* A function to restore from a Nix archive.

* addValue() can now import any dumpable FS object.

src/archive.cc

@@ -10,7 +10,10 @@
 #include "util.hh"
 
 
-static void pad(unsigned int len, DumpSink & sink)
+static string archiveVersion1 = "nix-archive-1";
+
+
+static void writePadding(unsigned int len, DumpSink & sink)
 {
     if (len % 8) {
         unsigned char zero[8];
@@ -37,10 +40,13 @@ 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);
+    writePadding(len, sink);
 }
 
 
+static void dump(const string & path, DumpSink & sink);
+
+
 static void dumpEntries(const string & path, DumpSink & sink)
 {
     DIR * dir = opendir(path.c_str());
@@ -65,8 +71,8 @@ static void dumpEntries(const string & path, DumpSink & sink)
         writeString("(", sink);
         writeString("name", sink);
         writeString(*it, sink);
-        writeString("file", sink);
-        dumpPath(path + "/" + *it, sink);
+        writeString("node", sink);
+        dump(path + "/" + *it, sink);
         writeString(")", sink);
     }
     
@@ -96,13 +102,13 @@ static void dumpContents(const string & path, unsigned int size,
     if (total != size)
         throw SysError("file changed while reading it: " + path);
 
-    pad(size, sink);
+    writePadding(size, sink);
 
     close(fd); /* !!! close on exception */
 }
 
 
-void dumpPath(const string & path, DumpSink & sink)
+static void dump(const string & path, DumpSink & sink)
 {
     struct stat st;
     if (lstat(path.c_str(), &st))
@@ -138,6 +144,182 @@ void dumpPath(const string & path, DumpSink & sink)
 }
 
 
-void restorePath(const string & path, ReadSource & source)
+void dumpPath(const string & path, DumpSink & sink)
 {
+    writeString(archiveVersion1, sink);
+    dump(path, sink);
 }
+
+
+static Error badArchive(string s)
+{
+    return Error("bad archive: " + s);
+}
+
+
+static void readPadding(unsigned int len, RestoreSource & source)
+{
+    if (len % 8) {
+        unsigned char zero[8];
+        unsigned int n = 8 - (len % 8);
+        source(zero, n);
+        for (unsigned int i = 0; i < n; i++)
+            if (zero[i]) throw badArchive("non-zero padding");
+    }
+}
+
+static unsigned int readInt(RestoreSource & source)
+{
+    unsigned char buf[8];
+    source(buf, sizeof(buf));
+    if (buf[4] || buf[5] || buf[6] || buf[7])
+        throw Error("implementation cannot deal with > 32-bit integers");
+    return
+        buf[0] |
+        (buf[1] << 8) |
+        (buf[2] << 16) |
+        (buf[3] << 24);
+}
+
+
+static string readString(RestoreSource & source)
+{
+    unsigned int len = readInt(source);
+    char buf[len];
+    source((const unsigned char *) buf, len);
+    readPadding(len, source);
+    return string(buf, len);
+}
+
+
+static void skipGeneric(RestoreSource & source)
+{
+    if (readString(source) == "(") {
+        while (readString(source) != ")")
+            skipGeneric(source);
+    }
+}
+
+
+static void restore(const string & path, RestoreSource & source);
+
+
+static void restoreEntry(const string & path, RestoreSource & source)
+{
+    string s, name;
+
+    s = readString(source);
+    if (s != "(") throw badArchive("expected open tag");
+
+    while (1) {
+        s = readString(source);
+
+        if (s == ")") {
+            break;
+        } else if (s == "name") {
+            name = readString(source);
+        } else if (s == "node") {
+            if (s == "") throw badArchive("entry name missing");
+            restore(path + "/" + name, source);
+        } else {
+            throw badArchive("unknown field " + s);
+            skipGeneric(source);
+        }
+    }
+}
+
+
+static void restoreContents(int fd, const string & path, RestoreSource & source)
+{
+    unsigned int size = readInt(source);
+    unsigned int left = size;
+    unsigned char buf[65536];
+
+    while (left) {
+        unsigned int n = sizeof(buf);
+        if (n > left) n = left;
+        source(buf, n);
+        if (write(fd, buf, n) != (ssize_t) n)
+            throw SysError("writing file " + path);
+        left -= n;
+    }
+
+    readPadding(size, source);
+}
+
+
+static void restore(const string & path, RestoreSource & source)
+{
+    string s;
+
+    s = readString(source);
+    if (s != "(") throw badArchive("expected open tag");
+
+    enum { tpUnknown, tpRegular, tpDirectory, tpSymlink } type = tpUnknown;
+    int fd = -1; /* !!! close on exception */
+
+    while (1) {
+        s = readString(source);
+
+        if (s == ")") {
+            break;
+        }
+
+        else if (s == "type") {
+            if (type != tpUnknown)
+                throw badArchive("multiple type fields");
+            string t = readString(source);
+
+            if (t == "regular") {
+                type = tpRegular;
+                fd = open(path.c_str(), O_CREAT | O_EXCL | O_WRONLY, 0666);
+                if (fd == -1)
+                    throw SysError("creating file " + path);
+            }
+
+            else if (t == "directory") {
+                type = tpDirectory;
+                if (mkdir(path.c_str(), 0777) == -1)
+                    throw SysError("creating directory " + path);
+            }
+
+            else if (t == "symlink") {
+                type = tpSymlink;
+            }
+            
+            else throw badArchive("unknown file type " + t);
+            
+        }
+
+        else if (s == "contents" && type == tpRegular) {
+            restoreContents(fd, path, source);
+        }
+
+        else if (s == "entry" && type == tpDirectory) {
+            restoreEntry(path, source);
+        }
+
+        else if (s == "target" && type == tpSymlink) {
+            string target = readString(source);
+            if (symlink(target.c_str(), path.c_str()) == -1)
+                throw SysError("creating symlink " + path);
+        }
+
+        else {
+            throw badArchive("unknown field " + s);
+            skipGeneric(source);
+        }
+        
+    }
+
+    if (fd != -1) close(fd);
+}
+
+
+void restorePath(const string & path, RestoreSource & source)
+{
+    if (readString(source) != archiveVersion1)
+        throw badArchive("expected Nix archive");
+    restore(path, source);
+}
+

src/archive.hh

@@ -48,7 +48,7 @@ struct DumpSink
 void dumpPath(const string & path, DumpSink & sink);
 
 
-struct ReadSource
+struct RestoreSource
 {
     /* The callee should store exactly *len bytes in the buffer
        pointed to by data.  It should block if that much data is not
@@ -56,3 +56,5 @@ struct ReadSource
        available. */
     virtual void operator () (const unsigned char * data, unsigned int len) = 0;
 };
+
+void restorePath(const string & path, RestoreSource & source);

src/eval.cc

@@ -123,8 +123,8 @@ static Hash computeDerived(Hash sourceHash, string targetName,
             
             } catch (exception & e) {
                 cerr << "build error: " << e.what() << endl;
-                _exit(1);
             }
+            _exit(1);
 
         }
 

src/nix.cc

@@ -133,7 +133,8 @@ struct StdoutSink : DumpSink
         (const unsigned char * data, unsigned int len)
     {
         /* Don't use cout, it's slow as hell! */
-        write(STDOUT_FILENO, (char *) data, len);
+        if (write(STDOUT_FILENO, (char *) data, len) != len)
+            throw SysError("writing to stdout");
     }
 };
 

src/test.cc

@@ -23,7 +23,21 @@ struct MySink : DumpSink
     virtual void operator () (const unsigned char * data, unsigned int len)
     {
         /* Don't use cout, it's slow as hell! */
-        write(STDOUT_FILENO, (char *) data, len);
+        if (write(STDOUT_FILENO, (char *) data, len) != (ssize_t) len)
+            throw SysError("writing to stdout");
+    }
+};
+
+
+struct MySource : RestoreSource
+{
+    virtual void operator () (const unsigned char * data, unsigned int len)
+    {
+        ssize_t res = read(STDIN_FILENO, (char *) data, len);
+        if (res == -1)
+            throw SysError("reading from stdin");
+        if (res != (ssize_t) len)
+            throw Error("not enough data available on stdin");
     }
 };
 
@@ -53,6 +67,14 @@ void runTests()
     cout << (string) hashPath("scratch") << endl;
 #endif
 
+    /* Restoring. */
+#if 1
+    MySource source;
+    restorePath("outdir", source);
+    cout << (string) hashPath("outdir") << endl;
+    return;
+#endif
+
     /* Set up the test environment. */
 
     mkdir("scratch", 0777);

src/values.cc

@@ -1,13 +1,85 @@
+#include <iostream>
+
+#include <sys/types.h>
+#include <sys/wait.h>
+
 #include "values.hh"
 #include "globals.hh"
 #include "db.hh"
+#include "archive.hh"
+
+
+struct CopySink : DumpSink
+{
+    int fd;
+    virtual void operator () (const unsigned char * data, unsigned int len)
+    {
+        if (write(fd, (char *) data, len) != (ssize_t) len)
+            throw SysError("writing to child");
+    }
+};
+
+
+struct CopySource : RestoreSource
+{
+    int fd;
+    virtual void operator () (const unsigned char * data, unsigned int len)
+    {
+        ssize_t res = read(fd, (char *) data, len);
+        if (res == -1)
+            throw SysError("reading from parent");
+        if (res != (ssize_t) len)
+            throw Error("not enough data available on parent");
+    }
+};
 
 
 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);
+    /* 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. */
+    int fds[2];
+    if (pipe(fds) == -1) throw SysError("creating pipe");
+
+    /* Fork. */
+    pid_t pid;
+    switch (pid = fork()) {
+
+    case -1:
+        throw SysError("unable to fork");
+
+    case 0: /* child */
+        try {
+            close(fds[1]);
+            CopySource source;
+            source.fd = fds[0];
+            restorePath(dst, source);
+            _exit(0);
+        }  catch (exception & e) {
+            cerr << "error: " << e.what() << endl;
+        }
+        _exit(1);        
+    }
+
+    close(fds[0]);
+    
+    /* Parent. */
+
+    CopySink sink;
+    sink.fd = fds[1];
+    dumpPath(src, sink);
+
+    /* Wait for the child to finish. */
+    int status;
+    if (waitpid(pid, &status, 0) != pid)
+        throw SysError("waiting for child");
+
+    if (!WIFEXITED(status) || WEXITSTATUS(status) != 0)
+        throw Error("cannot copy file: child died");
 }