samples/restApi: sanitize caller-controlled log fields (G706)

[randomizedcoder]

Hi 👋

Same static-analysis run as #124 — gosec also flagged G706 (log injection via taint analysis) at 15 sites across samples/restApi/handlers/{utils,dcgm}.go. All instances are this pattern:

log.Printf("error: %v%v: %v", req.Host, req.URL, err.Error())

req.Host is set from the Host: header, so a client can stuff \n, \r\n, \x00, ANSI escapes, etc. into it and forge log entries or abuse terminal log tails. Sample code → likely to be copy-pasted → worth fixing.

What this PR does

Adds a tiny helper in handlers/utils.go:

func logRequestError(req *http.Request, msg string) {
    var urlStr string
    if req.URL != nil {
        urlStr = req.URL.String()
    }
    log.Printf("error: host=%q url=%q msg=%q", req.Host, urlStr, msg)
}

%q is gosec's recognized taint-cleanser — Go renders LF/CR as \n/\r, NUL as \x00, ANSI ESC as \x1b, U+2028/U+2029 as 
/
, and backslash-escapes embedded quotes. No raw control character survives into the log line regardless of which field carried the payload.

All 15 G706 sites in utils.go (9) and dcgm.go (6) now call the helper.

TDD + table-driven tests with nasty cases

Added samples/restApi/handlers/utils_test.go (15-case TestLogRequestError + 1 TestLogRequestError_NilURL). Categories:

Category	Cases	What it covers
positive	1	Benign request renders quoted, readable
boundary	1	Empty fields don't panic
corner	1	Multibyte UTF-8 passes through readable
attacker	12	LF, CRLF, NUL, BEL, BS, ANSI ESC \x1b[2J, U+2028, U+2029, embedded quote, 10 KB string, and a mixed-all-attacks case

Every case enforces a blanket security invariant via a loop over {LF, CR, NUL, ESC, BEL, BS, U+2028, U+2029} — none of those raw bytes may appear anywhere in the captured log line. Tests are GPU-less (log.SetOutput(&buf) + synthetic *http.Request).

Heads-up on log line format

The format changes from error: <host><url>: <msg> (which had no separator between Host and URL — a small wart) to error: host="..." url="..." msg="...". More grep-friendly, but if anything downstream is structurally parsing these sample logs I can do a tighter %v→%q swap that preserves the wire format. Happy to switch.

Why this is low risk

• Helper is package-private, no public API change.
• Sample-only — no pkg/ code touched.
• All 9 sample binaries build cleanly (go build ./samples/...).
• go vet, gofmt, and the 16 new tests all green.

Test plan

• go build ./samples/restApi/...
• go test -v -count=1 ./samples/restApi/handlers/... — 16/16 pass
• go vet ./samples/restApi/...
• gofmt -l samples/restApi/handlers/ — empty
• CI green

🤖 Generated with Claude Code