# Step 2 — Per-Phase Breakdown

## What this step delivers

`latprobe` now shows a full breakdown of every phase of an HTTP request:

| Phase | What it measures |
|-------|-----------------|
| DNS lookup | Time to resolve the hostname (`DNSStart` → `DNSDone`) |
| TCP connect | Time to establish the TCP connection (`ConnectStart` → `ConnectDone`) |
| TLS handshake | Time to complete TLS negotiation — HTTPS only (`TLSHandshakeStart` → `TLSHandshakeDone`) |
| Server (TTFB) | Time from request sent to first response byte (`WroteRequest` → `GotFirstResponseByte`) |
| Transfer | Time to download the response body (`GotFirstResponseByte` → body closed) |
| Total | Wall-clock time for the entire request |

The TLS row is omitted automatically for plain `http://` URLs.

Implemented via `net/http/httptrace.ClientTrace` — stdlib only, no external dependencies.

## Build

```sh
cd go
go build -o latprobe .
```

## Usage

```sh
latprobe <url> [url ...]
```

## Examples

### HTTPS (all phases present)

```sh
$ ./latprobe https://example.com
https://example.com  (200)
  DNS lookup     :     18.21 ms
  TCP connect    :     10.12 ms
  TLS handshake  :     36.11 ms
  Server (TTFB)  :     21.95 ms
  Transfer       :      0.18 ms
  ─────────────────────────────
  Total          :     88.00 ms
```

### HTTP (TLS row omitted)

```sh
$ ./latprobe http://example.com
http://example.com  (200)
  DNS lookup     :      1.64 ms
  TCP connect    :      9.29 ms
  Server (TTFB)  :     17.96 ms
  Transfer       :      0.07 ms
  ─────────────────────────────
  Total          :     29.56 ms
```

### Multiple URLs

```sh
$ ./latprobe https://example.com https://www.google.com
https://example.com  (200)
  DNS lookup     :     18.21 ms
  ...

https://www.google.com  (200)
  DNS lookup     :      7.15 ms
  ...
```

## Notes

- **DNS absent on repeat connections**: when the OS has cached the DNS result,
  the DNS phase may be very short or absent. This is expected.
- **Phases don't always sum exactly to Total**: the trace hooks introduce
  negligible overhead between events; the difference is typically < 1 ms.