nix-channel: implement in c++

4 files changed, 300 insertions, 3 deletions

diff --git a/src/libstore/download.cc b/src/libstore/download.cc
index cf3929cadd65..9cc433228141 100644
--- a/src/libstore/download.cc
+++ b/src/libstore/download.cc
@@ -31,7 +31,7 @@ struct CurlDownloader : public Downloader
 {
     CURL * curl;
     ref<std::string> data;
-    string etag, status, expectedETag;
+    string etag, status, expectedETag, effectiveUrl;
 
     struct curl_slist * requestHeaders;
 
@@ -199,6 +199,11 @@ struct CurlDownloader : public Downloader
                 % url % curl_easy_strerror(res) % res);
         }
 
+        char *effectiveUrlCStr;
+        curl_easy_getinfo(curl, CURLINFO_EFFECTIVE_URL, &effectiveUrlCStr);
+        if (effectiveUrlCStr)
+            effectiveUrl = effectiveUrlCStr;
+
         if (httpStatus == 304) return false;
 
         return true;
@@ -212,6 +217,7 @@ struct CurlDownloader : public Downloader
             res.data = data;
         } else
             res.cached = true;
+        res.effectiveUrl = effectiveUrl;
         res.etag = etag;
         return res;
     }
@@ -224,6 +230,12 @@ ref<Downloader> makeDownloader()
 
 Path Downloader::downloadCached(ref<Store> store, const string & url_, bool unpack, const Hash & expectedHash)
 {
+    string ignored;
+    return downloadCached(store, url_, unpack, ignored, expectedHash);
+}
+
+Path Downloader::downloadCached(ref<Store> store, const string & url_, bool unpack, string & effectiveUrl, const Hash & expectedHash)
+{
     auto url = resolveUri(url_);
 
     string name;
@@ -259,9 +271,10 @@ Path Downloader::downloadCached(ref<Store> store, const string & url_, bool unpa
             auto ss = tokenizeString<vector<string>>(readFile(dataFile), "\n");
             if (ss.size() >= 3 && ss[0] == url) {
                 time_t lastChecked;
-                if (string2Int(ss[2], lastChecked) && lastChecked + ttl >= time(0))
+                if (string2Int(ss[2], lastChecked) && lastChecked + ttl >= time(0)) {
                     skip = true;
-                else if (!ss[1].empty()) {
+                    effectiveUrl = url_;
+                } else if (!ss[1].empty()) {
                     printMsg(lvlDebug, format("verifying previous ETag ‘%1%’") % ss[1]);
                     expectedETag = ss[1];
                 }
@@ -276,6 +289,7 @@ Path Downloader::downloadCached(ref<Store> store, const string & url_, bool unpa
             DownloadOptions options;
             options.expectedETag = expectedETag;
             auto res = download(url, options);
+            effectiveUrl = res.effectiveUrl;
 
             if (!res.cached) {
                 ValidPathInfo info;
diff --git a/src/libstore/download.hh b/src/libstore/download.hh
index efddc55281fe..d17e14400f1a 100644
--- a/src/libstore/download.hh
+++ b/src/libstore/download.hh
@@ -19,6 +19,7 @@ struct DownloadResult
 {
     bool cached;
     string etag;
+    string effectiveUrl;
     std::shared_ptr<std::string> data;
 };
 
@@ -31,6 +32,11 @@ struct Downloader
     Path downloadCached(ref<Store> store, const string & url, bool unpack,
         const Hash & expectedHash = Hash());
 
+    /* Need to overload because can't have an rvalue default value for non-const reference */
+
+    Path downloadCached(ref<Store> store, const string & url, bool unpack,
+        string & effectiveUrl, const Hash & expectedHash = Hash());
+
     enum Error { NotFound, Forbidden, Misc };
 };
 
diff --git a/src/nix-channel/local.mk b/src/nix-channel/local.mk
new file mode 100644
index 000000000000..49fc105c6f79
--- /dev/null
+++ b/src/nix-channel/local.mk
@@ -0,0 +1,7 @@
+programs += nix-channel
+
+nix-channel_DIR := $(d)
+
+nix-channel_LIBS = libmain libutil libformat libstore
+
+nix-channel_SOURCES := $(d)/nix-channel.cc
diff --git a/src/nix-channel/nix-channel.cc b/src/nix-channel/nix-channel.cc
new file mode 100755
index 000000000000..79c9d0eceb6b
--- /dev/null
+++ b/src/nix-channel/nix-channel.cc
@@ -0,0 +1,270 @@
+#include "shared.hh"
+#include "globals.hh"
+#include "download.hh"
+#include <fcntl.h>
+#include <regex>
+#include "store-api.hh"
+#include <pwd.h>
+
+using namespace nix;
+
+typedef std::map<string,string> Channels;
+
+static auto channels = Channels{};
+static auto channelsList = Path{};
+
+// Reads the list of channels.
+static void readChannels()
+{
+    if (!pathExists(channelsList)) return;
+    auto channelsFile = readFile(channelsList);
+
+    for (const auto & line : tokenizeString<std::vector<string>>(channelsFile, "\n")) {
+        chomp(line);
+        if (std::regex_search(line, std::regex("^\\s*\\#")))
+            continue;
+        auto split = tokenizeString<std::vector<string>>(line, " ");
+        auto url = std::regex_replace(split[0], std::regex("/*$"), "");
+        auto name = split.size() > 1 ? split[1] : baseNameOf(url);
+        channels[name] = url;
+    }
+}
+
+// Writes the list of channels.
+static void writeChannels()
+{
+    auto channelsFD = AutoCloseFD{open(channelsList.c_str(), O_WRONLY | O_CLOEXEC | O_CREAT | O_TRUNC, 0644)};
+    if (!channelsFD)
+        throw SysError(format("opening ‘%1%’ for writing") % channelsList);
+    for (const auto & channel : channels)
+        writeFull(channelsFD.get(), channel.second + " " + channel.first + "\n");
+}
+
+// Adds a channel.
+static void addChannel(const string & url, const string & name)
+{
+    if (!regex_search(url, std::regex("^(file|http|https)://")))
+        throw Error(format("invalid channel URL ‘%1%’") % url);
+    if (!regex_search(name, std::regex("^[a-zA-Z0-9_][a-zA-Z0-9_\\.-]*$")))
+        throw Error(format("invalid channel identifier ‘%1%’") % name);
+    readChannels();
+    channels[name] = url;
+    writeChannels();
+}
+
+static auto profile = Path{};
+
+// Remove a channel.
+static void removeChannel(const string & name)
+{
+    readChannels();
+    channels.erase(name);
+    writeChannels();
+
+    runProgram(settings.nixBinDir + "/nix-env", true, { "--profile", profile, "--uninstall", name });
+}
+
+static auto nixDefExpr = Path{};
+
+// Fetch Nix expressions and binary cache URLs from the subscribed channels.
+static void update(const StringSet & channelNames)
+{
+    readChannels();
+
+    auto store = openStore();
+
+    // Download each channel.
+    auto exprs = Strings{};
+    for (const auto & channel : channels) {
+        if (!channelNames.empty() && channelNames.find(channel.first) != channelNames.end())
+            continue;
+        auto name = channel.first;
+        auto url = channel.second;
+
+        // We want to download the url to a file to see if it's a tarball while also checking if we
+        // got redirected in the process, so that we can grab the various parts of a nix channel
+        // definition from a consistent location if the redirect changes mid-download.
+        auto effectiveUrl = string{};
+        auto dl = makeDownloader();
+        auto filename = dl->downloadCached(store, url, false, effectiveUrl);
+        url = chomp(std::move(effectiveUrl));
+
+        // If the URL contains a version number, append it to the name
+        // attribute (so that "nix-env -q" on the channels profile
+        // shows something useful).
+        auto cname = name;
+        std::smatch match;
+        auto urlBase = baseNameOf(url);
+        if (std::regex_search(urlBase, match, std::regex("(-\\d.*)$"))) {
+            cname = cname + (string) match[1];
+        }
+
+        auto extraAttrs = string{};
+
+        auto unpacked = false;
+        if (std::regex_search(filename, std::regex("\\.tar\\.(gz|bz2|xz)$"))) {
+            try {
+                runProgram(settings.nixBinDir + "/nix-build", false, { "--no-out-link", "--expr", "import <nix/unpack-channel.nix> "
+                            "{ name = \"" + cname + "\"; channelName = \"" + name + "\"; src = builtins.storePath \"" + filename + "\"; }" });
+                unpacked = true;
+            } catch (ExecError & e) {
+            }
+        }
+
+        if (!unpacked) {
+            // The URL doesn't unpack directly, so let's try treating it like a full channel folder with files in it
+            // Check if the channel advertises a binary cache.
+            DownloadOptions opts;
+            opts.showProgress = DownloadOptions::no;
+            try {
+                auto dlRes = dl->download(url + "/binary-cache-url", opts);
+                extraAttrs = "binaryCacheURL = \"" + *dlRes.data + "\";";
+            } catch (DownloadError & e) {
+            }
+
+            // Download the channel tarball.
+            auto fullURL = url + "/nixexprs.tar.xz";
+            try {
+                filename = dl->downloadCached(store, fullURL, false);
+            } catch (DownloadError & e) {
+                fullURL = url + "/nixexprs.tar.bz2";
+                filename = dl->downloadCached(store, fullURL, false);
+            }
+            chomp(filename);
+        }
+
+        // Regardless of where it came from, add the expression representing this channel to accumulated expression
+        exprs.push_back("f: f { name = \"" + cname + "\"; channelName = \"" + name + "\"; src = builtins.storePath \"" + filename + "\"; " + extraAttrs + " }");
+    }
+
+    // Unpack the channel tarballs into the Nix store and install them
+    // into the channels profile.
+    std::cerr << "unpacking channels...\n";
+    auto envArgs = Strings{ "--profile", profile, "--file", "<nix/unpack-channel.nix>", "--install", "--from-expression" };
+    for (auto & expr : exprs)
+        envArgs.push_back(std::move(expr));
+    envArgs.push_back("--quiet");
+    runProgram(settings.nixBinDir + "/nix-env", false, envArgs);
+
+    // Make the channels appear in nix-env.
+    struct stat st;
+    if (lstat(nixDefExpr.c_str(), &st) == 0) {
+        if (S_ISLNK(st.st_mode))
+            // old-skool ~/.nix-defexpr
+            if (unlink(nixDefExpr.c_str()) == -1)
+                throw SysError(format("unlinking %1%") % nixDefExpr);
+    } else if (errno != ENOENT) {
+        throw SysError(format("getting status of %1%") % nixDefExpr);
+    }
+    createDirs(nixDefExpr);
+    auto channelLink = nixDefExpr + "/channels";
+    replaceSymlink(profile, channelLink);
+}
+
+int main(int argc, char ** argv)
+{
+    return handleExceptions(argv[0], [&]() {
+        initNix();
+
+        // Turn on caching in nix-prefetch-url.
+        auto channelCache = settings.nixStateDir + "/channel-cache";
+        createDirs(channelCache);
+        setenv("NIX_DOWNLOAD_CACHE", channelCache.c_str(), 1);
+
+        // Figure out the name of the `.nix-channels' file to use
+        auto home = getEnv("HOME");
+        if (home.empty())
+            throw Error("$HOME not set");
+        channelsList = home + "/.nix-channels";
+        nixDefExpr = home + "/.nix-defexpr";
+
+        // Figure out the name of the channels profile.
+        auto name = string{};
+        auto pw = getpwuid(getuid());
+        if (!pw)
+            name = getEnv("USER", "");
+        else
+            name = pw->pw_name;
+        if (name.empty())
+            throw Error("cannot figure out user name");
+        profile = settings.nixStateDir + "/profiles/per-user/" + name + "/channels";
+        createDirs(dirOf(profile));
+
+        enum {
+            cNone,
+            cAdd,
+            cRemove,
+            cList,
+            cUpdate,
+            cRollback
+        } cmd = cNone;
+        auto args = std::vector<string>{};
+        parseCmdLine(argc, argv, [&](Strings::iterator & arg, const Strings::iterator & end) {
+            if (*arg == "--help") {
+                showManPage("nix-channel");
+            } else if (*arg == "--version") {
+                printVersion("nix-channel");
+            } else if (*arg == "--add") {
+                cmd = cAdd;
+            } else if (*arg == "--remove") {
+                cmd = cRemove;
+            } else if (*arg == "--list") {
+                cmd = cList;
+            } else if (*arg == "--update") {
+                cmd = cUpdate;
+            } else if (*arg == "--rollback") {
+                cmd = cRollback;
+            } else {
+                args.push_back(std::move(*arg));
+            }
+            return true;
+        });
+        switch (cmd) {
+            case cNone:
+                throw UsageError("no command specified");
+            case cAdd:
+                if (args.size() < 1 || args.size() > 2)
+                    throw UsageError("‘--add’ requires one or two arguments");
+                {
+                auto url = args[0];
+                auto name = string{};
+                if (args.size() == 2) {
+                    name = args[1];
+                } else {
+                    name = baseNameOf(url);
+                    name = std::regex_replace(name, std::regex("-unstable$"), "");
+                    name = std::regex_replace(name, std::regex("-stable$"), "");
+                }
+                addChannel(url, name);
+                }
+                break;
+            case cRemove:
+                if (args.size() != 1)
+                    throw UsageError("‘--remove’ requires one argument");
+                removeChannel(args[0]);
+                break;
+            case cList:
+                if (!args.empty())
+                    throw UsageError("‘--list’ expects no arguments");
+                readChannels();
+                for (const auto & channel : channels)
+                    std::cout << channel.first << ' ' << channel.second << '\n';
+                break;
+            case cUpdate:
+                update(StringSet(args.begin(), args.end()));
+                break;
+            case cRollback:
+                if (args.size() > 1)
+                    throw UsageError("‘--rollback’ has at most one argument");
+                auto envArgs = Strings{"--profile", profile};
+                if (args.size() == 1) {
+                    envArgs.push_back("--switch-generation");
+                    envArgs.push_back(args[0]);
+                } else {
+                    envArgs.push_back("--rollback");
+                }
+                runProgram(settings.nixBinDir + "/nix-env", false, envArgs);
+                break;
+        }
+    });
+}