blast

A concurrent HTTP load tester built in Go.

Usage

go run ./cmd/blast \
  --url https://httpbin.org/get \
  --c 20 \
  --n 500 \
  --rate 100 \
  --timeout 5s

Flags

Flag	Default	Description
--url	required	Target URL
--c	10	Concurrent workers
--n	100	Total requests
--rate	0 (unlimited)	Max requests/sec
--timeout	30s	Per-request timeout
--method	GET	HTTP method

Example Output

Blast → https://httpbin.org/get
Workers: 20 | Requests: 500 | Timeout: 5s

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Requests:    500
Duration:    4.21s
RPS:         118.8

Latency:
  p50   312ms
  p75   489ms
  p90   601ms
  p95   712ms
  p99   891ms
  max   1.2s

Status Codes:
  200    500

Errors: 0
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Architecture

main
 └─ signal.NotifyContext   ← ctrl-c cancels everything
 └─ dispatch goroutine     ← pushes N tokens into jobs channel
       └─ rate limiter     ← time.Ticker gates throughput
 └─ worker.Pool            ← N goroutines pulling from jobs
       └─ worker[0..N]     ← each makes HTTP requests
            └─ results channel (fan-in)
 └─ stats.Collect          ← drains results, builds report
 └─ stats.Print            ← percentiles, RPS, status codes

Concurrency Patterns

• Worker pool — fixed N goroutines pulling from a buffered jobs channel
• Fan-in — all workers write to a single results channel
• Rate limiting — time.Ticker controls dispatch throughput
• Graceful shutdown — signal.NotifyContext + select on ctx.Done()
• Atomic counter — sync/atomic tracks in-flight requests without a mutex
• WaitGroup — waits for all workers to drain before closing results
• Buffered channels — backpressure between dispatcher and workers