* Some hackery to propagate the worker's stderr and exceptions to the

client.

src/libstore/build.cc

@@ -872,7 +872,7 @@ static void drain(int fd)
             if (errno != EINTR)
                 throw SysError("draining");
         } else if (rd == 0) break;
-        else writeFull(STDERR_FILENO, buffer, rd);
+        else writeToStderr(buffer, rd);
     }
 }
 
@@ -1610,7 +1610,7 @@ void DerivationGoal::handleChildOutput(int fd, const string & data)
 {
     if (fd == logPipe.readSide) {
         if (verbosity >= buildVerbosity)
-            writeFull(STDERR_FILENO, (unsigned char *) data.c_str(), data.size());
+            writeToStderr((unsigned char *) data.c_str(), data.size());
         writeFull(fdLogFile, (unsigned char *) data.c_str(), data.size());
     }
 
@@ -1923,7 +1923,7 @@ void SubstitutionGoal::handleChildOutput(int fd, const string & data)
 {
     assert(fd == logPipe.readSide);
     if (verbosity >= buildVerbosity)
-        writeFull(STDERR_FILENO, (unsigned char *) data.c_str(), data.size());
+        writeToStderr((unsigned char *) data.c_str(), data.size());
     /* Don't write substitution output to a log file for now.  We
        probably should, though. */
 }

src/libstore/remote-store.cc

@@ -4,6 +4,10 @@
 #include "worker-protocol.hh"
 #include "archive.hh"
 
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
 #include <iostream>
 #include <unistd.h>
 
@@ -38,8 +42,14 @@ RemoteStore::RemoteStore()
             if (dup2(toChild.readSide, STDIN_FILENO) == -1)
                 throw SysError("dupping read side");
 
+            int fdDebug = open("/tmp/worker-log", O_WRONLY | O_CREAT | O_TRUNC, 0644);
+            assert(fdDebug != -1);
+            if (dup2(fdDebug, STDERR_FILENO) == -1)
+                throw SysError("dupping stderr");
+            close(fdDebug);
+            
             execlp(worker.c_str(), worker.c_str(),
-                "--slave", NULL);
+                "-vvv", "--slave", NULL);
 
             throw SysError(format("executing `%1%'") % worker);
             
@@ -66,9 +76,13 @@ RemoteStore::RemoteStore()
 
 RemoteStore::~RemoteStore()
 {
-    writeInt(wopQuit, to);
-    readInt(from);
+    try {
+        fromChild.readSide.close();
+        toChild.writeSide.close();
         child.wait(true);
+    } catch (Error & e) {
+        printMsg(lvlError, format("error (ignored): %1%") % e.msg());
+    }
 }
 
 
@@ -158,6 +172,7 @@ void RemoteStore::buildDerivations(const PathSet & drvPaths)
 {
     writeInt(wopBuildDerivations, to);
     writeStringSet(drvPaths, to);
+    processStderr();
     readInt(from);
 }
 
@@ -185,4 +200,18 @@ void RemoteStore::syncWithGC()
 }
 
 
+void RemoteStore::processStderr()
+{
+    unsigned int msg;
+    while ((msg = readInt(from)) == STDERR_NEXT) {
+        string s = readString(from);
+        writeToStderr((unsigned char *) s.c_str(), s.size());
+    }
+    if (msg == STDERR_ERROR)
+        throw Error(readString(from));
+    else if (msg != STDERR_LAST)
+        throw Error("protocol error processing standard error");
+}
+
+
 }

src/libstore/remote-store.hh

@@ -57,6 +57,8 @@ private:
     FdSink to;
     FdSource from;
     Pid child;
+
+    void processStderr();
 };
 
 

src/libstore/worker-protocol.hh

@@ -23,4 +23,9 @@ typedef enum {
 } WorkerOp;
 
 
+#define STDERR_NEXT  0x6f6c6d67
+#define STDERR_LAST  0x616c7473
+#define STDERR_ERROR 0x63787470
+
+
 #endif /* !__WORKER_PROTOCOL_H */

src/libutil/util.cc

@@ -437,7 +437,7 @@ void printMsg_(Verbosity level, const format & f)
     else if (logType == ltEscapes && level != lvlInfo)
         prefix = "\033[" + escVerbosity(level) + "s";
     string s = (format("%1%%2%\n") % prefix % f.str()).str();
-    writeFull(STDERR_FILENO, (const unsigned char *) s.c_str(), s.size());
+    writeToStderr((const unsigned char *) s.c_str(), s.size());
 }
 
 
@@ -450,6 +450,15 @@ void warnOnce(bool & haveWarned, const format & f)
 }
 
 
+static void defaultWriteToStderr(const unsigned char * buf, size_t count)
+{
+    writeFull(STDERR_FILENO, buf, count);
+}
+
+
+void (*writeToStderr) (const unsigned char * buf, size_t count) = defaultWriteToStderr;
+
+
 void readFull(int fd, unsigned char * buf, size_t count)
 {
     while (count) {

src/libutil/util.hh

@@ -131,6 +131,8 @@ void printMsg_(Verbosity level, const format & f);
 
 void warnOnce(bool & haveWarned, const format & f);
 
+extern void (*writeToStderr) (const unsigned char * buf, size_t count);
+
 
 /* Wrappers arount read()/write() that read/write exactly the
    requested number of bytes. */

src/nix-worker/main.cc

@@ -10,7 +10,7 @@
 using namespace nix;
 
 
-Path readStorePath(Source & from)
+static Path readStorePath(Source & from)
 {
     Path path = readString(from);
     assertStorePath(path);
@@ -18,7 +18,7 @@ Path readStorePath(Source & from)
 }
 
 
-PathSet readStorePaths(Source & from)
+static PathSet readStorePaths(Source & from)
 {
     PathSet paths = readStringSet(from);
     for (PathSet::iterator i = paths.begin(); i != paths.end(); ++i)
@@ -27,36 +27,56 @@ PathSet readStorePaths(Source & from)
 }
 
 
-void processConnection(Source & from, Sink & to)
+static Sink * _to; /* !!! should make writeToStderr an object */
+bool canSendStderr;
+
+
+static void tunnelStderr(const unsigned char * buf, size_t count)
 {
-    store = boost::shared_ptr<StoreAPI>(new LocalStore(true));
+    writeFull(STDERR_FILENO, buf, count);
+    if (canSendStderr) {
+        try {
+            writeInt(STDERR_NEXT, *_to);
+            writeString(string((char *) buf, count), *_to);
+        } catch (...) {
+            /* Write failed; that means that the other side is
+               gone. */
+            canSendStderr = false;
+            throw;
+        }
+    }
+}
 
-    unsigned int magic = readInt(from);
-    if (magic != WORKER_MAGIC_1) throw Error("protocol mismatch");
 
-    writeInt(WORKER_MAGIC_2, to);
+/* startWork() means that we're starting an operation for which we
+   want to send out stderr to the client. */
+static void startWork()
+{
+    canSendStderr = true;
+}
 
-    debug("greeting exchanged");
 
-    bool quit = false;
+/* stopWork() means that we're done; stop sending stderr to the
+   client. */
+static void stopWork()
+{
+    canSendStderr = false;
+    writeInt(STDERR_LAST, *_to);
+}
 
-    unsigned int opCount = 0;
-    
-    do {
-        
-        WorkerOp op = (WorkerOp) readInt(from);
-
-        opCount++;
 
+static void performOp(Source & from, Sink & to, unsigned int op)
+{
     switch (op) {
 
+#if 0        
     case wopQuit: {
         /* Close the database. */
         store.reset((StoreAPI *) 0);
         writeInt(1, to);
-            quit = true;
         break;
     }
+#endif
 
     case wopIsValidPath: {
         Path path = readStorePath(from);
@@ -115,7 +135,9 @@ void processConnection(Source & from, Sink & to)
 
     case wopBuildDerivations: {
         PathSet drvs = readStorePaths(from);
+        startWork();
         store->buildDerivations(drvs);
+        stopWork();
         writeInt(1, to);
         break;
     }
@@ -143,6 +165,39 @@ void processConnection(Source & from, Sink & to)
     default:
         throw Error(format("invalid operation %1%") % op);
     }
+}
+
+
+static void processConnection(Source & from, Sink & to)
+{
+    store = boost::shared_ptr<StoreAPI>(new LocalStore(true));
+
+    unsigned int magic = readInt(from);
+    if (magic != WORKER_MAGIC_1) throw Error("protocol mismatch");
+
+    writeInt(WORKER_MAGIC_2, to);
+
+    debug("greeting exchanged");
+
+    _to = &to;
+    canSendStderr = false;
+    writeToStderr = tunnelStderr;
+
+    bool quit = false;
+
+    unsigned int opCount = 0;
+    
+    do {
+        WorkerOp op = (WorkerOp) readInt(from);
+
+        opCount++;
+
+        try {
+            performOp(from, to, op);
+        } catch (Error & e) {
+            writeInt(STDERR_ERROR, *_to);
+            writeString(e.msg(), to);
+        }
 
     } while (!quit);