nix-super/src/libstore/store.cc

#include <iostream>
#include <algorithm>

#include <sys/wait.h>
#include <unistd.h>

#include "store.hh"
#include "globals.hh"
#include "db.hh"
#include "archive.hh"
#include "pathlocks.hh"


/* Nix database. */
static Database nixDB;


/* Database tables. */

/* dbValidPaths :: Path -> ()

   The existence of a key $p$ indicates that path $p$ is valid (that
   is, produced by a succesful build). */
static TableId dbValidPaths = 0;

/* dbSuccessors :: Path -> Path

   Each pair $(p_1, p_2)$ in this mapping records the fact that the
   Nix expression stored at path $p_1$ has a successor expression
   stored at path $p_2$.

   Note that a term $y$ is a successor of $x$ iff there exists a
   sequence of rewrite steps that rewrites $x$ into $y$.
*/
static TableId dbSuccessors = 0;

/* dbSuccessorsRev :: Path -> [Path]

   The reverse mapping of dbSuccessors (i.e., it stores the
   predecessors of a Nix expression).
*/
static TableId dbSuccessorsRev = 0;

/* dbSubstitutes :: Path -> [[Path]]

   Each pair $(p, subs)$ tells Nix that it can use any of the
   substitutes in $subs$ to build path $p$.  Each substitute defines a
   command-line invocation of a program (i.e., the first list element
   is the full path to the program, the remaining elements are
   arguments).

   The main purpose of this is for distributed caching of derivates.
   One system can compute a derivate and put it on a website (as a Nix
   archive), for instance, and then another system can register a
   substitute for that derivate.  The substitute in this case might be
   a Nix expression that fetches the Nix archive.
*/
static TableId dbSubstitutes = 0;


bool Substitute::operator == (const Substitute & sub)
{
    return program == sub.program
        && args == sub.args;
}


void openDB()
{
    if (readOnlyMode) return;
    try {
        nixDB.open(nixDBPath);
    } catch (DbNoPermission & e) {
        printMsg(lvlTalkative, "cannot access Nix database; continuing anyway");
        readOnlyMode = true;
        return;
    }
    dbValidPaths = nixDB.openTable("validpaths");
    dbSuccessors = nixDB.openTable("successors");
    dbSuccessorsRev = nixDB.openTable("successors-rev");
    dbSubstitutes = nixDB.openTable("substitutes");
}


void initDB()
{
}


void createStoreTransaction(Transaction & txn)
{
    Transaction txn2(nixDB);
    txn2.moveTo(txn);
}


/* Path copying. */

struct CopySink : DumpSink
{
    int fd;
    virtual void operator () (const unsigned char * data, unsigned int len)
    {
        writeFull(fd, data, len);
    }
};


struct CopySource : RestoreSource
{
    int fd;
    virtual void operator () (unsigned char * data, unsigned int len)
    {
        readFull(fd, data, len);
    }
};


void copyPath(const Path & src, const Path & dst)
{
    debug(format("copying `%1%' to `%2%'") % src % dst);

    /* Unfortunately C++ doesn't support coprocedures, so we have no
       nice way to chain CopySink and CopySource together.  Instead we
       fork off a child to run the sink.  (Fork-less platforms should
       use a thread). */

    /* Create a pipe. */
    Pipe pipe;
    pipe.create();

    /* Fork. */
    Pid pid;
    pid = fork();
    switch (pid) {

    case -1:
        throw SysError("unable to fork");

    case 0: /* child */
        try {
            pipe.writeSide.close();
            CopySource source;
            source.fd = pipe.readSide;
            restorePath(dst, source);
            _exit(0);
        } catch (exception & e) {
            cerr << "error: " << e.what() << endl;
        }
        _exit(1);        
    }

    /* Parent. */

    pipe.readSide.close();
    
    CopySink sink;
    sink.fd = pipe.writeSide;
    {
        SwitchToOriginalUser sw;
        dumpPath(src, sink);
    }

    /* Wait for the child to finish. */
    int status = pid.wait(true);
    if (!statusOk(status))
        throw Error(format("cannot copy `%1% to `%2%': child %3%")
            % src % dst % statusToString(status));
}


static bool isInStore(const Path & path)
{
    return path[0] == '/'
        && path.compare(0, nixStore.size(), nixStore) == 0
        && path.size() >= nixStore.size() + 2
        && path[nixStore.size()] == '/'
        && path.find('/', nixStore.size() + 1) == Path::npos;
}


void assertStorePath(const Path & path)
{
    if (!isInStore(path))
        throw Error(format("path `%1%' is not in the Nix store") % path);
}


static bool isValidPathTxn(const Path & path, const Transaction & txn)
{
    string s;
    return nixDB.queryString(txn, dbValidPaths, path, s);
}


bool isValidPath(const Path & path)
{
    return isValidPathTxn(path, noTxn);
}


static bool isUsablePathTxn(const Path & path, const Transaction & txn)
{
    if (isValidPathTxn(path, txn)) return true;
    Paths subs;
    nixDB.queryStrings(txn, dbSubstitutes, path, subs);
    return subs.size() > 0;
}


void registerSuccessor(const Transaction & txn,
    const Path & srcPath, const Path & sucPath)
{
    assertStorePath(srcPath);
    assertStorePath(sucPath);
    
    if (!isUsablePathTxn(sucPath, txn))	throw Error(
	format("path `%1%' cannot be a successor, since it is not usable")
	% sucPath);

    Path known;
    if (nixDB.queryString(txn, dbSuccessors, srcPath, known) &&
        known != sucPath)
    {
        throw Error(format(
            "the `impossible' happened: expression in path "
            "`%1%' appears to have multiple successors "
            "(known `%2%', new `%3%'")
            % srcPath % known % sucPath);
    }

    Paths revs;
    nixDB.queryStrings(txn, dbSuccessorsRev, sucPath, revs);
    if (find(revs.begin(), revs.end(), srcPath) == revs.end())
        revs.push_back(srcPath);

    nixDB.setString(txn, dbSuccessors, srcPath, sucPath);
    nixDB.setStrings(txn, dbSuccessorsRev, sucPath, revs);
}


void unregisterSuccessor(const Path & srcPath)
{
    assertStorePath(srcPath);

    Transaction txn(nixDB);

    Path sucPath;
    if (!nixDB.queryString(txn, dbSuccessors, srcPath, sucPath)) {
        txn.abort();
        return;
    }
    nixDB.delPair(txn, dbSuccessors, srcPath);

    Paths revs;
    nixDB.queryStrings(txn, dbSuccessorsRev, sucPath, revs);
    Paths::iterator i = find(revs.begin(), revs.end(), srcPath);
    assert(i != revs.end());
    revs.erase(i);
    nixDB.setStrings(txn, dbSuccessorsRev, sucPath, revs);

    txn.commit();
}


bool querySuccessor(const Path & srcPath, Path & sucPath)
{
    return nixDB.queryString(noTxn, dbSuccessors, srcPath, sucPath);
}


Paths queryPredecessors(const Path & sucPath)
{
    Paths revs;
    nixDB.queryStrings(noTxn, dbSuccessorsRev, sucPath, revs);
    return revs;
}


static Substitutes readSubstitutes(const Transaction & txn,
    const Path & srcPath)
{
    Strings ss;
    nixDB.queryStrings(txn, dbSubstitutes, srcPath, ss);

    Substitutes subs;
    
    for (Strings::iterator i = ss.begin(); i != ss.end(); ++i) {
        if (i->size() < 4 || (*i)[3] != 0) {
            /* Old-style substitute.  !!! remove this code
               eventually? */
            break;
        }
        Strings ss2 = unpackStrings(*i);
        if (ss2.size() == 3) {
            /* Another old-style substitute. */
            continue;
        }
        if (ss2.size() != 2) throw Error("malformed substitute");
        Strings::iterator j = ss2.begin();
        Substitute sub;
        sub.program = *j++;
        sub.args = unpackStrings(*j++);
        subs.push_back(sub);
    }

    return subs;
}


static void writeSubstitutes(const Transaction & txn,
    const Path & srcPath, const Substitutes & subs)
{
    Strings ss;

    for (Substitutes::const_iterator i = subs.begin();
         i != subs.end(); ++i)
    {
        Strings ss2;
        ss2.push_back(i->program);
        ss2.push_back(packStrings(i->args));
        ss.push_back(packStrings(ss2));
    }

    nixDB.setStrings(txn, dbSubstitutes, srcPath, ss);
}


void registerSubstitutes(const Transaction & txn,
    const SubstitutePairs & subPairs)
{
    for (SubstitutePairs::const_iterator i = subPairs.begin();
         i != subPairs.end(); ++i)
    {
        const Path & srcPath(i->first);
        const Substitute & sub(i->second);

        assertStorePath(srcPath);
    
        Substitutes subs = readSubstitutes(txn, srcPath);

        /* New substitutes take precedence over old ones.  If the
           substitute is already present, it's moved to the front. */
        remove(subs.begin(), subs.end(), sub);
        subs.push_front(sub);
        
        writeSubstitutes(txn, srcPath, subs);
    }
}


Substitutes querySubstitutes(const Path & srcPath)
{
    return readSubstitutes(noTxn, srcPath);
}


static void unregisterPredecessors(const Path & path, Transaction & txn)
{
    /* Remove any successor mappings to this path (but not *from*
       it). */
    Paths revs;
    nixDB.queryStrings(txn, dbSuccessorsRev, path, revs);
    for (Paths::iterator i = revs.begin(); i != revs.end(); ++i)
        nixDB.delPair(txn, dbSuccessors, *i);
    nixDB.delPair(txn, dbSuccessorsRev, path);
}
 

void clearSubstitutes()
{
    Transaction txn(nixDB);
    
    /* Iterate over all paths for which there are substitutes. */
    Paths subKeys;
    nixDB.enumTable(txn, dbSubstitutes, subKeys);
    for (Paths::iterator i = subKeys.begin(); i != subKeys.end(); ++i) {

        /* If this path has not become valid in the mean-while, delete
           any successor mappings *to* it.  This is to preserve the
           invariant the all successors are `usable' as opposed to
           `valid' (i.e., the successor must be valid *or* have at
           least one substitute). */
        if (!isValidPath(*i)) {
            unregisterPredecessors(*i, txn);
        }
        
        /* Delete all substitutes for path *i. */
        nixDB.delPair(txn, dbSubstitutes, *i);
    }

    txn.commit();
}


void registerValidPath(const Transaction & txn, const Path & _path)
{
    Path path(canonPath(_path));
    assertStorePath(path);
    debug(format("registering path `%1%'") % path);
    nixDB.setString(txn, dbValidPaths, path, "");
}


static void invalidatePath(const Path & path, Transaction & txn)
{
    debug(format("unregistering path `%1%'") % path);

    nixDB.delPair(txn, dbValidPaths, path);
    unregisterPredecessors(path, txn);
}


Path makeStorePath(const string & type,
    const Hash & hash, const string & suffix)
{
    /* e.g., "source:sha256:1abc...:/nix/store:foo.tar.gz" */
    string s = type + ":sha256:" + printHash(hash) + ":"
        + nixStore + ":" + suffix;

    return nixStore + "/"
        + printHash32(compressHash(hashString(htSHA256, s), 20))
        + "-" + suffix;
}


Path addToStore(const Path & _srcPath)
{
    Path srcPath(absPath(_srcPath));
    debug(format("adding `%1%' to the store") % srcPath);

    Hash h(htSHA256);
    {
        SwitchToOriginalUser sw;
        h = hashPath(htSHA256, srcPath);
    }

    string baseName = baseNameOf(srcPath);
    Path dstPath = makeStorePath("source", h, baseName);

    if (!readOnlyMode && !isValidPath(dstPath)) { 

        /* The first check above is an optimisation to prevent
           unnecessary lock acquisition. */

        PathSet lockPaths;
        lockPaths.insert(dstPath);
        PathLocks outputLock(lockPaths);

        if (!isValidPath(dstPath)) {

            if (pathExists(dstPath)) deletePath(dstPath);

            /* !!! race: srcPath might change between hashPath() and
               here! */
            
            copyPath(srcPath, dstPath);

            Hash h2 = hashPath(htSHA256, dstPath);
            if (h != h2)
                throw Error(format("contents of `%1%' changed while copying it to `%2%' (%3% -> %4%)")
                    % srcPath % dstPath % printHash(h) % printHash(h2));

            makePathReadOnly(dstPath);
            
            Transaction txn(nixDB);
            registerValidPath(txn, dstPath);
            txn.commit();
        }

        outputLock.setDeletion(true);
    }

    return dstPath;
}


Path addTextToStore(const string & suffix, const string & s)
{
    Hash hash = hashString(htSHA256, s);

    Path dstPath = makeStorePath("text", hash, suffix);
    
    if (!readOnlyMode && !isValidPath(dstPath)) {

        PathSet lockPaths;
        lockPaths.insert(dstPath);
        PathLocks outputLock(lockPaths);

        if (!isValidPath(dstPath)) {

            if (pathExists(dstPath)) deletePath(dstPath);

            writeStringToFile(dstPath, s);

            makePathReadOnly(dstPath);
            
            Transaction txn(nixDB);
            registerValidPath(txn, dstPath);
            txn.commit();
        }

        outputLock.setDeletion(true);
    }

    return dstPath;
}


void deleteFromStore(const Path & _path)
{
    Path path(canonPath(_path));

    assertStorePath(path);

    Transaction txn(nixDB);
    invalidatePath(path, txn);
    txn.commit();

    deletePath(path);
}


void verifyStore()
{
    Transaction txn(nixDB);

    Paths paths;
    PathSet validPaths;
    nixDB.enumTable(txn, dbValidPaths, paths);

    for (Paths::iterator i = paths.begin(); i != paths.end(); ++i) {
        Path path = *i;
        if (!pathExists(path)) {
            printMsg(lvlError, format("path `%1%' disappeared") % path);
            invalidatePath(path, txn);
        } else if (!isInStore(path)) {
            printMsg(lvlError, format("path `%1%' is not in the Nix store") % path);
            invalidatePath(path, txn);
        } else
            validPaths.insert(path);
    }

    /* !!! the code below does not allow transitive substitutes.
       I.e., if B is a substitute of A, then B must be a valid path.
       B cannot itself be invalid but have a substitute. */

    /* "Usable" paths are those that are valid or have a substitute.
       These are the paths that are allowed to appear in the
       right-hand side of a sute mapping. */
    PathSet usablePaths(validPaths);

    /* Check that the values of the substitute mappings are valid
       paths. */ 
    Paths subKeys;
    nixDB.enumTable(txn, dbSubstitutes, subKeys);
    for (Paths::iterator i = subKeys.begin(); i != subKeys.end(); ++i) {
        Substitutes subs = readSubstitutes(txn, *i);
	if (subs.size() > 0)
	    usablePaths.insert(*i);
        else
            nixDB.delPair(txn, dbSubstitutes, *i);
    }

    /* Check that the values of the successor mappings are usable
       paths. */ 
    Paths sucKeys;
    nixDB.enumTable(txn, dbSuccessors, sucKeys);
    for (Paths::iterator i = sucKeys.begin(); i != sucKeys.end(); ++i) {
        /* Note that *i itself does not have to be valid, just its
           successor. */
        Path sucPath;
        if (nixDB.queryString(txn, dbSuccessors, *i, sucPath) &&
            usablePaths.find(sucPath) == usablePaths.end())
        {
            printMsg(lvlError,
                format("found successor mapping to non-existent path `%1%'") % sucPath);
            nixDB.delPair(txn, dbSuccessors, *i);
        }
    }

    /* Check that the keys of the reverse successor mappings are valid
       paths. */ 
    Paths rsucKeys;
    nixDB.enumTable(txn, dbSuccessorsRev, rsucKeys);
    for (Paths::iterator i = rsucKeys.begin(); i != rsucKeys.end(); ++i) {
        if (usablePaths.find(*i) == usablePaths.end()) {
            printMsg(lvlError,
                format("found reverse successor mapping for non-existent path `%1%'") % *i);
            nixDB.delPair(txn, dbSuccessorsRev, *i);
        }
    }

    txn.commit();
}