138 lines
3.4 KiB
C++
138 lines
3.4 KiB
C++
#include "references.hh"
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#include "hash.hh"
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#include "logging.hh"
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#include <cstdlib>
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#include <mutex>
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#include <algorithm>
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namespace nix {
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static size_t refLength = 32; /* characters */
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static void search(
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std::string_view s,
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StringSet & hashes,
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StringSet & seen)
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{
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static std::once_flag initialised;
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static bool isBase32[256];
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std::call_once(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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});
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for (size_t i = 0; i + refLength <= s.size(); ) {
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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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std::string ref(s.substr(i, refLength));
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if (hashes.erase(ref)) {
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debug("found reference to '%1%' at offset '%2%'", 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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void RefScanSink::operator () (std::string_view data)
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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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auto s = tail;
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auto tailLen = std::min(data.size(), refLength);
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s.append(data.data(), tailLen);
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search(s, hashes, seen);
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search(data, hashes, seen);
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auto rest = refLength - tailLen;
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if (rest < tail.size())
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tail = tail.substr(tail.size() - rest);
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tail.append(data.data() + data.size() - tailLen, tailLen);
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}
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RewritingSink::RewritingSink(const std::string & from, const std::string & to, Sink & nextSink)
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: RewritingSink({{from, to}}, nextSink)
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{
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}
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RewritingSink::RewritingSink(const StringMap & rewrites, Sink & nextSink)
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: rewrites(rewrites), nextSink(nextSink)
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{
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std::string::size_type maxRewriteSize = 0;
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for (auto & [from, to] : rewrites) {
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assert(from.size() == to.size());
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maxRewriteSize = std::max(maxRewriteSize, from.size());
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}
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this->maxRewriteSize = maxRewriteSize;
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}
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void RewritingSink::operator () (std::string_view data)
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{
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std::string s(prev);
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s.append(data);
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s = rewriteStrings(s, rewrites);
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prev = s.size() < maxRewriteSize
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? s
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: maxRewriteSize == 0
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? ""
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: std::string(s, s.size() - maxRewriteSize + 1, maxRewriteSize - 1);
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auto consumed = s.size() - prev.size();
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pos += consumed;
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if (consumed) nextSink(s.substr(0, 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(prev);
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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 () (std::string_view data)
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{
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rewritingSink(data);
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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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hashSink(fmt("|%d", pos));
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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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