183 lines
4.9 KiB
C++
183 lines
4.9 KiB
C++
#include "references.hh"
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#include "hash.hh"
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#include "util.hh"
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#include "archive.hh"
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#include <map>
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#include <cstdlib>
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namespace nix {
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static unsigned int refLength = 32; /* characters */
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static void search(const unsigned char * s, size_t len,
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StringSet & hashes, StringSet & seen)
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{
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static bool initialised = false;
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static bool isBase32[256];
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if (!initialised) {
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for (unsigned int i = 0; i < 256; ++i) isBase32[i] = false;
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for (unsigned int i = 0; i < base32Chars.size(); ++i)
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isBase32[(unsigned char) base32Chars[i]] = true;
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initialised = true;
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}
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for (size_t i = 0; i + refLength <= len; ) {
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int j;
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bool match = true;
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for (j = refLength - 1; j >= 0; --j)
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if (!isBase32[(unsigned char) s[i + j]]) {
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i += j + 1;
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match = false;
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break;
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}
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if (!match) continue;
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string ref((const char *) s + i, refLength);
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if (hashes.erase(ref)) {
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debug(format("found reference to '%1%' at offset '%2%'")
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% ref % i);
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seen.insert(ref);
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}
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++i;
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}
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}
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struct RefScanSink : Sink
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{
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StringSet hashes;
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StringSet seen;
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string tail;
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RefScanSink() { }
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void operator () (const unsigned char * data, size_t len);
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};
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void RefScanSink::operator () (const unsigned char * data, size_t len)
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{
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/* It's possible that a reference spans the previous and current
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fragment, so search in the concatenation of the tail of the
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previous fragment and the start of the current fragment. */
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string s = tail + string((const char *) data, len > refLength ? refLength : len);
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search((const unsigned char *) s.data(), s.size(), hashes, seen);
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search(data, len, hashes, seen);
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size_t tailLen = len <= refLength ? len : refLength;
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tail =
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string(tail, tail.size() < refLength - tailLen ? 0 : tail.size() - (refLength - tailLen)) +
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string((const char *) data + len - tailLen, tailLen);
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}
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std::pair<PathSet, HashResult> scanForReferences(const string & path,
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const PathSet & refs)
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{
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RefScanSink refsSink;
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HashSink hashSink { htSHA256 };
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TeeSink sink { refsSink, hashSink };
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std::map<string, Path> backMap;
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/* For efficiency (and a higher hit rate), just search for the
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hash part of the file name. (This assumes that all references
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have the form `HASH-bla'). */
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for (auto & i : refs) {
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auto baseName = std::string(baseNameOf(i));
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string::size_type pos = baseName.find('-');
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if (pos == string::npos)
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throw Error("bad reference '%1%'", i);
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string s = string(baseName, 0, pos);
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assert(s.size() == refLength);
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assert(backMap.find(s) == backMap.end());
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// parseHash(htSHA256, s);
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refsSink.hashes.insert(s);
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backMap[s] = i;
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}
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/* Look for the hashes in the NAR dump of the path. */
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dumpPath(path, sink);
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/* Map the hashes found back to their store paths. */
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PathSet found;
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for (auto & i : refsSink.seen) {
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std::map<string, Path>::iterator j;
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if ((j = backMap.find(i)) == backMap.end()) abort();
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found.insert(j->second);
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}
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auto hash = hashSink.finish();
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return std::pair<PathSet, HashResult>(found, hash);
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}
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RewritingSink::RewritingSink(const std::string & from, const std::string & to, Sink & nextSink)
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: from(from), to(to), nextSink(nextSink)
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{
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assert(from.size() == to.size());
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}
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void RewritingSink::operator () (const unsigned char * data, size_t len)
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{
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std::string s(prev);
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s.append((const char *) data, len);
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size_t j = 0;
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while ((j = s.find(from, j)) != string::npos) {
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matches.push_back(pos + j);
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s.replace(j, from.size(), to);
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}
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prev = s.size() < from.size() ? s : std::string(s, s.size() - from.size() + 1, from.size() - 1);
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auto consumed = s.size() - prev.size();
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pos += consumed;
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if (consumed) nextSink((unsigned char *) s.data(), consumed);
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}
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void RewritingSink::flush()
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{
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if (prev.empty()) return;
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pos += prev.size();
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nextSink((unsigned char *) prev.data(), prev.size());
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prev.clear();
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}
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HashModuloSink::HashModuloSink(HashType ht, const std::string & modulus)
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: hashSink(ht)
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, rewritingSink(modulus, std::string(modulus.size(), 0), hashSink)
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{
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}
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void HashModuloSink::operator () (const unsigned char * data, size_t len)
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{
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rewritingSink(data, len);
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}
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HashResult HashModuloSink::finish()
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{
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rewritingSink.flush();
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/* Hash the positions of the self-references. This ensures that a
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NAR with self-references and a NAR with some of the
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self-references already zeroed out do not produce a hash
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collision. FIXME: proof. */
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for (auto & pos : rewritingSink.matches) {
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auto s = fmt("|%d", pos);
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hashSink((unsigned char *) s.data(), s.size());
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}
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auto h = hashSink.finish();
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return {h.first, rewritingSink.pos};
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}
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}
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