* Path hashing.

This commit is contained in:
Eelco Dolstra 2003-06-16 15:59:23 +00:00
parent a09e66da5a
commit 2f04e7102e
5 changed files with 178 additions and 8 deletions

View file

@ -148,10 +148,12 @@ static Hash computeDerived(Hash sourceHash, string targetName,
throw Error("program " + progPath +
" failed to create a result in " + targetPath);
#if 0
/* 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);
#endif
} catch (exception &) {
// system(("rm -rf " + targetPath).c_str());
@ -159,7 +161,7 @@ static Hash computeDerived(Hash sourceHash, string targetName,
}
/* Hash the result. */
Hash targetHash = hashFile(targetPath);
Hash targetHash = hashPath(targetPath);
/* Register targetHash -> targetPath. !!! this should be in
values.cc. */

View file

@ -1,9 +1,16 @@
#include <iostream>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <dirent.h>
#include <fcntl.h>
extern "C" {
#include "md5.h"
}
#include "hash.hh"
#include <iostream>
Hash::Hash()
@ -88,3 +95,135 @@ Hash hashFile(const string & fileName)
if (err) throw SysError("cannot hash file " + fileName);
return hash;
}
struct HashSink : DumpSink
{
struct md5_ctx ctx;
virtual void operator ()
(const unsigned char * data, unsigned int len)
{
md5_process_bytes(data, len, &ctx);
}
};
Hash hashPath(const string & path)
{
Hash hash;
HashSink sink;
md5_init_ctx(&sink.ctx);
dumpPath(path, sink);
md5_finish_ctx(&sink.ctx, hash.hash);
return hash;
}
static void pad(unsigned int len, DumpSink & sink)
{
if (len % 8) {
unsigned char zero[8];
memset(zero, 0, sizeof(zero));
sink(zero, 8 - (len % 8));
}
}
static void writeInt(unsigned int n, DumpSink & sink)
{
unsigned char buf[8];
memset(buf, 0, sizeof(buf));
buf[0] = n & 0xff;
buf[1] = (n >> 8) & 0xff;
buf[2] = (n >> 16) & 0xff;
buf[3] = (n >> 24) & 0xff;
sink(buf, sizeof(buf));
}
static void writeString(const string & s, DumpSink & sink)
{
unsigned int len = s.length();
writeInt(len, sink);
sink((const unsigned char *) s.c_str(), len);
pad(len, sink);
}
static void dumpEntries(const string & path, DumpSink & sink)
{
DIR * dir = opendir(path.c_str());
if (!dir) throw SysError("opening directory " + path);
struct dirent * dirent;
/* !!! sort entries */
while (errno = 0, dirent = readdir(dir)) {
string name = dirent->d_name;
if (name == "." || name == "..") continue;
writeString("entry", sink);
writeString("(", sink);
writeString("name", sink);
writeString(name, sink);
writeString("file", sink);
dumpPath(path + "/" + name, sink);
writeString(")", sink);
}
if (errno) throw SysError("reading directory " + path);
closedir(dir); /* !!! close on exception */
}
static void dumpContents(const string & path, unsigned int size,
DumpSink & sink)
{
writeString("contents", sink);
writeInt(size, sink);
int fd = open(path.c_str(), O_RDONLY);
if (!fd) throw SysError("opening file " + path);
unsigned char buf[16384];
unsigned int total = 0;
ssize_t n;
while ((n = read(fd, buf, sizeof(buf)))) {
if (n == -1) throw SysError("reading file " + path);
total += n;
sink(buf, n);
}
if (total != size)
throw SysError("file changed while reading it: " + path);
pad(size, sink);
close(fd); /* !!! close on exception */
}
void dumpPath(const string & path, DumpSink & sink)
{
cerr << path << endl;
struct stat st;
if (lstat(path.c_str(), &st))
throw SysError("getting attributes of path " + path);
writeString("(", sink);
if (S_ISREG(st.st_mode)) {
writeString("type", sink);
writeString("regular", sink);
dumpContents(path, st.st_size, sink);
} else if (S_ISDIR(st.st_mode)) {
writeString("type", sink);
writeString("directory", sink);
dumpEntries(path, sink);
} else throw Error("unknown file type: " + path);
writeString(")", sink);
}

View file

@ -50,6 +50,11 @@ Hash hashFile(const string & fileName);
follows:
hash(path) = md5(dump(path))
*/
Hash hashPath(const string & path);
/* Dump a path as follows:
IF path points to a REGULAR FILE:
dump(path) = attrs(
@ -60,7 +65,7 @@ Hash hashFile(const string & fileName);
IF path points to a DIRECTORY:
dump(path) = attrs(
[ ("type", "directory")
, ("entries", concat(map(f, entries(path))))
, ("entries", concat(map(f, sort(entries(path)))))
])
where f(fn) = attrs(
[ ("name", fn)
@ -72,17 +77,25 @@ Hash hashFile(const string & fileName);
attrs(as) = concat(map(attr, as)) + encN(0)
attrs((a, b)) = encS(a) + encS(b)
encS(s) = encN(len(s)) + s
encS(s) = encN(len(s)) + s + (padding until next 64-bit boundary)
encN(n) = 64-bit little-endian encoding of n.
contents(path) = the contents of a regular file.
sort(strings) = lexicographic sort by 8-bit value (strcmp).
entries(path) = the entries of a directory, without `.' and
`..'.
`+' denotes string concatenation. */
Hash hashPath(const string & path);
struct DumpSink
{
virtual void operator () (const unsigned char * data, unsigned int len) = 0;
};
void dumpPath(const string & path, DumpSink & sink);
#endif /* !__HASH_H */

View file

@ -19,6 +19,15 @@ void evalTest(Expr e)
}
struct MySink : DumpSink
{
virtual void operator () (const unsigned char * data, unsigned int len)
{
cout.write((char *) data, len);
}
};
void runTests()
{
/* Hashing. */
@ -36,6 +45,13 @@ void runTests()
abort();
} catch (BadRefError err) { };
/* Dumping. */
#if 0
MySink sink;
dumpPath("scratch", sink);
cout << (string) hashPath("scratch") << endl;
#endif
/* Set up the test environment. */

View file

@ -19,7 +19,7 @@ static string absValuePath(string s)
Hash addValue(string path)
{
Hash hash = hashFile(path);
Hash hash = hashPath(path);
string name;
if (queryDB(nixDB, dbRefs, hash, name)) {
@ -72,8 +72,8 @@ string queryValuePath(Hash hash)
if (queryDB(nixDB, dbRefs, hash, name)) {
string fn = absValuePath(name);
/* Verify that the file hasn't changed. !!! race */
if (hashFile(fn) != hash)
/* Verify that the file hasn't changed. !!! race !!! slow */
if (hashPath(fn) != hash)
throw Error("file " + fn + " is stale");
return fn;