Pluggable fetchers

Flakes are now fetched using an extensible mechanism. Also lots of
other flake cleanups.

src/libstore/fetchers/github.cc

@@ -0,0 +1,183 @@
+#include "fetchers.hh"
+#include "download.hh"
+#include "globals.hh"
+#include "parse.hh"
+#include "regex.hh"
+#include "store-api.hh"
+
+#include <nlohmann/json.hpp>
+
+namespace nix::fetchers {
+
+std::regex ownerRegex("[a-zA-Z][a-zA-Z0-9_-]*", std::regex::ECMAScript);
+std::regex repoRegex("[a-zA-Z][a-zA-Z0-9_-]*", std::regex::ECMAScript);
+
+struct GitHubInput : Input
+{
+    std::string owner;
+    std::string repo;
+    std::optional<std::string> ref;
+    std::optional<Hash> rev;
+
+    bool operator ==(const Input & other) const override
+    {
+        auto other2 = dynamic_cast<const GitHubInput *>(&other);
+        return
+            other2
+            && owner == other2->owner
+            && repo == other2->repo
+            && rev == other2->rev
+            && ref == other2->ref;
+    }
+
+    bool isImmutable() const override
+    {
+        return (bool) rev;
+    }
+
+    std::optional<std::string> getRef() const override { return ref; }
+
+    std::optional<Hash> getRev() const override { return rev; }
+
+    std::string to_string() const override
+    {
+        auto s = fmt("github:%s/%s", owner, repo);
+        assert(!(ref && rev));
+        if (ref) s += "/" + *ref;
+        if (rev) s += "/" + rev->to_string(Base16, false);
+        return s;
+    }
+
+    void clone(const Path & destDir) const override
+    {
+        std::shared_ptr<const Input> input = inputFromURL(fmt("git+ssh://git@github.com/%s/%s.git", owner, repo));
+        input = input->applyOverrides(ref.value_or("master"), rev);
+        input->clone(destDir);
+    }
+
+    std::pair<Tree, std::shared_ptr<const Input>> fetchTreeInternal(nix::ref<Store> store) const override
+    {
+        auto rev = this->rev;
+
+    #if 0
+        if (rev) {
+            if (auto gitInfo = lookupGitInfo(store, "source", *rev))
+                return *gitInfo;
+        }
+    #endif
+
+        if (!rev) {
+            auto url = fmt("https://api.github.com/repos/%s/%s/commits/%s",
+                owner, repo, ref ? *ref : "master");
+            CachedDownloadRequest request(url);
+            request.ttl = rev ? 1000000000 : settings.tarballTtl;
+            auto result = getDownloader()->downloadCached(store, request);
+            auto json = nlohmann::json::parse(readFile(result.path));
+            rev = Hash(json["sha"], htSHA1);
+            debug("HEAD revision for '%s' is %s", url, rev->gitRev());
+        }
+
+        // FIXME: use regular /archive URLs instead? api.github.com
+        // might have stricter rate limits.
+
+        auto url = fmt("https://api.github.com/repos/%s/%s/tarball/%s",
+            owner, repo, rev->to_string(Base16, false));
+
+        std::string accessToken = settings.githubAccessToken.get();
+        if (accessToken != "")
+            url += "?access_token=" + accessToken;
+
+        CachedDownloadRequest request(url);
+        request.unpack = true;
+        request.name = "source";
+        request.ttl = 1000000000;
+        request.getLastModified = true;
+        auto dresult = getDownloader()->downloadCached(store, request);
+
+        assert(dresult.lastModified);
+
+        Tree result{
+            .actualPath = dresult.path,
+            .storePath = store->parseStorePath(dresult.storePath),
+            .rev = *rev,
+            .lastModified = *dresult.lastModified
+        };
+
+    #if 0
+        // FIXME: this can overwrite a cache file that contains a revCount.
+        cacheGitInfo("source", gitInfo);
+    #endif
+
+        auto input = std::make_shared<GitHubInput>(*this);
+        input->ref = {};
+        input->rev = *rev;
+
+        return {std::move(result), input};
+    }
+
+    std::shared_ptr<const Input> applyOverrides(
+        std::optional<std::string> ref,
+        std::optional<Hash> rev) const override
+    {
+        if (!ref && !rev) return shared_from_this();
+
+        auto res = std::make_shared<GitHubInput>(*this);
+
+        if (ref) res->ref = ref;
+        if (rev) res->rev = rev;
+
+        return res;
+    }
+};
+
+struct GitHubInputScheme : InputScheme
+{
+    std::unique_ptr<Input> inputFromURL(const ParsedURL & url) override
+    {
+        if (url.scheme != "github") return nullptr;
+
+        auto path = tokenizeString<std::vector<std::string>>(url.path, "/");
+        auto input = std::make_unique<GitHubInput>();
+        input->type = "github";
+
+        if (path.size() == 2) {
+        } else if (path.size() == 3) {
+            if (std::regex_match(path[2], revRegex))
+                input->rev = Hash(path[2], htSHA1);
+            else if (std::regex_match(path[2], refRegex))
+                input->ref = path[2];
+            else
+                throw BadURL("in GitHub URL '%s', '%s' is not a commit hash or branch/tag name", url.url, path[2]);
+        } else
+            throw BadURL("GitHub URL '%s' is invalid", url.url);
+
+        for (auto &[name, value] : url.query) {
+            if (name == "rev") {
+                if (!std::regex_match(value, revRegex))
+                    throw BadURL("GitHub URL '%s' contains an invalid commit hash", url.url);
+                if (input->rev)
+                    throw BadURL("GitHub URL '%s' contains multiple commit hashes", url.url);
+                input->rev = Hash(value, htSHA1);
+            }
+            else if (name == "ref") {
+                if (!std::regex_match(value, refRegex))
+                    throw BadURL("GitHub URL '%s' contains an invalid branch/tag name", url.url);
+                if (input->ref)
+                    throw BadURL("GitHub URL '%s' contains multiple branch/tag names", url.url);
+                input->ref = value;
+            }
+        }
+
+        if (input->ref && input->rev)
+            throw BadURL("GitHub URL '%s' contains both a commit hash and a branch/tag name", url.url);
+
+        input->owner = path[0];
+        input->repo = path[1];
+
+        return input;
+    }
+};
+
+static auto r1 = OnStartup([] { registerInputScheme(std::make_unique<GitHubInputScheme>()); });
+
+}