diff --git a/src/conf.cpp b/src/conf.cpp
index 03c4d29a..712eda98 100644
--- a/src/conf.cpp
+++ b/src/conf.cpp
@@ -151,22 +151,22 @@ void save_config()
     d.AddMember("listenip", StringRef(cfg.listenip.data()), allocator);
 
     Value peers(kArrayType);
-    d.AddMember("peers", peers, allocator);
-    for (int i = 0; i < cfg.peers.size(); i++)
+    for (string peer : cfg.peers)
     {
         Value v;
-        v.SetString(StringRef(cfg.peers[i].data()), allocator);
+        v.SetString(StringRef(peer.data()), allocator);
         peers.PushBack(v, allocator);
     }
+    d.AddMember("peers", peers, allocator);
 
     Value unl(kArrayType);
-    d.AddMember("unl", unl, allocator);
-    for (int i = 0; i < cfg.unl.size(); i++)
+    for (string node : cfg.unl)
     {
         Value v;
-        v.SetString(StringRef(cfg.unl[i].data()), allocator);
+        v.SetString(StringRef(node.data()), allocator);
         unl.PushBack(v, allocator);
     }
+    d.AddMember("unl", unl, allocator);
 
     d.AddMember("peerport", cfg.peerport, allocator);
     d.AddMember("roundtime", cfg.roundtime, allocator);
@@ -241,10 +241,6 @@ int init(int argc, char **argv)
         //Clear the keys. crpyto::init will automatically init the keys.
         clear_keys();
     }
-    else if (ctx.command == "run")
-    {
-        //TO DO: Contract run logic.
-    }
 
     return 1;
 }
diff --git a/src/main.cpp b/src/main.cpp
index fbb58387..e4961cac 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -4,8 +4,10 @@
 
 #include <cstdio>
 #include <iostream>
+#include <unistd.h>
 #include "conf.h"
 #include "crypto.h"
+#include "proc.h"
 
 using namespace std;
 
@@ -28,6 +30,11 @@ int main(int argc, char **argv)
             cerr << "Init error\n";
             return -1;
         }
+
+        if (conf::ctx.command == "run")
+        {
+            //TODO
+        }
     }
 
     cout << "exited normally\n";
diff --git a/src/proc.cpp b/src/proc.cpp
new file mode 100644
index 00000000..acf59cf8
--- /dev/null
+++ b/src/proc.cpp
@@ -0,0 +1,134 @@
+#include <cstdio>
+#include <iostream>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <rapidjson/document.h>
+#include "rapidjson/stringbuffer.h"
+#include <rapidjson/writer.h>
+#include "proc.h"
+#include "conf.h"
+
+using namespace std;
+
+namespace proc
+{
+
+/**
+ * Keeps the currently executing contract process id (if any)
+ */
+int contract_pid;
+
+void write_to_stdin(ContractExecArgs &msg);
+bool is_contract_running();
+int exec_contract(ContractExecArgs &msg);
+int read_contract_outputs(vector<ContractUser> users);
+
+int exec_contract(ContractExecArgs &msg)
+{
+    if (is_contract_running())
+    {
+        cerr << "Contract process still running.\n";
+        return 0;
+    }
+
+    int pid = fork();
+    if (pid > 0)
+    {
+        contract_pid = pid;
+    }
+    else if (pid == 0)
+    {
+        //Set the contract process working directory.
+        chdir(conf::ctx.contractDir.data());
+
+        //Write the contract args to the stdin (0) of the contract process.
+        write_to_stdin(msg);
+
+        char *args[] = {conf::cfg.binary.data(), conf::cfg.binargs.data(), NULL};
+
+        execv(args[0], args);
+    }
+    else
+    {
+        cerr << "fork() failed.\n";
+        return 0;
+    }
+
+    return 1;
+}
+
+//Read per-user outputs produced by the contract process.
+int read_contract_outputs(vector<ContractUser> users)
+{
+    if (is_contract_running())
+    {
+        cerr << "Contract process still running.\n";
+        return 0;
+    }
+    
+    for (ContractUser user : users)
+    {
+        int fdout = user.outpipe[0];
+        int bytes_available = 0;
+        ioctl(fdout, FIONREAD, &bytes_available);
+
+        if (bytes_available > 0)
+        {
+            char data[bytes_available];
+            read(fdout, data, bytes_available);
+            cout << "user:" << user.pubkeyb64 << " reply: '" << data << "'" << endl;
+        }
+    }
+
+    return 1;
+}
+
+void write_to_stdin(ContractExecArgs &msg)
+{
+    Document d;
+    d.SetObject();
+    Document::AllocatorType &allocator = d.GetAllocator();
+    d.AddMember("version", StringRef(_HP_VERSION_), allocator);
+
+    Value users(kArrayType);
+    for (ContractUser user : msg.users)
+    {
+        Value v;
+        v.SetObject();
+        v.AddMember("fdin", user.inpipe[0], allocator);
+        v.AddMember("fdout", user.outpipe[1], allocator);
+        users.PushBack(v, allocator);
+    }
+    d.AddMember("users", users, allocator);
+
+    StringBuffer buffer;
+    Writer<StringBuffer> writer(buffer);
+    d.Accept(writer);
+    const char *json = buffer.GetString();
+
+    int stdinpipe[2];
+    pipe(stdinpipe);
+    dup2(stdinpipe[0], STDIN_FILENO);
+    close(stdinpipe[0]);
+
+    write(stdinpipe[1], json, strlen(json));
+    close(stdinpipe[1]);
+}
+
+bool is_contract_running()
+{
+    if (contract_pid > 0)
+    {
+        int status = 0;
+        if (!waitpid(contract_pid, &status, WNOHANG))
+            return true;
+    }
+
+    contract_pid = 0;
+    return false;
+}
+
+} // namespace proc
\ No newline at end of file
diff --git a/src/proc.h b/src/proc.h
new file mode 100644
index 00000000..c6f21eb8
--- /dev/null
+++ b/src/proc.h
@@ -0,0 +1,30 @@
+#ifndef _HP_PROC_H_
+#define _HP_PROC_H_
+
+#include <cstdio>
+#include <vector>
+
+using namespace std;
+
+namespace proc
+{
+
+struct ContractUser
+{
+    string pubkeyb64;
+    int inpipe[2];  //from User to Contract
+    int outpipe[2]; //from Contract to User
+};
+
+struct ContractExecArgs
+{
+    vector<ContractUser> users;
+};
+
+int exec_contract(ContractExecArgs &msg);
+int read_contract_outputs(vector<ContractUser> users);
+bool is_contract_running();
+
+} // namespace proc
+
+#endif
\ No newline at end of file