Jan Novak
0ecfb9bb1a
Instruments HTTP requests with net/http/httptrace.ClientTrace to capture timestamps for DNS, TCP connect, TLS handshake, TTFB, and body transfer. TLS row is omitted automatically for plain http:// URLs. Output is an aligned text table with a separator before the Total row. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
81 lines
2.2 KiB
Markdown
81 lines
2.2 KiB
Markdown
# Step 2 — Per-Phase Breakdown
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## What this step delivers
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`latprobe` now shows a full breakdown of every phase of an HTTP request:
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| Phase | What it measures |
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|-------|-----------------|
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| DNS lookup | Time to resolve the hostname (`DNSStart` → `DNSDone`) |
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| TCP connect | Time to establish the TCP connection (`ConnectStart` → `ConnectDone`) |
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| TLS handshake | Time to complete TLS negotiation — HTTPS only (`TLSHandshakeStart` → `TLSHandshakeDone`) |
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| Server (TTFB) | Time from request sent to first response byte (`WroteRequest` → `GotFirstResponseByte`) |
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| Transfer | Time to download the response body (`GotFirstResponseByte` → body closed) |
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| Total | Wall-clock time for the entire request |
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The TLS row is omitted automatically for plain `http://` URLs.
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Implemented via `net/http/httptrace.ClientTrace` — stdlib only, no external dependencies.
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## Build
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```sh
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cd go
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go build -o latprobe .
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```
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## Usage
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```sh
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latprobe <url> [url ...]
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```
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## Examples
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### HTTPS (all phases present)
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```sh
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$ ./latprobe https://example.com
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https://example.com (200)
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DNS lookup : 18.21 ms
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TCP connect : 10.12 ms
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TLS handshake : 36.11 ms
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Server (TTFB) : 21.95 ms
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Transfer : 0.18 ms
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─────────────────────────────
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Total : 88.00 ms
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```
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### HTTP (TLS row omitted)
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```sh
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$ ./latprobe http://example.com
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http://example.com (200)
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DNS lookup : 1.64 ms
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TCP connect : 9.29 ms
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Server (TTFB) : 17.96 ms
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Transfer : 0.07 ms
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─────────────────────────────
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Total : 29.56 ms
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```
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### Multiple URLs
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```sh
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$ ./latprobe https://example.com https://www.google.com
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https://example.com (200)
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DNS lookup : 18.21 ms
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...
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https://www.google.com (200)
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DNS lookup : 7.15 ms
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...
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```
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## Notes
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- **DNS absent on repeat connections**: when the OS has cached the DNS result,
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the DNS phase may be very short or absent. This is expected.
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- **Phases don't always sum exactly to Total**: the trace hooks introduce
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negligible overhead between events; the difference is typically < 1 ms.
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