embed blogs.json instead of fetching it at runtime (closes #1)

The library needed network access on first use and its results changed
under the caller between runs. blogs.json is now vendored and compiled in
with go:embed, so the dataset is fixed for a given build.

FetchBlogs keeps its name, signature and sync.Once memoization but now
decodes the embedded bytes; its error return is only reachable if the
committed blogs.json is malformed. net/http is gone from the package, and
a test asserts that no net/* package appears anywhere in the dependency
graph of the non-test build, not only in its direct imports.

make update-data refreshes the vendored file, reading the upstream
location from the BlogsURL constant so the URL has one definition. It
downloads to a temporary file and replaces blogs.json only once that file
parses as a non-empty JSON array of blog entries, so neither a truncated
transfer nor a complete-but-wrong response such as an error page can
overwrite the good dataset. It then runs the test suite against the new
data. That target now needs jq as well as curl.

blogs.json is an unmodified copy of a third party's file, redistributed
here and in every binary that links the package, and the upstream
repository publishes no licence. The README and the embed doc comment now
record where it came from and that this repository's LICENSE does not
extend to it. Whether that arrangement is acceptable is the owner's call.

The dataset is committed verbatim as upstream serves it, which is ~8 MB
of JSON in the repo and in every linking binary; most of that is per-blog
post history that the Blog struct does not expose.

Model: opus-5

Makefile

@@ -23,13 +23,19 @@ lint:
 
 # Refresh the vendored dataset from the BlogsURL constant in hnblogs.go, which
 # is the single source of truth for the upstream location. The download lands
-# on a temporary file and only replaces blogs.json once it is complete, so an
+# on a temporary file and only replaces blogs.json once it has been checked to
-# interrupted fetch cannot leave a truncated dataset committed.
+# be a non-empty JSON array of blog entries, so neither an interrupted transfer
+# nor a complete-but-wrong response (an error page, a redirect landing page)
+# can overwrite the good dataset.
 update-data:
+	@command -v jq >/dev/null || { echo "update-data requires jq" >&2; exit 1; }
 	@url=$$(sed -n 's/^const BlogsURL = "\(.*\)"$$/\1/p' hnblogs.go); \
 	test -n "$$url" || { echo "could not parse BlogsURL from hnblogs.go" >&2; exit 1; }; \
 	echo "fetching $$url"; \
 	curl -fsSL "$$url" -o blogs.json.tmp
-	@test -s blogs.json.tmp || { echo "downloaded dataset is empty" >&2; rm -f blogs.json.tmp; exit 1; }
+	@jq -e 'type == "array" and length > 0 and all(.[]; type == "object" and has("url"))' \
+		blogs.json.tmp >/dev/null 2>&1 \
+		|| { echo "download is not a non-empty JSON array of blog entries; blogs.json left unchanged" >&2; \
+		     rm -f blogs.json.tmp; exit 1; }
 	mv blogs.json.tmp blogs.json
 	$(MAKE) test

README.md

@@ -24,6 +24,17 @@ The trade-off is that the dataset is a build-time artifact: it is roughly 8 MB
 of JSON, it lands in every binary that links the package, and it is only as
 fresh as the last commit that refreshed it.
 
+### Where blogs.json came from
+
+`blogs.json` is not this project's work. It is an unmodified copy of
+
+<https://raw.githubusercontent.com/surprisetalk/blogs.hn/main/blogs.json>
+
+from the [surprisetalk/blogs.hn](https://github.com/surprisetalk/blogs.hn)
+repository, which publishes no licence. This repository's `LICENSE` covers the
+code here and does not extend to `blogs.json`, and a binary that links this
+package redistributes that file too.
+
 ## Refreshing the dataset
 
 ```sh
@@ -31,10 +42,12 @@ make update-data
 ```
 
 That target reads the upstream location from the `BlogsURL` constant in
-`hnblogs.go` — the single source of truth — downloads to a temporary file,
+`hnblogs.go` — the single source of truth — and downloads it to a temporary
-replaces `blogs.json` only once the download completes, and then runs the test
+file. It replaces `blogs.json` only once that file parses as a non-empty JSON
-suite against the new data. Commit the resulting `blogs.json` to publish the
+array of blog entries, so a response that arrives complete but is not the
-update.
+dataset leaves the vendored copy untouched. It then runs the test suite
+against the new data. Requires `curl` and `jq`. Commit the resulting
+`blogs.json` to publish the update.
 
 ## Development
 
@@ -44,4 +57,4 @@ make lint
 make docker
 ```
 
-`make docker` runs lint and tests in containers, matching CI.
+`make docker` runs lint and tests in containers.

hnblogs.go

@@ -18,7 +18,9 @@ import (
 // it documents where "make update-data" pulls the vendored copy from.
 const BlogsURL = "https://raw.githubusercontent.com/surprisetalk/blogs.hn/main/blogs.json"
 
-// blogsJSON is the vendored dataset, refreshed by "make update-data".
+// blogsJSON is the vendored dataset, refreshed by "make update-data". It is an
+// unmodified copy of a third party's file, not this project's work; see "Where
+// blogs.json came from" in README.md.
 //
 //go:embed blogs.json
 var blogsJSON []byte

hnblogs_test.go

@@ -1,8 +1,9 @@
 package hnblogs
 
 import (
+	"bytes"
 	"encoding/json"
-	"go/build"
+	"os/exec"
 	"strings"
 	"testing"
 )
@@ -39,17 +40,25 @@ func TestEmbeddedDataIsUsable(t *testing.T) {
 }
 
 // TestNoRuntimeNetworkImports is the regression guard for the reason this data
-// is embedded: the package must not reach the network on any code path. A
+// is embedded: the package must not reach the network on any code path. It
-// transport dependency reintroduced in non-test code fails here.
+// walks the whole dependency graph of the non-test build rather than the direct
+// import list, so a net/* package reached through an intermediate import fails
+// here too. Test-only imports are outside that graph, which is why this test
+// may use os/exec itself.
 func TestNoRuntimeNetworkImports(t *testing.T) {
-	pkg, err := build.ImportDir(".", 0)
+	cmd := exec.Command("go", "list", "-deps", ".")
+
+	var stderr bytes.Buffer
+	cmd.Stderr = &stderr
+
+	out, err := cmd.Output()
 	if err != nil {
-		t.Fatalf("Failed to inspect package imports: %v", err)
+		t.Fatalf("Failed to list package dependencies: %v\n%s", err, stderr.String())
 	}
 
-	for _, imported := range pkg.Imports {
+	for _, dep := range strings.Fields(string(out)) {
-		if imported == "net" || strings.HasPrefix(imported, "net/") {
+		if dep == "net" || strings.HasPrefix(dep, "net/") {
-			t.Fatalf("Package must not perform network I/O, but imports %q", imported)
+			t.Fatalf("Package must not perform network I/O, but depends on %q", dep)
 		}
 	}
 }