feat(go): step 1 — total wall-clock latency per URL

probe.Measure performs an HTTP GET and records total elapsed time from
request start to body fully read. main.go prints URL, status code, and
total for each positional URL argument, exiting 1 on any failure.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -4,6 +4,15 @@ All completed features are logged here in reverse-chronological order.
 
 ---
 
+## 2026-07-01 00:08 — Simple total latency (Go, Step 1)
+
+- `probe.Measure` performs an HTTP GET and records wall-clock total time
+- `main.go` prints URL, HTTP status code, and total duration for each URL
+- Exits with code 1 if any URL fails
+- Multiple URLs accepted as positional arguments
+
+---
+
 ## 2026-07-01 00:08 — Project scaffold (Go, Step 0)
 
 - Created project structure: `go/`, `python/`, `docs/plans/`, `docs/usage/`

README.md

@@ -90,7 +90,7 @@ https://example.com  (5 samples)
 | Step | Feature | Status |
 |------|---------|--------|
 | 0 | Project scaffold — directory structure, `go.mod`, minimal binary | ✅ Done |
-| 1 | Simple total latency — single URL, wall-clock time | ⬜ Pending |
+| 1 | Simple total latency — single URL, wall-clock time | ✅ Done |
 | 2 | Per-phase breakdown — DNS, TCP, TLS, TTFB, transfer (`net/http/httptrace`) | ⬜ Pending |
 | 3 | Multiple URLs + `--count`/`-n` — min/avg/max aggregates | ⬜ Pending |
 | 4 | `--json` output flag | ⬜ Pending |

docs/usage/step-1-total-latency.md

@@ -0,0 +1,57 @@
+# Step 1 — Simple Total Latency
+
+## What this step delivers
+
+`latprobe` accepts one or more URLs and prints the total wall-clock time of
+each HTTP GET request (including body download). No per-phase breakdown yet —
+that comes in Step 2.
+
+## Build
+
+```sh
+cd go
+go build -o latprobe .
+```
+
+## Usage
+
+```sh
+latprobe <url> [url ...]
+```
+
+## Examples
+
+Single URL:
+
+```sh
+$ ./latprobe https://example.com
+https://example.com                            200  70ms
+```
+
+Multiple URLs:
+
+```sh
+$ ./latprobe https://example.com https://www.google.com
+https://example.com                            200  70ms
+https://www.google.com                         200  127ms
+```
+
+Error (unreachable host):
+
+```sh
+$ ./latprobe https://doesnotexist.invalid
+error https://doesnotexist.invalid: Get "https://doesnotexist.invalid": ...
+# exits with code 1
+```
+
+## Output columns
+
+| Column | Description |
+|--------|-------------|
+| URL | The requested URL |
+| Status | HTTP response status code |
+| Total | Wall-clock time from request start to body fully received |
+
+## Flags accepted (not yet functional)
+
+`-n`/`--count` and `--json` are parsed but produce no effect until Steps 3–4.

go/internal/probe/probe.go

@@ -1,10 +1,13 @@
 // Package probe measures per-phase HTTP request latency.
 package probe
 
-import "time"
+import (
+	"io"
+	"net/http"
+	"time"
+)
 
 // Phase holds the measured duration of a single request phase.
-// A zero Duration means the phase did not occur (e.g. TLS on plain HTTP).
 type Phase struct {
 	Duration time.Duration
 	// Present is false when the phase was skipped (e.g. no TLS for http://).
@@ -27,8 +30,27 @@ type Result struct {
 	Err error
 }
 
-// Measure performs an HTTP GET request to url and returns a populated Result.
-// It is a placeholder until Step 1 wires in the actual implementation.
+// Measure performs an HTTP GET to url and returns a Result.
+// In Step 1 only the Total phase is populated.
 func Measure(url string) Result {
-	return Result{URL: url}
+	r := Result{URL: url}
+
+	start := time.Now()
+
+	resp, err := http.Get(url) //nolint:noctx
+	if err != nil {
+		r.Err = err
+		r.Total = Phase{Duration: time.Since(start), Present: true}
+		return r
+	}
+	defer resp.Body.Close()
+
+	_, err = io.Copy(io.Discard, resp.Body)
+
+	r.Total = Phase{Duration: time.Since(start), Present: true}
+	r.StatusCode = resp.StatusCode
+	if err != nil {
+		r.Err = err
+	}
+	return r
 }

go/main.go

@@ -4,6 +4,9 @@ import (
 	"flag"
 	"fmt"
 	"os"
+	"time"
+
+	"latprobe/internal/probe"
 )
 
 const usageText = `latprobe — measure per-phase HTTP request latency
@@ -36,9 +39,22 @@ func main() {
 		os.Exit(1)
 	}
 
-	// Placeholders — implementations wired in per step.
-	_, _ = count, jsonOut
+	// --json and -n are parsed but not yet functional (wired in Steps 3–4).
+	_ = jsonOut
+	_ = count
 
-	fmt.Fprintf(os.Stderr, "latprobe: not yet implemented (scaffold only)\n")
-	os.Exit(1)
+	failed := false
+	for _, url := range urls {
+		r := probe.Measure(url)
+		if r.Err != nil {
+			fmt.Fprintf(os.Stderr, "error %s: %v\n", url, r.Err)
+			failed = true
+			continue
+		}
+		fmt.Printf("%-45s  %d  %v\n", r.URL, r.StatusCode, r.Total.Duration.Round(time.Millisecond))
+	}
+
+	if failed {
+		os.Exit(1)
+	}
 }