* Started implementing the new evaluation model.

* Lots of refactorings.
* Unit tests.
This commit is contained in:
Eelco Dolstra 2003-06-16 13:33:38 +00:00
parent b9f09b3268
commit 822794001c
15 changed files with 742 additions and 202 deletions

View file

@ -9,16 +9,15 @@ nix_LDADD = -ldb_cxx-4 -lATerm
fix_SOURCES = fix.cc util.cc hash.cc md5.c
fix_LDADD = -lATerm
test_SOURCES = test.cc util.cc hash.cc md5.c
test_SOURCES = test.cc util.cc hash.cc md5.c eval.cc values.cc globals.cc db.cc
test_LDADD = -ldb_cxx-4 -lATerm
install-data-local:
$(INSTALL) -d $(localstatedir)/nix
$(INSTALL) -d $(localstatedir)/nix/descriptors
$(INSTALL) -d $(localstatedir)/nix/sources
$(INSTALL) -d $(localstatedir)/nix/links
$(INSTALL) -d $(localstatedir)/nix/prebuilts
$(INSTALL) -d $(localstatedir)/nix/prebuilts/imports
$(INSTALL) -d $(localstatedir)/nix/prebuilts/exports
# $(INSTALL) -d $(localstatedir)/nix/prebuilts
# $(INSTALL) -d $(localstatedir)/nix/prebuilts/imports
# $(INSTALL) -d $(localstatedir)/nix/prebuilts/exports
$(INSTALL) -d $(localstatedir)/log/nix
$(INSTALL) -d $(prefix)/pkg
$(INSTALL) -d $(prefix)/values
$(bindir)/nix init

297
src/eval.cc Normal file
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@ -0,0 +1,297 @@
#include <map>
#include <iostream>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>
#include "eval.hh"
#include "globals.hh"
#include "values.hh"
#include "db.hh"
/* A Unix environment is a mapping from strings to strings. */
typedef map<string, string> Environment;
/* Return true iff the given path exists. */
bool pathExists(string path)
{
int res;
struct stat st;
res = stat(path.c_str(), &st);
if (!res) return true;
if (errno != ENOENT)
throw SysError("getting status of " + path);
return false;
}
/* Compute a derived value by running a program. */
static Hash computeDerived(Hash sourceHash, string targetName,
string platform, Hash prog, Environment env)
{
string targetPath = nixValues + "/" +
(string) sourceHash + "-nf";
/* Check whether the target already exists. */
if (pathExists(targetPath))
throw Error("derived value in " + targetPath + " already exists");
/* Find the program corresponding to the hash `prog'. */
string progPath = queryValuePath(prog);
/* Finalize the environment. */
env["out"] = targetPath;
/* Create a log file. */
string logFileName =
nixLogDir + "/" + baseNameOf(targetPath) + ".log";
/* !!! auto-pclose on exit */
FILE * logFile = popen(("tee " + logFileName + " >&2").c_str(), "w"); /* !!! escaping */
if (!logFile)
throw SysError("unable to create log file " + logFileName);
try {
/* Fork a child to build the package. */
pid_t pid;
switch (pid = fork()) {
case -1:
throw SysError("unable to fork");
case 0:
try { /* child */
#if 0
/* Try to use a prebuilt. */
string prebuiltHashS, prebuiltFile;
if (queryDB(nixDB, dbPrebuilts, hash, prebuiltHashS)) {
try {
prebuiltFile = getFile(parseHash(prebuiltHashS));
} catch (Error e) {
cerr << "cannot obtain prebuilt (ignoring): " << e.what() << endl;
goto build;
}
cerr << "substituting prebuilt " << prebuiltFile << endl;
int res = system(("tar xfj " + prebuiltFile + " 1>&2").c_str()); // !!! escaping
if (WEXITSTATUS(res) != 0)
/* This is a fatal error, because path may now
have clobbered. */
throw Error("cannot unpack " + prebuiltFile);
_exit(0);
}
#endif
build:
/* Fill in the environment. We don't bother freeing
the strings, since we'll exec or die soon
anyway. */
const char * env2[env.size() + 1];
int i = 0;
for (Environment::iterator it = env.begin();
it != env.end(); it++, i++)
env2[i] = (new string(it->first + "=" + it->second))->c_str();
env2[i] = 0;
/* Dup the log handle into stderr. */
if (dup2(fileno(logFile), STDERR_FILENO) == -1)
throw Error("cannot pipe standard error into log file: " + string(strerror(errno)));
/* Dup stderr to stdin. */
if (dup2(STDERR_FILENO, STDOUT_FILENO) == -1)
throw Error("cannot dup stderr into stdout");
/* Make the program executable. !!! hack. */
if (chmod(progPath.c_str(), 0755))
throw Error("cannot make program executable");
/* Execute the program. This should not return. */
execle(progPath.c_str(), baseNameOf(progPath).c_str(), 0, env2);
throw Error("unable to execute builder: " +
string(strerror(errno)));
} catch (exception & e) {
cerr << "build error: " << e.what() << endl;
_exit(1);
}
}
/* parent */
/* Close the logging pipe. Note that this should not cause
the logger to exit until builder exits (because the latter
has an open file handle to the former). */
pclose(logFile);
/* Wait for the child to finish. */
int status;
if (waitpid(pid, &status, 0) != pid)
throw Error("unable to wait for child");
if (!WIFEXITED(status) || WEXITSTATUS(status) != 0)
throw Error("unable to build package");
/* Check whether the result was created. */
if (!pathExists(targetPath))
throw Error("program " + progPath +
" failed to create a result in " + targetPath);
/* Remove write permission from the value. */
int res = system(("chmod -R -w " + targetPath).c_str()); // !!! escaping
if (WEXITSTATUS(res) != 0)
throw Error("cannot remove write permission from " + targetPath);
} catch (exception &) {
// system(("rm -rf " + targetPath).c_str());
throw;
}
/* Hash the result. */
Hash targetHash = hashFile(targetPath);
/* Register targetHash -> targetPath. !!! this should be in
values.cc. */
setDB(nixDB, dbNFs, sourceHash, targetName);
/* Register that targetHash was produced by evaluating
sourceHash; i.e., that targetHash is a normal form of
sourceHash. !!! this shouldn't be here */
setDB(nixDB, dbNFs, sourceHash, targetHash);
return targetHash;
}
/* Throw an exception if the given platform string is not supported by
the platform we are executing on. */
static void checkPlatform(string platform)
{
if (platform != thisSystem)
throw Error("a `" + platform +
"' is required, but I am a `" + thisSystem + "'");
}
/* Throw an exception with an error message containing the given
aterm. */
static Error badTerm(const string & msg, Expr e)
{
char * s = ATwriteToString(e);
return Error(msg + ", in `" + s + "'");
}
/* Hash an expression. Hopefully the representation used by
ATwriteToString() won't change, otherwise all hashes will
change. */
static Hash hashExpr(Expr e)
{
char * s = ATwriteToString(e);
debug(s);
return hashString(s);
}
/* Evaluate an expression; the result must be a string. */
static string evalString(Expr e)
{
e = evalValue(e).e;
char * s;
if (ATmatch(e, "Str(<str>)", &s)) return s;
else throw badTerm("string value expected", e);
}
/* Evaluate an expression; the result must be a external
non-expression reference. */
static Hash evalExternal(Expr e)
{
EvalResult r = evalValue(e);
char * s;
if (ATmatch(r.e, "External(<str>)", &s)) return r.h;
else throw badTerm("external non-expression value expected", r.e);
}
/* Evaluate an expression. */
EvalResult evalValue(Expr e)
{
EvalResult r;
char * s;
Expr eBuildPlatform, eProg;
ATermList args;
/* Normal forms. */
if (ATmatch(e, "Str(<str>)", &s) ||
ATmatch(e, "Bool(True)") ||
ATmatch(e, "Bool(False)"))
{
r.e = e;
}
/* External expressions. */
/* External non-expressions. */
else if (ATmatch(e, "External(<str>)", &s)) {
r.e = e;
r.h = parseHash(s);
}
/* Execution primitive. */
else if (ATmatch(e, "Exec(<term>, <term>, [<list>])",
&eBuildPlatform, &eProg, &args))
{
string buildPlatform = evalString(eBuildPlatform);
checkPlatform(buildPlatform);
Hash prog = evalExternal(eProg);
Environment env;
while (!ATisEmpty(args)) {
debug("arg");
Expr arg = ATgetFirst(args);
throw badTerm("foo", arg);
args = ATgetNext(args);
}
Hash sourceHash = hashExpr(
ATmake("Exec(Str(<str>), External(<str>), [])",
buildPlatform.c_str(), ((string) prog).c_str()));
/* Do we know a normal form for sourceHash? */
Hash targetHash;
string targetHashS;
if (queryDB(nixDB, dbNFs, sourceHash, targetHashS)) {
/* Yes. */
targetHash = parseHash(targetHashS);
debug("already built: " + (string) sourceHash
+ " -> " + (string) targetHash);
} else {
/* No, so we compute one. */
targetHash = computeDerived(sourceHash,
(string) sourceHash + "-nf", buildPlatform, prog, env);
}
r.e = ATmake("External(<str>)", ((string) targetHash).c_str());
r.h = targetHash;
}
/* Barf. */
else throw badTerm("invalid expression", e);
return r;
}

86
src/eval.hh Normal file
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@ -0,0 +1,86 @@
#ifndef __EVAL_H
#define __EVAL_H
extern "C" {
#include <aterm2.h>
}
#include "hash.hh"
using namespace std;
/* Abstract syntax of Nix values:
e := Hash(h) -- reference to expression value
| External(h) -- reference to non-expression value
| Str(s) -- string constant
| Bool(b) -- boolean constant
| App(e, e) -- application
| Lam(x, e) -- lambda abstraction
| Exec(platform, e, [(s, e)])
-- primitive; execute e with args e* on platform
;
Semantics
Each rules given as eval(e) => (e', h'), i.e., expression e has a
normal form e' with hash code h'. evalE = fst . eval. evalH = snd
. eval.
eval(Hash(h)) => eval(loadExpr(h))
eval(External(h)) => (External(h), h)
eval(Str(s)@e) => (e, 0) # idem for Bool
eval(App(e1, e2)) => eval(App(e1', e2))
where e1' = evalE(e1)
eval(App(Lam(var, body), arg)@in) =>
eval(subst(var, arg, body))@out
[AND write out to storage, and dbNFs[hash(in)] = hash(out) ???]
eval(Exec(platform, prog, args)@e) =>
(External(h), h)
where
hIn = hashExpr(e)
fn = ... form name involving hIn ...
h =
if exec(evalE(platform) => Str(...)
, getFile(evalH(prog))
, map(makeArg . eval, args)
) then
hashExternal(fn)
else
undef
makeArg((argn, (External(h), h))) => (argn, getFile(h))
makeArg((argn, (Str(s), _))) => (argn, s)
makeArg((argn, (Bool(True), _))) => (argn, "1")
makeArg((argn, (Bool(False), _))) => (argn, undef)
getFile :: Hash -> FileName
loadExpr :: Hash -> FileName
hashExpr :: Expr -> Hash
hashExternal :: FileName -> Hash
exec :: Platform -> FileName -> [(String, String)] -> Status
*/
typedef ATerm Expr;
struct EvalResult
{
Expr e;
Hash h;
};
/* Evaluate an expression. */
EvalResult evalValue(Expr e);
#endif /* !__EVAL_H */

19
src/globals.cc Normal file
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@ -0,0 +1,19 @@
#include "globals.hh"
#include "db.hh"
string dbRefs = "refs";
string dbNFs = "nfs";
string dbNetSources = "netsources";
string nixValues = "/UNINIT";
string nixLogDir = "/UNINIT";
string nixDB = "/UNINIT";
void initDB()
{
createDB(nixDB, dbRefs);
createDB(nixDB, dbNFs);
createDB(nixDB, dbNetSources);
}

60
src/globals.hh Normal file
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@ -0,0 +1,60 @@
#ifndef __GLOBALS_H
#define __GLOBALS_H
#include <string>
using namespace std;
/* Database names. */
/* dbRefs :: Hash -> FileName
Maintains a mapping from hashes to filenames within the NixValues
directory. This mapping is for performance only; it can be
reconstructed unambiguously. The reason is that names in this
directory are not printed hashes but also might carry some
descriptive element (e.g., "aterm-2.0-ae749a..."). Without this
mapping, looking up a value would take O(n) time because we would
need to read the entire directory. */
extern string dbRefs;
/* dbNFs :: Hash -> Hash
Each pair (h1, h2) in this mapping records the fact that the value
referenced by h2 is a normal form obtained by evaluating the value
referenced by value h1.
*/
extern string dbNFs;
/* dbNetSources :: Hash -> URL
Each pair (hash, url) in this mapping states that the value
identified by hash can be obtained by fetching the value pointed
to by url.
TODO: this should be Hash -> [URL]
TODO: factor this out into a separate tool? */
extern string dbNetSources;
/* Path names. */
/* nixValues is the directory where all Nix values (both files and
directories, and both normal and non-normal forms) live. */
extern string nixValues;
/* nixLogDir is the directory where we log evaluations. */
extern string nixLogDir;
/* nixDB is the file name of the Berkeley DB database where we
maintain the dbXXX mappings. */
extern string nixDB;
/* Initialize the databases. */
void initDB();
#endif /* !__GLOBALS_H */

View file

@ -46,6 +46,8 @@ Hash::operator string() const
Hash parseHash(const string & s)
{
Hash hash;
if (s.length() != Hash::hashSize * 2)
throw BadRefError("invalid hash: " + s);
for (unsigned int i = 0; i < Hash::hashSize; i++) {
string s2(s, i * 2, 2);
if (!isxdigit(s2[0]) || !isxdigit(s2[1]))
@ -73,15 +75,24 @@ bool isHash(const string & s)
}
/* Compute the MD5 hash of a file. */
Hash hashString(const string & s)
{
Hash hash;
md5_buffer(s.c_str(), s.length(), hash.hash);
return hash;
}
/* Compute the MD5 hash of a file. */
Hash hashFile(const string & fileName)
{
Hash hash;
FILE * file = fopen(fileName.c_str(), "rb");
if (!file)
throw Error("file `" + fileName + "' does not exist");
throw SysError("file `" + fileName + "' does not exist");
int err = md5_stream(file, hash.hash);
fclose(file);
if (err) throw Error("cannot hash file");
if (err) throw SysError("cannot hash file " + fileName);
return hash;
}

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@ -29,6 +29,7 @@ public:
Hash parseHash(const string & s);
bool isHash(const string & s);
Hash hashString(const string & s);
Hash hashFile(const string & fileName);
#endif /* !__HASH_H */

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@ -11,155 +11,15 @@
#include <sys/types.h>
#include <sys/wait.h>
extern "C" {
#include <aterm1.h>
}
#include "util.hh"
#include "hash.hh"
#include "db.hh"
#include "nix.hh"
#include "eval.hh"
using namespace std;
/* Database names. */
/* dbRefs :: Hash -> FileName
Maintains a mapping from hashes to filenames within the NixValues
directory. This mapping is for performance only; it can be
reconstructed unambiguously from the nixValues directory. The
reason is that names in this directory are not printed hashes but
also might carry some descriptive element (e.g.,
"aterm-2.0-ae749a..."). Without this mapping, looking up a value
would take O(n) time because we would need to read the entire
directory. */
static string dbRefs = "refs";
/* dbNFs :: Hash -> Hash
Each pair (h1, h2) in this mapping records the fact that h2 is a
normal form obtained by evaluating the value h1.
We would really like to have h2 be the hash of the object
referenced by h2. However, that gives a cyclic dependency: to
compute the hash (and thus the file name) of the object, we need to
compute the object, but to do that, we need the file name of the
object.
So for now we abandon the requirement that
hashFile(dbRefs[h]) == h.
I.e., this property does not hold for computed normal forms.
Rather, we use h2 = hash(h1). This allows dbNFs to be
reconstructed. Perhaps using a pseudo random number would be
better to prevent the system from being subverted in some way.
*/
static string dbNFs = "nfs";
/* dbNetSources :: Hash -> URL
Each pair (hash, url) in this mapping states that the object
identified by hash can be obtained by fetching the object pointed
to by url.
TODO: this should be Hash -> [URL]
TODO: factor this out into a separate tool? */
static string dbNetSources = "netsources";
/* Path names. */
/* nixValues is the directory where all Nix values (both files and
directories, and both normal and non-normal forms) live. */
static string nixValues;
/* nixLogDir is the directory where we log evaluations. */
static string nixLogDir;
/* nixDB is the file name of the Berkeley DB database where we
maintain the dbXXX mappings. */
static string nixDB;
/* Abstract syntax of Nix values:
e := Hash(h) -- external reference
| Str(s) -- string constant
| Bool(b) -- boolean constant
| Name(e) -- "&" operator; pointer (file name) formation
| App(e, e) -- application
| Lam(x, e) -- lambda abstraction
| Exec(platform, e, e*)
-- primitive; execute e with args e* on platform
;
*/
/* Download object referenced by the given URL into the sources
directory. Return the file name it was downloaded to. */
string fetchURL(string url)
{
string filename = baseNameOf(url);
string fullname = nixSourcesDir + "/" + filename;
struct stat st;
if (stat(fullname.c_str(), &st)) {
cerr << "fetching " << url << endl;
/* !!! quoting */
string shellCmd =
"cd " + nixSourcesDir + " && wget --quiet -N \"" + url + "\"";
int res = system(shellCmd.c_str());
if (WEXITSTATUS(res) != 0)
throw Error("cannot fetch " + url);
}
return fullname;
}
/* Obtain an object with the given hash. If a file with that hash is
known to exist in the local file system (as indicated by the dbRefs
database), we use that. Otherwise, we attempt to fetch it from the
network (using dbNetSources). We verify that the file has the
right hash. */
string getFile(Hash hash)
{
bool checkedNet = false;
while (1) {
string fn, url;
if (queryDB(nixDB, dbRefs, hash, fn)) {
/* Verify that the file hasn't changed. !!! race */
if (hashFile(fn) != hash)
throw Error("file " + fn + " is stale");
return fn;
}
if (checkedNet)
throw Error("consistency problem: file fetched from " + url +
" should have hash " + (string) hash + ", but it doesn't");
if (!queryDB(nixDB, dbNetSources, hash, url))
throw Error("a file with hash " + (string) hash + " is requested, "
"but it is not known to exist locally or on the network");
checkedNet = true;
fn = fetchURL(url);
setDB(nixDB, dbRefs, hash, fn);
}
}
typedef map<string, string> Params;
void readPkgDescr(Hash hash,
Params & pkgImports, Params & fileImports, Params & arguments)
{
@ -204,9 +64,6 @@ void readPkgDescr(Hash hash,
string getPkg(Hash hash);
typedef map<string, string> Environment;
void fetchDeps(Hash hash, Environment & env)
{
/* Read the package description file. */
@ -538,15 +395,6 @@ void registerInstalledPkg(Hash hash, string path)
}
void initDB()
{
createDB(nixDB, dbRefs);
createDB(nixDB, dbInstPkgs);
createDB(nixDB, dbPrebuilts);
createDB(nixDB, dbNetSources);
}
void verifyDB()
{
/* Check that all file references are still valid. */

3
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@ -0,0 +1,3 @@
#! /bin/sh
echo "Hello World" > $out

5
src/test-builder-2.sh Normal file
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@ -0,0 +1,5 @@
#! /bin/sh
mkdir $out || exit 1
cd $out || exit 1
echo "Hello World" > bla

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@ -1,16 +1,82 @@
#include <iostream>
#include <sys/stat.h>
#include <sys/types.h>
#include "hash.hh"
#include "util.hh"
#include "eval.hh"
#include "values.hh"
#include "globals.hh"
void evalTest(Expr e)
{
EvalResult r = evalValue(e);
char * s = ATwriteToString(r.e);
cout << (string) r.h << ": " << s << endl;
}
void runTests()
{
/* Hashing. */
string s = "0b0ffd0538622bfe20b92c4aa57254d9";
Hash h = parseHash(s);
if ((string) h != s) abort();
try {
h = parseHash("blah blah");
abort();
} catch (BadRefError err) { };
try {
h = parseHash("0b0ffd0538622bfe20b92c4aa57254d99");
abort();
} catch (BadRefError err) { };
/* Set up the test environment. */
mkdir("scratch", 0777);
string testDir = absPath("scratch");
cout << testDir << endl;
nixValues = testDir;
nixLogDir = testDir;
nixDB = testDir + "/db";
initDB();
/* Expression evaluation. */
evalTest(ATmake("Str(\"Hello World\")"));
evalTest(ATmake("Bool(True)"));
evalTest(ATmake("Bool(False)"));
Hash builder1 = addValue("./test-builder-1.sh");
evalTest(ATmake("Exec(Str(<str>), External(<str>), [])",
thisSystem.c_str(), ((string) builder1).c_str()));
Hash builder2 = addValue("./test-builder-2.sh");
evalTest(ATmake("Exec(Str(<str>), External(<str>), [])",
thisSystem.c_str(), ((string) builder2).c_str()));
}
int main(int argc, char * * argv)
{
Hash h = hashFile("/etc/passwd");
cout << (string) h << endl;
ATerm bottomOfStack;
ATinit(argc, argv, &bottomOfStack);
h = parseHash("0b0ffd0538622bfe20b92c4aa57254d9");
cout << (string) h << endl;
return 0;
try {
runTests();
} catch (exception & e) {
cerr << "error: " << e.what() << endl;
return 1;
}
}

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@ -1,47 +1,55 @@
#include <iostream>
#include "util.hh"
string thisSystem = SYSTEM;
string nixHomeDir = "/nix";
string nixHomeDirEnvVar = "NIX";
string absPath(string filename, string dir)
SysError::SysError(string msg)
{
if (filename[0] != '/') {
char * sysMsg = strerror(errno);
err = msg + ": " + sysMsg;
}
string absPath(string path, string dir)
{
if (path[0] != '/') {
if (dir == "") {
char buf[PATH_MAX];
if (!getcwd(buf, sizeof(buf)))
throw Error("cannot get cwd");
throw SysError("cannot get cwd");
dir = buf;
}
filename = dir + "/" + filename;
path = dir + "/" + path;
/* !!! canonicalise */
char resolved[PATH_MAX];
if (!realpath(filename.c_str(), resolved))
throw Error("cannot canonicalise path " + filename);
filename = resolved;
if (!realpath(path.c_str(), resolved))
throw SysError("cannot canonicalise path " + path);
path = resolved;
}
return filename;
return path;
}
/* Return the directory part of the given path, i.e., everything
before the final `/'. */
string dirOf(string s)
string dirOf(string path)
{
unsigned int pos = s.rfind('/');
if (pos == string::npos) throw Error("invalid file name");
return string(s, 0, pos);
unsigned int pos = path.rfind('/');
if (pos == string::npos) throw Error("invalid file name: " + path);
return string(path, 0, pos);
}
/* Return the base name of the given path, i.e., everything following
the final `/'. */
string baseNameOf(string s)
string baseNameOf(string path)
{
unsigned int pos = s.rfind('/');
if (pos == string::npos) throw Error("invalid file name");
return string(s, pos + 1);
unsigned int pos = path.rfind('/');
if (pos == string::npos) throw Error("invalid file name: " + path);
return string(path, pos + 1);
}
void debug(string s)
{
cerr << "debug: " << s << endl;
}

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@ -12,13 +12,21 @@ using namespace std;
class Error : public exception
{
protected:
string err;
public:
Error() { }
Error(string _err) { err = _err; }
~Error() throw () { };
~Error() throw () { }
const char * what() const throw () { return err.c_str(); }
};
class SysError : public Error
{
public:
SysError(string msg);
};
class UsageError : public Error
{
public:
@ -33,15 +41,20 @@ typedef vector<string> Strings;
extern string thisSystem;
/* The prefix of the Nix installation, and the environment variable
that can be used to override the default. */
extern string nixHomeDir;
extern string nixHomeDirEnvVar;
/* Return an absolutized path, resolving paths relative to the
specified directory, or the current directory otherwise. */
string absPath(string path, string dir = "");
/* Return the directory part of the given path, i.e., everything
before the final `/'. */
string dirOf(string path);
/* Return the base name of the given path, i.e., everything following
the final `/'. */
string baseNameOf(string path);
string absPath(string filename, string dir = "");
string dirOf(string s);
string baseNameOf(string s);
void debug(string s);
#endif /* !__UTIL_H */

100
src/values.cc Normal file
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#include "values.hh"
#include "globals.hh"
#include "db.hh"
static void copyFile(string src, string dst)
{
int res = system(("cat " + src + " > " + dst).c_str()); /* !!! escape */
if (WEXITSTATUS(res) != 0)
throw Error("cannot copy " + src + " to " + dst);
}
static string absValuePath(string s)
{
return nixValues + "/" + s;
}
Hash addValue(string path)
{
Hash hash = hashFile(path);
string name;
if (queryDB(nixDB, dbRefs, hash, name)) {
debug((string) hash + " already known");
return hash;
}
string baseName = baseNameOf(path);
string targetName = (string) hash + "-" + baseName;
copyFile(path, absValuePath(targetName));
setDB(nixDB, dbRefs, hash, targetName);
return hash;
}
#if 0
/* Download object referenced by the given URL into the sources
directory. Return the file name it was downloaded to. */
string fetchURL(string url)
{
string filename = baseNameOf(url);
string fullname = nixSourcesDir + "/" + filename;
struct stat st;
if (stat(fullname.c_str(), &st)) {
cerr << "fetching " << url << endl;
/* !!! quoting */
string shellCmd =
"cd " + nixSourcesDir + " && wget --quiet -N \"" + url + "\"";
int res = system(shellCmd.c_str());
if (WEXITSTATUS(res) != 0)
throw Error("cannot fetch " + url);
}
return fullname;
}
#endif
string queryValuePath(Hash hash)
{
bool checkedNet = false;
while (1) {
string name, url;
if (queryDB(nixDB, dbRefs, hash, name)) {
string fn = absValuePath(name);
/* Verify that the file hasn't changed. !!! race */
if (hashFile(fn) != hash)
throw Error("file " + fn + " is stale");
return fn;
}
throw Error("a file with hash " + (string) hash + " is requested, "
"but it is not known to exist locally or on the network");
#if 0
if (checkedNet)
throw Error("consistency problem: file fetched from " + url +
" should have hash " + (string) hash + ", but it doesn't");
if (!queryDB(nixDB, dbNetSources, hash, url))
throw Error("a file with hash " + (string) hash + " is requested, "
"but it is not known to exist locally or on the network");
checkedNet = true;
fn = fetchURL(url);
setDB(nixDB, dbRefs, hash, fn);
#endif
}
}

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#ifndef __VALUES_H
#define __VALUES_H
#include <string>
#include "hash.hh"
using namespace std;
/* Copy a value to the nixValues directory and register it in dbRefs.
Return the hash code of the value. */
Hash addValue(string pathName);
/* Obtain the path of a value with the given hash. If a file with
that hash is known to exist in the local file system (as indicated
by the dbRefs database), we use that. Otherwise, we attempt to
fetch it from the network (using dbNetSources). We verify that the
file has the right hash. */
string queryValuePath(Hash hash);
#endif /* !__VALUES_H */