │
│  Download / Upload / Request / Disconnect   │
├──────────┬──────────┬───────────────────┤
│  HTTP    │ WebSocket│  Raw TCP/UDP      │
│  Engine  │  Engine  │  Engine           │
├──────────┴──────────┴───────────────────┤
│  TLS Engine (SSPI/Schannel)             │
├─────────────────────────────────────────┤
│  WinSock Engine (ws2_32.dll)            │
│  Async I/O via WSAEventSelect + Timer   │
├─────────────────────────────────────────┤
│  Windows DLLs (built-in, zero install)  │
│  ws2_32 · secur32 · advapi32 · crypt32 │
└─────────────────────────────────────────┘

Requirements

Requirement	Value
IDE	Visual Basic 6.0 SP6
OS	Windows 7 or later
Dependencies	None (zero external DLLs)
File	Single `czSocket.ctl` (~130 KB)

Performance

All file transfers use streaming I/O with 64KB chunks. Files are never loaded entirely into memory.

Changelog

v1.2

Performance

Fix: O(n²) string accumulation in pvHttpProcessResponse — download now streams bytes directly to file via Put #, bypassing m_sHttpRawResponse accumulation after headers are parsed
Fix: Single recv per timer tick — pvOnReceive now loops until WSAEWOULDBLOCK to drain all available data, increasing download throughput from ~3 MB/s to 175+ MB/s
Fix: Upload loaded entire file into memory — Upload now streams file in 64KB chunks via pvSendNextFileChunk iterative loop
Fix: pvSendNextFileChunk only sent one chunk per FD_WRITE event — now loops until WSAEWOULDBLOCK with periodic DoEvents for UI responsiveness

Download

New: Resume support — Download accepts optional ResumeFrom parameter, sends Range: bytes=N- header, seeks file to correct position, handles 206 Partial Content response
New: Streaming file write — received bytes written directly to disk via file handle, never accumulated in memory

Upload

New: Streaming upload — HTTP headers + multipart prefix sent first, then file streamed in 64KB chunks, then multipart suffix. Replaces old approach of loading entire file into baBody array
New: Upload progress — Progress event fires during upload with bytes sent, total, speed, and ETA
Fix: State setup ordering — upload state set after Connect call (which internally calls Disconnect and resets state)

Demo: Parallel Downloader & Uploader

New: Pause/Resume buttons with click-to-select on progress bar
New: Stop/Cancel button for active, paused, and queued downloads
New: IDM-style block mosaic progress visualization (40 blocks per file)
New: Auto-retry (2 attempts) on connection failure
New: Upload progress display with percentage, speed, and ETA
New: Dynamic button states (Pause ↔ Resume) based on selected download
New: Status bar shows Active / Queued / Done / Paused / Errors counts
New: Total download time logging per file
Fix: DrawProgress throttled to ~10 fps to prevent CPU saturation
Fix: Unicode characters (Chr$(&H25BA)) causing Runtime Error 5 in compiled EXE — replaced with ASCII-safe indicators

v1.1

Fix: Err.Raise 0 crash in compiled EXE — error handler now guards against empty error codes
Fix: Request method (HTTP/HTTPS) not sending data — state setup moved after async Connect call
Fix: WebSocket handshake not sent — state setup ordering corrected
Fix: HTTPS response silently dropped when TLS close arrives in same packet as response data
Fix: Double Disconnected event firing — guard against redundant pvOnClose calls
Fix: Double Connect event for WebSocket — suppress TLS-level connect when WS handshake pending
Fix: Stale HTTP response data contaminating WebSocket handshake parser — proper state cleanup in Disconnect
New: TLS Server — Listen now accepts PFX certificate for HTTPS/WSS server support
New: pvLoadPfxCertificate — loads PFX/P12 certificate files via Windows CryptoAPI
New: Server-side TLS handshake using AcceptSecurityContext (SSPI/Schannel)
New: WebServer demo in Demo/WebServer/ with self-signed certificate generator
Improved: TLS feature description updated to include TLS 1.3 support
Improved: HTTP response parsing description updated (chunked + Content-Length)

v1.0

Initial release

License

MIT License — see source file header for details.

Inspired by VbAsyncSocket by wqweto@gmail.com.

Name		Name	Last commit message	Last commit date
Latest commit History 6 Commits
Demo		Demo
LICENSE		LICENSE
README.md		README.md
czSocket.ctl		czSocket.ctl

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czSocket

Features

Quick Start

1. Add to your VB6 project

2. Use it

Universal API

Methods

Events

Properties

Examples

Raw TCP (Classic Winsock Replacement)

HTTPS JSON API

WebSocket

Web3 / JSON-RPC

Download File with Progress

Resume Download (Pause/Resume)

Upload File

Send Large File via WebSocket

TCP Server

HTTPS Server (TLS)

Auto-Detection Logic

Architecture

Requirements

Performance

Changelog

v1.2

Performance

Download

Upload

Demo: Parallel Downloader & Uploader

v1.1

v1.0

License

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