Add C++ functions for .narinfo processing / signing

This is currently only used by the Hydra queue runner rework, but like
eff5021eaa it presumably will be useful
for the C++ rewrite of nix-push and
download-from-binary-cache. (@shlevy)

src/libstore/nar-info.cc

@@ -0,0 +1,134 @@
+#include "crypto.hh"
+#include "globals.hh"
+#include "nar-info.hh"
+
+namespace nix {
+
+NarInfo::NarInfo(const std::string & s, const std::string & whence)
+{
+    auto corrupt = [&]() {
+        throw Error("NAR info file ‘%1%’ is corrupt");
+    };
+
+    auto parseHashField = [&](const string & s) {
+        string::size_type colon = s.find(':');
+        if (colon == string::npos) corrupt();
+        HashType ht = parseHashType(string(s, 0, colon));
+        if (ht == htUnknown) corrupt();
+        return parseHash16or32(ht, string(s, colon + 1));
+    };
+
+    size_t pos = 0;
+    while (pos < s.size()) {
+
+        size_t colon = s.find(':', pos);
+        if (colon == std::string::npos) corrupt();
+
+        std::string name(s, pos, colon - pos);
+
+        size_t eol = s.find('\n', colon + 2);
+        if (eol == std::string::npos) corrupt();
+
+        std::string value(s, colon + 2, eol - colon - 2);
+
+        if (name == "StorePath") {
+            if (!isStorePath(value)) corrupt();
+            path = value;
+        }
+        else if (name == "URL")
+            url = value;
+        else if (name == "Compression")
+            compression = value;
+        else if (name == "FileHash")
+            fileHash = parseHashField(value);
+        else if (name == "FileSize") {
+            if (!string2Int(value, fileSize)) corrupt();
+        }
+        else if (name == "NarHash")
+            narHash = parseHashField(value);
+        else if (name == "NarSize") {
+            if (!string2Int(value, narSize)) corrupt();
+        }
+        else if (name == "References") {
+            auto refs = tokenizeString<Strings>(value, " ");
+            if (!references.empty()) corrupt();
+            for (auto & r : refs) {
+                auto r2 = settings.nixStore + "/" + r;
+                if (!isStorePath(r2)) corrupt();
+                references.insert(r2);
+            }
+        }
+        else if (name == "Deriver") {
+            auto p = settings.nixStore + "/" + value;
+            if (!isStorePath(p)) corrupt();
+            deriver = p;
+        }
+        else if (name == "System")
+            system = value;
+        else if (name == "Sig")
+            sig = value;
+
+        pos = eol + 1;
+    }
+
+    if (compression == "") compression = "bzip2";
+
+    if (path.empty() || url.empty()) corrupt();
+}
+
+std::string NarInfo::to_string() const
+{
+    std::string res;
+    res += "StorePath: " + path + "\n";
+    res += "URL: " + url + "\n";
+    assert(compression != "");
+    res += "Compression: " + compression + "\n";
+    assert(fileHash.type == htSHA256);
+    res += "FileHash: sha256:" + printHash32(fileHash) + "\n";
+    res += "FileSize: " + std::to_string(fileSize) + "\n";
+    assert(narHash.type == htSHA256);
+    res += "NarHash: sha256:" + printHash32(narHash) + "\n";
+    res += "NarSize: " + std::to_string(narSize) + "\n";
+
+    res += "References: " + concatStringsSep(" ", shortRefs()) + "\n";
+
+    if (!deriver.empty())
+        res += "Deriver: " + baseNameOf(deriver) + "\n";
+
+    if (!system.empty())
+        res += "System: " + system + "\n";
+
+    if (!sig.empty())
+        res += "Sig: " + sig + "\n";
+
+    return res;
+}
+
+std::string NarInfo::fingerprint() const
+{
+    return
+        "1;" + path + ";"
+        + printHashType(narHash.type) + ":" + printHash32(narHash) + ";"
+        + std::to_string(narSize) + ";"
+        + concatStringsSep(",", references);
+}
+
+Strings NarInfo::shortRefs() const
+{
+    Strings refs;
+    for (auto & r : references)
+        refs.push_back(baseNameOf(r));
+    return refs;
+}
+
+void NarInfo::sign(const SecretKey & secretKey)
+{
+    sig = secretKey.signDetached(fingerprint());
+}
+
+bool NarInfo::checkSignature(const PublicKeys & publicKeys) const
+{
+    return sig != "" && verifyDetached(fingerprint(), sig, publicKeys);
+}
+
+}