Demo Zero Chunk bug with ClickHouse server

demo_zero_chunk.go

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
	"strings"
	"time"
)

// This demonstrates how the client WOULD work if ClickHouse properly
// terminated chunked encoding with 0\r\n\r\n

func main() {
	url := "http://localhost:8123/?database=default&wait_end_of_query=0&max_threads=1"
	query := "SELECT throwIf(number=3, 'there is a exception') FROM system.numbers SETTINGS max_block_size=1 FORMAT Native"

	client := &http.Client{
		Timeout: 120 * time.Second,
	}

	req, err := http.NewRequest("POST", url, strings.NewReader(query))
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error creating request: %v\n", err)
		os.Exit(1)
	}

	resp, err := client.Do(req)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error making request: %v\n", err)
		os.Exit(1)
	}
	defer resp.Body.Close()

	// With proper chunked encoding, this would work!
	body, err := io.ReadAll(resp.Body)
	if err != nil {
		// Currently fails here with: unexpected EOF
		// Would work if ClickHouse sent 0\r\n\r\n terminator
		fmt.Fprintf(os.Stderr, "❌ Error reading body: %v\n", err)
		fmt.Fprintf(os.Stderr, "   This happens because ClickHouse doesn't send proper chunk terminator!\n")
		fmt.Fprintf(os.Stderr, "   Captured %d bytes before error\n", len(body))
		os.Exit(1)
	}

	// If we got here, chunked encoding was proper
	fmt.Printf("✅ Successfully read complete response (%d bytes)\n", len(body))

	// Save to file
	os.WriteFile("response.native", body, 0644)

	// Check for exception in the body
	if bytes.Contains(body, []byte("__exception__")) {
		fmt.Println("\n⚠️  Query completed with exception (streamed in body)")

		// Extract exception details
		exceptionStart := bytes.Index(body, []byte("__exception__"))
		if exceptionStart >= 0 {
			exceptionData := body[exceptionStart:]

			// Find the error code
			if codeIdx := bytes.Index(exceptionData, []byte("Code: ")); codeIdx >= 0 {
				errorLine := exceptionData[codeIdx:]
				endLine := bytes.Index(errorLine, []byte("\n"))
				if endLine > 0 {
					fmt.Printf("Exception: %s\n", errorLine[:endLine])
				}
			}
		}
		os.Exit(1)
	}

	// Success - no exception
	fmt.Println("\n✅ Query completed successfully")
	fmt.Println("Data contains valid results")
}