Register builtin builders

src/libstore/builtins/buildenv.cc

@@ -1,4 +1,5 @@
 #include "nix/store/builtins/buildenv.hh"
+#include "nix/store/builtins.hh"
 #include "nix/store/derivations.hh"
 #include "nix/util/signals.hh"
 
@@ -166,17 +167,15 @@ void buildProfile(const Path & out, Packages && pkgs)
     debug("created %d symlinks in user environment", state.symlinks);
 }
 
-void builtinBuildenv(
-    const BasicDerivation & drv,
-    const std::map<std::string, Path> & outputs)
+static void builtinBuildenv(const BuiltinBuilderContext & ctx)
 {
     auto getAttr = [&](const std::string & name) {
-        auto i = drv.env.find(name);
-        if (i == drv.env.end()) throw Error("attribute '%s' missing", name);
+        auto i = ctx.drv.env.find(name);
+        if (i == ctx.drv.env.end()) throw Error("attribute '%s' missing", name);
         return i->second;
     };
 
-    auto out = outputs.at("out");
+    auto out = ctx.outputs.at("out");
     createDirs(out);
 
     /* Convert the stuff we get from the environment back into a
@@ -203,4 +202,6 @@ void builtinBuildenv(
     createSymlink(getAttr("manifest"), out + "/manifest.nix");
 }
 
+static RegisterBuiltinBuilder registerBuildenv("buildenv", builtinBuildenv);
+
 }

src/libstore/builtins/fetchurl.cc

@@ -6,33 +6,29 @@
 
 namespace nix {
 
-void builtinFetchurl(
-    const BasicDerivation & drv,
-    const std::map<std::string, Path> & outputs,
-    const std::string & netrcData,
-    const std::string & caFileData)
+static void builtinFetchurl(const BuiltinBuilderContext & ctx)
 {
     /* Make the host's netrc data available. Too bad curl requires
        this to be stored in a file. It would be nice if we could just
        pass a pointer to the data. */
-    if (netrcData != "") {
+    if (ctx.netrcData != "") {
         settings.netrcFile = "netrc";
-        writeFile(settings.netrcFile, netrcData, 0600);
+        writeFile(settings.netrcFile, ctx.netrcData, 0600);
     }
 
     settings.caFile = "ca-certificates.crt";
-    writeFile(settings.caFile, caFileData, 0600);
+    writeFile(settings.caFile, ctx.caFileData, 0600);
 
-    auto out = get(drv.outputs, "out");
+    auto out = get(ctx.drv.outputs, "out");
     if (!out)
         throw Error("'builtin:fetchurl' requires an 'out' output");
 
-    if (!(drv.type().isFixed() || drv.type().isImpure()))
+    if (!(ctx.drv.type().isFixed() || ctx.drv.type().isImpure()))
         throw Error("'builtin:fetchurl' must be a fixed-output or impure derivation");
 
-    auto storePath = outputs.at("out");
-    auto mainUrl = drv.env.at("url");
-    bool unpack = getOr(drv.env, "unpack", "") == "1";
+    auto storePath = ctx.outputs.at("out");
+    auto mainUrl = ctx.drv.env.at("url");
+    bool unpack = getOr(ctx.drv.env, "unpack", "") == "1";
 
     /* Note: have to use a fresh fileTransfer here because we're in
        a forked process. */
@@ -56,8 +52,8 @@ void builtinFetchurl(
         else
             writeFile(storePath, *source);
 
-        auto executable = drv.env.find("executable");
-        if (executable != drv.env.end() && executable->second == "1") {
+        auto executable = ctx.drv.env.find("executable");
+        if (executable != ctx.drv.env.end() && executable->second == "1") {
             if (chmod(storePath.c_str(), 0755) == -1)
                 throw SysError("making '%1%' executable", storePath);
         }
@@ -79,4 +75,6 @@ void builtinFetchurl(
     fetch(mainUrl);
 }
 
+static RegisterBuiltinBuilder registerFetchurl("fetchurl", builtinFetchurl);
+
 }

src/libstore/builtins/unpack-channel.cc

@@ -3,17 +3,15 @@
 
 namespace nix {
 
-void builtinUnpackChannel(
-    const BasicDerivation & drv,
-    const std::map<std::string, Path> & outputs)
+static void builtinUnpackChannel(const BuiltinBuilderContext & ctx)
 {
     auto getAttr = [&](const std::string & name) -> const std::string & {
-        auto i = drv.env.find(name);
-        if (i == drv.env.end()) throw Error("attribute '%s' missing", name);
+        auto i = ctx.drv.env.find(name);
+        if (i == ctx.drv.env.end()) throw Error("attribute '%s' missing", name);
         return i->second;
     };
 
-    std::filesystem::path out{outputs.at("out")};
+    std::filesystem::path out{ctx.outputs.at("out")};
     auto & channelName = getAttr("channelName");
     auto & src = getAttr("src");
 
@@ -42,4 +40,6 @@ void builtinUnpackChannel(
     }
 }
 
+static RegisterBuiltinBuilder registerUnpackChannel("unpack-channel", builtinUnpackChannel);
+
 }

src/libstore/include/nix/store/builtins.hh

@@ -5,15 +5,30 @@
 
 namespace nix {
 
-// TODO: make pluggable.
-void builtinFetchurl(
-    const BasicDerivation & drv,
-    const std::map<std::string, Path> & outputs,
-    const std::string & netrcData,
-    const std::string & caFileData);
-
-void builtinUnpackChannel(
-    const BasicDerivation & drv,
-    const std::map<std::string, Path> & outputs);
+struct BuiltinBuilderContext
+{
+    const BasicDerivation & drv;
+    std::map<std::string, Path> outputs;
+    std::string netrcData;
+    std::string caFileData;
+    Path tmpDirInSandbox;
+};
+
+using BuiltinBuilder = std::function<void(const BuiltinBuilderContext &)>;
+
+struct RegisterBuiltinBuilder
+{
+    typedef std::map<std::string, BuiltinBuilder> BuiltinBuilders;
+
+    static BuiltinBuilders & builtinBuilders() {
+        static BuiltinBuilders builders;
+        return builders;
+    }
+
+    RegisterBuiltinBuilder(const std::string & name, BuiltinBuilder && fun)
+    {
+        builtinBuilders().insert_or_assign(name, std::move(fun));
+    }
+};
 
 }

src/libstore/include/nix/store/builtins/buildenv.hh

@@ -45,8 +45,4 @@ typedef std::vector<Package> Packages;
 
 void buildProfile(const Path & out, Packages && pkgs);
 
-void builtinBuildenv(
-    const BasicDerivation & drv,
-    const std::map<std::string, Path> & outputs);
-
 }

src/libstore/unix/build/derivation-builder.cc

@@ -1857,15 +1857,18 @@ void DerivationBuilderImpl::runChild()
         /* Make the contents of netrc and the CA certificate bundle
            available to builtin:fetchurl (which may run under a
            different uid and/or in a sandbox). */
-        std::string netrcData;
-        std::string caFileData;
+        BuiltinBuilderContext ctx{
+            .drv = drv,
+            .tmpDirInSandbox = tmpDirInSandbox,
+        };
+
         if (drv.isBuiltin() && drv.builder == "builtin:fetchurl") {
            try {
-               netrcData = readFile(settings.netrcFile);
+               ctx.netrcData = readFile(settings.netrcFile);
            } catch (SystemError &) { }
 
            try {
-               caFileData = readFile(settings.caFile);
+               ctx.caFileData = readFile(settings.caFile);
            } catch (SystemError &) { }
         }
 
@@ -2286,19 +2289,16 @@ void DerivationBuilderImpl::runChild()
             try {
                 logger = makeJSONLogger(getStandardError());
 
-                std::map<std::string, Path> outputs;
                 for (auto & e : drv.outputs)
-                    outputs.insert_or_assign(e.first,
+                    ctx.outputs.insert_or_assign(e.first,
                         store.printStorePath(scratchOutputs.at(e.first)));
 
-                if (drv.builder == "builtin:fetchurl")
-                    builtinFetchurl(drv, outputs, netrcData, caFileData);
-                else if (drv.builder == "builtin:buildenv")
-                    builtinBuildenv(drv, outputs);
-                else if (drv.builder == "builtin:unpack-channel")
-                    builtinUnpackChannel(drv, outputs);
+                std::string builtinName = drv.builder.substr(8);
+                assert(RegisterBuiltinBuilder::builtinBuilders);
+                if (auto builtin = get(RegisterBuiltinBuilder::builtinBuilders(), builtinName))
+                    (*builtin)(ctx);
                 else
-                    throw Error("unsupported builtin builder '%1%'", drv.builder.substr(8));
+                    throw Error("unsupported builtin builder '%1%'", builtinName);
                 _exit(0);
             } catch (std::exception & e) {
                 writeFull(STDERR_FILENO, e.what() + std::string("\n"));